Environmental associations of Pacific bluefin tuna (Thunnus orientalis) catch in the California Current system

We investigate the impact of oceanographic variability on Pacific bluefin tuna (Thunnus orientalis: PBF) distributions in the California Current system using remotely sensed environmental data, and fishery‐dependent data from multiple fisheries in a habitat‐modeling framework. We examined the effects of local oceanic conditions (sea surface temperature, surface chlorophyll, sea surface height, eddy kinetic energy), as well as large‐scale oceanographic phenomena, such as El Niño, on PBF availability to commercial and recreational fishing fleets. Results from generalized additive models showed that warmer temperatures of around 17–21°C with low surface chlorophyll concentrations (<0.5 mg/m³) increased probability of occurrence of PBF in the Commercial Passenger Fishing Vessel and purse seine fisheries. These associations were particularly evident during a recent marine heatwave (the “Blob”). In contrast, PBF were most likely to be encountered on drift gillnet gear in somewhat cooler waters (13–18°C), with moderate chlorophyll concentrations (0.5–1.0 mg/m³). This discrepancy was likely a result of differing spatiotemporal distribution of fishing effort among fleets, as well as the different vertical depths fished by each gear, demonstrating the importance of understanding selectivity when building correlative habitat models. In the future, monitoring and understanding environmentally driven changes in the availability of PBF to commercial and recreational fisheries can contribute to the implementation of ecosystem approaches to fishery management.     

Interannual changes in sablefish (Anoplopoma fimbria) recruitment in relation to oceanographic conditions within the California Current System

Sablefish (Anoplopoma fimbria) supports substantial fisheries in both the eastern and western Pacific Oceans. Juvenile recruitment along the west coast of the continental United States has been highly variable over the past three decades. Using a generalized additive model, we demonstrate that physical oceanographic variables within the California Current System have significant effects on sablefish recruitment. Significant relationships were found between juvenile recruitment and northward Ekman transport, eastward Ekman transport, and sea level during key times and at key locations within the habitat of this species. The model explains nearly 70% of the variability in sablefish recruitment between the years 1974 and 2000. The predictive power of the model was demonstrated by refitting without the last 5 yr of data and subsequent prediction of those years. Bootstrap assessments of bias associated with parameter estimates and jackknife‐after‐bootstrap assessments of the influence of individual data on parameter estimates are presented and discussed. Using this model, it is possible to draw preliminary conclusions concerning year‐class strength of cohorts not yet available to the survey gear as well as historic year‐class strengths. We discuss changes in zooplankton abundance and shifts in species of copepods associated with fluctuations in the physical variables that appear to have a major influence on sablefish recruitment.     

Distribution and community structure of ichthyoplankton from the northern and central California Current in May 2004–06

The distributions, concentrations, and community structure of pelagic larval fishes collected from the central and northern California Current in the northeast Pacific Ocean during May 2004, 2005, and 2006 were analyzed to investigate inter-annual, latitudinal, cross-shelf, and depth-stratified variability. The inter-annual climate-induced variability during the sampling period provided a unique opportunity to observe how larval fish communities adjust to rapidly changing environmental conditions. The 170 depth-stratified samples collected from three cruises yielded 14 819 fish larvae from 56 taxa representing 23 families. Dominant larval taxa were Engraulis mordax , Citharichthys spp., Sebastes spp., and Stenobrachius leucopsarus . Larval concentrations decreased significantly in 2006 from 2004 and 2005 levels following the anomalous oceanic conditions observed in 2005 and decreased water temperature in 2006. Larvae were generally found in higher concentrations at northern (>43°N) versus southern (<43°N) stations, with larval E. mordax and Citharichthys spp. found almost exclusively in the north during all sampled years. Inter-annual variability related to dynamic upwelling intensity was observed in cross-shelf larval distributions, although concentrations of S. leucopsarus larvae consistently increased in the offshore direction, while larval Sebastes spp. were generally found in highest concentrations at intermediate stations along the shelf. Multivariate analyses revealed that latitude, station depth, and sea-surface temperature were the most important factors explaining variability in larval concentrations. The present study shows that the ichthyoplankton community of the central and northern California Current changed dramatically in response to the variable environmental conditions of 2004–06.     

Albacore (Thunnus alalunga) fishing ground in relation to oceanographic conditions in the western North Pacific Ocean using remotely sensed satellite data

Satellite‐based oceanographic data of sea surface temperature (SST), sea surface chlorophyll‐a concentration (SSC), and sea surface height anomaly (SSHA) together with catch data were used to investigate the relationship between albacore fishing ground and oceanographic conditions and also to predict potential habitats for albacore in the western North Pacific Ocean. Empirical cumulative distribution function and high catch data analyses were used to calculate preferred ranges of the three oceanographic conditions. Results indicate that highest catch per unit efforts (CPUEs) corresponded with areas of SST 18.5–21.5°C, SSC 0.2–0.4 mg m^?3, and SSHA ?5.0 to 32.2 cm during the winter in the period 1998–2000. We used these ranges to generate a simple prediction map for detecting potential fishing grounds. Statistically, to predict spatial patterns of potential albacore habitats, we applied a combined generalized additive model (GAM) / generalized linear model (GLM). To build our model, we first constructed a GAM as an exploratory tool to identify the functional relationships between the environmental variables and CPUE; we then made parameters out of these relationships using the GLM to generate a robust prediction tool. The areas of highest CPUEs predicted by the models were consistent with the potential habitats on the simple prediction map and observation data, suggesting that the dynamics of ocean eddies (November 1998 and 2000) and fronts (November 1999) may account for the spatial patterns of highest albacore catch rates predicted in the study area. The results also suggest that multispectrum satellite data can provide useful information to characterize and predict potential tuna habitats.