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Fisheries-independent surveys are commonly used to create indices of relative abundance. If properly designed and calibrated, these surveys may also be used to estimate absolute abundance. Here, we demonstrate the efficacy of this approach by estimating the absolute abundance of red lionfish ( Pterois volitans), gray triggerfish ( Balistes capriscus), and red snapper ( Lutjanus campechanus) across an extensive network of artificial reefs using camera counts, indices of relative abundance, calibration factors, and index-removal estimators. From 2012 to 2017, per reef estimates increased for red lionfish (20×), gray triggerfish (2.1×), and red snapper (2.2×). Network-wide absolute abundances were calculated by multiplying the average per reef estimate by the estimated number of reefs in the network. All increases were consistent with predictions of stock assessment (red snapper), management actions (gray triggerfish), or invasive species colonization (red lionfish). Our methodology demonstrates how estimates of absolute abundance can be derived from fishery-independent surveys and used to evaluate the outputs of stock assessments both in direction and magnitude and quantify critical ecosystem components.

Identifying critical habitat for highly mobile species such as sharks is difficult, but essential for effective management and conservation. In regions where baseline data are lacking, non‐traditional data sources have the potential to increase observational capacity for species distribution and habitat studies. In this study, a research and education organization conducted a 5‐year (2013–2018) survey of shark populations in the coastal waters of west‐central Florida, an area where a diverse shark assemblage has been observed but no formal population analyses have been conducted. The objectives of this study were to use boosted regression tree (BRT) modeling to quantify environmental factors impacting the distribution of the shark assemblage, create species distribution maps from the model outputs, and identify spatially explicit hot spots of high shark abundance. A total of 1036 sharks were captured, encompassing eleven species. Abundance hot spots for four species and for immature sharks (collectively) were most often located in areas designated as “No Internal Combustion Engine” zones and seagrass bottom cover, suggesting these environments may be fostering more diverse and abundant populations. The BRT models were fitted for immature sharks and five species where n > 100: the nurse shark (Ginglymostoma cirratum), blacktip shark (Carcharhinus limbatus), blacknose shark (C. acronotus), Atlantic sharpnose shark (Rhizoprionodon terraenovae), and bonnethead (Sphyrna tiburo). Capture data were paired with environmental variables: depth (m), sea surface temperature (°C), surface, middle, and bottom salinity (psu), dissolved oxygen (mg/L), and bottom type (seagrass, artificial reef, or sand). Depth, temperature, and bottom type were most frequently identified as predictors with the greatest marginal effect on shark distribution, underscoring the importance of nearshore seagrass and barrier island habitats to the shark assemblage in this region. This approach demonstrates the potential contribution of unconventional science to effective management and conservation of coastal sharks., Identifying critical habitat for highly mobile species such as sharks is difficult, but essential for effective management and conservation. Using shark capture data collected by a research and education group in Florida, this study used boosted regression tree (BRT) modeling to quantify environmental factors impacting the distribution of the shark assemblage, create species distribution maps from the model outputs, and identify spatially explicit hot spots of high shark abundance. This approach for identifying spatially explicit areas and environmental conditions suited for shark abundance demonstrates the potential contribution of unconventional science to effective management and conservation of coastal sharks.

Two different methods, metagenetics and free-otolith identification, were used to identify prey in the stomach contents of 531 Gymnura lessae captured by trawling in Mobile Bay, Alabama 2016-2018. Both methods were found to produce analogous results and were therefore combined into a single complete dataset. All prey were teleosts; the families Sciaenidae and Engraulidae were the most important prey (prey specie index of relative importance 89.3% IPSRI ). Multivariate analyses indicated that the diet of G. lessae varied with sex and seasonality. Specifically, variability was probably due to morphologically larger females consuming larger teleost prey species compared with males, whereas seasonal variability was probably due to changes in the available prey community composition. The findings indicate that both metagenetics and free otolith identification, used independently or complementarily, offer robust means of characterising dietary habits for teleost-specialised species such as G. lessae, which may play an important role in the structure and maintenance of coastal food webs such as those in Mobile Bay.

Many elasmobranchs display K-selected life history characteristics, making species-specific life history parameters critical to development of the most accurate stock assessment models. Age, growth, and maturity were examined for Finetooth Sharks, Carcharhinus isodon, in coastal waters of the Western North Atlantic Ocean (WNA) from Winyah Bay, South Carolina to Cape Canaveral, Florida. Ages were estimated from the vertebrae of 200 males and 232 females. The maximum observed age for males and females was 21.9 years and 22.3 years, respectively. Sizes ranged from 376 mm to 1174 mm fork length (FL) for males and 380 mm to 1282 mm FL for females. Significant differences were detected between the sexes necessitating sex-specific von Bertalanffy growth models yielding the following parameters: male, L∞ = 1140 mm FL, k = 0.29, L0 = 460 mm FL; female, L∞ = 1253 mm FL, k = 0.20, L0 = 464 mm FL. Median length (L50) at maturity was 1010 mm FL for males and 1043 mm FL for females corresponding to an age at median maturity (A50) of 6.6 years and 6.8 years, respectively. Significant differences in growth and maturity were detected between the current study and previously published parameters for the WNA and Gulf of Mexico (GOM). Observed differences in the WNA were driven by ageing methods, with current methods yielding significant differences in age estimates between studies. Results from the current study, in conjunction with previously published reproductive, tag-recapture and genetic studies, provide support for separate stocks between the WNA and GOM.

The overexploitation of many traditionally targeted reef fishes, such as red snapper, Lutjanus campechanus (Poey, 1860), alongside the implementation of increasingly restrictive management measures on those species, has led to increased targeting of conventionally discarded Gulf of Mexico gray triggerfish, Balistes capriscus Gmelin, 1789, commercially and recreationally. The goal of this study was to assess age and growth of gray triggerfish from the Alabama Artificial Reef Zone in the north-central Gulf of Mexico. Gray triggerfish (n = 1135) were collected predominantly from artificial habitat during 1999–2017. Specimens were sexed macroscopically and ages were assigned by counting translucent increments in sections of the first dorsal spine. Fish ranged in size from 22 to 617 mm fork length. The oldest female was assigned an age of 9 yrs; the oldest male, 10 yrs. A suite of growth models was tested to develop combined and sex-specific models. The von Bertalanffy growth function best fit the combined data with parameters L∞ = 488.63 (SE 5.19), k = 0.57 (SE 0.02), and t 0= –0.27 (SE 0.03). Mean size-at-age differed between sexes for six of the eight ages which possessed sample sizes large enough to make comparisons. Growth differed between sexes, and the best-fitting version of the von Bertalanffy growth function permitted L∞ to vary by sex [female L∞ = 480.26 (SE 7.99); male L∞ = 532.89 (SE 8.95); k = 0.44 (SE 0.04); t 0 = –0.78 (SE 0.16)]. These findings enhance our knowledge of the age and growth of Gulf of Mexico gray

The timing and extent of international crossings by billfishes, tunas, and sharks in the Cuba-Mexico-United States (U.S.) triangle was investigated using electronic tagging data from eight species that resulted in >22,000 tracking days. Transnational movements of these highly mobile marine predators were pronounced with varying levels of bi- or tri-national population connectivity displayed by each species. Billfishes and tunas moved throughout the Gulf of Mexico and all species investigated (blue marlin, white marlin, Atlantic bluefin tuna, yellowfin tuna) frequently crossed international boundaries and entered the territorial waters of Cuba and/or Mexico. Certain sharks (tiger shark, scalloped hammerhead) displayed prolonged periods of residency in U.S. waters with more limited displacements, while whale sharks and to a lesser degree shortfin mako moved through multiple jurisdictions. The spatial extent of associated movements was generally associated with their differential use of coastal and open ocean pelagic ecosystems. Species with the majority of daily positions in oceanic waters off the continental shelf showed the greatest tendency for transnational movements and typically traveled farther from initial tagging locations. Several species converged on a common seasonal movement pattern between territorial waters of the U.S. (summer) and Mexico (winter).

The tiger shark (Galeocerdo cuvier) is globally distributed with established coastal and open-ocean movement patterns in many portions of its range. While all life stages of tiger sharks are known to occur in the Gulf of Mexico (GoM), variability in habitat use and movement patterns over ontogeny have never been quantified in this large marine ecosystem. To address this data gap we fitted 56 tiger sharks with Smart Position and Temperature transmitting tags between 2010 and 2018 and examined seasonal and spatial distribution patterns across the GoM. Additionally, we analyzed overlap of core habitats (i.e., 50% kernel density estimates) among individuals relative to large benthic features (oil and gas platforms, natural banks, bathymetric breaks). Our analyses revealed significant ontogenetic and seasonal differences in distribution patterns as well as across-shelf (i.e., regional) and sex-linked variability in movement rates. Presumably sub-adult and adult sharks achieved significantly higher movement rates and used off-shelf deeper habitats at greater proportions than juvenile sharks, particularly during the fall and winter seasons. Further, female maximum rate of movement was higher than males when accounting for size. Additionally, we found evidence of core regions encompassing the National Oceanographic and Atmospheric Administration designated Habitat Areas of Particular Concern (i.e., shelf-edge banks) during cooler months, particularly by females, as well as 2,504 oil and gas platforms. These data provide a baseline for future assessments of environmental impacts, such as climate variability or oil spills, on tiger shark movements and distribution in the region. Future research may benefit from combining alternative tracking tools, such as acoustic telemetry and genetic approaches, which can facilitate long-term assessment of the species' movement dynamics and better elucidate the ecological significance of the core habitats identified here.

The Gulf of Mexico greater amberjack (Seriola dumerili) stock has been designated as “overfished” by the National Marine Fisheries Service and is currently under a rebuilding plan. Its fishery in the Gulf of Mexico is dominated by recreational landings, where 75% of the total recreational catch are regulatory discards; as such, uncertainty regarding the post-release mortality rate represents a data deficiency in the stock assessment. To determine post-release mortality, a combination of acoustic and pop-up satellite archival transmitting (PSAT) tags were used to monitor the release fate and depth-use of greater amberjack. Thirty-six greater amberjack were tagged with acoustic transmitters at two sites in the northern GOM and monitored for up to 30 days. Sublegal-sized fish (n = 18) ranged from 591 to 740 mm FL (mean = 674.6 ± 40.6 SE) and legal-sized fish (n = 18) ranged from 768 to 1081 mm FL (mean = 871.3 ± 77.5 SE). All 36 fish were detected in the array after release. Based on examination of time series depth profiles, post-release mortality was estimated to be 18.8% ± 6.9%, strikingly similar to the estimate used in the most recent stock assessment. Stepwise model selection using AIC identified the Cox proportional hazards model containing only release condition as the most parsimonious model to predict post-release mortality. Despite differences in depth between the two tagging sites, fish showed slight, but consistent, size-specific segregation patterns. Our findingsadd to a body of literature demonstrating that biotelemetry is an effective tool in catch and release mortality studies, and provide best practices that can aid in the recovery of this stock.

Since the onset of fisheries science, monitoring programs have been implemented to support stock assessments and fisheries management. Here, we take inventory of the monitoring programs of the U.S. Gulf of Mexico (GOM) surveying fish and invertebrates and conduct a gap analysis of these programs. We also compile a large monitoring database encompassing much of the monitoring data collected in the U.S. GOM using random sampling schemes and employ this database to fit statistical models to then map the spatial distributions of 61 fish and invertebrate functional groups, species and life stages of the U.S. GOM. Finally, we provide recommendations for improving current monitoring programs and designing new programs, and guidance for more comprehensive use and sharing of monitoring data, with the ultimate goal of enhancing the inputs provided to stock assessments and ecosystem-based fisheries management (EBFM) projects in the U.S. GOM. Our inventory revealed that 73 fisheries-independent and fisheries-dependent programs have been conducted in the U.S. GOM, most of which (85%) are still active. One distinctive feature of monitoring programs of the U.S. GOM is that they include many fisheries-independent surveys conducted almost year-round, contrasting with most other marine regions. A major sampling recommendation is the development of a coordinated strategy for collecting diet information by existing U.S. GOM monitoring programs for advancing EBFM.

Background Biotelemetry applications have advanced our understanding of many highly migratory species, but present a challenge for species that suffer high capture and/or post-release stress. Failing to accurately characterize post-release fate can obfuscate our understanding of animal movement patterns and complicate the development of effective conservation and management plans. The great hammerhead (Sphyrna mokarran) is a long-lived, highly migratory shark listed by the International Union for the Conservation of Nature as Endangered. Accordingly, we used a combination of tags designed to report horizontal position estimates and verify post-release fate, to examine movements of great hammerheads in the northern Gulf of Mexico. Results Between May and September 2016, three individuals (one male and two females) were equipped with both fin-mounted smart position and temperature transmitting (SPOT) tags and survivorship pop-off archival tags (sPAT) to provide information on post-release fate. Tagged sharks measured 187 (F), 203 (M), and 250 (M) cm total length. All three sharks surfaced daily, yet individuals showed variability in vertical habitat use, with maximum daily depths ranging from 5 to 98 m. A single fin-mounted SPOT tag, attached to the smallest of the three sharks, reported position estimates over an 81-day period and moved a straight-line distance of approximately 400 km; however, the other two fin-mounted SPOT tags failed to generate position estimates. All three sPAT tags indicated post-release survival. Final positions of the sPAT tags from the two largest sharks suggested restricted horizontal movements (

Despite the perilous status of many shark populations, rallying support for their conservation has been challenging, due in part to both long held negative perceptions and desire for shark fisheries. Recreational anglers are often advocates of conservation and can act as valuable partners with resource managers in developing fisheries management and conservation strategies. However, understanding their attitudes and perceptions, particularly towards resource status and management, is essential to developing successful management strategies and predicting outcomes. As a case study for assessing the complex challenges of sustainable shark fisheries, Florida recreational anglers were surveyed to understand how attitudes and perceptions influenced their willingness to donate for shark 1) conservation and protection or 2) fisheries sustainability. Overall, recreational angler willingness to donate was 25.5%, but attitudes and perceptions helped explain dramatic divides. For instance, willingness to donate was only 6% among the subset of anglers that perceived a growing large coastal shark population as a threat to recreational fishing opportunities. Highest support for shark conservation was shown by anglers who value seeing sharks in the wild (41.4%), and even more so among individuals who occasionally target sharks while fishing recreationally (65.8%). Pervasive among anglers unwilling to donate was a perception that shark populations were increasing, and thus not in need of further protection. These findings illustrate attitudes and perceptions that challenge shark conservation and fisheries management, as well as the critical importance of engaging anglers when developing strategies that rely on the recreational angling community for support.

In 2011, an intensive, multiple-gear, fishery-independent survey was carried out in the northern Gulf of Mexico (GOM) to collect comprehensive age and length information on Red Snapper Lutjanus campechanus. Based on this synoptic survey, we produced a spatial map of Red Snapper relative abundance that integrates both gear selectivity effects and ontogenetically varying habitat usage. Our methodology generated a spatial map of Red Snapper at a 10-km2 grid resolution that is consistent with existing knowledge of the species: Red Snapper occurred in relatively high abundances at depths of 50–90 m along the coasts of Texas and Louisiana and in smaller, patchy “hot spots” at a variety of depths along the Alabama coast and the west Florida shelf. Red Snapper biomass and fecundity estimates were higher for the northwestern GOM than for the northeastern GOM, as the latter area contained mostly smaller, younger individuals. The existence of similar surveys on petroleum platforms and artificial reefs also enabled us to calculate their relative contribution to Red Snapper distribution compared with that of natural habitats. We estimated that for the youngest age-classes, catch rates were approximately 20 times higher on artificial structures than on natural reefs. Despite the high catch rates observed on artificial structures, they represent only a small fraction of the total area in the northern GOM; thus, we estimated that they held less than 14% of Red Snapper abundance. Because artificial structures—particularly petroleum platforms—attract mostly the youngest individuals, their contribution was even lower in terms of total population biomass (7.8%) or spawning potential (6.4%). Our estimates of Red Snapper relative abundance, biomass, and spawning potential can be used to design spatial management strategies or as inputs to spatial modeling techniques. Received January 1, 2016; accepted October 28, 2016

Quantifying the trophic dynamics of mesopredators in coastal habitats is an essential precursor to understanding their role in linking multiple trophic levels. Traditional dietary analyses may miss key aspects of a species’ feeding ecology and may thus fail to identify trophic linkages between predators and economically important prey populations. We applied stomach content and stable isotope analyses to estimate diet and trophic dynamics and investigated intraspecific dietary diversity of bonnetheads (Sphyrna tiburo) and red drum (Sciaenops ocellatus). Both juvenile and adult bonnetheads and juvenile red drum had diets comprised mainly of crustaceans, notably portunid crabs and penaeid shrimp, with varying degrees of dietary and isotopic niche overlap. Juvenile and adult bonnetheads had high dietary and isotopic niche overlap, whereas the degree of overlap between bonnetheads and red drum varied. Our findings indicate that bonnetheads are dietary specialists whereas red drum are dietary generalists. Further analysis identified intraspecific variability in the diet of each species; adult bonnetheads had the highest prey diversity whereas red drum had the lowest. We show that dietary and isotopic niche overlap and intraspecific variation in diet exist among juvenile and adult bonnetheads and juvenile red drum, though to varying degrees. Our findings demonstrate the importance of fully examining the trophic ecology of species that share habitats and resources, both at individual and population levels.

Conservation and management efforts of marine apex predators are more reliable when information on movement and habitat use patterns are known. The scalloped hammerhead (Sphyrna lewini) was the first shark species to be protected under the U.S. Endangered Species Act and has life history characteristics that make this species particularly at risk for local depletion. Consequently, the goal of this study was to better understand the movement dynamics of this species in the Gulf of Mexico (GOM) where discards through the longline fishery can be substantial. A total of 33 scalloped hammerheads were tagged with fin mounted satellite tags and tracked for an average of 146 days (ranging from 5 to 479 days) to examine horizontal movements and quantify space use. Scalloped hammerheads showed a wide range of movements throughout the GOM continental shelf with limited long-distance dispersal and females displayed a shelf-edge association relative to more mid-shelf use by males. A generalized additive model was developed to identify habitat suitability for scalloped hammerheads in the GOM, while state-space modeling was used to examine movement behaviors. Model results highlighted the use of continental shelf waters with high occurrence at close proximities to both artificial and hard-bottom habitat combined with low chlorophyll a concentrations (∼0–4 mg m-3) and moderate salinities (33–35.5). Habitat suitability for scalloped hammerheads was predicted to be high on the mid to outer continental shelf inside the 200 m isobath and state-space model results suggest area-restricted behavior was most common relative to transient behavior. Findings from this study provide important information on movement of this species in the GOM and highlight their restricted use of continental shelf habitat and resident behavior that will need to be incorporated in future stock assessments and extinction risk analyses.

Documenting and responding to species invasions requires innovative strategies that account for ecological and societal complexities. We used the recent expansion of Indo-Pacific lionfish (Pterois volitans/miles) throughout northern Gulf of Mexico coastal waters to evaluate the role of stakeholders in documenting and responding to a rapid marine invasion. We coupled an online survey of spearfishers and citizen science monitoring programs with traditional fishery-independent data sources and found that citizen observations documented lionfish 1–2 years earlier and more frequently than traditional reef fish monitoring programs. Citizen observations first documented lionfish in 2010 followed by rapid expansion and proliferation in 2011 (+367%). From the survey of spearfishers, we determined that diving experience and personal observations of lionfish strongly influenced perceived impacts, and these perceptions were powerful predictors of support for initiatives. Our study demonstrates the value of engaging citizens for assessing and responding to large-scale and time-sensitive conservation problems.

Large sharks are top predators in most coastal and marine ecosystems throughout the world, and evidence of their reduced prominence in marine ecosystems has been a serious concern for fisheries and ecosystem management. Unfortunately, quantitative data to document the extent, timing, and consequences of changes in shark populations are scarce, thwarting examination of long-term (decadal, century) trends, and reconstructions based on incomplete data sets have been the subject of debate. Absence of quantitative descriptors of past ecological conditions is a generic problem facing many fields of science but is particularly troublesome for fisheries scientists who must develop specific targets for restoration. We were able to use quantitative measurements of shark sizes collected annually and independently of any scientific survey by thousands of recreational fishermen over the last century to document decreases in the size of large sharks from the northern Gulf of Mexico. Based on records from fishi...

A common critique of many stock assessments is the lack of fishery-independent abundance indices and age composition data. Such data streams are essential in evaluating population trajectories that are derived largely from harvest and age composition of landings. For example, high scientific uncertainty in the most recent stock assessment of Gulf of Mexico red snapper Lutjanus campechanus resulted from a conflict between trends in fishery-dependent and fishery-independent data. Because sample sizes for the latter data were an order of magnitude lower, resolution of the conflicting trends was even more problematic. Recognizing the need for cost-effective expansion of fishery-independent data in the region, we evaluated the performance of vertical longline surveys for sampling reef fish within a large artificial reef zone in the northern Gulf of Mexico. Specifically, we (1) determined species composition and the length frequency of red snapper (the dominant species captured) as a function of hook s...

Quantifying the trophic role of sharks in coastal ecosystems is crucial for the construction of accurate ecosystem models. This is particularly important for wide-ranging species like the Atlantic sharpnose shark (Rhizoprionodon terraenovae), ubiquitous across the northern Gulf of Mexico. We used gut content and stable isotope analyses to determine if differences in abundance of Atlantic sharpnose sharks in the waters around Mobile Bay, Alabama translated into differences in dietary sources or trophic position among sharks sampled east and west relative to the mouth of the bay. Gut content analysis suggested that Atlantic sharpnose sharks eat primarily teleost fishes (%IRI > 90% across size classes), and both stomach content and stable isotope analyses highlighted an ontogenetic shift in diet. Nitrogen stable isotope data from liver and muscle tissues indicated regional shifts in trophic position for Atlantic sharpnose sharks. The mixing model SIAR (stable isotope analysis in R) v.4.0.2 was used to suggest possible contributions from likely prey items for Atlantic sharpnose sharks sampled east and west of Mobile Bay. Portunid crabs and shrimp made higher contributions to the diet of Atlantic sharpnose sharks in the western region, compared to higher and more variable contributions from fish like croaker (Micropogonias undulatus) and hardhead catfish (Arius felis) in the eastern region. Our results suggest trophic plasticity in Atlantic sharpnose sharks, findings that emphasize the importance of examining regional variation in trophic position when constructing coastal foodweb models.

Declines in shark populations have sparked researchers and fishery managers to investigate more prudent approaches to the conservation of these fish. As managers strive to improve data collection for stock assessment, fisheries-independent surveys have expanded to include data-deficient areas such as coastal regions. To that end, a catch series from a nearshore survey off Alabama was combined with data from a concurrent offshore survey with identical methodology to examine the depth use of sharks across the continental shelf (2–366 m). The combined data set contained 22 species of sharks collected from 1995 to 2008: 21 species in the offshore data set (1995–2008) and 12 species in the nearshore data set (2006–2008). Depth was a significant factor determining species' distributions, primarily for Atlantic sharpnose Rhizoprionodon terraenovae, blacknose Carcharhinus acronotus, and blacktip C. limbatus sharks. Blacknose sharks had the highest catch per unit effort (CPUE) in the middepth stratum (10–...

Barrier islands are dynamic features of the northern Gulf of Mexico that are affected by natural processes and more frequently, anthropogenic disturbances. In addition to providing a barrier from storms, these islands offer habitat for many marine species. In an effort to prevent oiling of the Alabama coastline following the Deepwater Horizon oil spill, an artificial rock-rubble berm was constructed in 2010 to reconnect two portions of Dauphin Island, a northern Gulf of Mexico barrier island that was separated during Hurricane Katrina. An acoustic array established prior to the closure of “Katrina Cut” was used to investigate the potential effect of this anthropogenic alteration on the movement patterns of acoustically tagged Bonnetheads (Sphyrna tiburo). Across the entire acoustic array, the largest proportion of detections occurred on receivers before construction at Katrina Cut (0.55), followed by the period after the construction (0.25), and the period during the construction (0.20). Focusing on the area near Katrina Cut, the two hydrophones in this area had the highest proportion of detections before construction (0.10), followed by the period during construction (0.02), and then the period after construction and closure of Katrina Cut (

Understanding the complex nature of direct and indirect species interactions is a critical precursor to successful resource management. In the northern Gulf of Mexico fisheries ecosystem, red snapper (Lutjanus campechanus) and vermilion snapper (Rhomboplites aurorubens) are two commercially harvested species within a larger reef fish complex. These two species share similar habitats and diets; however, little is known about how these species partition habitat and dietary resources. In this study we examined the extent of spatial and dietary overlap between red snapper and vermilion snapper, and experimentally compared their feeding behavior. Field data from multiple gear types demonstrates that red snapper and vermilion snapper frequently cohabited reefs in the northern Gulf of Mexico, and Pianka’s niche overlap indices suggest significantly overlapping diets. Experimental manipulations show that red snapper are the dominant forager of the two species, as red snapper foraging alone ate more shrimp per fish than vermilion snapper in both the single species (p = 0.003) and mixed species (p = 0.02) treatments. In addition, red snapper ate significantly more shrimp per fish in the mixed species treatment than in the single species treatment (p = 0.04). Vermilion snapper shrimp consumption per fish did not differ significantly between mixed and single species treatments. Cumulatively, our results suggest that spatial and dietary overlap could lead to competition between red and vermilion snapper in the study area; however, conclusively determining the existence of such competition would require further research.

Understanding how animals alter habitat use in response to changing abiotic conditions is important for effective conservation management. For bull sharks (Carcharhinus leucas), habitat use has been widely examined in the eastern and western Gulf of Mexico; however, knowledge of their movements and the factors influencing them is lacking for populations in the more temperate north-central Gulf of Mexico. To examine how changes in hydrographic conditions affected the presence of young bull sharks in Mobile Bay, Alabama, thirty-five sharks were fitted with internal acoustic transmitters and monitored with an acoustic monitoring array consisting of thirty-three receivers between June 2009 and December 2010. Tagged sharks ranged in size from 60 to 114 cm fork length and were detected between the upper and lower portions of Mobile Bay. Despite a variety of freshwater sources associated with this highly productive estuary, sharks were most consistently detected at the largest input to the system – the Mobile and Tensaw Rivers. Our findings suggest a combination of hydrographic factors interact to influence the distribution of juvenile bull sharks in Mobile Bay. The factors affecting the probability of detecting at least one bull shark varied both temporally (2009 vs 2010) and spatially (upper vs lower bay). Electivity analysis demonstrated that bull sharks showed highest affinity for warm water (29–32°C), moderate salinities (10–11 psu) and normoxic waters (5–7 mg/l), although these patterns were not consistent between regions or across years. We suggest future studies coupling telemetry and hydrographic variables should, when possible, consider the interactions of multiple environmental parameters when defining the dynamic factors explaining the spatial distribution of coastal sharks.

The pelagic brown alga Sargassum forms an oasis of biodiversity and productivity in an otherwise featureless ocean surface. The vast pool of oil resulting from the Deepwater Horizon oil spill came into contact with a large portion of the Gulf of Mexico’s floating Sargassum mats. Aerial surveys performed during and after the oil spill show compelling evidence of loss and subsequent recovery of Sargassum. Expanding on the trends observed in the aerial surveys, we conducted a series of mesocosm experiments to test the effect of oil and dispersants on the vertical position and weight of the Sargassum complex (Sargassum natans and S. fluitans), as well as on the dissolved oxygen concentrations surrounding the algae. Dispersant and dispersed-oil had significant effects on the vertical position of both species of Sargassum over a period of 72 hours. Similarly, dissolved oxygen concentrations were lowest in dispersant and dispersed-oil treatments, respectively. Cumulatively, our findings suggest three pathways for oil-spill related injury: (1) Sargassum accumulated oil on the surface exposing animals to high concentrations of contaminants; (2) application of dispersant sank Sargassum, thus removing the habitat and potentially transporting oil and dispersant vertically; and (3) low oxygen surrounded the habitat potentially stressing animals that reside in the alga. These pathways represent direct, sublethal, and indirect effects of oil and dispersant release that minimize the ecosystem services provided by floating Sargassum – the latter two effects are rarely considered in assessing impacts of oil spills or response procedures.

Identification of the spatial scale at which marine communities are organized is critical to proper management, yet this is particularly difficult to determine for highly migratory species like sharks. We used shark catch data collected during 2006–09 from fishery-independent bottom-longline surveys, as well as biotic and abiotic explanatory data to identify the factors that affect the distribution of coastal sharks at 2 spatial scales in the northern Gulf of Mexico. Centered principal component analyses (PCAs) were used to visualize the patterns that characterize shark distributions at small (Alabama and Mississippi coast) and large (northern Gulf of Mexico) spatial scales. Environmental data on temperature, salinity, dissolved oxygen (DO), depth, fish and crustacean biomass, and chlorophyll-a (chl-a) concentration were analyzed with normed PCAs at both spatial scales. The relationships between values of shark catch per unit of effort (CPUE) and environmental factors were then analyzed at each scale with co-inertia analysis (COIA). Results from COIA indicated that the degree of agreement between the structure of the environmental and shark data sets was relatively higher at the small spatial scale than at the large one. CPUE of Blacktip Shark (Carcharhinus limbatus) was related positively with crustacean biomass at both spatial scales. Similarly, CPUE of Atlantic Sharpnose Shark (Rhizoprionodon terraenovae) was related positively with chl-a concentration and negatively with DO at both spatial scales. Conversely, distribution of Blacknose Shark (C. acronotus) displayed a contrasting relationship with depth at the 2 scales considered. Our results indicate that the factors influencing the distribution of sharks in the northern Gulf of Mexico are species specific but generally transcend the spatial boundaries used in our analyses.