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Species-specific ecological traits in fishes are likely to vary between populations or stocks due to differences in regional oceanic conditions, such as latitudinal temperature. We examined potential intraspecific differences in the swimming performance and metabolism of Pacific chub mackerel (Scomber japonicus) from the Northwest and Northeast Pacific stocks, which are distributed on opposite sides of the North Pacific at similar latitudes, but where the temperature contrast is large. Swimming bioenergetics and metabolic data of Northwest stock mackerel were measured at 14, 18, and 24°C using variable-speed swim-tunnel respirometers, and then the resulting bioenergetic parameters were compared with previous findings from the Northeast stock. At a given size, the maximum sustainable swimming speed (Umax) of the Northwest stock showed no significant difference compared to the Northeast stock at 18 and 24°C, but was lower at 14°C. In addition, the oxygen consumption rate (MO2) of the Northwest stock showed lower mass dependence and different temperature dependence at a given swimming speed than in the Northeast stock. Combined with stock-specific data on growth and experienced temperatures in the wild, these bioenergetic differences indicate that the swimming performance and metabolism of the two stocks are specific to their local environment to maximize bioenergetic efficiency.

The fishery for market squid (Doryteuthis opalescens) in California is typical of many of the world’s cephalopod fisheries, in that a very short life span and the effect of environmental forcing on recruitment result in enormous interannual variability in catches and population size. We evaluate the utility of a pre-recruit index of squid abundance that is based on midwater trawl sampling in the 3–5 months preceding the onset of the fishery as a basis for predicting landings. Catches in the survey largely represent squid in the 30–50 mm dorsal mantle length size range, representing individuals 30–90 day old. Catch-per-unit-effort statistics are derived from simple two-factor Δ-Generalized Linear Models, with year and station as main effects and numbers per tow as the dependent variable. Regional models for northern and southern squid populations are developed. Pre-recruit indices, as well as indices of squid prey (krill) abundance are compared with landings data, as well as estimates of squid spawning stock biomass derived from an egg escapement model. Our results show that the abundance of pre-recruit market squid and krill sampled in the survey tracks both catches and overall population size, providing the potential to forecast landings. Our findings are consistent with a sparse but growing literature showing the potential utility of pre-recruit surveys to inform fisheries participants and managers.

Pacific sardine ( Sardinops sagax ), a commercially valuable species, have a broad distribution along the North American coast that spans Canada, the United States, and Mexico. The goal of this research was to evaluate water temperature history of the fish inferred from stable oxygen isotopes in otoliths in order to differentiate and connect stocks across regions, and between juveniles and adults. Local seawater composition in the Pacific Northwest affected major north–south trends in δ 18 O composition of juvenile otoliths. Inferred temperature correlated inversely with the age (otolith weight) of juveniles within a region, possibly resulting from changes in depth preferences as the fish grew. The correlations between δ 13 C and δ 18 O in juvenile otoliths were relatively weak in the northernmost and southernmost samples, but comparisons of the sample means indicated significant differences between some regions. Otoliths from adult sardine captured between California and Canada recorded δ 18 O values reflecting cooler temperatures than otoliths from juveniles, and without regional differentiation. These results are consistent with a northern stock that mixes during annual migrations.

Pacific sardines ( Sardinops sagax ) are commercially fished in Canada, USA, and Mexico along approximately 5000 km of coastal waters that experience a wide range of temperatures. Trinational management of the species can be problematic because the connectivity between spawning, recruitment, stock residency, and migration in some years may not be well predicted. Oxygen isotopic value of otoliths (δ 18 O otolith ) has been used to infer stock residency and movement of fish populations within regions, but few studies have used laboratory data to establish a predictive temperature model to validate δ 18 O otolith values of wild fish. We conducted a growth experiment with juveniles at different temperatures using Southern California Bight (SCB) seawater to test the assumption that Pacific sardine otoliths accurately record environmental water temperature in the presence of constant salinity. Sardine δ 18 O otolith values were significantly and negatively correlated with temperature according to the linear model: δ 18 O otolith ( ‰ ) − δ 18 O water ( ‰ ) = − 0.132 ( ± 0.003 SE ) × Temperature ( ° C ) + 2.455 ( ± 0.043 SE ) We used this model to predict the temperature history of wild age-1 sardine collected in the SCB from 1995 to 2003. The field samples generally fit the model of SCB residency when both the average coastal sea surface temperatures and temperatures at 30 m were used to bracket the range of calculated otolith temperatures.

Concentrations of rare earth elements (REE) were measured in the fine fraction of shallow surface sediments from the lower Chesapeake Bay as studies suggest that coagulation of colloids dominates the removal of REE from the dissolved load in low salinity regions of estuaries. REE in sediments showed spatial heterogeneity, both laterally and longitudinally. We observed the influence of salinity on the spatial and temporal variability in total REE content and on Eu-anomalies. Lower total REE was found in sediments deposited along the Eastern Shore. The chemistry of the mid-Bay Islands was distinct with higher overall REE content and slightly more positive Ce-anomaly values. Positive Ce/Ce* in the mid-Bay are attributed to Coriolis acceleration restricting freshwater flow towards the west away from the Islands leading to oxidative removal of Ce from the pore waters to the sediments. The presence of positive Eu/Eu* in sediments deposited along the Eastern Shore is linked to salinity. We suggest that unique local conditions along the Eastern Shore, possibly including submarine groundwater discharge of nutrient-rich reducing waters, combined with organic matter decay and the predominance of oceanic water flow toward this region leads to the development of a strong localized salinity gradient. This study demonstrates the utility of REE sediment chemistry in identifying and resolving local and estuarine-wide geochemical processes.

Although laboratory studies confirm that otoliths incorporate trace elements and stable isotopes from surrounding waters, few studies explore the relationship of otolith chemistry to water chemistry in the field and none include a larger suite of environmental tracers, such as rare earth elements. Using spotted seatrout (Cynoscion nebulosus) as model species, we tested the hypothesis that otoliths record the water chemistry of seagrass habitats in Chesapeake Bay. In summer 2001, we sampled water and juvenile fish in seagrass beds of the bay. Weighted linear regressions showed that [Ba/Ca]otolith and [La/Ca]otolith were best predicted by salinity and were modeled as [Ba/Ca]otolith (µmol·mol–1) = –2.25 ± 0.35 × salinity + 59.47 ± 7.01) and [La/Ca]otolith (pmol·mol–1) = –8.71 ± 0.65 × salinity + 243.87 ± 12.52. [Ba/Ca]otolith increased with [Ba/Ca]water, but the relationship was nonlinear. Salinity did not influence [Mn/Ca]otolith, but this ratio was positively correlated with [Mn/Ca]water. Although the partition coefficient of Sr (DSr = 0.23 ± 0.019) was similar to that in laboratory experiments, [Sr/Ca] in waters and otoliths was decoupled despite equal temperature exposure, suggesting that [Sr/Ca]otolith concentration may not be a simple function of water composition. However, there was a predictive relationship between [δ18O]otolith and [Sr/Ca]water ([δ18O]otolith = 1.18 ± 0.09 × [Sr/Ca]water (mmol·mol–1) – 14.286 ± 0.78) resulting from mixing between fluvial and oceanic waters. Water chemistry showed mixed values as a proxy for otolith chemistry and may not be a surrogate for otolith chemistry in wide estuaries.

We tested the hypothesis that the physical and chemical processes acting in sea grass habitats of the lower Chesapeake Bay are spatially structured and that dissolved elemental chemistry of sea grass-habitat surface waters have their own unique identity. We sampled surface waters from July to September 2001 in five sea grass habitats of the lower bay: Potomac, Rappahannock, York, Island (Tangier-Bloodsworth), and Eastern Shore. Dissolved Mg, Mn, Sr, and Ba concentrations were measured by sector field inductively coupled plasma-mass spectrometry. As expected, Mg, Sr, and Ba exhibited conservative behavior, but Mn exhibited nonconservative behavior along the salinity gradient. Spatial differences in the chemistry of surface waters over sea grass habitats were fully resolvable independently of time. Moreover, classification accuracy of water samples was low in Rappahannock, moderate in Potomac and Eastern Shore, and high in the York and Island habitats. The chemistry of York was distinct because of the effects of physical mixing, whereas Island chemistry was unique, potentially because of the influence of Coriolis acceleration and river discharges from the Susquehanna River. The results of this study show that sites so close to one another in physical space maintain distinct chemical differences.

Market squid (Doryteuthis opalescens) are ecologically and economically important to the California Current Ecosystem, but populations undergo dramatic fluctuations that greatly affect food web dynamics and fishing communities. These population fluctuations are broadly attributed to 5–7-years trends that can affect the oceanography across 1,000 km areas; however, monthly patterns over kilometer scales remain elusive. To investigate the population dynamics of market squid, we analysed the density and distribution of paralarvae in coastal waters from San Diego to Half Moon Bay, California, from 2011 to 2016. Warming local ocean conditions and a strong El Nino event drove a dramatic decline in relative paralarval abundance during the study period. Paralarval abundance was high during cool and productive La Nina conditions from 2011 to 2013, and extraordinarily low during warm and eutrophic El Nino conditions from 2015 to 2016 over the traditional spawning grounds in Southern and Central California. Market squid spawned earlier in the season and shifted northward during the transition from cool to warm ocean conditions. We used a general additive model to assess the variability in paralarval density and found that sea surface temperature (SST), zooplankton displacement volume, the log of surface chlorophyll-a, and spatial and temporal predictor variables explained >40% of the deviance (adjusted r2 of .29). Greatest paralarval densities were associated with cool SST, moderate zooplankton concentrations and low chlorophyll-a concentrations. In this paper we explore yearly and monthly trends in nearshore spawning for an economically important squid species and identify the major environmental influences that control their population variability.

Etang Saumâtre (also known as Lac Azuei, Lago del Fondo, or Yainagua) is a brackish lake located in eastern Haiti. Sources of irrigation and drinking water for the surrounding communities in Thomazeau, Ganthier, and Fond Parisien are freshwater springs and shallow wells tapping the complex fractured aquifer system surrounding Etang Saumâtre. In some groundwater samples, we found concentrations of trace metals exceeding World Health Organization guideline values. Lake sediment trace metal concentrations were also high. For example, chromium (Cr) ranged from 26.24 to 198.44 mg/kg, exceeding the USEPA sediment quality guideline value for heavily polluted. High concentrations of potentially toxic trace metals in both lake sediments and groundwater suggest that the population relying on this lake for drinking water, irrigation, and subsistence fishing may be at risk for metal-induced health effects. By understanding the geochemical behavior of redox-sensitive trace metals such as Cr, in the context of limnology and long-term fate and transport within the system, our results provide unique insights into the geochemical controls on remobilization of redox metals from the sediments and the potential impact of future environmental change on the sediment and water quality in this system.

Fish larval densities are frequently used as an index of spawning biomass. Three time series of larval densities of Pacific mackerel (Scomber japonicus) per 10 m2 were estimated from 1951 to 2008 based on data collected by California Cooperative Oceanic Fisheries Investigations (calcofi) survey during Peak spawning season off California: April to July, and by the Investigaciones Mexicanas de la Corriente de California (imecocal) survey off Mexico: June-September. 1) Daily larval production at hatching; 2) bias-corrected larval densities; and 3) simple mean larval densities. All three time series were constructed for California in 1951-2008. The third was constructed for the Mexican waters in 1951-1984, 1996 and 1998-2000. Weighted mean larval densities were obtained for the combined area of California and Mexico. Daily larval production index showed a major peak in 1987 (46.39·10 m2 ·d-1) and two minor peaks, in 1981 and 1986. All three time series indicated that larval densities have been decreasing since 1997 and were particularly low in 2003-2008. Larval densities off Mexico, higher than those off California in recent years, were high in the mid-1960’s, and low in the early 1980’s. The cost-effective fishery-independent time series off California and Mexico is informative for assessing the population fluctuation and beneficial to the Pacific mackerel stock assessment. Due to the different peak spawning periods off California and Mexico, periodic extensive coast-wide surveys to cover the whole time period are recommended, as they would contribute to a better understanding of the dynamics of the population along the Pacific coast.

With an average yield of 70 000 Mt from 1999 to 2006, market squid (Doryteuthis opalescens) represents one of the most commercially valuable and biologically productive populations off California. An egg escapement model was developed for evaluating the population’s reproductive response to varying levels of fishing pressure and, potentially, for aiding management of the fishery. The model is founded on eggs-per-recruit theory, assuming catch fecundity is related to daily-based fishing mortality (F), i.e. analysis generated estimates of proportional egg escapement, S(F), as a function of F per quarter from 1999 to 2006 in three spawning grounds off northern and southern California. Fishing pressure was generally high, with mean derived F ranging from 0.20 to 6 per day. Mean estimated S(F) ranged from 0.08 to 0.75, but in most quarters was higher than 0.30. The classical model was extended for estimating absolute abundance of the resource based on F. Market squid were more abundant in southern California, where mean spawning stock peaked at 1.50 × 109 females, ~108 000 and 130 000 Mt in autumn 2000 and winter 2005 respectively. Although time demanding, this per-recruit analysis represents an effective approach for monitoring reproductive outputs and for aiding stock status determinations of harvested market squid.

We investigated the variability of otolith chemistry in juvenile spotted seatrout from Chesapeake Bay seagrass habitats in 1998 and 2001, to assess whether otolith elemental and isotopic composition could be used to identify the most essential seagrass habitats for those juvenile fish. Otolith chemistry (Ca, Mn, Sr, Ba, and La; δ13C, δ18O) of juvenile fish collected in the five major seagrass habitats (Potomac, Rappahannock, York, Island, and Pocomoke Sound) showed significant variability within and between years. Although the ability of trace elements to allocate individual fish may vary between years, in combination with stable isotopes, they achieve high classification accuracy averaging 80–82% in the Pocomoke Sound and the Island, and 95–100% in the York and the Potomac habitats. The trace elements (Mn, Ba, and La) provided the best discrimination in 2001, a year of lower freshwater discharge than 1998. This is the first application of a rare earth element measured in otoliths (La) to discriminate habitats, and identify seagrass habitats for juvenile spotted seatrout at spatial scales of 15 km. Such fine spatial scale discrimination of habitats has not been previously achieved in estuaries and will distinguish fish born in individual seagrass beds in the Bay.