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ABSTRACT The Gulf of Maine (GOM) northern shrimp, Pandalus borealis, once supported a significant winter fishery, but a moratorium has been placed on the fishery since 2014 because of a population collapse and recruitment failures that have been attributed to unfavorably warm water temperatures. The GOM is at the southernmost end of the northern shrimp's range, suggesting its population dynamics and distribution may be vulnerable to warming water temperatures. In this study, we used survey data to estimate spatial indicators for GOM northern shrimp at four life history stages to identify possible temporal trends and examine relationships between the indicators and northern shrimp abundance and bottom temperature. We observed patchier distributions over time, which were related to declining population abundance, and a distributional shift northward that was associated with warming bottom water temperatures. Northern shrimp habitat distribution was strongly associated with bottom temperature. Shrimp of all life stages were found in bottom waters cooler than the station's average bottom temperature. [ABSTRACT FROM AUTHOR]

The introduction of thousands of wind turbines along the North American Atlantic continental shelf over the next decade will constitute the largest regional change in marine substrates since the retreat of the Laurentide Ice Sheet over 14,000 years ago. Here, two large data sets, SMAST drop camera survey (242,949 samples, 2003 to 2019) and the US Geological Survey databases (27,784 samples, 1966 to 2011), are combined to derive sea floor surficial substrate probability maps for the Northeastern US continental shelf from Virginia Beach to the Gulf of Maine to 300 m depth (218,571 km2). Geostatistical models were used to estimate the probability of five geologic and one biogenic substrate types being present at a 250 m resolution, and the proportional contribution of each substrate type to the seabed composition at a 500 m resolution. By providing the first synoptic maps depicting the probability of a particular substrate or combination of substrates occurring at any location on the Northeastern US continental shelf, including planned wind energy sites, we aim to (1) provide insights regarding how substrates in the areas selected for wind energy development compare with other locations, (2) motivate the development of a priori expectations for ecosystem changes to inform monitoring and research efforts going forward, and (3) to provide a baseline characterization of the Northeastern US continental shelf surficial substrates to support robust examination of the future changes observed in areas impacted by wind energy installations. [ABSTRACT FROM AUTHOR]

Ecological theory predicts that kelp forests structured by trophic cascades should experience recovery and persistence of their foundation species when herbivores become rare. Yet, climate change may be altering the outcomes of top‐down forcing in kelp forests, especially those located in regions that have rapidly warmed in recent decades, such as the Gulf of Maine. Here, using data collected annually from 30+ sites spanning >350 km of coastline, we explored the dynamics of Maine's kelp forests in the ~20 years after a fishery‐induced elimination of sea urchin herbivores. Although forests (Saccharina latissima and Laminaria digitata) had broadly returned to Maine in the late 20th century, we found that forests in northeast Maine have since experienced slow but significant declines in kelp, and forest persistence in the northeast was juxtaposed by a rapid, widespread collapse in the southwest. Forests collapsed in the southwest apparently because ocean warming has—directly and indirectly—made this area inhospitable to kelp. Indeed, when modeling drivers of change using causal techniques from econometrics, we discovered that unusually high summer seawater temperatures the year prior, unusually high spring seawater temperatures, and high sea urchin densities each negatively impacted kelp abundance. Furthermore, the relative power and absolute impact of these drivers varied geographically. Our findings reveal that ocean warming is redefining the outcomes of top‐down forcing in this system, whereby herbivore removal no longer predictably leads to a sustained dominance of foundational kelps but instead has led to a waning dominance (northeast) or the rise of a novel phase state defined by "turf" algae (southwest). Such findings indicate that limiting climate change and managing for low herbivore abundances will be essential for preventing further loss of the vast forests that still exist in northeast Maine. They also more broadly highlight that climate change is "rewriting the rules" of nature, and thus that ecological theory and practice must be revised to account for shifting species and processes. [ABSTRACT FROM AUTHOR]

Management of thorny skate (Amblyraja radiata) in the Northwest Atlantic has posed a conservation dilemma for several decades due to the species' lack of response to strong conservation efforts in the US Gulf of Maine and the Canadian Scotian Shelf, confusion over the relationship between two reproductive size morphs of differing life histories that are sympatric in the Northwest Atlantic, and conflicting data on regional population connectivity throughout the species' broader range. To better assess potential A. radiata regional population differentiation and genetic links to life‐history variation, we analysed complete mitochondrial genome sequences from 527 specimens collected across the species' North Atlantic geographic range, with particular emphasis on the Northwest Atlantic region. A high level of genetic diversity was evident across the North Atlantic, but significant genetic differentiation was identified between specimens inhabiting the Northwest (Gulf of Maine and Newfoundland) and Northeast (Greenland, Iceland, North Sea, and Arctic Circle) Atlantic. In the Northwest Atlantic, significant differentiation between the Gulf of Maine and Newfoundland regions was revealed; however, the overall level of differentiation was very low. No genetic difference was identified between the large and small reproductive morphs. The results of this study advance our understanding of A. radiata population structure in the North Atlantic but do not resolve all the questions confounding our understanding of the species' biology and evolutionary history. [ABSTRACT FROM AUTHOR]

Advances in active acoustic technology have outpaced the ability to process and analyze the data in a timely manner. Currently, scientists rely on manual scrutiny or limited automation to translate acoustic backscatter to biologically meaningful metrics useful for fisheries and ecosystem management. The National Oceanic and Atmospheric Administration Northeast Fisheries Science Center has monitored the Atlantic herring population in the Gulf of Maine and Georges Bank since 1999 due to the stocks' important economic and ecological role for the commercial lobster industry. Manual scrutinization to identify Atlantic herring schools from the water column sonar data is time‐consuming and impractical for large‐scale studies. To automate this process, a hybrid model with multiview learning was proposed for automatic Atlantic herring school detection, which consists of two steps: (1) region‐of‐interest (ROI) detection and (2) ROI classification. The ROI detection step was designed to detect school‐like objects, and the ROI classification step was designed to distinguish Atlantic herring schools from other objects. The co‐training algorithm was employed for multiview learning as well as semi‐supervised learning. Within this framework, single‐view vs. multiview learning and supervised vs. semi‐supervised learning were evaluated and compared. Our results showed that multiview learning can improve the performance of the hybrid model in Atlantic herring school detection, and the utilization of unlabeled data is also helpful when the training set is small. The best‐performed model achieved an F1‐score of 0.804. This new framework provides an efficient and effective tool for automatic Atlantic herring school detection. [ABSTRACT FROM AUTHOR]

Objective: Energy density (ED) estimates for marine forage species have been limited, impeding our understanding of this important trophic level. We studied the EDs of eight key forage species: Alewife Alosa pseudoharengus, Atlantic Herring Clupea harengus, Silver Hake Merluccius bilinearis, Northern Sand Lance Ammodytes dubius, Atlantic Mackerel Scomber scombrus, Butterfish Peprilus triacanthus, northern shortfin squid Illex illecebrosus, and longfin inshore squid Doryteuthis pealeii (also known as Loligo pealeii). Methods: Samples were obtained during spring and fall bottom trawl surveys across five regions (Gulf of Maine, Georges Bank, southern New England, northern Middle Atlantic Bight, and southern Middle Atlantic Bight) from 2017 to 2019. In the laboratory, we developed predictive relations between the percent dry weight (%DW) and ED (kJ/g wet weight) determined by proximate composition analysis (n = 606; r2 = 0.76–0.98) to estimate the ED of additional samples (n = 4583). For each species, we modeled ED as a function of size, depth, season, and year (as factors) as well as location (latitude, longitude) using generalized additive models (GAMs). Result: Alewife, Atlantic Herring, Northern Sand Lance, Atlantic Mackerel, and Butterfish were classified as high‐quality prey (ED > 6 kJ/g), although Atlantic Herring ED was nearly half the values reported in earlier studies. Silver Hake, northern shortfin squid, and longfin inshore squid were classified as moderate‐quality prey (4 kJ/g < ED < 6 kJ/g). Most species had higher EDs in the fall following summer feeding than in the spring after spawning and/or reduced winter feeding. The best‐fitting GAMs included weight, depth (by season), season, and year effects for most species. Location (by season) explained significant amounts of variation. Conclusion: Observed variation in ED across regions, species, seasons, and years provides the empirical data necessary to consider hypotheses related to "upstream" regulation of ED (via environmental drivers and productivity) and "downstream" effects on recruitment for these forage species as well the species that prey on them. Impact statementForage fish and squid are a link between primary production and upper‐level predators. We used proximate composition analysis to determine energy density of forage species, which varied across species, ontogeny, seasons, and location, affecting their value as prey and the flow of energy in the ecosystem. [ABSTRACT FROM AUTHOR]

The impacts of global change—from shifts in climate to overfishing to land use change—can depend heavily on local abiotic context. Building an understanding of how to downscale global change scenarios to local impacts is often difficult, however, and requires historical data across large gradients of variability. Such data are often not available—particularly in peer reviewed or gray literature. However, these data can sometimes be gleaned from casual records of natural history—field notebooks, data sheet marginalia, course notes, and more. Here, we provide an example of one such approach for the Gulf of Maine, as we seek to understand how environmental context can influence local outcomes of region‐wide shifts in subtidal community structure. We explore a decade of hand‐drawn algal cover maps around Appledore Island made by Dr. Art Borror while teaching at the Shoals Marine Lab. Appledore's steep wave exposure gradient—from exposed to the open ocean to fully protected—provides a living laboratory to test interactions between global change and local conditions. We then recreate Borror's methods two and a half decades later. We show that overfishing‐driven urchin outbreaks in the 1980s were slowed or stopped by wave exposure and benthic topography. Similarly, local variation appears to have curtailed current invasions by filamentous red algae. Last, some formerly dominant kelps have disappeared over the past 40 years—an observation verified by subtidal surveys. Global change is altering life in the seas around us. While underutilized, solid natural history observations stand as a key resource for us to begin to understand how global change will translate to the heterogeneous mosaic of life in a future Gulf of Maine and other ecosystems around the world. [ABSTRACT FROM AUTHOR]

The Gulf of Maine (GOM) is one of the most productive and ecologically important marine environments on the planet. The Gulf of Maine Coastal Current (GMCC), which stretches along the western side of the GOM from the Bay of Fundy to Cape Cod, plays an important role in supporting this productivity by transporting nutrients, larvae and dinoflagellates southwestward along the Canadian and New England coastlines. Climate change has led to alterations in GOM ecosystems in recent years: GOM water temperatures have warmed and distributions of marine species have shifted. However, the impacts of the changing climate on the circulation within the GOM, including the path and velocity of the GMCC, have remained unclear. Here, we examine data collected by satellite tracked surface drifters and velocity data collected by the NERACOOS buoy array in order to investigate inter‐decadal changes to the flow of the GMCC. We find that over inter‐decadal timescales, the alongshore surface flow of the GMCC has slowed, particularly in the region southwest of Penobscot Bay. The slowdown observed in the GMCC surface flow is most likely attributed to a local strengthening of the southwesterly winds over the time period of interest. [ABSTRACT FROM AUTHOR]

Invasive predators can cause substantial evolutionary change in native prey populations. Although invasions by predators typically occur over large scales, their distributions are usually characterized by substantial spatiotemporal heterogeneity that can lead to patchiness in the response of native prey species. Our ability to understand how local variation shapes patterns of inducible defense expression has thus far been limited by insufficient replication of populations within regions. Here, we examined local and regional variation in the inducible defenses of 12 native marine snail (Littorina obtusata) populations within two geographic regions in the Gulf of Maine that are characterized by vastly different contact histories with the invasive predatory green crab (Carcinus maenas). When exposed in the field to waterborne risk cues from the green crab for 90 days, snails expressed plastic increases in shell thickness that reduced their vulnerability to this shell‐crushing predator. Despite significant differences in contact history with this invasive predator, snail populations from both regions produced similar levels of shell thickness and shell thickness plasticity in response to risk cues. Such phenotypic similarity emerged even though there were substantial geographic differences in the shell thickness of juvenile snails at the beginning of the experiment, and we suggest that it may reflect the effects of warming ocean temperatures and countergradient variation. Consistent with plasticity theory, a trend in our results suggests that southern snail populations, which have a longer contact history with the green crab, paid less in the form of reduced tissue mass for thicker shells than northern populations. [ABSTRACT FROM AUTHOR]

Invertebrate larvae are often abundant in the surface ocean, which plays a key role in their dispersal and connectivity. Pelagic microhabitats characterized by small‐scale hydrographic variability are complex and ubiquitous in the coastal ocean, but their study is challenging, and they have been largely neglected in meroplankton ecology. Surface convergences, i.e., surface microhabitats featuring convergent horizontal currents, may aggregate the last larval stage of the American lobster and could provide shelter and food for Stage IV postlarvae and thus enhance their condition. We tested these hypotheses by conducting a series of cruises in the southwestern Gulf of Maine in summer 2021, sampling 15 paired sets of potential convergences and off‐convergence unstructured habitat. We measured postlarval abundance, surface hydrography, acoustic backscatter, and circulation. Experiments and image analysis compared condition, color, and morphology of postlarvae sampled inside and outside potential convergences. Potential convergences varied in near‐surface hydrographic patterns, with most displaying consistency among two transects and diverse patterns in salinity and temperature (e.g., across‐convergence gradients with equal or different signs). While the highest postlarval abundances were found in convergences, abundance patterns on and off convergences were not consistent, and another analysis indicated higher abundance in convergences than in a 7‐year untargeted surface ocean data set. Experiments indicated no survivorship differences among convergence and non‐convergence individuals at two temperatures, while image analyses revealed differences in color and size. Physical measurements and qualitative neuston community analyses indicated substantial heterogeneity among potential convergences. Our results reinforce that small‐scale heterogeneities are highly variable but important to the ecology of meroplankton, including the pelagic and neustonic habitats where lobster postlarvae are abundant. [ABSTRACT FROM AUTHOR]

Understanding community responses to climate is critical for anticipating the future impacts of global change. However, despite increased research efforts in this field, models that explicitly include important biological mechanisms are lacking. Quantifying the potential impacts of climate change on species is complicated by the fact that the effects of climate variation may manifest at several points in the biological process. To this end, we extend a dynamic mechanistic model that combines population dynamics, such as species interactions, with species redistribution by allowing climate to affect both processes. We examine their relative contributions in an application to the changing biomass of a community of eight species in the Gulf of Maine using over 30 years of fisheries data from the Northeast Fishery Science Center. Our model suggests that the mechanisms driving biomass trends vary across space, time, and species. Phase space plots demonstrate that failing to account for the dynamic nature of the environmental and biologic system can yield theoretical estimates of population abundances that are not observed in empirical data. The stock assessments used by fisheries managers to set fishing targets and allocate quotas often ignore environmental effects. At the same time, research examining the effects of climate change on fish has largely focused on redistribution. Frameworks that combine multiple biological reactions to climate change are particularly necessary for marine researchers. This work is just one approach to modeling the complexity of natural systems and highlights the need to incorporate multiple and possibly interacting biological processes in future models. [ABSTRACT FROM AUTHOR]

Crustaceans, which are highly susceptible to the effects of climate change, are critical for food security worldwide. Yet, management rarely evaluates the performance of alternative regulatory strategies under climate‐driven life history change. This limits the development of climate‐ready management plans, undermining fisheries sustainability. We compared the performance of alternative minimum legal size (MLS) regulations under shifts in growth and maturity for American lobster in the Gulf of Maine, the most valuable single‐species commercial fishery in the United States. Across the life history change scenarios examined, increasing MLS improved status indicators, while decreasing MLS eroded status indicators for spawning stock biomass, legal abundance, landings, and exploitation rate. Our results demonstrate that protecting the lobster stock by increasing MLS improves fishery output, highlighting that conservation and industry goals can be complementary. This study exemplifies the utility of MLS as a conservation measure for crustacean fisheries under climate change. [ABSTRACT FROM AUTHOR]

Subsurface nutrients on the Scotian Shelf, an ocean region at the convergence of the subpolar and subtropical western boundary currents (i.e., Labrador Current (LC) and Gulf Stream (GS)), are chiefly modulated by upstream shelf and slope waters. Yet little is known about long‐term fluctuations in the advective transport of nutrients to the shelf. Here, we synthesized nutrient and hydrographic data from 1975 to 2020 to characterize decadal changes in upper (60–150 m) and lower (150–200 m) subsurface nutrient availability across the shelf. Hydrographic and nutrient anomalies highlight a transition from a warm, saline, high‐nutrient GS‐dominated system in the 1980 to colder, fresher, lower‐nutrient LC‐dominated conditions in the late 1980 and early 1990. In the mid‐1990, an increase in excess silicate and phosphate (relative to nitrate) marks a shift in the LC contribution toward a strengthening of the inner shelf component relative to the outer shelf‐edge branch. Since 2010, rapid increases in subsurface temperature and salinity indicate the transition back to a GS‐dominated system, albeit with a distinct decline in dissolved nutrients relative to the previous warm period, which diverges from the nutrient increase generally associated with GS water. Declines in lower subsurface nutrient concentrations since 2010 are likely driven by a density‐related shift in the GS source water toward a less dense, lower‐nutrient GS contribution. This shift is evidenced by a decrease in excess phosphate amidst minor declines in excess silicate, reflecting the characteristic density‐related patterns of excess nutrients in GS waters. Plain Language Summary: The Northwest Atlantic continental shelf is a highly productive region, sustaining large ecologically and commercially important fisheries from the Grand Banks across the Scotian Shelf into the Gulf of Maine. This high productivity depends on the supply of bioavailable nutrients, which are essential components feeding phytoplankton growth and ecosystem productivity. On the Scotian Shelf, surface productivity is thought to be fueled by the vertical supply of nutrient‐rich subsurface water, deriving from upstream coastal waters, and the onshore transport of deeper slope waters. In this study, we used hydrographic and nutrient data from 1975 to 2020 to investigate long‐term trends in nutrient availability on the shelf. We show that over the past 45 years, subsurface properties have shifted from warm, salty, nutrient‐rich waters at the beginning of the time series to colder, fresher, lower‐nutrient conditions in the 1990/early 2000, and back to warm, salty, yet nutrient‐poor conditions after 2010 due to changes in the dominant source water advected onto the shelf. The significant decline in nutrients since 2010 suggests a shift to a less dense, lower‐nutrient source from the Gulf Stream compared to the previous warm period. Key Points: Subsurface nutrients on the shelf are modulated by advection of upstream coastal water, and offshore Gulf Stream and Labrador Slope WaterNutrient properties indicate a shift in Labrador Current contributions, with a strengthening of the inner versus outer branch in 1995–2010Enhanced contributions from lower‐density Gulf Stream water drive a warming and decrease in subsurface nutrient concentrations since 2010 [ABSTRACT FROM AUTHOR]

Lumpfish, Cyclopterus lumpus, have historically been harvested throughout Atlantic Canada and are increasingly in demand as a solution to controlling sea lice in Atlantic salmon farms—a process which involves both the domestication and the transfer of lumpfish between geographic regions. At present, little is known regarding population structure and diversity of wild lumpfish in Atlantic Canada, limiting attempts to assess the potential impacts of escaped lumpfish individuals from salmon pens on currently at‐risk wild populations. Here, we characterize the spatial population structure and genomic‐environmental associations of wild populations of lumpfish throughout the Northwest Atlantic using both 70K SNP array data and whole‐genome re‐sequencing data (WGS). At broad spatial scales, our results reveal a large environmentally associated genetic break between the southern populations (Gulf of Maine and Bay of Fundy) and northern populations (Newfoundland and the Gulf of St. Lawrence), linked to variation in ocean temperature and ice cover. At finer spatial scales, evidence of population structure was also evident in a distinct coastal group in Newfoundland and significant isolation by distance across the northern region. Both evidence of consistent environmental associations and elevated genome‐wide variation in FST values among these three regional groups supports their biological relevance. This study represents the first extensive description of population structure of lumpfish in Atlantic Canada, revealing evidence of broad and fine geographic scale environmentally associated genomic diversity. Our results will facilitate the commercial use of lumpfish as a cleaner fish in Atlantic salmon aquaculture, the identification of lumpfish escapees, and the delineation of conservation units of this at‐risk species throughout Atlantic Canada. [ABSTRACT FROM AUTHOR]

Objective: A recent expansion of the northern stock of Black Sea Bass Centropristis striata into the northern Gulf of Maine raises questions about this species' movement and population dynamics in this region. Determining the origin of these fish is essential, as dramatic changes in migration patterns or current population boundaries could have profound effects on stock assessment estimates and subsequent management regulations. Methods: In this study, we measured otolith core concentrations of stable isotopes (δ18O, δ13C) and trace element:calcium ratios (Mg:Ca, Mn:Ca, Cu:Ca, Zn:Ca, Ba:Ca, Sr:Ca) to assess the natal origin of Black Sea Bass that were caught off the coast of Maine. Spawning condition adults from southern New England (SNE) and the mid‐Atlantic Bight (MAB) were used to characterize the chemical fingerprint of these known spawning regions. Result: Unique chemical fingerprints were identified for fish from SNE and the MAB, with high reclassification success using random forest analysis (16% error rate). The classification of Black Sea Bass of unknown origin that were caught in Maine waters indicated that 85% of the samples matched to SNE and 13% to the MAB, whereas one sample remained unclassified. Conclusion: Results from this study support the current management population separation of the northern stock of Black Sea Bass between SNE and the MAB and lends additional information to the understanding of this species' movement into the northern Gulf of Maine. As fish stocks around the world continue to shift into new regions due to climate change, knowledge of their natal origin will be critical to long‐term sustainable management of this species. Impact statementDetermining which population Black Sea Bass located in Maine came from helps scientists understand how these fish migrated there, their potential for success, and their expected growth and maturity. If this species becomes more abundant in the region, this information could help inform regulation surrounding conservation and fishing practices. [ABSTRACT FROM AUTHOR]

Perceptions of past ecological change affect views of current ecosystem state, but how do baselines help to shape stakeholders' visions of an idealized future?Here, we investigate links between perceptions of natural baselines and visions for the nearshore Gulf of Maine among a key stakeholder group, active lobster fishers. We ask three related questions: (1) What do fishers perceive as a 'natural' Gulf of Maine? (2) How do perceptions of the past predict individual and collective visions of an ideal future? and (3) How is existing management perceived as supporting these visions?We found that fishers perceived the ecosystem to be 'natural' an average of one decade before they started fishing. Three species dominated views of natural systems: cod Gadus morhua, lobster Homarus americanus, and herring Clupea harengus, but while long‐time fishers associated abundant cod with a natural nearshore Gulf of Maine, memories of a historically cod‐rich Gulf of Maine were fading among some younger fishers who began their careers after the cod crash in the 1990s. Perceptions of 'natural' ecosystems dictated future visions for the majority of taxa; on average, fishers remembered and desired abundant cod and herring, but perceived halibut Hippoglossus hippoglossus and endangered right whales Eubalaena glacialis to have always been rare.Fishers described a vision for the future based on views of past ecological and social baselines, including fisheries deconsolidation and diversification, but expressed a lack of shared vision with and trust in federal management institutions to achieve these goals. In particular, memories of cod abundance in the 1970s and 1980s were coupled with memories of a diversified and accessible fishery, but fishers doubted that the recovery of cod would result in their restored access to cod fisheries.Together our results demonstrate that past personal experiences limit perceptions of what is possible, highlighting both the value and limitations of local ecological knowledge in places that have experienced ecological change over centuries. They also demonstrate how stakeholder perceptions of both social and ecological baselines shape visions for future ecosystems but are mediated by contemporary issues like trust in institutions and fisheries access. Read the free Plain Language Summary for this article on the Journal blog. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Over the past several decades, the Gulf of Maine has experienced significant socio‐ecological change. Coastlines have become more densely populated and developed, rapid and dramatic climate change has affected coastal ocean environments, and seal populations have grown as a result of federal protections. Long‐term data sets from marine mammal stranding networks represent a valuable resource for investigating indicator species for coastal ocean health during this period of change. Using data collected from stranded harbor (Phoca vitulina), harp (Pagophilus groenlandicus), and gray (Halichoerus grypus) seals from 2002 to 2017 in Massachusetts, New Hampshire, and Maine, we tested for spatiotemporal correlations between stranding density and human population density, size of and proximity to seal haul‐outs, sea surface temperature, North Atlantic Oscillation, snowfall, and sea ice extent. We found that in the Gulf of Maine proximity to coastal human population centers and large seal haul‐outs are the greatest drivers of reported seal stranding density. Environmental factors played an important role only for harp seals, which do not breed in the study area, although recent shifts in the environmental seascape have the potential to affect all seal species in the Gulf of Maine. [ABSTRACT FROM AUTHOR]

The Gulf of Maine's lunar semidiurnal (M2) ocean tide exhibits spatially coherent amplitude changes of ∼1–3 cm on interannual time scales, though no causative mechanism has been identified. Here we show, using a specially designed numerical modeling framework, that stratification changes account for 32%–48% (Pearson coefficient 0.58–0.69) of the observed M2 variability at tide gauges from 1994 to 2019. Masking experiments and energy diagnoses reveal that the modeled variability is primarily driven by fluctuations in barotropic‐to‐baroclinic energy conversion on the continental slope south of the gulf's mouth, with a 1‐cm amplitude increase at Boston corresponding to a ∼7% (0.30 GW) drop in the area‐integrated conversion rate. Evidence is given for the same process to have caused the decade‐long M2 amplitude decrease in the Gulf of Maine beginning in 1980/81. The study has implications for nuisance flooding predictions and space geodetic analyses seeking highest accuracies. Plain Language Summary: The height of the twice‐daily tide at Boston is about 135 cm, but researchers have long noted that this value fluctuates by about 1–3 cm from year to year. Here we show that the annual tidal height changes—seen in fact throughout the Gulf of Maine—are closely linked to how seawater density is distributed three‐dimensionally in the region. In particular, as tidal currents enter the gulf over steep underwater topography, the vertical distribution of density determines how much of the incoming wave energy is scattered back as internal tides into the deeper Northwest Atlantic. In years where this conversion of wave energy drops by 7% from its nominal value of 4 Gigawatt, the surface tide at Boston typically increases by 1 cm. Climate‐induced changes in ocean temperature and density may strengthen or weaken the conversion effect and thus slightly alter the role of tides in coastal flood events. Key Points: We propagate the M2 tide through realistic, annually varying density structures (1993–2019) in a regional Gulf of Maine modelStratification changes explain 32%–48% of the observed, cm‐level M2 amplitude variability at coastal tide gauges from 1994 to 2019Modeled M2 changes mainly reflect fluctuations in the barotropic‐baroclinic energy conversion rate on the New England continental slope [ABSTRACT FROM AUTHOR]

An unusually large positive salinity anomaly was observed across the eastern Gulf of Maine in winter 2017–2018. Buoy measurements in Jordan Basin found this anomaly extended down to at least 100 m, the deepest mixing observed in the past 19 years. Similarly, this is the strongest positive regional salt anomaly ever observed in sea surface salinity (SSS) satellite observations. To determine the source waters driving this event and to diagnose the relative importance of forcing processes, passive tracer adjoint sensitivity experiments are performed using a data assimilating version of the Regional Ocean Modeling System. The model suggests that northeastward Scotian Shelf wind anomalies is one factor in the dramatic decrease in freshwater transport to Jordan Basin, which leads to an early winter upper water column salinity surplus. This salinity change weakens the normally haline‐controlled vertical stratification across the eastern Gulf. Modeled upper ocean density and vertical diffusivity from 2007 to 2021 both show a maximum in January 2018. Winter 2017–2018 is the only period where the enhanced winter mixing extends below 100 m. Thus, anomalous vertical entrainment of saltier subsurface Gulf water is the major factor driving the extreme positive satellite‐observed SSS anomaly across the eastern Gulf including Jordan Basin. Other factors, including a modest increase in wind‐forced slope water transport, and positive fall 2017 salinity anomalies on the Scotian Shelf and Slope Sea, appear to play lesser roles in the observed salinification. The adjoint sensitivity analysis demonstrates its utility for back tracing transport pathways for periods of several months. Plain Language Summary: An unusually large positive salinity anomaly observed in the Gulf of Maine (GoM) in winter 2017–2018 is studied using both model‐derived and observational data from satellites and buoys. The study shows that wind anomalies cause a dramatic decrease in freshwater transport from the Scotian Shelf to the GoM, which leads to an upper water column salinity surplus that in turn leads to enhanced winter mixing. Key Points: Multi‐year regional assimilative model simulates winter 2017–2018 abnormal salinification of the eastern Gulf of Maine (eGoM)Model adjoint sensitivity analysis suggests a dramatic reduction of both Scotian Shelf inflow and haline stability during this eventAbnormally deep 2017–2018 winter overturning due to lack of surface freshwater is responsible for the uplift of salty water in the eGoM [ABSTRACT FROM AUTHOR]

Cusk Brosme brosme are fished across the northern Atlantic Ocean, but even basic biological data are limited in part by their difficult‐to‐sample deep and structured habitats. We sampled fish from a variety of sources across the Gulf of Maine to provide comprehensive life history information (age and size at maturity, fecundity, sex ratio, growth) for this data‐poor species considered by National Oceanic and Atmospheric Administration Fisheries as a species of concern. Gonad histology and gonadosomatic index data indicated peak spawning in late spring (May–June), with limited spawning activity into summer. The histologically derived length at 50% maturity for female Cusk was 39.5 cm TL. Fecundity varied from a quarter million to four million oocytes, with a positive allometry versus size indicating that larger females have proportionally higher fecundity than smaller females. Male Cusk had unusually low gonadal investment for a gadiform, and males of all sizes examined (down to 21 cm) had spermatozoa present. Male maturity was equivocal even when the relative proportions of sperm stages were quantified through image analysis of gonad histology; further anatomical and physiological studies of small males are required to assess functional maturity in male cusk. The sex ratio at length indicated more males at larger sizes, and males had faster growth and larger size at age than females. Condition patterns also suggested lower condition for females than males after spawning and generally less variable condition for males. Gonadal investment, relative condition, and growth patterns all suggest differences in energy allocation between the sexes. This data‐poor species has an uncertain stock status in U.S. waters; therefore, the results of the current work provide important information to its management. [ABSTRACT FROM AUTHOR]

Rapid warming in the Gulf of Maine may influence the success or invasiveness of the Asian shore crab, Hemigrapsus sanguineus. To better predict the effects of climate change on this invasive species, it is necessary to measure its energy dynamics under a range of conditions. However, previous research has only focused on the metabolism of this intertidal species in water. We sampled adult crabs from three different sites and measured their metabolic rates in the air. We show that metabolic rate increases with body mass and the number of missing limbs, but decreases with the number of regenerating limbs, possibly reflecting the timing of energy allocation to limb regeneration. Importantly, metabolic rates measured here in the air are ~4× higher than metabolic rates previously measured for this species in water. Our results provide baseline measurements of aerial metabolic rates across body sizes, which may be affected by climate change. With a better understanding of respiration in H. sanguineus, we can make more informed predictions about the combined effects of climate change and invasive species on the northeast coasts of North America. [ABSTRACT FROM AUTHOR]

Aim: Anthropogenic warming of marine systems has caused biological and physiological responses that are fundamentally altering ecosystem structure. Because estuaries exist at the land‐ocean interface, they are particularly vulnerable to the effects of ocean warming as they can undergo rapid biogeochemical and hydrological shifts due to climate and land‐use change. We explored how multiple components of estuarine fish diversity—turnover, richness, and abundance—have changed in the North Atlantic and Gulf of Mexico estuaries across space and time and the drivers of change. Location: North Atlantic and Gulf of Mexico. Taxa: Fish. Method: We compiled long‐term (>30 years), continent‐wide fisheries independent trawl surveys conducted in estuaries—from the Gulf of Maine to the Gulf of Mexico (U.S. waters)—and combined these with climate and land‐use‐land‐cover data to examine trends and ecological drivers of fish richness, abundance and turnover using mixed‐effect models. Results: Species richness, abundance and turnover have increased in North Atlantic and Gulf of Mexico estuaries in the last 30 years. These changes were mediated largely by sea‐surface temperature anomalies, especially in more northern estuaries where warming has been relatively pronounced. Main Conclusion: The increasing trajectory of turnover in many estuaries suggests that fish communities have changed fundamentally from the baselines. A fundamental change in community composition can lead to an irreversible trophic imbalance or alternative stable states among other outcomes. Thus, predicting how shifting community structures might influence food webs, ecosystem stability, and human resource use remain a pertinent task. [ABSTRACT FROM AUTHOR]

Species' response to rapid climate change can be measured through shifts in timing of recurring biological events, known as phenology. The Gulf of Maine is one of the most rapidly warming regions of the ocean, and thus an ideal system to study phenological and biological responses to climate change. A better understanding of climate‐induced changes in phenology is needed to effectively and adaptively manage human‐wildlife conflicts. Using data from a 20+ year marine mammal observation program, we tested the hypothesis that the phenology of large whale habitat use in Cape Cod Bay has changed and is related to regional‐scale shifts in the thermal onset of spring. We used a multi‐season occupancy model to measure phenological shifts and evaluate trends in the date of peak habitat use for North Atlantic right (Eubalaena glacialis), humpback (Megaptera novaeangliae), and fin (Balaenoptera physalus) whales. The date of peak habitat use shifted by +18.1 days (0.90 days/year) for right whales and +19.1 days (0.96 days/year) for humpback whales. We then evaluated interannual variability in peak habitat use relative to thermal spring transition dates (STD), and hypothesized that right whales, as planktivorous specialist feeders, would exhibit a stronger response to thermal phenology than fin and humpback whales, which are more generalist piscivorous feeders. There was a significant negative effect of western region STD on right whale habitat use, and a significant positive effect of eastern region STD on fin whale habitat use indicating differential responses to spatial seasonal conditions. Protections for threatened and endangered whales have been designed to align with expected phenology of habitat use. Our results show that whales are becoming mismatched with static seasonal management measures through shifts in their timing of habitat use, and they suggest that effective management strategies may need to alter protections as species adapt to climate change. [ABSTRACT FROM AUTHOR]

In many species, group foraging is a strategy used to increase the efficiency of individuals to find and exploit patchy prey. Humpback whales (Megaptera novaeangliae) are one of the few baleen whale species reported to use coordinated foraging strategies. One of these behaviors, bubble‐net feeding, has been observed in several populations, though the behaviors of individuals within these groups are largely unknown. This study used multisensor kinematic tag data from 26 whales foraging in the Southern Gulf of Maine to analyze individual bubble‐net feeding behaviors. Linear mixed effects models were used to test if there were differences in individual whales' dive behaviors across group size. The results indicate that individuals performed consistent bubble‐net feeding behaviors regardless of the size of their foraging group, except when using one specific foraging behavior, the upward spiral. Overall complexity of foraging dives, based on the three‐dimensional movements of the dive, decreased with increasing group size when group members used upward spirals. This may indicate that in larger groups, participants in coordinated feeding events need to move less and expend less energy to corral prey. This study provides new insights into the effects of group size on individual behavior and group coordination in humpback whales. [ABSTRACT FROM AUTHOR]

Spring phytoplankton blooms in the Gulf of Maine (GoM) are sensitive to climate‐related local and remote forcing. Nutrient supply through the slope water intrusion has been viewed as critical in regulating the GoM spring blooms, with an assumption that nitrogen is the primary limiting nutrient. In recent years, this paradigm has been challenged, with silicate being recognized as another potential limiting nutrient, but the source of silicate and its associated water mass remain difficult to be determined. In this study, a time series of spring bloom magnitude was constructed using a self‐organizing map algorithm, and then correlated with the fluctuation of water composition in the deep Northeast Channel. The results reveal the importance of silicate supply from previously less‐recognized deep Scotian Shelf Water inflow. This study offers a new hypothesis for spring bloom regulation, providing a better understanding of mechanisms controlling the spring bloom magnitude in the GoM. [ABSTRACT FROM AUTHOR]

The Gulf of Maine North Atlantic Time Series (GNATS) has been run since 1998, across the Gulf of Maine (GoM), between Maine and Nova Scotia. GNATS goals are to provide ocean color satellite validation and to examine change in this coastal ecosystem. We have sampled hydrographical, biological, chemical, biogeochemical, and bio‐optical variables. After 2008, warm water intrusions (likely North Atlantic Slope Water [NASW]) were observed in the eastern GoM at 50–180 m depths. Shallow waters (<50 m) significantly warmed in winter, summer, and fall but cooled during spring. Surface salinity and density of the GoM also significantly increased over the 20 years. Phytoplankton standing stock and primary production showed highly‐significant decreases during the period. Concentrations of phosphate increased, silicate decreased, residual nitrate [N*; nitrate‐silicate] increased, and the ratio of dissolved inorganic nitrogen:phosphate decreased, suggesting increasing nitrogen limitation. Dissolved organic carbon (DOC) and its optical indices generally increased over two decades, suggesting changes to the DOC cycle. Surface seawater carbonate chemistry showed winter periods where the aragonite saturation (Ωar) dropped below 1.6 gulf‐wide due to upward winter mixing of cool, corrosive water. However, associated with increased average GoM temperatures, Ωar has significantly increased. These results reinforce the hypothesis that the observed decrease in surface GoM primary production resulted from a switch from Labrador Sea Water to NASW entering the GoM. A multifactor analysis shows that decreasing GoM primary production is most significantly correlated to decreases in chlorophyll and particulate organic carbon plus increases in N* and temperature. Plain Language Summary: A 20‐year coastal time series, the Gulf of Maine North Atlantic Time Series, has included regular oceanographic measurements across the Gulf of Maine (GoM), one of the fastest warming ocean water bodies on Earth. Physical, chemical, biological, biogeochemical, and bio‐optical measurements demonstrate: (a) unexpected, statistically‐significant surface cooling in spring months along with surface warming in all other seasons, (b) deep warm water in the GoM after 2008, likely associated with intrusions of warm, saline N. Atlantic Slope water, (c) declines in phytoplankton primary production over 20 years, most significantly associated with chlorophyll, particulate organic carbon, temperature, and residual nitrate (the excess of nitrate over silicate), (d) deep mixing events in winter bring corrosive water to the surface, making it more likely to dissolve carbonates of shell formers and (e) dissolved organic carbon and its colored constituents progressively increased in the GoM, yet this does not correlate significantly with the drop in primary production. These results link the control of GoM productivity to waters originating outside of the GoM in the Northwest Atlantic. Key Points: A 20‐year Gulf of Maine (GoM) time series shows surface cooling in spring months but warming in all other seasonsPrimary production declined over 20 years, mostly associated with changes in chlorophyll, particulate organic carbon, temperature, and residual nitrate (nitrate‐silicate)Deep intrusions of warm, saline North Atlantic Slope Water occurred post‐2008 into the GoM [ABSTRACT FROM AUTHOR]

Northern sand lance (Ammodytes dubius) are among the most critically important forage fish throughout the Northeast US shelf. Despite their ecological importance, little is known about the larval transport of this species. Here, we use otolith microstructure analysis to estimate hatch and settlement dates of sand lance and then use these measurements to parametrize particle tracking experiments to assess the source–sink dynamics of three prominent sand lance habitats in the Gulf of Maine: Stellwagen Bank, the Great South Channel, and Georges Bank. Our results indicate the pelagic larval duration of northern sand lance lasts about 2 months (range: 50–84 days) and exhibit a broad range of hatch and settlement dates. Forward and backward particle tracking experiments show substantial interannual variability, yet suggest transport generally follows the north to south circulation in the Gulf of Maine region. We find that Stellwagen Bank is a major source of larvae for the Great South Channel, while the Great South Channel primarily serves as a sink for larvae from Stellwagen Bank and Georges Bank. Retention is likely the primary source of larvae on Georges Bank. Retention within both Georges Bank and Stellwagen Bank varies interannually in response to changes in local wind events, while the Great South Channel only exhibited notable retention in a single year. Collectively, these results provide a framework to assess population connectivity among these sand lance habitats, which informs the species' recruitment dynamics and impacts its vulnerability to exploitation. [ABSTRACT FROM AUTHOR]

Fish reproduction is energetically costly, leading to a suite of energy allocation strategies for maximizing lifetime reproductive potential. Assessing energetic allocation for species that inhabit a wide distributional range can provide insight into different strategies found across individuals and populations. The Northern stock of black sea bass (Centropristis striata) inhabits the U.S. Northeast continental shelf from Cape Hatteras, NC, to the Gulf of Maine, and spawns inshore throughout this distribution from April to October. To assess energy allocation towards spawning, C. striata were collected in four regions across this distribution and throughout their spawning season. By assessing energetic allocation (lipid, energy density and total energy) in muscle, liver and gonad tissues, C. striata were identified as mixed breeders because while they mobilized somatic energy stores towards reproductive development, they also used energy acquired from their diet to sustain reproductive output throughout the spawning season. Unlike male fish, female fish both invested more energy into liver and gonad tissues and exhibited regional differences in energetic values. For both sexes, C. striata in the northern portion of the distribution had lower energetic values both in the somatic stores and towards gonadal development than the fish in the southern portion of the distribution, possibly because of longer migration distance. Overall, the authors found significant spatial variation in energetic constraints that may affect reproductive output and success (recruitment), a relevant result as C. striata are a popular recreational and commercial species throughout this distribution. [ABSTRACT FROM AUTHOR]

Seal populations in the Gulf of Maine have been recovering from historical bounty‐driven declines since they received federal protection in 1972. In the past few decades, their population growth has sparked renewed concerns over conflict between pinniped and fish conservation.In the Penobscot River in Maine, USA, where restoration efforts over the past decade have aimed at restoring diadromous fish runs, seal predation on the endangered Atlantic salmon (Salmo salar) has become a growing concern.Quantitative and qualitative data for individual salmon, as well as the presence of putative seal‐induced injury, have been collected from salmon passing upriver at dams in the Penobscot River since 2012.An analysis of seal‐induced injury rate with demographic data, river herring returns, estuary fish biomass estimates, and timing of peak estuary fish biomass revealed that the seal‐induced injury rate declined in the Penobscot River from 2012 to 2019, coincident with increasing river herring returns and estuary fish biomass. Despite a potentially increasing seal population, these results suggest that predator swamping from increasing forage fish may provide protection to salmon against seal predation.The presence of multiple injuries on an individual salmon was also significantly associated with the probability of a salmon having a seal‐induced injury. Lamprey wounds and lacerations on salmon were commonly associated with seal‐induced injury, suggesting a confounding effect of multiple stressors.This assessment illustrates how multi‐species diadromous restoration activities may alter predator–prey interactions in ways that support salmon conservation efforts. As demonstrated in the Penobscot River, a focus on overall ecosystem health and restoration can benefit multiple species that use the river. Insights from this study may help inform future management decisions in other human‐impacted systems where protected predators come into conflict with endangered prey. [ABSTRACT FROM AUTHOR]

In the U.S. western Atlantic Ocean, North Atlantic right whales Eubalaena glacialis are subject to gear entanglement in fixed‐gear vertical line fisheries, with mortality risk increasing with line strength and spatial density. U.S. federal management agencies have mandated vertical line strength limits (235.033‐kg‐m [1,700‐ft‐lb] breaking strength) to curtail the injury and mortality risk that entanglement poses to right whales. Limiting the strength of vertical lines used in the trap fishery for American lobster Homarus americanus, however, could negatively impact the economic resilience of New England fishing communities if it forces the purchase of new equipment or increases the incidence of break‐offs and lost gear. We provide a novel look at the spatially distinct vertical line strength requirements for the Maine American lobster trap fishery. The hauling load requirements of the fishery were modeled using measurements of strain put on vertical lines used in typical lobster trap operations to determine the minimum strength necessary to fish safely and avoid dangerous line breaks. New regulations on minimum trawl lengths (number of traps fished per vertical line) taking effect in 2022 will cause increases in lobster fishery vertical line loads across all fishing grounds, considerably increasing with depth and distance from shore. Our models indicated that inshore areas can be safely fished with vertical lines within the recommended whale‐safe 235.033‐kg‐m (1,700‐ft‐lb) breaking strength specification, whereas the offshore lobster fishery will need a suite of measures beyond line strength reductions to reduce entanglement risk and mortality of right whales. We provide guidelines for the minimum line strength necessary for fishery operations, which can be used to inform management goals that balance the need for a sustainable lobster fishery and the conservation of right whales. [ABSTRACT FROM AUTHOR]

In shallow, tidally dominated regions, overtides and the mean state of the ocean are coupled through their simultaneous generation by nonlinear processes. We present a new method that uses observed overtides (e.g., M4) and mean currents to independently assess the accuracy of mean dynamic topography (MDT) predicted by ocean models. This is useful in regions where no sufficiently long, geodetically referenced sea level records are available for validation of the predicted MDT. We apply the new method to a regional model of the Gulf of Maine/Scotian Shelf region (GoMSS) and a barotropic, higher resolution model focused on the upper Bay of Fundy (UBoF). We first show that the tides and mean circulation predicted by UBoF are in good agreement with observations and a significant improvement over GoMSS. Next, we use UBoF to demonstrate that observed overtides are useful in selecting the optimal bathymetry and constraining parameters of an ocean model. An accurate bathymetry is critical for capturing the dominant nonlinear processes that generate overtides and control the form of MDT in shallow, tidally dominated regions. Finally, we use the observed overtides to argue that the MDT predicted by UBoF is more realistic than the prediction by GoMSS. In the vicinity of headlands, both horizontal advection and bottom friction in UBoF generate harmonics of the tidal flow and local setdowns of coastal MDT of O $\mathcal{O}$(10 cm). The prediction of such features, validated by observed overtides, can provide guidance in future deployments of tide gauges in support of geoid and ocean model validation. Plain Language Summary: Overtides are higher harmonics of the main astronomical tidal constituents. They are often observed in shallow, tidally dominated regions and are dynamically linked to spatial variations in the mean state. In this study, we use observed overtides to compare predictions by a regional model of the Gulf of Maine/Scotian Shelf region (GoMSS) and a simpler, but higher resolution, model of the upper Bay of Fundy (UBoF). It is first shown that the tides and mean circulation predicted by UBoF are in good agreement with observations and a significant improvement over GoMSS. UBoF is then used to demonstrate that observed overtides are useful in optimizing the configuration of ocean models, including the representation of the sea floor. We next show that observed overtides can be used to assess the accuracy of the mean state predicted by ocean models, including spatial variations in mean sea level. An advantage of this approach is that overtides can be estimated from short records of sea level and currents thereby increasing the number of locations at which models can be assessed. Finally, we argue that ocean models validated using overtides can provide guidance in the design of geodetic and ocean observing systems in tidally dominated regions. Key Points: Observed overtides are useful in selecting the optimal bathymetry and constraining parameters of ocean models in tidally dominated regionsThey can also be used to validate, and physically interpret, mean dynamic topography predicted by ocean modelsOvertides are useful in the design of geodetic and ocean observing systems in tidally dominated regions [ABSTRACT FROM AUTHOR]

Recent work in the Gulf of Maine multispecies recreational fishery has established responsible fishing practices that anglers can use to reduce bycatch and the discard mortality of three key groundfish species. However, anglers represent a diverse stakeholder group whose backgrounds and experiences may influence how they receive, support, and adopt responsible fishing practices that aim to sustain catch‐and‐release angling opportunities. We therefore surveyed Gulf of Maine recreational anglers who target groundfish, including Atlantic Cod Gadus morhua, Haddock Melanogrammus aeglefinus, and Cusk Brosme brosme, to assess whether differences among anglers influenced how likely anglers were to voluntarily adopt or consider adopting responsible fishing practices and which information channels they used to obtain such information. By broadly sampling Gulf of Maine recreational fishing license holders via an online survey, we collected responses from 306 respondents who targeted groundfish in some capacity; several topics, including fishing activity and experience, responsible fishing practices, information channels, and sociodemographics, were addressed in the survey. A latent class cluster analysis found that respondents who participate in this regional fishery can be broadly categorized into three distinct classes (Striped Bass [Morone saxatilis] Enthusiasts, All‐rounders, and Offshore Groundfishers) from their primary fishing mode and target species. Despite the presence of these latent classes, class membership did not affect how likely respondents were to voluntarily adopt or consider adopting species‐specific fishing practices from previous scientific investigations. However, class membership was observed to influence how respondents used information channels to receive angling information, with Offshore Groundfishers relying more often on captains and crew than the other classes. Therefore, to promote responsible fishing practices alongside regulations, we recommend that fishery managers use a mixed outreach program to effectively communicate and engage with this portion of the community until more directed studies can be conducted. [ABSTRACT FROM AUTHOR]

To investigate the coastal current in the Gulf of Maine (GoME) and its relation to forcing from outside of the gulf, a high‐resolution circulation model was developed and validated. Our model shows that the Eastern Maine Coastal Current (EMCC) possesses two cores, an offshore and a nearshore core that peak in summer and spring, respectively. The two cores can be traced back to outflows from the Bay of Fundy from opposite sides of Grand Manan Island, and both cores are deeper and slightly more onshore in summer and fall in response to tidal mixing, surface thermal stratification and wind. The two cores merge south of Pleasant Bay, then split into two branches again east of Mount Desert Rock, where the nearshore branch flows along the coast, while the offshore branch turns southward to recirculate in the eastern GoME. Subject to variations of Scotian Shelf Water and Slope Water (SW) inflows, the offshore veering occurs further upstream (northeastward) in late winter and summer, but gradually shifts downstream (southwestward) from summer to winter. Diagnosis of momentum balance demonstrates that the EMCC is primarily driven by the pressure gradient force (PG), of which the barotropic PG is dominant and offshore, while the baroclinic PG is onshore and increases with depth. The large baroclinic PG at depths, modulated by SW, that is, blended by tidal mixing, offsets the barotropic PG. Near the surface, the barotropic PG is nearly balanced by the Coriolis force, forming the geostrophic EMCC. Plain Language Summary: The coastal current in the Gulf of Maine (GoME) plays an important role in modulating fisheries in Maine. To investigate the coastal current and its relation to different forcing, a high‐resolution circulation model was developed and validated. Our model shows that in the eastern GoME, the coastal current has two cores, namely an offshore and a nearshore core peaking in summer and spring, respectively. The two cores can be traced back to outflows from the adjacent Bay of Fundy. Both cores are deeper and slightly more onshore in summer and fall due to tidal mixing, large solar radiation and weak wind. The two cores merge as they flow downstream, then bifurcate again east of Mount Desert Rock, where the nearshore branch flows along the coast, while the offshore one turns southward. Subject to variations of inflows from outside of the gulf, the offshore turning occurs further upstream in late winter and summer, but gradually shifts downstream from summer to winter. Analyses of momentum balance show that the coastal current is primarily modulated by the variation of deep denser water inflow that is blended by tidal mixing. Key Points: Eastern Maine Coastal Current (EMCC) exhibits two cores, stemming from outflows from Bay of FundyEMCC is driven by the pressure gradient force that is modulated by Slope Water spreading over Jordan BasinOffshore veering of EMCC resets further upstream in late winter and again in early summer [ABSTRACT FROM AUTHOR]

Our team has initiated a selective breeding program for regional strains of sugar kelp, Saccharina latissima, to improve the competitiveness of kelp farming in the United States. Within our breeding program, we also include an endemic putative species, Saccharina angustissima, locally referred to as skinny kelp. We crossed uniclonal gametophyte cultures derived from 37 wild‐collected blades representing five sugar kelp strains and one skinny kelp strain to produce 104 unique crosses. Each cross was outplanted on a near‐shore research farm located in the Gulf of Maine (GOM). After the first farming season, our results indicated that sugar kelp and skinny kelp were interfertile, and produced mature and reproductively viable sporophytes. Morphological traits of individual blades varied depending on the parental contribution (sugar vs. skinny), with significant differences found in progeny blade length, width, thickness, and in stipe length and diameter. Despite these differences, wet weight and blade density per plot showed no statistical differences regardless of the cross. Given their published genetic similarity and their interfertility shown here, S. angustissima and S. latissima may not be different species, and may each contribute genetic diversity to breeding programs aimed at meeting ocean farming and market needs. [ABSTRACT FROM AUTHOR]

The oceanographic conditions in the Gulf of Maine, Scotian Shelf, Slope Sea, and surroundings are determined by interplay of two major circulation systems—the Gulf Stream and Labrador Current. This study aims to better understand regional long‐term climate trends caused by the Gulf Stream decadal variability. The in situ data analysis confirms a continuous slow warming within all three areas over the last five decades. It is shown that the warming accelerated in the recent 10 years coinciding with a strengthened northward incursion of warm water in the summer months. Such strong northward migration of warm water was not seen in the four preceding decades, making the current rapid warming different from previous ones. We argue that the recent decadal‐scale warming is unique and may signal that the shift of the thermal regime in this region may be at least partially caused by a changed pattern of the Gulf Stream extension zone's long‐term variability. We found that the Scotian Shelf and Slope Water region has recently been warming much faster than the Gulf of Maine, both in the subsurface (the upper ~ 50 m) and in deeper layers, indicating that the probable cause of the faster warming in the most recent decade is due to the regime change in the Gulf Stream extension region. [ABSTRACT FROM AUTHOR]

Atlantic cod (Gadus morhua, Linnaeus 1758) in the western Gulf of Maine are managed as a single stock despite several lines of evidence supporting two spawning groups (spring and winter) that overlap spatially, while exhibiting seasonal spawning isolation. Low‐coverage whole‐genome sequencing was used to evaluate the genomic population structure of Atlantic cod spawning groups in the western Gulf of Maine and Georges Bank using 222 individuals collected over multiple years. Results indicated low total genomic differentiation, while also showing strong differentiation between spring and winter‐spawning groups at specific regions of the genome. Guided regularized random forest and ranked FST methods were used to select panels of single nucleotide polymorphisms (SNPs) that could reliably distinguish spring and winter‐spawning Atlantic cod (88.5% assignment rate), as well as males and females (95.0% assignment rate) collected in the western Gulf of Maine. These SNP panels represent a valuable tool for fisheries research and management of Atlantic cod in the western Gulf of Maine that will aid investigations of stock production and support accuracy of future assessments. [ABSTRACT FROM AUTHOR]

Terminal tackle regulations can be a valuable tool for fisheries management, especially in multispecies fisheries where bycatch and discards are common issues. In the Gulf of Maine, recreational anglers frequently discard critically depleted Atlantic cod Gadus morhua L. as bycatch when targeting the abundant haddock Melanogrammus aeglefinus (L.) stock. The present study investigated species catch composition, catch rates and animal welfare across various terminal tackle setups, and aspects of capture and handling with the goal of reducing bycatch and discard mortality. Overall, 2558 cod and 4266 haddock were captured with six terminal tackle setups in the western Gulf of Maine from April to October 2018. Along with angler experience and capture depth, lure type primarily influenced species catch composition and catch‐per‐unit‐effort; hook types additionally influenced hook‐removal times and physical injuries to fish. Results indicate that using baited hooks can both promote haddock catch and reduce cod bycatch, with specific hook types promoting increased survival. [ABSTRACT FROM AUTHOR]

People in the Northeast United States have a long history of benefitting from the ocean in many ways, exemplified by the region's important cod and lobster fisheries, coastal tourism and recent expansion of offshore energy. Over the past few decades, the region has become one of the fastest warming spots on the planet, has seen significant growth in coastal populations, and expansion of new sectors into the marine environment, resulting in ecosystem shifts and changes to the supply and distribution of these benefits. With these changes comes a need for measuring ocean health to understand how engagement with the ocean may be affected, and how regional management may need to adapt.To address this need, we tailored the Ocean Health Index framework to the U.S. Northeast region, scoring eight distinct goals for ocean health on a scale of 0 to 100 for 11 sub‐regions over 13 years (2005–2017).All goal scores were averaged resulting in an Ocean Health Index score of 83 for the Northeast in 2017. This score fluctuated by 1 point in either direction (82–84) in the previous 12 years.The lowest scoring goals in 2017 also exhibited the highest volatility since 2005, Food Provision (64) and Resource Access Opportunities (71).The region's highest goal scores came from Livelihoods & Economies (99) and Biodiversity (90) and remained stable during the study period.Clean Waters scores had a steady, significant downward trend since 2005, while Resource Access Opportunities and Aquaculture show the largest improvements.This synthesis of over 50 datasets to create annual aggregate scores provides the public, government and non‐government agencies with an easily digestible summary of how the region is faring in regards to ocean health. Perhaps even more importantly, this synthesis allows for the tracking of trends over time and the ability to quickly identify and prioritize low‐scoring components of ocean health that could benefit from dedicated resources for improvement.As managers plan for the future in a changing Northeast marine region, the ability to track annual changes in ocean health and its respective components is key to making decisions that benefit the entire social‐ecological system. A free Plain Language Summary can be found within the Supporting Information of this article. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Climate change has been shown to impact marine fish populations and communities. With small population sizes, long reproduction times, and a rapidly warming habitat, thorny skate (Amblyraja radiata) could be particularly vulnerable. To examine this possibility, we used a two‐stage generalized additive model to project future thorny skate abundances under two different climate scenarios. This is the first study in the northeastern United States to compare projections based on different survey methods (bottom trawl and longline), and results were heavily impacted by survey methodology. Models trained with the NOAA Bottom Trawl Survey projected a decrease in abundance of ~60%–80% in the Gulf of Maine and Georges Bank under the RCP 8.5 climate scenario. With aggressive mitigation (RCP 4.5), these decreases could be reduced to ~35%–45%. Models trained with a recent NOAA longline survey indicated that thorny skate abundance would be reduced 22% and 37% under business as usual and mitigation, respectively. There are substantial methodological differences between the two data sets, including capture technique and efficiency, total habitat coverage, and spatio‐temporal coverage. This underscores the importance of continued, methodologically diverse surveys on the Northeast US continental shelf. Our results indicate that climate change will continue to negatively impact thorny skate populations by reducing the amount of thermally suitable habitat in the southern extent of their range. This information should be considered in future management decisions. [ABSTRACT FROM AUTHOR]

As the nutrient‐rich subsurface slope water intruding into the deep basin of the Gulf of Maine (GoM) supports the high biological productivity in the semi‐enclosed gulf, it is important to understand the process and time scale of such slope water intrusion. This study focuses on variations of the GoM deep water on seasonal to interannual time scales and the influences of open ocean processes on the temporal variation of the deep water properties. Based on long‐term monitoring data, it is found that the deep water at Jordan Basin (one of three major basins in the GoM) is persistently warmer in winter than in summer, which is distinctly different from the seasonality of surface water in the basin and the deep water on neighboring shelf seas. The unique seasonality in the deep GoM reflects a time‐lagged response to shoreward intrusion of the subsurface slope water off the GoM. Both observation‐based lag‐correlation analyses and numerical simulations confirm a timescale of approximately 3 months for the intruding subsurface slope water to flow from Northeast Channel to Jordan Basin. Properties of the intruding slope water at the Northeast Channel were significantly correlated with the Gulf Stream position and dramatically impacted by episodic warm‐core rings shed from Gulf Stream. Inside the deep GoM, the intruding slope water was also indirectly affected by the fresher water input from Nova Scotia Current. Spreading of the fresher water inside the gulf strengthens near‐surface stratification, suppresses deep convection, and preserves heat and salt in the deep GoM during the wintertime. Plain Language Summary: Nutrient‐rich slope water intruding into the deep basin of the Gulf of Maine provides 30% of the nutrients needed to support the high biological productivity and high yield fisheries in the gulf. Our analysis of long‐term mooring data shows that the deep water in the Gulf of Maine changes in a unique fashion: being warmer in winter and colder in summer. This unique seasonality differs dramatically from the deep water on the neighboring continental shelves. It represents a delayed response of the deep water in the gulf to seasonal changes of the major currents in the adjacent open ocean. We explained the timescale of this delayed response from multiple angles using mooring data, numerical simulations, and remote sensing data. We found that signal of open ocean change at shelf edge (e.g., induced by Gulf Stream meandering and associated eddies) propagates into the deep gulf basin in about 3 months. Meanwhile, the surface buoyant and low‐salinity inflow from the upstream Scotian Shelf into the Gulf of Maine tends to suppress vertical mixing in the gulf and helps maintain the heat and salt stored in the deep gulf even in the wintertime when the surface ocean loses heat to the cold atmosphere. Key Points: Bottom water temperature at Jordan Basins is warmer during winter than summer, which is distinctly different from neighboring shelf seasThis unique seasonality reflects a delayed response (approximately 3 months) of Jordan Basin to the changes in the slope seaDeep water at Jordan Basin is affected by the Nova Scotia Current and Gulf Stream warm‐core rings [ABSTRACT FROM AUTHOR]

In mosaic marine habitats, such as intertidal zones, ocean acidification (OA) is exacerbated by high variability of pH, temperature, and biological CO2 production. The nonlinear interactions among these drivers can be context‐specific and their effect on organisms in these habitats remains largely unknown, warranting further investigation.We were particularly interested in Mytilus edulis (the blue mussel) from intertidal zones of the Gulf of Maine (GOM), USA, for this study. GOM is a hot spot of global climate change (average sea surface temperature (SST) increasing by >0.2°C/year) with >60% decline in mussel population over the past 40 years.Here, we utilize bioenergetic underpinnings to identify limits of stress tolerance in M. edulis from GOM exposed to warming and OA. We have measured whole‐organism oxygen consumption rates and metabolic biomarkers in mussels exposed to control and elevated temperatures (10 vs. 15°C, respectively) and current and moderately elevated PCO2 levels (~400 vs. 800 µatm, respectively).Our study demonstrates that adult M. edulis from GOM are metabolically resilient to the moderate OA scenario but responsive to warming as seen in changes in metabolic rate, energy reserves (total lipids), metabolite profiles (glucose and osmolyte dimethyl amine), and enzyme activities (carbonic anhydrase and calcium ATPase).Our results are in agreement with recent literature that OA scenarios for the next 100–300 years do not affect this species, possibly as a consequence of maintaining its in vivo acid‐base balance. [ABSTRACT FROM AUTHOR]

Spatial relationships between predators and prey provide critical information for understanding and predicting climate‐induced shifts in ecosystem dynamics and mitigating human impacts. We used Stellwagen Bank National Marine Sanctuary as a case study to investigate spatial overlap among sand lance (Ammodytes dubius), a key forage fish species, and two protected predators: humpback whales (Megaptera novaeangliae) and great shearwaters (Ardenna gravis). We conducted 6 years (2013–2018) of standardized surveys and quantified spatial overlap using the global index of collocation. Results showed strong, consistent collocation among species across seasons and years, suggesting that humpback whales and great shearwater distributions are tightly linked to sand lance. We propose that identifying sand lance habitats may indicate areas where humpbacks and shearwaters aggregate and are particularly vulnerable to human activities. Understanding how sand lance influence predator distributions can inform species protection and sanctuary management under present and future scenarios. [ABSTRACT FROM AUTHOR]

Climate change is one of the biggest challenges facing development and continuation of sustainable aquaculture in temperate regions. We primarily consider the ecological and physical resilience of aquaculture in the Gulf of Maine (GoM), where a thriving industry includes marine algae, extensive and intensive shellfish aquaculture, and a well‐established Atlantic salmon industry, as well as the infrastructure required to support these economically important ventures. The historical record of sea surface temperature in the GoM, estimated from gridded, interpolated in situ measurements, shows considerable interannual and decade‐scale variability superimposed on an overall warming trend. Climate model projections of sea surface temperature indicate that the surface waters in the GoM could warm 0.5–3.5°C beyond recent values by the year 2100. This suggests that, while variability will continue, anomalous warmth of marine heatwaves that have been observed in the past decade could become the norm in the GoM ca. 2050, but with the most significant impacts to existing aquaculture along the southernmost region of the coast. We consider adaptations leading to aquacultural resilience despite the effects of warming, larger numbers of harmful nonindigenous species (including pathogens and parasites), acidification, sea‐level rise, and more frequent storms and storm surges. Some new species will be needed, but immediate attention to adapt existing species (e.g. preserve/define wild biodiversity, breed for temperature tolerance and incorporate greater husbandry) and aquaculture infrastructure can be successful. We predict that these measures and continued collaboration between industry, stakeholders, government and researchers will lead to sustaining a vibrant working waterfront in the GoM. [ABSTRACT FROM AUTHOR]

Oceanic conditions along the Atlantic Coast of North America are changing rapidly. Surface water temperatures in the Gulf of Maine have increased faster than 99% of the global oceans, and major infrastructure projects, including the largest windfarm in the world, are under development along this seaboard. In Canada and the US, the Atlantic sea scallop (Placopecten magellanicus) supports lucrative fisheries, which were originally founded on an extensive scientific framework focusing on stock assessment. The sea scallop is an ideal sentinel species, as it is highly sensitive to changes in marine conditions. We used a drop camera system to estimate the number and size of scallops, as well as the distribution of their reproductive potential, over 70,000 km2 of the continental shelf in 2016–2018, an area that nearly covers the entire range of this species. In total, we estimated that there were 34 billion individual scallops (95% confidence limits: 22–46 billion) within the species' range. In this paper, we examine the role of the sea scallop as a baseline sentinel species that can be used to measure the impacts of environmental change and anthropogenic developments. [ABSTRACT FROM AUTHOR]

Conventional observations show spiny dogfish (Squalus acanthius Linnaeus) rarely eat Atlantic cod (Gadus morhua Linnaeus; 0.02% of stomachs) in the northwestern Atlantic Ocean. Critics express concern that digestion may limit species‐level prey identification, and with recovery from overfishing, dogfish populations may be suppressing cod by competition or predation. This study applied a real‐time PCR TaqMan assay to identify cod in dogfish stomachs collected by cooperating fishing boats during normal trawling operations (May 2014–May 2015; Gulf of Maine, Georges Bank). Conventional methods observed 51 different prey taxa and nearly 1,600 individual prey items, but no cod were observed. Cod DNA was detected in 31 (10.5%) of the dogfish stomachs, with a higher percentage of these from the homogenate of amorphous, well‐digested prey and stomach fluids (20 stomachs or 65%) than from discrete animal tissues (11 stomachs or 35%). Re‐examination of photographs of these 11 tissue samples revealed one whole, partially digested fish that could be recognized in hindsight as cod. Cod DNA was observed in dogfish stomachs year round: in January (1 of 1 trip), February (1 of 1), May (1 of 3), June (0 of 1), July (3 of 4), August (1 of 2), and October (3 of 3). Although these data suggest higher interaction rates between dogfish and cod than previously observed, addressing the population consequences of this predator–prey relationship requires a robust sampling design, estimates of digestion rates by dogfish to account for complete degradation of DNA sequences, and consideration for dogfish scavenging during fishing operations. [ABSTRACT FROM AUTHOR]

Variability in life history traits and structural diversity of commercially exploited fishes in response to stress can impact their population dynamics and sustainability. Using data from a fishery dependent sampling program from 1978 to 2011, we evaluated temporal variability of size and growth of adult Atlantic herring (Clupea harengus) in the Gulf of Maine. We then developed and tested the hypotheses on the links of such temporal changes to population density and environmental factors and found decreases in size and growth potential. Generalized additive models found that density dependence was the main driver of such changes over sea surface temperature and salinity. Our results highlight the importance of density dependent processes in regulating growth and population size structure for Atlantic herring in the Gulf of Maine. [ABSTRACT FROM AUTHOR]

The Gulf of Maine (GOM) commercial lobster fishery has approximately 3.5 million actively fished traps and captures several nontargeted groundfish species, including Atlantic Cod Gadus morhua, as bycatch, yet there has been limited research on the incidental mortality of groundfish in this fishery. Although the mortality of Atlantic Cod has been estimated in other GOM commercial fisheries, unaccounted discard mortality in the lobster fishery may impair recovery efforts for this stock. To help meet research needs, we assessed the discard mortality rate of Atlantic Cod captured in the Maine Lobster Management Zone G commercial lobster fishery using acoustic transmitters and observations of viability. From 2016 to 2017, 111 Atlantic Cod were captured in 18,853 individual trap hauls and were observed for viability. A subsample of 54 Atlantic Cod was externally tagged with acoustic transmitters and observed after release. The combined at‐vessel mortality (9.3%) and model‐based long‐term discard mortality (17.1%) estimates indicated an overall discard mortality rate of 24.8% for Atlantic Cod captured in commercial lobster gear. Based on this finding and the low bycatch of Atlantic Cod in the lobster fishery, the commercial lobster fishery may not be responsible—to the extent previously assumed—for hindering the GOM Atlantic Cod stock's regrowth. [ABSTRACT FROM AUTHOR]

Astronomical variations in tidal magnitude can strongly modulate the severity of coastal flooding on daily, monthly, and interannual timescales. Here we present a new quasi‐nonstationary skew surge joint probability method (qn‐SSJPM) that estimates interannual fluctuations in flood hazard caused by the 18.6‐ and quasi 4.4‐year modulations of tides. We demonstrate that qn‐SSJPM‐derived storm tide frequency estimates are more precise and stable compared with the standard practice of fitting an extreme value distribution to measured storm tides, which is often biased by the largest few events within the observational period. Applying the qn‐SSJPM in the Gulf of Maine, we find significant tidal forcing of winter storm season flood hazard by the 18.6‐year nodal cycle, whereas 4.4‐year modulations and a secular trend in tides are small compared to interannual variation and long‐term trends in sea‐level. The nodal cycle forces decadal oscillations in the 1% annual chance storm tide at an average rate of ±13.5 mm/year in Eastport, ME; ±4.0 mm/year in Portland, ME; and ±5.9 mm/year in Boston, MA. Currently (in 2020), nodal forcing is counteracting the sea‐level rise‐induced increase in flood hazard; however, in 2025, the nodal cycle will reach a minimum and then begin to accelerate flood hazard increase as it moves toward its maximum phase over the subsequent decade. Along the world's meso‐to‐macrotidal coastlines, it is therefore critical to consider both sea‐level rise and tidal nonstationarity in planning for the transition to chronic flooding that will be driven by sea‐level rise in many regions over the next century.Plain Language Summary: Coastal management practices around flood risk often rely on estimates of the percent chance of a particular flood height occurring within a year. For example, U.S. flood insurance requires designating areas with a 100‐year flood recurrence interval (the “100‐year flood zone”). When storms hit regions with large tides, the height and timing of high tide often determine flood severity. Thus, the relationship between flood height and annual frequency can be altered by natural, daily‐to‐decadal cyclical variation in tide heights. Here we present a new method for calculating annually varying flood height‐frequency relationships based on known tidal cycles. Applying the new method in the Gulf of Maine, we find an 18.6‐year‐long tidal cycle (the nodal cycle) has forced decadal variation in the 1% annual chance flood at a faster rate than the historical average rate of sea‐level rise over the past century. Currently, nodal cycle forcing is counteracting the sea‐level rise‐induced increase in flood hazard; however, in 2025, the nodal cycle will reach a minimum in the Gulf and then begin to accelerate flood hazard as it moves toward its maximum over the subsequent decade. It is therefore critical to consider sea‐level rise and tidal variation in medium‐term flood hazard planning.Key Points: We present a new quasi‐nonstationary joint probability method that estimates tidally driven interannual fluctuations in flood hazardThis method provides more precise and stable storm tide frequency estimates than extreme value distributions fit to measured storm tidesIn the Gulf of Maine, tides force decadal oscillations in the 1% annual chance storm tide at a rate exceeding mean historical sea‐level rise [ABSTRACT FROM AUTHOR]

Temperature is an important factor in defining the habitats of marine resource species. While satellite sensors operationally measure ocean surface temperatures, we depend on in situ measurements to characterize benthic habitats. Ship‐based measurements were interpolated to develop a time series of gridded spring and fall, surface and bottom temperature fields for the US Northeast Shelf. Surface and bottom temperatures have increased over the study period (1968–2018) at rates between 0.18–0.31°C per decade and over a shorter time period (2004–2018) at rates between 0.26–1.49°C per decade. A change point analysis suggests that a warming regime began in the surface waters in 2011 centered on Georges Bank and the Nantucket Shoals; in following years, most of the Northeast Shelf had experienced a shift in surface temperature. A similar analysis of bottom temperature suggests a warming regime began in 2008 in the eastern Gulf of Maine; in following years, change points in temperature occurred further to the west in the Gulf of Maine, finally reaching the Middle Atlantic Bight by 2010. The spatial pattern in bottom water warming is consistent with well‐known oceanographic patterns that advect warming North Atlantic waters into the Gulf of Maine. The varying spatial and temporal progression of warming in the two layers suggests they were actuated by different sets of forcing factors. We then compared these trends and change points to responses of lower and higher trophic level organisms and identified a number of coincident shifts in distribution and biomass of key forage and fisheries species. [ABSTRACT FROM AUTHOR]