Relating Water and Otolith Chemistry in Chesapeake Bay, and Their Potential to Identify Essential Seagrass Habitats for Juveniles of an Estuarine-Dependent Fish, Spotted Seatrout (\u3ci\u3eCynoscion nebulosus\u3c/i\u3e)

A quantitative understanding of habitat use of estuarine-dependent fishes is critical to the conservation of their most essential habitats. Because recruitment and fitness may be influenced by the quality of juvenile habitats, developing methods to quantify habitat-specific survivorship is pivotal to such understanding. An initial step to quantify survivorship is to validate the habitat-specific natural tags contained in otoliths. To this aim I investigated the variability in the chemistry of surface waters and otoliths of juvenile spotted seatrout, Cynoscion nebulosus, in five seagrass habitats of Chesapeake Bay, namely: Potomac, Rappahannock, York, Island, and Eastern Shore. I measured Mg, Ca, Mn, Sr, Ba, and La in water and otoliths by inductively coupled plasma-mass spectrometry, and δ13C and δ18O in otoliths using an automated carbonate analyzer. Multivariate analyses of variance and regressions were used to test the hypothesis that otoliths accurately record the chemistry of natal habitats of juveniles, whereas cross-validated k-nearest neighbor functions were derived to discriminate habitats based on water and otolith chemistry. Concentration of Mg, Mn, Sr, and Ba in water was significantly different between habitats independent of temporal variation. Classification accuracy of water samples was low in Rappahannock (37%), moderate in Potomac and Eastern Shore (60–70%), and high in York and Island (81–82%) habitats. Weighted regressions showed that salinity could predict accurately [Ba/Ca]otolith and [La/Ca]otolith. There was a positive correlation between [Ba/Ca]otolith and [Ba/Ca]water, but the relation was not linear as previously found in laboratory experiments. Contrary to expectation, [Sr/Ca]otolith did not correlate with water chemistry, however there was a predictive relation between [δ18O]otolith and [Sr/Ca]water. Otolith microchemistry of juveniles collected in 1998 and 2001 was significantly different among habitats within and between years, but the ability of trace elements to allocate individual fish to natal habitats was variable (0–82%). However, the combination of [Ba/Ca], [Mn/Ca], with δ13C and δ18O in 2001 otoliths significantly improved classification rates, allowing 82–100% accuracy. These results showed that otolith microchemistry might be useful in identifying specific seagrass beds in Chesapeake Bay, with the potential of being used as natural tag to quantify survivorship and to determine essential habitats for juvenile spotted seatrout

Chemistry of Surface Waters: Distinguishing Fine-Scale Differences in Sea Grass Habitats of Chesapeake Bay

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

Predicting market squid (Doryteuthis opalescens) landings from pre-recruit abundance

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 twofactor 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 prerecruit 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

Vulnerability to climate change of managed stocks in the California Current large marine ecosystem

Introduction: Understanding how abundance, productivity and distribution of individual species may respond to climate change is a critical first step towards anticipating alterations in marine ecosystem structure and function, as well as developing strategies to adapt to the full range of potential changes. Methods: This study applies the NOAA (National Oceanic and Atmospheric Administration) Fisheries Climate Vulnerability Assessment method to 64 federally-managed species in the California Current Large Marine Ecosystem to assess their vulnerability to climate change, where vulnerability is a function of a species’ exposure to environmental change and its biological sensitivity to a set of environmental conditions, which includes components of its resiliency and adaptive capacity to respond to these new conditions. Results: Overall, two-thirds of the species were judged to have Moderate or greater vulnerability to climate change, and only one species was anticipated to have a positive response. Species classified as Highly or Very Highly vulnerable share one or more characteristics including: 1) having complex life histories that utilize a wide range of freshwater and marine habitats; 2) having habitat specialization, particularly for areas that are likely to experience increased hypoxia; 3) having long lifespans and low population growth rates; and/or 4) being of high commercial value combined with impacts from non-climate stressors such as anthropogenic habitat degradation. Species with Low or Moderate vulnerability are either habitat generalists, occupy deep-water habitats or are highly mobile and likely to shift their ranges. Discussion: As climate-related changes intensify, this work provides key information for both scientists and managers as they address the long-term sustainability of fisheries in the region. This information can inform near-term advice for prioritizing species-level data collection and research on climate impacts, help managers to determine when and where a precautionary approach might be warranted, in harvest or other management decisions, and help identify habitats or life history stages that might be especially effective to protect or restore

Predicting market squid (Doryteuthis opalescens) landings from pre-recruit abundance

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 twofactor 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 prerecruit 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

Utilities of larval densities of Pacific mackerel (Scomber japonicus) off California, USA and west coast of Mexico from 1951 to 2008, as spawning biomass indices

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

ASSESSMENT OF THE PACIFIC SARDINE RESOURCE IN 2011 FOR U.S. MANAGEMENT IN 2012

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