Fisheries Oceanography最新文献

This study aims to find reliable vertical environmental variables for modeling the fishing grounds of albacore (Thunnus alalunga) in the tropical waters of the Atlantic Ocean. Logbook data of 13 Chinese longliners operating in the high seas of the Atlantic Ocean from 2016 to 2019 were collected and matched with vertical environmental variables including dissolved oxygen, temperature, and salinity from 0 to 500 m at 50-m depth intervals. Then four machine learning (ML) models: decision tree (DT), random forest (RF), light gradient boosting (LGB) and categorical boosting (CGB) were constructed and compared with generalized additive models (GAMs) within spatial resolutions of .5° × .5°, 1° × 1°, and 2° × 2° grids to find the significant features. The importance of each variable was ranked and compared based on Shapley additive explanations (SHAP) approach across five ML models at three resolutions. Results showed that (1) the vertical environmental variables—temperature at the depth of 100 m and dissolved oxygen concentration at the depth of 100 and 150 m—were the significant features that contributed most to all the ML models at three spatial resolutions; (2) the models with a spatial resolution of 2° × 2° grid exhibited higher accuracy compared to the models with .5° × .5° and 1° × 1° grids; (3) the RF model had the best prediction performance among all the models tested. Our results suggested that significant vertical environmental variables showed similar importance across different ML models at different resolutions, and these specific variables can be relied upon for accurately predicting the fishing grounds of albacore in the tropical waters of the Atlantic Ocean.

Climate change is altering the distribution of marine organisms worldwide. This may, in turn, affect the overall structure and functioning of ecosystems, sometimes leading to low productive regimes. Pronounced shifts in distribution and migration have been observed for capelin (Mallotus villosus), one of the ecologically and commercially important species in the Arctic. This study attempts to discern whether a relationship existed between the altered capelin dynamics and the changing physical environmental conditions in the Iceland-East Greenland-Jan Mayen region. More specifically, three species distribution models were used to predict hindcasts (pre-shift years 1993–2002) and nowcasts (post-shift years 2003–2019) of capelin distribution based on relationships with temperature, salinity, current speed, net primary productivity, and bathymetry. The predicted probability of occurrence over these two time periods demonstrates that the changing environmental conditions have contributed to the modified distribution of the stock during its late feeding season in autumn and during the onset of spawning season in winter. The multi-model approach used in this study has provided a solid statistical framework to describe the environmental niche of capelin and its potential responses to changing ocean climate.

Gut contents and nitrogen isotope ratio (δ¹⁵N) analyses were conducted on splendid alfonsino Beryx splendens collected in the vicinity of Kuroshio from May 2015 to November 2016 (n = 708) to identify their feeding habits in the Western North Pacific. Micronektonic fish, shrimp, and squid were the dominant prey species, with the Decapoda Acanthephyra quadrispinosa, Prehensilosergia prehensilis, Cephalopoda Enoploteuthis chunii, Chiroteuthis calyx, Teleostei Sigmops gracilis, and Gonostoma elongatum. These micronektons are common in the Kuroshio Current; thus, B. splendens is a possible opportunistic feeder. Gut content weight (GCW), occurrence (%O) of fish and squid, and δ¹⁵N were significantly increased with the fork length (FL) of B. splendens. Only the %O of shrimp does not show a significant relationship with the FL of B. splendens. These indicated the ontogenetic shift of dominant prey from shrimp to fish. Fattened specimens could also prey on a greater number of fish. The seasonality of GCW and %O values was high in spring and autumn and low in summer and winter. This seasonality indicated that the feeding habits of B. splendens are controlled by primary productivity in the surface layer and/or by maturity. When the Kuroshio flowed in the north of Hachijojima Island, the GCW was significantly increased, and some organisms, including C. calyx, G. elongatum, and S. gracilis, were preyed on more. While the offshore area of the Kuroshio has low productivity, B. splendens can actively prey in this area, indicating that it is an important feeding ground for this species.

Trace element analysis of otoliths from core to edge was used to reveal differences in habitats of larvae and early juveniles of Japanese jack mackerel (Trachurus japonicus) caught in the East China Sea (ECS), Pacific Ocean, and Sea of Japan. Multi-element signatures (Sr:Ca, Mg:Ca, Na:Ca, K:Ca, and Ba:Ca) were analyzed with multivariate statistics to determine whether these element signatures provide insight into regional population structure. The median values of elements: Ca ratios in otolith core region differed significantly among areas, with most elements between the ECS and the Pacific Ocean or Sea of Japan showing significant differences. The Sr:Ca ratios exhibited a V-shaped trend from the otolith core to the edge, which was likely related to the vertical habitat layer shift of larvae and early juveniles of T. japonicus. Canonical analysis of principal coordinates using the element: Ca ratios and the hatching day were re-classified according to the sampling area with higher accuracy in the ECS (88–95%) and the Sea of Japan (76–83%) compared to the Pacific Ocean (69–72%). These results indicate that the proportion of eggs, larvae, and early juveniles transported by the Kuroshio Current from the southern ECS—the main spawning ground—to the Pacific Ocean or the Sea of Japan is low and that juveniles distributed in the coastal waters off southwestern Japan may have originated from local spawners. These results suggest that determining the elemental composition of larvae and juveniles of T. japonicus is effective in determining the habitat differences of this species in the three regions. These findings will help to understand population structure and recruitment process of this species around Japan.

Vertical egg distributions are needed knowledge for understanding exposure to physical forcing, predation pressure, and modelling initial transport from the spawning areas. Egg density and size are the biotic factors determining vertical distributions while the ambient salinity and turbulent mixing are the physical factors contributing to their vertical distributions. Egg buoyancies and densities of Atlantic cod (Gadus morhua) have been extensively studied, while limited information on haddock (Melanogrammus aeglefinus) egg density is available. This is the first comprehensive study on haddock egg densities in Norwegian waters. Eggs were collected from pairs of spawning fish caught at the coast of western Norway and inserted into a density gradient column where density was measured. The haddock eggs were neutrally buoyant at salinities ranging from 28.5 to 31. The density changed during egg development, and the results from the measurements were used to model the vertical distribution of the eggs. The simulations showed that the changes in buoyancy substantially affected vertical distributions. A comparison to previously published data on cod eggs showed that haddock eggs are considerably more buoyant than the cod eggs and are—particularly during calm wind conditions—confined to the surface layer to a larger extent than the cod eggs. The more buoyant attribute of the haddock eggs, together with the lipophilic surface of the egg membrane, is suggested to make haddock eggs more vulnerable to buoyant pollutants, like hydrocarbons.

Vertical migration and dispersal processes during the marine crab larval stage markedly affect transport, habitat selection, population connectivity, and resource replenishment success rates. However, not much is known of the reproductive ecology of swimming crabs in the nearshore waters of the northwest Pacific shelf. Here, we investigated the diel vertical migration (DVM) characteristics and transport patterns of the swimming crab zoea (Portunus trituberculatus) in this area. A Lagrangian particle-tracking algorithm coupled with a hydrodynamic model, incorporating a DVM pattern of zoeae based on observations from a field survey of the diurnal distribution of swimming crab zoea, was used to simulate the transport of zoeae, and the impact of zoeal transport on population connectivity was explored. The results revealed that particles were predominantly transported in a nearshore direction from the particle release point, with short dispersal distances during the zoeal stages. In nearshore waters on the continental shelf, the swimming crab zoeae are exposed to shoreward-moving currents with the aid of prolonged daytime locations in the lower water column, whereas larvae migrate upward to the middle and upper layers of the water column at night rather than the most superficial layer, potentially avoiding surface offshore-moving currents that may be responsible for the retention and shoreward transport of larvae. Most zoeae are transported to shallow waters, and the contribution of transport to population connectivity during the zoeal stages is relatively limited. The findings here have considerable implications for understanding the mechanisms governing the early recruitment dynamics of this species, as well as for fisheries management and conservation of marine biodiversity.

Understanding how ecosystem change influences fishery resources through trophic pathways is a key tenet of ecosystem-based fishery management. System models (SM), which use numerical modeling to describe physical and biological processes, can advance inclusion of ecosystem and prey information in fisheries management; however, incorporating SMs in management requires evaluation against empirical data. The Bering Ecosystem Study Nutrient-Phytoplankton-Zooplankton (BESTNPZ) model is an SM (originally created by the Bering Ecosystem Study, which initiated in 2006 and was expanded by Kearney et al.) includes zooplankton biomass hindcasts for the Bering Sea. In the Bering Sea, zooplankton are an important prey item for fishery species, yet the zooplankton component of this SM has not been validated against empirical data. We compared empirical zooplankton data to BESTNPZ hindcast estimates for three zooplankton functional groups and found that the two sources of information are on different absolute scales. We found high correlation between relative seasonal biomass trends estimated by BESTNPZ and empirical data for large off-shelf copepods (Neocalanus spp.) and low correlations for large on-shelf copepods and small copepods (Calanus spp. and Pseudocalanus spp., respectively). To address these discrepancies, we constructed hybrid species distribution models (H-SDM), which predict zooplankton biomass using the BESTNPZ hindcast and environmental covariates. We found that H-SDMs offered marginal improvements over correlative species distribution models (C-SDMs) relying solely on empirical data for spatial extrapolation and little improvement for most functional groups when forecasting short-term temporal zooplankton biomass trends. Overall, we suggest that interpretation of current BESTNPZ hindcasts should be tempered by our understanding of key mismatches in absolute scale, seasonality, and annual indices between BESTNPZ and empirical data.

For small pelagic fish, the physical and feeding environments during the larval and juvenile periods significantly affect recruitment to standing stock. To understand the variation in environmental conditions experienced by larvae and juveniles, this study determined the distribution of larval and juvenile Pacific saury Cololabis saira over a distance of more than 6900 km in an east–west direction in relation to the ocean environment in winter. Specimens were collected from the western and central parts of the North Pacific Ocean, mainly in January and February 2018 and 2020. Larvae (≤39.9 mm) were broadly distributed around the Kuroshio Current and the Kuroshio Extension Current. Larval densities in the water masses around the Kuroshio Extension Current were as high as, or even significantly higher than, those around the Kuroshio Current, which is considered the main spawning ground. Most juveniles (≥40.0 mm) were captured north of the Kuroshio Extension Current, where sea surface temperatures were lower and chlorophyll a concentrations were higher. The generalized additive model analysis also suggested that, compared to larvae, juveniles tended to be distributed in areas with lower sea surface temperatures and in more eastern areas. The extensive distribution of Pacific saury larvae and juveniles indicates that it is necessary to focus not only on the marine environment around the Kuroshio region but also on the Kuroshio Extension region to understand the recruitment variability of this species.

After ocean entry, juvenile Japanese chum salmon migrate northeastward to the Sea of Okhotsk. However, some juveniles originating in rivers along the Pacific coast of Hokkaido were reported to migrate in the opposite direction (westward). We compiled historical data to determine which river-origin juveniles migrate westward and to what extent. Then, the ocean-entry conditions and growth rates of 398 juveniles from two rivers along the Pacific coast of Hokkaido were estimated with otolith daily-increment analysis. Many juveniles migrated >100 km westward from multiple natal river mouths. Juveniles collected to the west of their natal rivers tended to enter the ocean earlier than those collected to the east, and many did so before sea surface temperatures reached 5°C (the lower limit of the empirically favorable temperature range). In the west, many small juveniles were collected soon after ocean entry, suggesting that they migrated passively with the Coastal Oyashio, a westward cold current. By contrast, juveniles collected in the east tended to grow faster in length and have a lower body condition factor at capture, possibly due to growth-dependent mortality during their migration against the flow of the Coastal Oyashio. Moreover, many juveniles in the west were exposed to temperatures near 13°C (the upper limit of favorable temperatures) at capture. In recent years, there has been a shortening of the favorable water-temperature period and a drastic decline in adult chum returns in the region. There is hence concern that the likelihood of abortive migrations for juveniles transported westward will increase.

Continental shelves experience many human pressures with demersal fisheries central to disturbing the ocean floor. However, ecological processes such as predation rates of benthos and their relationship with bottom fishing are often unknown for large marine ecosystems. We examined the amount of benthos consumed by 14 benthivorous fishes, the overlap between benthos predation and bottom fishing (dredge and trawl gear), and temporal trends in benthivorous fish abundance and the number of fishing trips on the northeast US continental shelf. Mean annual predation (biomass of prey removed) and 95% confidence intervals ranged from .0002 (.0001–.0003) to 3967 (1761–7112) t per 10-min area squared grid cell and prey taxa for these benthivorous fishes. Predation and bottom fishing had overlapping footprints of activity, which were slightly stronger for dredge gear. Trophic success (ratio of prey biomass eaten to the biomass of the benthivore community per grid cell) revealed more Bivalvia, Gammaridea, and Polychaeta eaten in areas targeted by trawling with more fish biomass. In contrast, dredging did not target fish biomass, but these areas had increased (Echinoidea, Gammaridea, and other benthos) or decreased (Ophiuroidea) trophic success relative to dredging footprint, suggesting habitat preferences for benthic prey and demersal fisheries have converged rather than diverged. Despite declines in bottom fishing, recent increases in benthivorous fish abundance and growing interest in ocean floor use suggest that fisheries managers should ensure benthivores have sufficient prey resources relative to their community size and human pressures to promote long-term sustainability of demersal fisheries and healthy ecosystems.