Fisheries Oceanography最新文献

The winter feeding ecology of Pacific salmon and Steelhead trout in the North Pacific Ocean was investigated, with a focus on species-specific diets and interannual and spatial variability in diet composition. We used results from the 2022 International Year of the Salmon Pan-Pacific Expedition to examine diet composition across the North Pacific and compared our findings with earlier surveys conducted in 2009–2011 and 2019–2020. Stomach contents were dominated by prey items typically associated with that species' diet: primarily cnidarians for Chum salmon, cephalopods and fish for Coho and Chinook salmon, and euphausiids for Pink and Sockeye salmon. The diet of Steelhead trout, encountered in one region in 2022, was composed of cephalopods, fish, and euphausiids. Some significant interannual and regional variability was observed, particularly in the eastern North Pacific, where prey resources have been noted to be more limited. This suggests that prey partitioning and adaptability may influence interspecific competition. Chum and Sockeye salmon exhibited interannual variability in most regions where multiple years of surveys were conducted. Pink salmon had the most spatial variability in winter diet with differences detected in all regions. We found minimal evidence of diet shifts based on size, with some exceptions in Chum and Sockeye salmon. Overall, these findings contribute to a deeper understanding of the trophic dynamics and feeding strategies of Pacific salmon during the winter months in the open ocean, highlighting the potential for competition and the importance of fine-scale spatial analyses for future research on salmon ecology and conservation.

The Atlantic chub mackerel, Scomber colias Gmelin, 1789, is a pelagic species, found in schools throughout the Atlantic Ocean. The objective of the present study is to identify the relationship between oceanographic conditions and catches of the Atlantic chub mackerel fishing resource in the Southwest Atlantic Ocean (21°S–29°S). The generalized additive model (GAM) was used to determine the influence of oceanographic variables on the catch per unit effort (CPUE) of S. colias. Fishing for Atlantic chub mackerel by the purse seine fleet in the Southwest Atlantic is irregular and is related to resource availability. From 2007 onward, the fleet expanded its operating area, which may have increased the CPUE between 2008 and 2012. GAM model results showed that sea surface temperature (SST) had a nonlinear effect on CPUE, peaking between 24°C and 26°C. Chlorophyll-a also influenced CPUE; however, its effect was weaker, with higher CPUE values linked to lower chlorophyll-a concentrations. The Oceanic Niño Index (ONI) exhibited a nonlinear effect, with both El Niño and La Niña periods associated with lower CPUE than during neutral conditions.

Limpet harvesting is a size-selective activity that primarily removes the largest individuals, leading to reduced reproductive output. This study investigates the fecundity strategies of two limpet species, Patella aspera and Patella crenata, inhabiting the rocky shores of Gran Canaria. Between September 2023 and April 2024, a total of 288 P. aspera and 364 P. crenata specimens were sampled from four coastal settlements. Both species exhibited determinate fecundity with synchronous spawning, as evidenced by the progression of dominant oocyte cohorts and the corresponding changes in oocyte size and number throughout the spawning season. Orientation and substrate type significantly influenced fecundity, with the North coast showing a higher number of vitellogenic oocytes, particularly in artificial substrates for P. crenata. Natural substrates on the North coast were associated with larger vitellogenic oocytes. Additionally, sex proportions were significantly affected by substrate type, with natural substrates containing a higher proportion of females. In artificial substrates, P. crenata exhibited notably higher gonadosomatic index values. The analysis of the gonadosomatic index and oocyte dynamics highlights the adaptive strategies of these limpets to local environmental conditions, contributing to our understanding of reproductive ecology in intertidal habitats. This research not only enhances our understanding of reproductive dynamics in limpets under varying environmental conditions but also emphasizes the importance of habitat and seasonal factors in shaping fecundity strategies. Such studies are crucial for conservation efforts, as they provide essential insights into how environmental pressures and human activities, like harvesting, impact the reproductive success and sustainability of these commercial species.

Tropical tunas, including yellowfin (Thunnus albacares), are recognized as a crucial contributor to global food security. Moreover, yellowfin tuna is the most commercially valuable tropical tuna. The Spanish purse seine freezer fleet, actively operating in the Indian Ocean, emerges as a leading contributor to the global yellowfin tuna catch. Currently, the planet is undergoing a climate change, which is poised to alter habitats on a global scale, particularly impacting tropical regions by causing an increase in sea surface temperatures at an unprecedented rate as well as ocean deoxygenation. Consequently, it is foreseeable that large pelagic highly migratory species like tunas may shift their distribution areas, resulting in the translocation of the current fishing grounds. In this context, the main goal of this work is to study the potential shifts of the Spanish purse seine fishing grounds targeting yellowfin tuna within the tropical belt in the Indian Ocean. Our findings suggest that although the largest yellowfin tuna catches have moved northward in latitude, most of the fishing effort, indicated by the greater number of fishing sets, has been located toward the equatorial region. Present results can only be interpreted from a human perspective and following a commercial strategy in response to the management of yellowfin tuna. Therefore, according to the 38 years of the analyzed dataset, a shift in fleet dynamics is apparent. However, we suggest that this new fishing strategy could be not so much attributed to the movement of free schools toward higher latitudes but to complex trade-off strategies.

Bigeye tuna (Thunnus obesus) is among the most prized tuna species sustaining fisheries worldwide. However, information on the feeding habits for the species is mostly restricted to the size range harvested by commercial fisheries. In this study, we report the diet composition of juvenile bigeye tuna schooling near the surface at night in the oceanic area of the southwestern Atlantic Ocean. We combined short-term dietary information derived from stomach content analysis (n = 14) with time-integrated diet information from carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope analysis (n = 8) to characterize diet composition and estimate trophic position (TP_bulk) of the individuals. The prey-specific index of relative importance (%PSIRI) indicated that Teleostei (79.1%) was the most important taxon, followed by Cephalopoda (7.6%) and Crustacea (3.9%). Myctophidae was the most frequent Teleostei in the diet (frequency of occurrence: 85.7%). The δ¹³C values on juvenile tuna muscle tissue ranged from −18.6‰ to −17.4‰ (mean ± SD: −18.1 ± 0.5‰) and δ¹⁵N values ranged from 7.2‰ to 8.4‰ (mean ± SD: 7.8 ± 0.3‰). TP_bulk (4.15 ± 0.47) results corroborated a diet based on lanternfishes and the predation upon relatively small-sized oceanic squids. Our results address a knowledge gap by highlighting important trophic links for bigeye tuna before they reach a size suitable for exploitation.