Fisheries Oceanography最新文献

This research examines Trachurus lathami diet composition and ontogenetic shifts (stomach content analysis and multiple hypothesis modeling) in the Northern Argentinean Continental Shelf (NACS, 34°–41° S, Southwest Atlantic Ocean), related to season (warm: October–March; cold: April–September) and water salinity (low < 33.5, ls; high ≥ 33.5, hs), influenced by the Río de la Plata plume. A diet shift with fish size and a preference for larger prey during the cold season, linked to offshore distribution in hs waters, are hypothesized. Copepods dominated the diet, with larger species (> 1.5 mm, e.g., Calanoides carinatus) prevalent in hs waters and smaller species (< 1.5 mm, e.g., Oncaea spp.) in ls waters. Amphipods (Themisto gaudichaudii), decapod, and barnacle larvae were significant in the warm season, and the former was absent in the cold period. Ontogenetic shifts were minimal, being copepods the primary prey across sizes. Results indicate T. lathami is a generalist feeder, with diet changes driven by seasonal copepod availability linked to the Río de la Plata plume dynamics. These findings underscore the importance of long-term monitoring amid NACS warming and prey shifts to support fisheries' sustainability, given T. lathami rising biomass since the mid-90s and interactions with commercial pelagic species.

Lumpfish (Cyclopterus lumpus) spawn in coastal waters in the North Atlantic Ocean, yet little is known about the distribution outside of the spawning season. Using data from an extensive pelagic trawl survey that takes place annually in the Nordic Seas, we examine the distribution and abundance of different life stages of lumpfish during summer. Utilising generalised additive models, random forest and support vector machine, we investigate environmental variables that potentially could influence their distribution. Our results reveal that lumpfish have an extensive distribution covering the Irminger Sea, Denmark Strait and Norwegian Sea. However, their frequency of capture is lower south of Iceland and in the North Sea in comparison with other coastal and oceanic areas. Temperature emerged as a primary constraint on the distribution. Lumpfish were caught at over 90% of the stations when temperature at 20-m depth ranged between 4°C and 9°C but less frequently when temperature was outside of this range. Other environmental variables, such as salinity, mixed layer depth and measures of primary and secondary production, had low influence on the distribution of lumpfish.

Sardina pilchardus, Walbaum 1792, and Sardinella aurita, Valenciennes 1847, are the fish most consumed by the Algerian population. Sardine has become increasingly rare in commercial fishing catches, whereas round sardinella is being sold at excessively high prices. Given the importance of trophic interactions between clupeids and the low levels of the pelagic food web (plankton and others), the stomach contents of the two species of S. pilchardus and S. aurita are studied. Samples are collected from the spring commercial fishery (April and May 2023) associated with the two main ports on the central coast (Algiers and Bou Ismail) justified by the intense trophic activity of these two predators. High feeding intensity (or stomach vacuity coefficient) is recorded in both males and females. Our results support the hypothesis that the diet of species in specific zones remains consistent due to stable local trophic resources. This is underscored by the lack of variation in prey quality and quantity across size and sex in both clupeid species, emphasizing the role of these interactions within the pelagic food web. Using the morphological identification and counting technique, the preys are linked to 12 taxonomic units belonging to the zooplankton, phytoplankton, and miscellaneous communities. The analysis of the diet is carried out by classifying the prey on the basis of the frequency index (If), taking into account the sex and the size where three categories of prey are defined. Copepods are the preferred prey with rates that did not differ significantly by sex and place of origin of the two clupeids. These findings extended to secondary prey (other zooplankton and phytoplankton). Also, the composition of the diet remained homogeneous in the Gulfs of Algiers and Bou Ismail. Quantitative and qualitative results on diet composition of the two clupeids and their trophic interactions within the two target ecosystems will serve as a basis for fisheries management (i.e., Ecosystem Approach to Fisheries Management [EAFM] and Ecosystem-Based Fisheries Management [EBFM]). The modeling of all the variables will allow decision makers to predict the level of exploitable biomass in the medium and long term.

Pacific saury (Cololabis saira) and the Pacific stock of Japanese sardine (Sardinops melanostictus) are dominant small pelagic fishes and are targeted by international fisheries in the western North Pacific (WNP). Using monitoring results of a pelagic trawl survey during 2003–2019 in WNP and central North Pacific, a previous study detected a shift in the center of distribution along sea surface temperature gradient (GT) of saury only in WNP, together with “parapatric” horizontal distribution between the two species during the 2010s, when saury biomass declined and sardine biomass increased. Thus, it suggested biological interactions between the two species. To corroborate this “parapatric” distribution, we applied basically the identical statistical analyses to driftnet survey results along longitudinal transects at 155°E, 170°E, and 175.5°E during 1979–1999, when saury stock was abundant and sardine stock declined since 1989. Our results indicated GT of saury slightly shifted after 1989 at 155°E, and spatial distribution of the two species largely overlapped before 1989, which do not support the previous study. While saury biomass drastically declined in the western areas of their overall distribution since 2003 and age-0 sardine dominated in the pelagic trawl survey, age-0 sardine occupied the southern area of overall distribution in the driftnet survey. These observations suggest that interspecies interactions between saury and sardine, if existed, are unlikely to take a form of parapatry. The apparent parapatric distribution can be explained by different age compositions of sardine between the two surveys and biomass-derived eastward shrinkage of saury distribution since 2003.

In the last decades, the population of the squat lobster Munida gregaria inhabiting the water column in the Patagonian Sea, Argentina, has expanded. This crustacean shares its habitat with the Argentine anchovy Engraulis anchoita, a key species in the marine food web. Existing information suggests that M. gregaria may compete with anchovy causing spatial segregation or interfere with the formation of fish schools. This study examines anchovy schools and squat lobster swarms sharing the water column in San Matías and Nuevo gulfs, in northern Patagonia. A total of four acoustic zigzag surveys were performed in San Matías gulf and five in Nuevo gulf, covering all the seasons. The echoes of both species were characterized and discriminated, measuring a set of shape, location, and density properties. A linear model was built to determine which factors affect anchovy school morphology. Anchovy schools presented well-defined edges, were amoeboid in shape, and occupied a wide range of depths in the water column. M. gregaria formed large and irregular aggregations, mainly in the upper half water column. Anchovy schools that interacted with M. gregaria tended to be larger and less dense, especially in spring and summer. This may result from either physical interference between individuals, leading to greater laxity in anchovy schools, or the partial dispersal of anchovies feeding on juvenile M. gregaria.

The growth rate during the early life stages is a key factor influencing fish recruitment variability. Extrinsic environmental factors such as temperature are generally having significant effects on early growth of larvae, while the intrinsic effects (e.g., ontogenetic or individual-specific differences) are often underestimated. In this study, the early growth pattern of Japanese anchovy (Engraulis japonicus) in the coastal Yellow Sea was estimated using otolith daily growth increments and the effects of both extrinsic and intrinsic factors on the early growth of anchovy were investigated using increasingly complex mixed-effects models. Mean growth rate during first otolith increment deposition to capture, estimated from otolith daily increment trajectories, was 0.43 ± 0.11 mm day⁻¹, and the proportion of anchovy larvae that hatched during neap tidal periods was relatively high. Early growth rate of anchovy was positively correlated with intrinsic factors (age, width of the first daily increment) and extrinsic factors (seawater temperature at hatching and during growth). The results of mixed-effects model also detected the faster growth occurred during the spring tide and that later hatching larvae were characterised by a higher growth rate. In addition, anchovy larvae exhibited a marked aggregation in the nearshore area and showed negative distribution characteristics in the upwelling areas. These results provide new evidence on the early growth pattern with intrinsic factors and spring tide; it is crucial for understanding the early growth and recruitment variability of anchovy in the context of climate change and may contribute to sustainable management policies for this valuable resource.