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1. Theory and previous studies have shown that commercial fishers with a diversified catch across multiple species may experience benefits such as increased revenue and reduced variability in revenue. However, fishers can only increase the species diversity of their catch if they own fishing permits that allow multiple species to be targeted, or if they own multiple single-species permits. Individuals holding a single permit can only increase catch diversity within the confines of their permit (e.g. by fishing longer or over a broader spatial area). 2. Using a large dataset of individual salmon fishers in Alaska, we build a Bayesian variance function regression model to understand how diversification impacts revenue and revenue variability, and how these effects have evolved since the 1970s. 3. Applying these models to six salmon fisheries that encompass a broad geographic range and a variety of harvesting methods and species, we find that the majority of these fisheries have experienced reduced catch diversity through time and increasing benefits of specialization on mean individual revenues. 4. One factor that has been hypothesized to reduce catch diversity in salmon fisheries is large-scale hatchery production. While our results suggest negative correlations between hatchery returns and catch diversity for some fisheries, we find little evidence for a change in variability of annual catches associated with increased hatchery production. 5. Synthesis and applications. Despite general trends towards more specialization among commercial fishers in Alaska, and more fishers exclusively targeting salmon, we find that catching fewer species can have positive effects on revenue. With increasing specialization, it is important to understand how individuals buffer against risk, as well as any barriers that prevent diversification. In addition to being affected by environmental variability, fishers are also affected by economic factors including demand and prices offered by processors. Life-history variation in the species targeted may also play a role. Individuals participating in Alaskan fisheries with high contributions of pink salmon — which have the shortest life cycles of all Pacific salmon — also have the highest variability in year-to-year revenue.

Diversification of fisheries and agroecosystems can increase and stabilize production and revenue, despite unpredictable changes in ecosystems and markets. Recent work suggests that diversification can provide multiple benefits simultaneously, but empirical evidence of relationships between catch or crop diversification and the provision of multiple benefits is scarce. The effect of diversification on multiple benefits may vary temporally and among systems. Using long‐term (11–54 years) capture fishery statistics from five Japanese lakes, we examined whether catch diversity increased multiple benefits, including revenue, nitrogen and phosphorus removal, and seasonal commercial species diversity. We also assessed whether catch species diversity increased the stability of each benefit via a portfolio effect (PE). Our study revealed positive relationships between catch diversity and the bundle of benefits (the mean of all normalized benefits; i.e., the provisioning of multiple benefits) in all five lakes, even after controlling for the total catch. The effects of catch diversity on individual benefits were positive or insignificant and differed among the study lakes. These differences were likely caused by the range and variation of functional characteristics among catch species. The influence of the annual mean price on revenue suggested that market forces did have an effect. We also found that aggregated revenue as well as N and P removal were 1.6–2.1 times (four lakes), 1.5–2.2 times (four lakes), and 1.4–2.2 times (all five lakes) more stable, respectively, than would be expected if only a single species were harvested. This greater stability suggests that maintaining catch species diversity may increase the stability of multiple benefits through PEs. Synthesis and applications. Our analysis suggests that catch diversification has great potential to increase the magnitude and stability of multiple benefits. Although total catch alone was sufficient to provide multiple benefits, a goal of maximization with specialization may decrease stability and deplete resources. Under fluctuating environmental and economic conditions, diversification strategies promise to be a potential management option for achieving resilient and sustainable inland fisheries. Our analysis suggests that catch diversification has great potential to increase the magnitude and stability of multiple benefits. Although total catch alone was sufficient to provide multiple benefits, a goal of maximization with specialization may decrease stability and deplete resources. Under fluctuating environmental and economic conditions, diversification strategies promise to be a potential management option for achieving resilient and sustainable inland fisheries.

Information is presented on fishing effort, efficiency, techniques, and catch composition for Pumé men, women, and children along with a conceptual model of fishing as a food procurement strategy. The Pumé are a native lowland South American group living in the topical savanna region of southwestern Venezuela characterized by seasonal flooding. Results are discussed in relation to the Pumé environmental and social situation, and briefly compared with results from other lowland South American groups.

Insect decline has become a major topic in scientific research, yet the relative roles of multiple factors on insect communities are still incompletely known. Our aim was to elucidate the significance of variation in local habitat quality and landscape context on moth diversity in two nature reserves in North-eastern Italy. We evaluated 14 local descriptors like plant diversity or forest structure, and 14 landscape-scale components like habitat diversity and the distance to forest edges, condensed through a Principal Component Analysis. PC-axes served as predictors in linear mixed effects models, with moth diversity and catch size (corrected for the influence of temperature and humidity) as response variables. Furthermore, sites were sorted into four groups: ‘high habitat quality’, ‘high landscape diversity’, ‘moderate quality’ and ‘low quality’. This was done to test whether local or landscape factors interact in modulating insect diversity. Our results indicate a strong influence of local factors, especially plant richness and biomass, on small-scale moth diversity. High diversity of nearby natural habitats also had a positive effect, while there was no correlation with landscape-scale attributes. Contrastingly, moth numbers were influenced by landscape diversity in 500–1000 m radius. So, although high local habitat quality supports higher moth alpha diversity, it is also important to maintain the diversity of natural habitats on the landscape-scale to preserve insect biomass and gamma diversity inside isolated reserves. Conservation efforts should be directed to preserve high vegetation and habitat diversity within reserves, while simultaneously keeping more varied landscapes around reserves might help stabilizing local insect assemblages.

The identification of biodiversity hotspots and their management for conservation have been hypothesized as effective ways to protect many species. There has been a significant effort to identify and map these areas at a global scale, but the coarse resolution of most datasets masks the small-scale patterns associated with coastal habitats or seamounts. Here we used tuna longline observer data to investigate the role of seamounts in aggregating large pelagic biodiversity and to identify which pelagic species are associated with seamounts. Our analysis indicates that seamounts are hotspots of pelagic biodiversity. Higher species richness was detected in association with seamounts than with coastal or oceanic areas. Seamounts were found to have higher species diversity within 30–40 km of the summit, whereas for sets close to coastal habitat the diversity was lower and fairly constant with distance. Higher probability of capture and higher number of fish caught were detected for some shark, billfish, tuna, and other by-catch species. The study supports hypotheses that seamounts may be areas of special interest for management for marine pelagic predators.

Upwelling ecosystems exhibit strong spatio-temporal variations of environmental conditions that drive the dynamics of marine diversity and ressources. Yet little is known in these ecosystems concerning the diversity of groundfishes. We studied the effects of environment (sea surface temperature, chlorophyll a concentration and bathymetric strata) and fishing pressure on this variability in the Mauritanian Exclusive Economic Zone (MEEZ), based on abundance data collected from 2158 hauls from scientific surveys performed on the continental shelf (15–200 m) between 1997 and 2010. First, for each haul (i.e. alpha-diversity), Species richness S and Berger Parker dominance Dbp were used as proxies of two complementary groups of nine indices, belonging to three main components of diversity (species number, evenness and taxonomic diversity), identified by a principal component analysis based on Spearman correlation coefficient. Thus the set of diversity indices used in this work suggests that a single component of diversity cannot represent the biodiversity of MEEZ groundfish. Second, generalized linear models (GLM) highlighted the stability of both indices for environmental variables, fishing effort and time, while, as shown by a previous study in the MEEZ, these variables influence species composition (i.e. beta-diversity). A longitudinal gradient of S and Dbp was highlighted, with coastal strata being richer in species and abundances more evenly distributed among species than offshore strata. Overall, this study provides a baseline of groundfish diversity in the MEEZ, that is also useful for comparison to other upwelling ecosystems, and essential for monitoring its potential shifts faced to climate change.

Analysis of long-term data provides a valuable approach to determining the extent of biodiversity decline and likely causes, but such approaches are rare in large tropical rivers. We investigated the response of the fish fauna to hydrological, climate and anthropogenic factors over the period 1982–2017 in the lower Ganges (Padma) River, Bangladesh. Systematic effort-based sampling of fish between 2007 and 2017 from a 70-km reach showed a decreasing trend in abundance and diversity. Compared to 1982 data for the same sites and fishing methods, 28 fish species, including 16 nationally threatened ones, were absent in recent catches, suggesting local extinction of these. Fish community diversity was negatively affected by fishing pressure (71 fishermen in 1980, 2616 in 2019, 37.8-fold increase) and non-native species abundance (6.8-fold increase in abundance between 2007 and 2017). Permanent water area has reduced by ~ 50% since 1984. Annual mean rainfall, Ganges water depth and river discharge at the study location decreased significantly since 1980 (by 19.2%, 17.8% and 27.6% respectively, while annual air temperature increased (25.1 °C in 1981 to 26.2 °C in 2019). Water diversion at the Farakka Barrage, ~ 70 km upstream, is partially responsible for reductions in permanent water area in the study reach. Potential sources of biological invasion and water pollution have been identified. Widespread ecological consequences on fish diversity and productivity, resulting from multiple factors, are occurring in the lower Ganges. Reduction of fisheries impacts and improved prevention of accidental aquaculture releases of non-native fishes are identified as conservation priorities for arresting the decline of native fishes in the lower Ganges.

Ecological Focus Areas (EFAs) are one of the three new greening measures of the European Common Agricultural Policy (CAP). We used an interdisciplinary and European‐scale approach to evaluate ecological effectiveness and farmers’ perception of the different EFA options. We assessed potential benefits of EFA options for biodiversity using a survey among 88 ecologists from 17 European countries. We further analyzed data on EFA uptake at the EU level and in eight EU Member States, and reviewed socio‐economic factors influencing farmers’ decisions. We then identified possible ways to improve EFAs. Ecologists scored field margins, buffer strips, fallow land, and landscape features as most beneficial whereas farmers mostly implemented “catch crops and green cover,” nitrogen‐fixing crops, and fallow land. Based on the expert inputs and a review of the factors influencing farmers’ decisions, we suggest that EFA implementation could be improved by (a) prioritizing EFA options that promote biodiversity (e.g., reducing the weight or even excluding ineffective options); (b) reducing administrative constraints; (c) setting stricter management requirements (e.g., limiting agrochemical use); and (d) offering further incentives for expanding options like landscape features and buffer strips. We finally propose further improvements at the next CAP reform, to improve ecological effectiveness and cost‐effectiveness.

In an ecosystem approach to fisheries management (EAFM) framework of the tuna purse-seine fishery, the assessment of target species, but also that of bycatch species, is essential. In the Atlantic and Indian oceans, purse-seine nets are sometimes set around tuna schools associated with whale sharks and baleen whales, although less frequently than around free-swimming tuna schools or those associated with fish aggregating devices (FAD). However, knowledge on the targeted catch and bycatch in these megafauna associated fishing sets is still relatively limited. Therefore, the aims of this study were to assess species and size composition of the target tuna species, as well as the diversity of bycatch species in whale and whale shark associated sets. Whale associated sets were found to be very similar to free school sets in terms of tuna catch (large yellowfin tuna), bycatch occurrence (presence in half the sets) and species assemblage (alpha and beta diversity). Whale shark associated sets were intermediate between FAD and free school sets, with tuna catch (skipjack and juvenile yellowfin) closer to FAD than to free school sets. However, the presence of large yellowfin, the bycatch composition (with almost no finfish, abundantly captured in FAD sets) and the species assemblage showed similarity with free school sets. This study highlights the need for an EAFM in the tuna purse-seine fishery by providing knowledge on pelagic multi-specific catches and bycatches.

Monitoring marine resource exploitation is a key activity in fisheries science and biodiversity conservation. Since research surveys are time consuming and costly, fishery-dependent data (i.e., derived directly from fishing vessels) are increasingly credited with a key role in expanding the reach of ocean monitoring. Fishing vessels may be seen as widely ranging data-collecting platforms, which could act as a fleet of sentinels for monitoring marine life, in particular exploited stocks. Here, we investigate the possibility of assessing catch composition of single hauls carried out by trawlers by applying DNA metabarcoding to the dense water draining from fishing nets just after the end of hauling operations (hereafter “slush”). We assess the performance of this approach in portraying β-diversity and examining the quantitative relationship between species abundances in the catch and DNA amount in the slush (read counts generated by amplicon sequencing). We demonstrate that the assemblages identified using DNA in the slush satisfactorily mirror those returned by visual inspection of net content (about 71% of species and 86% of families of fish) and detect a strong relationship between read counts and species abundances in the catch. We therefore argue that this approach could be upscaled to serve as a powerful source of information on the structure of demersal assemblages and the impact of fisheries.