Fisheries Management and Ecology最新文献

Three-dimensional hydrodynamic numerical simulation and laboratory fish-passage experiment with juvenile grass carp (Ctenopharyngodon idella) were used to systematically estimate hydrodynamic parameters, fish passage efficiency, fish swimming behavior, and fish swimming trajectories in a vertical-slot fishway (VSF) under five different flow discharges. The spatial-mean time-averaged velocity magnitude along the slot section determined passage success rate. The absolute value of the time-averaged Reynolds-shear-stress component in the X–Y direction played a decisive role in selecting the swimming path. In addition, fish energy expenditure along the mean-50% swimming route indicated that higher mainstream velocity did not necessarily signify larger energy consumption, because successfully-migrating fish selected the relatively lower velocity zone during the migration process. Our findings for fish swimming behavior in response to velocity and turbulence can be used to develop high-efficiency fishways for grass carps or other species with similar traits.

Recovery of many seal populations has intensified seal-fishery conflicts. Acoustic deterrent devices (ADDs), designed to deter seals while minimising collateral harm, provide a potential solution. We investigated feasibility of ADDs to protect a European whitefish (Coregonus lavaretus) fishery in the River Iijoki, Finland, which enters the Baltic Sea. A sound barrier produced by a line of ADDs across the river efficiently prevented grey (Halichoerus grypus) and ringed (Pusa hispida) seals from passing the barrier line, thereby increasing catches, decreasing damage to fishing gear and catch and resulting in fewer seal sightings in the area safeguarded by ADDs. Hence, blocking access of seals to a river or its section by ADDs during a critical fishing period is a promising method for reducing seal-induced catch losses. However, long-term assessments of impacts of ADDs are still needed to verify the overall effectiveness.

We comprehensively assessed marine recreational fishing of threatened guitarfishes (Pseudobatos percellens, Pseudobatos horkelii, and Zapteryx brevirostris) in Southern and Southeastern regions of Brazil. A dual-method approach integrated social media reports and in-person interviews to explore practices, challenges, and conservation implications of recreational fishing for these species. Seasonal capture of guitarfishes required the promotion of catch-and-release, especially during gestational periods, and the development of best angling practices manuals and accessible identification guides. With a focus on land-based activities and engagement with fishers, our findings underscored the importance of collaboration among researchers, recreational fishers, and conservationists to map and monitor recreational capture and contribute to guitarfish research and conservation.

To improve spatiotemporal data collection and inform future spurdog Squalus acanthias stock assessment, a new dedicated longline survey was initiated in 2021 in coastal waters of southern Norway. The survey comprised a mixture of randomly predefined stations to facilitate unbiased abundance estimates and supplementary stations including informant putative hotspots. During 25 survey days in autumn 2021, 287 stations were sampled, of which 280 were categorized as “satisfactory” in terms of gear quality deployment. Spurdog catches (n = 954) were more abundant in southeast coastal shallower waters (19–150 m). No length, sex, or maturity stratified schooling behavior was found with increasing catches. Females were more abundant and larger than males, but males were older. Growth and reproduction parameters were within ranges reported for the stock. Our results provide valuable input for spurdog survey designs with regards to optimizing boat time, location of stations, and biological sampling protocols. The survey provides important data for monitoring the spurdog stock and other data-limited species, especially considering the newly re-opened spurdog fishery but also to study possible future effects of climatic changes on spurdog distribution.

The Paddlefish (Polyodon spathula) has been extirpated from portions of its native range due to anthropogenic habitat degradation and fragmentation, most notably the impoundment of rivers. To mitigate some of these losses in Oklahoma, Paddlefish have been stocked into reservoirs throughout the state, with variable success in establishing self-sustaining populations. Two factors thought to contribute to success of Paddlefish stocking are spawning substrate and prey availability, which were quantified in six reservoirs and nine reservoir tributaries. Side-scan sonar and supervised classification of aerial imagery were used to classify 4517-ha of river substrate upstream of the river-reservoir interface in reservoir tributaries. Zooplankton community structure, water clarity, and nutrient availability were also assessed in the same reservoirs and tributaries. One tributary had suitable spawning substrate (>40%), and the rest had minimal (<1.5%), which suggested that availability of suitable spawning substrate was not directly correlated with Paddlefish stocking success. Reservoirs with self-sustaining Paddlefish populations had higher abundance of large zooplankton (copepods and cladocerans) than reservoirs without a reproducing population. Notably, tributaries associated with Lake Texoma, the one known example of failed restoration, were much more turbid than other rivers. We conclude that abiotic factors such as water clarity may contribute more to variable recruitment than spawning substrate or zooplankton abundance by mediating foraging success of Paddlefish post-larvae.

During the last three decades, the Kafue flats floodplain fishery on the Kafue River in Zambia has been increasingly exploited due to more individuals settling in the area and seasonal travellers gaining access to the fishery during flood season. Despite successful governance arrangements that effectively regulated access to fish stocks for many generations, evidence shows that these arrangements are not working as new entrants continue to gain access and overexploit remaining fish stocks. Managing new entrants is a crucial factor in achieving sustainable use. Our objective was to gain an understanding of fisheries governance on the Kafue floodplain fishery, particularly in Shimungalu and Nyimba fishing villages, where different levels of government support for co-management structures produced different outcomes. Our research approach was qualitative, by utilising the snowball sampling technique and incorporating interviews and documentary analysis. Our aim was to investigate discrepancies in the efficacy of resource access and utilisation in the two fishing camps, and to offer recommendations on how governance systems for the fishery could be refined to improve their efficacy. This comparative analysis of the two fishing communities, which share numerous characteristics with various small-scale fisheries in Africa, provides an opportunity to understand how polycentric governance offers a solution by enabling other organisations to fill capacity gaps faced by relevant authorities. The lessons derived from this analysis offer valuable insights into enhancing fisheries governance and future research directions in Zambia, and Africa at large.

Estimates of recreational fishing effort and catch are needed to inform fisheries management, but such estimates can be challenging to obtain. We combined a zig-zag line transect survey of buoys, a fisheries enforcement survey and a drone survey to estimate recreational effort in the open-access trap fishery for signal crayfish (Pacifastacus leniusculus) in the sixth largest lake in Europe, Lake Vättern, Sweden. Using supporting variables such as size of nearby ports and bathymetry, our model-assisted estimate of total effort was 6400 (±4300 CI) buoys during the three-weekend season. Using the frequency of buoys to traps as a constant, the total number of crayfish traps was estimated to be 25,500 (±17,000 CI). The sampling design and methods presented are useful for ecologists and resource managers to design future multi-source surveys of recreational trap fishing effort.

Spatial scales are important for examining health of exploited fishery stocks and guiding management actions. However, information about the optimal spatial scale is still unclear for assessment of transit fisheries, such as elver fisheries of the American eel Anguilla rostrata. We applied a generalized depletion model to assess catch and effort data from three nearby rivers (within 50 km) to test the hypothesis that modeling on pooled and separate data from nearby rivers would give similar estimates of abundance and exploitation rate. Overall, pooling data from rivers within 50 km did not result in large differences (<20% in relative difference) in estimates of abundance and exploitation rate with close mean abundance estimates and similar temporal trends in abundance, exploitation rate, and relative escapement. Pooling nearby river systems can greatly reduce modeling effort, at the cost of ignoring fine-scale variability in elver recruitment and having coarser spatial scale for the management. When only an index of annual recruitment and exploitation rate are of interest, pooling data may be practical from different locations up to 50 km.

We developed a management framework based on community size-spectra (CSS) to establish targets to maximize desirable gamefish. We evaluated the influence of relative abundance of fish functional groups and watershed characteristics on the slope of the CSS or ecological efficiency. Both ecological efficiency and capacity were strongly influenced by relative abundance of fish functional groups and the degree of water level variation. Steeper slopes indicated overfished gamefish populations, whereas flatter slopes indicated systems dominated by undesirable invasive large-bodied low trophic position fish. We hypothesize that a desirable fishery would have a target range of CSS slopes that provides a deterministic community-based framework of predictable responses to environmental and food web changes that can be used to evaluate outcomes of management actions and a means to assess annual progress toward desirable conditions.