Fisheries Research最新文献

Catch-per-unit-effort (CPUE) standardization is crucial for fishery stock assessment but often presents challenges due to spatial-temporal variations in species distribution and fishing effort. In this simulation study, we propose the use of customized artificial neural networks (ANNs) for modeling the spatial-temporal variations in CPUE standardization. This is achieved by encoding prior knowledge of the dependency structure between the variables into the architecture of the ANNs. We conducted numerical experiments on simulated data to compare our customized ANNs with Generalized Linear Models (GLMs), Generalized Additive Models (GAMs), and fully connected ANNs used in previous studies. Our simulated data cover three spatial-temporal dynamics scenarios with different degrees of species distribution shift over time: (1) steady fish distribution; (2) gradual directional shift over time; (3) sudden directional shift. In predicting the standardized CPUE in this simulation study, the customized ANNs demonstrated greater accuracy compared to the commonly used fully connected ANNs with an error reduction of over 70 %, more than 80 % compared to GLMs, and more than 40 % compared to GAMs, in terms of an error metric called the scaled mean absolute relative error. Our findings suggest that customized ANNs can serve as an alternative modeling tool alongside GLMs and GAMs in fisheries modeling.

The influence of bait type and leader material on target and bycatch species was assessed through fishing experiments in the Portuguese shallow pelagic longline fishery in the Atlantic Ocean. Wire leaders were found to decrease catch rates of commercially valuable species such as bigeye tuna and yellowfin tuna, while increasing catch rates of elasmobranchs, including the blue shark and shortfin mako. The odds ratios of capture swordfish and tunas also decrease when using wire leaders, while elasmobranchs have higher odds ratios of capture and at-haulback mortality when using wire leaders. Squid bait led to higher catches of targeted tuna species, however it also resulted in higher catches of marine turtles. For most of the taxa caught at-haulback mortality risk was found to be higher on squid bait, which may be related with increased deep-hooking events. While bait type and leader material did not significantly affect size selectivity for most species, wire leaders were found to retain larger blue sharks and fish bait attracted smaller-sized swordfish. This study showed that banning wire leaders on pelagic longline fisheries is an effective measure for reducing the retention of pelagic shark species, particularly of large size blue sharks.

In recent decades, recruitment of young-of-year lobsters to benthic nursery habitats in the Gulf of Maine was regionally synchronized and exhibited correlative links with changes in the abundance of the copepod Calanus finmarchicus, a foundational zooplankton species of the pelagic food web. The spatial scale at which recruitment dynamics were correlated indicated that recruitment processes were not as strongly coupled to trends in spawner abundance as might be expected, but, rather, were influenced by common, ecosystem-scale processes. Here we explored how local- and basin-scale zooplankton dynamics and oceanographic indicators in the Gulf of Maine correlated with lobster settlement indices and each other since the late 1980s. Our analysis indicates that lobster settlement trends in southwestern Gulf of Maine study areas, from Midcoast Maine to Cape Cod Bay, tend to be significantly correlated with basin-wide C. finmarchicus dynamics and the composition of waters entering the Gulf of Maine through the Northeast Channel. In contrast, lobster settlement in the northeastern Gulf, from Penobscot Bay to the Bay of Fundy, tended to correlate more strongly to C. finmarchicus variability in the Bay of Fundy region, which was distinct in earlier years but converged with the broader basin-scale processes in the latter years. Our results are consistent with the hypothesis that the combined effect of climate-related declines in abundance and phenological shifts of C. finmarchicus have contributed to declines in lobster settlement over the past decade, and justify further research into the mechanisms of this interaction. These changes also align with the weakening influence of cold Labrador Slope Water and strengthening effects of warm Gulf Stream waters that precipitated an ecosystem-wide regime shift in the Gulf of Maine over the past decade and may have greater implications for lobster recruitment than previously suspected.

The present study, covering 2018–2022, evaluated the cetacean interactions with a bottom-set net fishery along the mainland Portuguese Southern coast (Algarve), estimating bycatch, depredation, gear damage and net length influence on Landing per Unit Effort (LPUE). The fishery employed various métiers (gillnets - mesh sizes: < 60, 60–75, 80 and 220 mm; trammel nets - 120 inner and 640 mm outer panels). Observations from 655 hauls revealed depredation by bottlenose dolphins in 17.7 % of hauls, while bycatch (isolated events of 4 bottlenose dolphins and one common dolphin) occurred in < 1 %. Depredation typically results in heavy damage to the net and occurs throughout the year, with elevated rates observed during the spring and winter months. Depredation rates varied among métiers, being higher in gears targeting red mullet and hake. The impact of depredation on LPUE varied based on net length and the targeted fish species. However, when comparing LPUE in hauls without depredation, there was no significant influence on the total and hake LPUE for nets shorter or longer than 6 km (p > 0.05). Interestingly, in hauls targeting red mullets without depredation, nets shorter than 6 km had a significantly higher LPUE (p < 0.01) compared to nets 6 km or longer, suggesting that longer nets increase fishing effort due to prolonged soaking times and a higher likelihood of depredation.

Evaluating the status and trends of natural-origin anadromous fish populations over time requires robust estimates of out-migrating juvenile abundance. Information on abundance is typically acquired by capturing actively migrating fish as they pass stationary monitoring platforms. Challenges to estimation include protracted migration timing, temporally varying capture probabilities and the contemporaneous presence of unmarked hatchery-origin fish. The confounding effects of unmarked hatchery fish are especially pernicious in systems hosting multiple hatchery programs with variable mark-rates among releases. Here, we address this problem for a regionally and culturally important population of Chinook salmon (Oncorhynchus tshawytscha) supported by a hatchery-supplementation program implemented in response to the listing of this population under the U.S. Endangered Species Act. We developed a model to estimate daily and annual abundance of naturally produced age-0 fall Chinook salmon passing Lower Granite Dam (Snake River, USA) for each of the last 30 years. We accounted for variable hatchery marking rates by integrating two related data sources: 1) release-recapture data of fish with individually identifiable tags and 2) counts of marked and unmarked sample of fish captured each day. We fit joint parameters for daily fish arrival and capture probabilities to these data to estimate the daily abundance of hatchery- and natural-origin fish. Our results show that from 1992 to 2021, the annual abundance of juvenile natural-origin Snake River fall Chinook salmon increased by two orders of magnitude. These results are the first comprehensive evaluation of multi-decadal trends in abundance and run-timing for this population. Our approach can be adapted to other runs and locations within the Columbia River basin or similar systems where out-migrating fish are monitored at fixed locations.

The blue crab (Callinectes sapidus) is an ecologically and economically important species in estuaries of the Western Atlantic Ocean and Gulf of Mexico. Given the importance of reproductive output and spawner demography on population dynamics, blue crab management may be improved if individual-based changes in egg production are identified and incorporated into management advice. We determined the spawning history, batch fecundity, and stored sperm quantity of 126 ovigerous blue crabs in 2022 to estimate the reproductive potential of female blue crabs in Chesapeake Bay. Our mean estimate of fecundity, 2.17 million eggs/female, is similar to a fecundity estimate from 1986 (2.6 million eggs/female), but lower than an estimate from 1987 (4.0 million eggs/female). The 1987 estimate was likely biased high due to methodological differences. In 2022, size-specific fecundity did not differ from that in 1986. Size-specific fecundity was lower by 0.28 million eggs in multiparous females (i.e., those that produced at least one previous egg mass) compared with primiparous females (i.e., those producing their first egg mass). Size-specific fecundity was also greater in July and August than in June, however, females in June had a greater capacity for future reproductive potential because their average stored sperm quantity was three times greater than that of females in July and August. Most females in June were primiparous and would become multiparous females in July and August with higher size-specific fecundity. Our study is the first to pair individual fecundity, stored sperm quantity, and spawning history for blue crabs, which allows for a robust assessment of reproductive potential. Generally, the reproductive potential of individual female blue crabs was high at the individual level, such that sperm limitation is unlikely at the population level. Population-level production may be increased by protecting primiparous spawners as these crabs have the highest capacity to contribute offspring to the population. Furthermore, fisheries management may be improved by using our updated estimate of size-specific fecundity (Fecundity = 268,337 × exp(0.015 × Carapace Width)) and incorporating month or spawner history in models of stock production.

Large pelagic finfish are highly mobile, distributed across broad geographical scales, and often targeted by both commercial and recreational sectors. Fishing effort in these fisheries is variable due to seasonal patterns in fish behaviour and accessibility of fishing locations. Similarly, fisher behaviour and access are likely to differ within the recreational sector, between private boat-based fishing and charter (or for hire) fishing. Here, we compare spatio-temporal patterns in catch per unit effort (CPUE), effort (boat days) and catch (total catch per fishing party) for private boat-based and charter fishing, and identify environmental variables that may influence those patterns, for two pelagic species (the tropical narrow-barred Spanish mackerel and temperate Samson fish) in Western Australia. Spatial and temporal patterns of CPUE were investigated using geostatistical indices, such as the global and local index of collocation which compares the spatial distribution of CPUE locations across years and CPUE values at common locations respectively, and the centre of gravity which calculates the mean fishing location weighted by CPUE, along with the influence of environmental variables (including rainfall and sea surface temperature) on catch using generalised additive models (GAMs). The global index of collocation showed consistency in spatial distribution of CPUE and effort between private boat-based and charter fishing for both species. In contrast, the local index of collocation showed differences in the ranges of CPUE and effort within common locations. Private boat-based fishing often occurred close to the coast and adjacent to population centres, while charter fishing occurred further offshore. Spatial shifts over time were more prominent for Spanish mackerel with an overall northerly shift. For private boat-based fishing, higher catches of Spanish mackerel were associated with higher rainfall, along with an increase in ambient air temperature. For charter fishing, higher catches of Spanish mackerel occurred with ambient air temperatures of around 30 degrees Celsius and a decrease in rainfall, where high catches of Samson fish were associated with a decrease in sea surface temperatures and austral winter months. This study highlights changes in the distributions of pelagic species over time and the potential to incorporate spatio-temporal monitoring of recreational harvest into fisheries management.

Otolith shape variation in Labeo dussumieri from the four west-flowing rivers of India was analyzed using Wavelet coefficients and elliptic Fourier descriptors in the ShapeR package. The mean otolith shape of L. dussumieri varied significantly among sampling locations, with the posterior margin of the otolith showing the maximum variation. Otolith shape analysis also revealed variations between regions of different latitudes, with the northern (Narmada and Kundalika River) and southern populations (Achankovil and Chalakudy River) forming two distinct clusters. This variability in otolith shape might be attributed to the variation in environmental conditions prevailing in the sampling locations. The linear discriminant analysis based on elliptic Fourier descriptors and Wavelet coefficients showed an overall classification success of 89.03 % and 89.20 %, respectively. The present study validated that the lapillar otoliths are ideal for investigating the population structure of cyprinid fishes like L. dussumieri. The present study provided the first comprehensive information on the otolith shape analysis of L. dussumieri from the four west-flowing rivers of India.

Ectotherms, including American lobsters (Homarus americanus), can modify their body temperature using behavioral thermoregulation, by moving to areas closer to their preferred temperature. To better understand the potential consequences of climate change on lobster reproduction and recruitment, we measured the thermal preferences and locomotor activity of adult female lobsters that were carrying eggs (ovigerous; n = 139), or not (n = 143), in a thermal gradient tank with a temperature range of 6–20 °C. Trials were carried out year-round so that we could compare the thermal preferences of ovigerous lobsters carrying eggs at varying developmental stages and determine if ambient water temperatures influenced their preferred temperatures. Seasonal temperature preferences were similar for both ovigerous and non-ovigerous females with cooler temperatures preferred in the fall and winter, and warmer temperatures during the summer. However, in general, females with newly extruded eggs preferred temperatures warmer than our model predicted for all females combined, while those with eggs that were very close to hatching preferred cooler temperatures than predicted. While there were no significant differences in the relative activity of females with or without eggs, females with eggs that were hatching tended to move more. These findings demonstrate that seasonally changing water temperatures have a large impact on the thermal preferences of American lobsters, while the developmental stage of their eggs also plays a role in temperature preferences. These data should be taken into account when assessing the potential impact of warming oceans on the distribution of lobsters in the Gulf of Maine.

Hakaluki Haor, rich in fish and wildlife, has been declared an Ecologically Critical Area and recommended as a Ramsar site. The fisheries and aquatic wildlife of Hakaluki Haor have declined drastically and continue to face sustainability challenges. The present study has demonstrated an evidence-based multidisciplinary tool, RAPFISH (Rapid Appraisal Technique for Fisheries), was applied to underpin the status of fisheries sustainability of Hakaluki Haor. Exploiting the RAPFISH technique flexibility, out of 51 indicators, we customized (omitted, added, and modified) the 46 indicators under five dimensions of ecological, economic, social, technological, and management, appropriate for inland fisheries of Hakaluki Haor. A questionnaire interview with 150 fishers was carried out based on the selected indicators of the five RAPFISH dimensions. The sustainability indicators were subjected to a validation process based on feedback from fishers, using the Weighted Sum Model and Analytic Hierarchy Process. The WSM index indicators with scores over 0.5 and the top-ranked AHP indicators were primarily adopted to assess the sustainability of the fisheries. The results revealed that indicators under the ecological dimension were the most vulnerable condition, followed by the social, technological, economic, and management dimensions. In this circumstance, to keep the fisheries resources of Hakaluki Haor in a sustainable condition, the government, particularly the Department of Fisheries, is required to give special attention to effective management and conservation strategies by prioritizing comparatively weak indicators.