Fish and Fisheries最新文献

Fishing with active bottom-contacting gears (here collectively described as 'bottom trawling') is considered the greatest source of anthropogenic disturbance to marine sediments. However, uncertainties are apparent in studies evaluating the severity of their impacts from fishing with these gears at the global scale. A major uncertainty is the estimation of the area of seabed disturbed by applying European-based vessel size to gear footprint (i.e., gear width) relationships to the global fleet, thereby assuming these relations hold worldwide. To test the strength of this assumption, we conducted a structured review to understand global variation in fishing gear parameters and, thus, footprint of bottom trawling gears. While we find a European bias in the primary literature, we find that the relationship between vessel size and gear footprint differs significantly among FAO Major Fishing Areas, suggesting that European-based relationships are not representative of fleets worldwide. For example, otter trawler footprints in the Mediterranean and the Black Sea increase by 10.2 m for every meter increase in overall vessel length compared to just 3.3 m for otter trawlers in the Northwest Atlantic. These findings challenge the reliability of previous estimates of the global footprint of bottom trawling gears, thus highlighting the urgent need for improved availability of commercial data to create a globally representative data set that can address uncertainties in the quantification of anthropogenic disturbance of the benthic environment and the consequential impacts on biodiversity, ecosystem integrity and carbon losses.

The importance of connectivity for freshwater organisms is widely recognised, yet in-stream barriers associated with population declines and increased risk of extinction remain globally ubiquitous. Despite their negative consequences, these barriers can protect aquatic communities by limiting the spread of invasive species, leading to conflicting management goals in some regions. Selective fish passage is a solution for the conflicting goals of passing native, desirable species while restricting the spread of invasives. Approaches that can target groups of species sharing similar attributes (i.e. guilds) are likely to be more efficient than those that target species individually, particularly in taxonomically diverse systems. We explored the guild structure of 220 Great Lakes freshwater fishes based on morphological, phenological, physiological and behavioural attributes associated with passage and movement. We identified five distinct guilds as well as the attributes most important for defining these groupings: maximum total length, trophic level, relative eye size, spawning temperature, spawning season, presence/absence of ampullary electroreceptors and the presence/absence of hearing specialisations. The approaches outlined in this work can be generalised to enhance selective fish passage in aquatic ecosystems worldwide.

Small-scale fisheries (SSF) are commonly governed through co-management, a widely advocated approach for promoting equitable governance. However, evidence suggests that this governance approach can sometimes exacerbate power imbalances, facilitate elite capture and intensify conflicts. To foster co-management that successfully enhances equity in SSF governance, it is crucial to understand when and why it leads to positive or negative equity outcomes. To this end, we undertook a scoping review to identify empirical research on the relationship between SSF co-management and equity outcomes. We identified 30 empirical studies that assessed equity outcomes in SSF co-management initiatives. Our analysis revealed four key findings: (1) distributional and procedural equity received approximately equal levels of attention, largely without an explicit equity lens; (2) co-management had mixed impacts on equity, with the most prevalent outcome being improvement to equity; (3) delegated and cooperative co-management types were more often associated with improved equity outcomes, while consultative co-management was more often associated with reductions or no change; and (4) inclusive participation, strong social capital and secure property rights were most often associated with improved equity outcomes, while weak social capital, institutional design and management oversight were most often associated with reduced equity outcomes. However, the evidence supporting our findings was limited, with only seven studies robustly documenting the role of inclusive participation in enhancing equity. Our review offers valuable insights into the complex interplay between SSF co-management and equity, informing future research and practice and policy interventions aimed at achieving social goals through co-management governance approaches.

Sharks are among the most threatened groups of exploited fishes, comprising common bycatch across many fisheries. Management efforts intended to safeguard threatened species have increasingly focused on retention bans to reduce bycatch mortality. However, the population effects of such measures remain unevaluated across species. We combined available data from 160 studies providing estimates of at-vessel or post-release mortality for 147 taxa caught by different fishing gears to create random-forest regression models and predict mortality rates for 341 shark species incidentally captured by longlines or gillnets. Smaller-bodied species inhabiting shallow waters were more likely to suffer at-vessel mortality compared to their deep-water counterparts, for which post-release mortality was more likely to occur. We then used results for longlines to simulate the effect of retention bans in reducing fishing mortality to sustainable levels. Our metric consists of the ratio between the proportion of each species' population caught and discarded (P_MAX) under a retention ban divided by the fishing mortality (F) predicted to achieve maximum sustainable yield (F_MSY). Our calculations show that a retention ban yielded an average ~ three-fold higher P_MAX compared to F_MSY, with 18% of the species having P_MAX/F_MSY < 2, 72.3% having 2 < P_MAX/F_MSY < 5, and 9.7% having P_MAX/F_MSY > 5. For threatened species, median P_MAX/F_MSY = 2.28 and non-threatened ones had median P_MAX/F_MSY = 2.77. Our study shows that retention bans could reduce shark mortality, but must be combined with additional measures to stop overfishing, especially for low-productivity species. 

Scientific advice for fisheries management rarely takes into account how fishers react to regulations, which can lead to unexpected results and unrealistic expectations of the effectiveness of the management measures. Short-term decisions about when and where to fish are one of the greatest sources of uncertainty in predicting management outcomes. Several models have been developed to predict how fishers allocate effort in space and time, including mechanistic methods such as gravity and dynamic state variable models, and statistical methods such as random utility and Markov models. These have been individually used to predict effort allocation for various fisheries, but there is no comparative synthesis of their structure and characteristics. We demonstrate strong theoretical links between utility and choice in gravity, random utility, Markov and dynamic state variable models. Using an advanced event-based simulation framework, we find that mechanistic models bias effort allocation to certain areas when applying commonly used strong assumptions about drivers of effort allocation; and conversely, statistical models accurately predict the distribution of fishing effort under business as usual. However, predictive performance degrades with previously unobserved dynamics, such as a spatial closure. Mechanistic models were less suited to general application under business as usual but provide a useful framework for testing hypotheses about a fishery system in response to policy change. Comparison of simple model formulations yielded significant insight into the characteristics of the models and how they could be used to evaluate alternative management approaches for mixed fisheries.

Species with complex life cycles, such as anadromous fish that perform spawning migrations between freshwater and the ocean, may be particularly sensitive to global change because freshwater and marine habitats experience distinct shifts in climate and ecosystem dynamics. Abundances of wild steelhead trout (Oncorhynchus mykiss) have declined across most of their range over the past 40–50 years. We examined whether declines in steelhead survival can be linked to changing climate conditions and species interactions. A novel hierarchical integrated population model that accounts for the species' complex life history was fitted to data from multiple wild steelhead populations on the Washington coast, U.S.A. The model estimates recruitment residuals and kelt survival rates as time-varying processes, which reflect annual variation in survival before and after first maturation. We found that survival rates of immature steelhead (recruits) and adult steelhead (kelts) have declined over time and that survival trends across populations were strongly associated with climate and ecosystem change, specifically summer sea surface temperature and pink salmon abundance in the North Pacific Ocean, the NPGO index and river flows. Including these drivers in the model reduced unexplained annual variation in shared recruitment and kelt survival anomalies and largely accounted for their negative long-term trends. Our findings provide evidence that rising temperatures and increased interspecific competition at sea have contributed to declines in steelhead survival over the last five decades. Considering projected warming and high pink salmon abundances in the ocean, steelhead will likely continue to experience low marine survival rates.

Salmonid fishes are one of the best studied fish taxa, but little is known about their biomass distribution. We created a dataset using published material for over 1000 rivers with estimated salmonid biomass, covering 27 countries, and 11 species. The distribution of salmonid biomass and production across streams was skewed to the right with a mean biomass and production of 5.2 g/m² (range = 0–70.3 g/m²) and 6.3 g/m²/year (range = 0.03–50.2 g/m²/year), respectively. The top 10% and 1% of salmonid streams in the world had a biomass > 11.9 and 36.5 g/m², respectively, and a production > 13.9 and 25.6 g/m²/year, respectively. Salmonid production was positively correlated with biomass (r = 0.82, n = 194), with a mean production to biomass (P/B) ratio of 1.08, which differed among species. Mean biomass declined 38% over time, from 8.6 g/m² before 1980 to 5.4 g/m² in 2000–2020. Biomass was also higher in small streams (< 10 m wide) and in streams where smaller areas were sampled. Brown trout (Salmo trutta) streams represented a higher proportion of those with biomass > 10 g/m² than many other species. In addition to the variables mentioned above, salmonid biomass in streams was affected by species, season, method of sampling, elevation, latitude, and migratory strategy. Expanding the list of variables would be useful for developing models to predict salmonid biomass and the conditions for an outstanding salmonid stream, defined as a stream which has a biomass estimate in the top 1% worldwide.