Fisheries Oceanography最新文献

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.

Variation in the recruitment of salmon is often found to be correlated with marine climate indices, but mechanisms behind environment–recruitment relationships remain unclear and correlations often break down over time. We used an ecosystem modeling approach to explore bottom-up and top-down mechanisms linking a variable environment to salmon recruitment variations. Our ecosystem model incorporates a regional ocean circulation submodel for hydrodynamics, a nutrient-phytoplankton-zooplankton submodel for producing planktonic prey fields, and an individual-based model (IBM) representing juvenile Chinook salmon (Oncorhynchus tshawytscha), combined with observations of foraging distributions and diet of a seabird predator. The salmon IBM consists of modules, including a juvenile salmon growth module based on temperature and salmon–prey availability, a behavior-based movement module, and a juvenile salmon predation mortality module based on juvenile salmon size distribution and predator–prey interaction probability. Seabird–salmon interactions depend on spatial overlap and juvenile salmon size, whereby salmon that grow past the size range of the prey distribution of the predator will escape predation. We used a 21-year historical simulation to explore interannual variability in juvenile Chinook salmon growth and predation-mediated survival under a range of ocean conditions for sized-based mortality scenarios. We based a series of increasingly complex predation scenarios on seabird observational data to explore variability in predation mortality on juvenile Chinook salmon. We initially included information about the predator spatial distribution, then added population size, and finally the predator's diet percentage made up of juvenile salmon. Model agreement improves with added predator complexity, especially during periods when predator abundance is high. Overall, our model found that when the fraction of juvenile salmon in seabird diet increased relative to alternate prey (e.g., Northern anchovy Engraulis mordax, and juvenile rockfish Sebastes spp.), there was a concomitant decrease in salmon cohort survival during their first year at sea.

Clupeid fish species are widely distributed and of highly variable stock sizes. In the North Sea, the common clupeid species are herring (Clupea harengus) and sprat (Sprattus sprattus), but during recent decades, the generally more southerly distributed sardine (Sardina pilchardus) have been more frequently observed. Comparative studies of early life stages of small pelagic clupeids are scarce, and their abilities to co-exist and relations to environmental characteristics are vastly understudied. We here investigated and compared distributional patterns of co-occurring larval sprat and sardine in the North Sea, hypothesizing that they are separated into spatial niches linked to specific hydrographical characteristics. Sampling was carried out by a large ring-net during standard fish surveys (IBTS Q3) in August 2018, 2019, and 2020. Sprat larvae were found widespread across the area of investigation, with the highest concentration in the central North Sea off the eastern and northern flanks of Dogger Bank, where abundances could reach 20 larvae/m². Sardine larvae, on the other hand, showed their highest abundances in the Southern and German Bights. Distributions of the two species appeared complementary, and statistical correlations were indicative of separate hydrographical niches, where sardine larvae resided in relatively warmer and fresher water. The relative abundances of sardine versus sprat varied between years. Sardine larvae were especially abundant in 2020, twice as abundant as sprat, and observations indicate increasing importance of sardines in the North Sea.

To help determine whether planktonic eggs of fishes on the West Florida Shelf (WFS) are retained locally or exported elsewhere, we collected fish eggs by plankton net from 17 locations (stations) and identified them using DNA barcoding. We then entered the station coordinates into the West Florida Coastal Ocean Model (WFCOM) and simulated the trajectories of the passively drifting eggs over 2 weeks at three depths (surface, midwater, and near bottom). The results indicated there were two groups of trajectories: a nearshore group that tended to be retained and an offshore group that tended toward export and potential long-distance dispersal. We also found evidence of a relationship between retention and higher fish-egg abundance; nearshore stations were associated with higher fish-egg abundances and higher retention. We suggest this is the result of (1) increased spawning in high-retention areas, (2) increased drift convergence in high-retention areas, or both processes acting together. Community analysis using SIMPROF indicated the presence of a depth-related (retention-related) difference in species assemblages. Fish-egg species were also categorized as pelagics or non-pelagics; there was no evidence of pelagic species being more likely to be exported.

Turban snails are targeted for their high-quality meat and, consequently, are often subjected to heavy harvesting pressure. Managing recreational and small-scale fisheries is challenging, partly due to a lack of biological data underpinning certain regulatory measures. This study aimed to fill current knowledge gaps on the reproductive cycle of the recreationally and culturally harvested Australian turbinid, Turbo militaris. The objectives were to investigate the reproductive timing of T. militaris in New South Wales (NSW) and identify likely environmental drivers of reproductive periodicity. Oocytes and gonads were sampled from wild animals monthly over 15 months at two sites separated by ~500 km. Analysis of oocyte size frequency and gonadosomatic index revealed that T. militaris has a pattern of extended reproduction, which is synchronous between sexes. Turbo militaris was ripest during summer, and spawning appears to have occurred over multiple events, although primarily during winter. Reproductive timing was associated with environmental explanatory variables, including sea surface temperature, wave height, salinity, phytoplankton and nitrate concentration, together accounting for 81% of the variation in oocyte size frequency and 67% in the gonadosomatic index. Reproductive periodicity was correlated with wave conditions and phytoplankton concentrations inconsistently between sites, indicating that the effect of some environmental conditions may be unpredictable or site-specific. Reproductive timing was asynchronous between two sites in the NSW fishery, posing challenges for designing seasonal fishing closures and community-based harvesting rules. Spatial closures for species with spawning over extended timeframes, or spatially asynchronous reproductive cycles, are potentially more suitable for achieving fisheries management objectives.

Swordtip squid (Uroteuthis edulis), which is sometimes eaten alive (lively squid) in northwest Kyushu, Japan, is an economically important fish species in the region. However, the total catch of this species in Japan has declined by more than 80% in the last three decades. To understand and predict the spatio-temporal distribution of fish species, we developed a one-dimensional ecosystem (NPZD) model and a habitat suitability index (HSI) model for southwest Iki Island, northwest Kyushu, Japan. Subsequently, we conducted three numerical experiments with the HSI model, with and without the NPZD model data (with the NPZD model data: phytoplankton or zooplankton concentrations, without the NPZD model data: only the physical data of the ocean). In the HSI model with zooplankton concentrations, we found a stronger positive relationship between the HSI model values and the daily fisheries catch data of U. edulis than that using only the physical variables of the ocean as the environmental parameters. Our study thus indicates that the performance of the fishing ground prediction model will improve by utilizing the lower trophic ecosystem model such as zooplankton concentrations. Furthermore, our results would provide important implications for the efficiency of fishing operations and the conservation and management of this species.

Many mobile marine taxa are changing their distributions in response to climate change. Such movements pose a challenge to fisheries monitoring and management, particularly in systems where climate-adaptive and ecosystem-based management objectives are emphasized. While shifts in species distributions can be discerned from long-term fisheries-independent monitoring data, distilling coherent patterns across space and time from such datasets can be challenging, particularly for transboundary stocks. One approach for identifying dominant patterns of spatiotemporal variation that has been widely used in physical atmospheric and oceanographic studies is empirical orthogonal function (EOF) analysis, wherein spatiotemporal variation is separated into time-series of annual factor loadings and spatial response maps. Here, we apply an extension of EOF analysis that has been modified for compatibility with biological sampling data to a combined US–Russian fisheries-independent survey dataset that spans the eastern (United States) and western (Russia) Bering Sea shelf to estimate dominant patterns of spatiotemporal variation for 10 groundfish species at a shelf-wide scale. EOF identified one axis of variability that was coherent with the extent of cold (≤0°C) near-bottom waters (the cold pool) previously shown to be a key influence on species distributions and ecosystem structure for the Bering Sea. However, the leading axis of variability identified by our EOF analysis was characterized by low frequency changes in the distributions of several species over longer time scales. Our analysis has important implications for predicting variation in species distributions over time and demonstrates a widely applicable method for leveraging combined fisheries-independent survey datasets to characterize community-level responses to ecosystem change at basin-wide scales.

Understanding environmental drivers of recruitment variability in marine fishes remains an important challenge in fish ecology and fisheries management. We developed a conceptual life-history model for Pacific hake (Merluccius productus) along the west coast of the United States and Canada to generate stage-specific and spatiotemporally-specific hypotheses regarding the oceanographic and biological variables that likely influence their recruitment. Our model included seven life stages from pre-spawning female conditioning through pelagic juvenile recruitment (age-0 fish) for the coastal Pacific hake stock. Model-estimated log recruitment deviations from the 2020 hake assessment were used as the dependent variable, with predictor variables drawn primarily from a regional ocean reanalysis for the California Current Ecosystem. Indices of prey and predator abundance were also included in our analysis, as were predictors of local- and basin-scale climate. Five variables explained 59% of the recruitment variability not accounted for by the stock–recruitment relationship in the hake assessment. Recruitment deviations were negatively correlated with May–September eddy kinetic energy between 34.5° and 42.5°N, the North Pacific Current Bifurcation Index, and Pacific herring (Clupea pallasii) biomass during the spawner preconditioning stage, alongshore transport during the yolk-sac larval stage, and the number of days between storm events during the first-feeding larval stage. Other important predictors included upwelling strength during the preconditioning stage, the number of calm periods during the first-feeding larval stage, and age-1 hake predation on age-0 pelagic juveniles. These findings suggest that multiple mechanisms affect Pacific hake survival across different life stages, leading to variability in population-level recruitment.

Bigeye tuna (BET) and yellowfin tuna (YFT) are economically important target species of pelagic fisheries worldwide, especially for tropical Pacific nations whose economies and food sources are heavily affected by commercial and sustenance tuna fishing. The El Niño-Southern Oscillation (ENSO) has a strong effect on the oceanographic conditions in the equatorial Pacific, including BET and YFT equatorial habitat and fishing grounds. For optimal fisheries management, the effects of environmental variability such as ENSO on the stocks and on the performance of fisheries must be known and predictable. However, besides some model predictions, the effects of ENSO on these two tuna species are not well understood. In this study, I investigate the statistical relationships between past ENSO conditions and equatorial fisheries using the Multivariate ENSO Index, sea surface temperature (SST), and catch and effort records from the longline fisheries in the region. Results of this study indicate that El Niño events have both delayed and concurrent positive effects on BET and YFT catch per unit effort (CPUE). The delayed positive ENSO effect on CPUE is hypothesized to be the result of enhanced recruitment acting via different mechanisms in the west than in the east. The concurrent positive effects on CPUE could be due to catchability, abundance, and/or vertical distribution of BET and YFT relative to fishing gear and require further investigation. Further exploration of the mechanisms that may underlie the results presented here could lead to predictability of CPUE of these two tuna species.