Fisheries Management and Ecology最新文献

As conditions of Chicago's (Illinois, USA) waterways improved following implementation of the Clean Water Act, interest in recreational use of the waterways continued to grow, but the ability of this system to support quality recreational fishing opportunities remained unclear. We analyzed historical electrofishing data (1985–2020) to determine the status and trends in body-size metrics of fish populations throughout Chicago's waterways. Many species exhibited increases in abundance, size, and diversity of lengths. Despite these increases, the number of quality-sized or larger fish was sparse. While many species increased in abundance, Common Carp (Cyprinus carpio) and Gizzard Shad (Dorosoma cepedianum) declined in abundance during 2001–2020. Improvements to the availability and diversity of key habitats within Chicago's waterways would likely improve target fish demographics further and resultant recreational fishery opportunities.

The Lake Sturgeon is a long-lived, late-maturing fish that declined significantly in abundance over the past 150 years. Since the 1990s, stocking has been used to recover numerous Lake Sturgeon populations across North America. Ill-informed genetic mixing among populations can have unintended negative consequences, so a genotype-by-sequencing (GBS) study was undertaken to help guide the stocking strategy for Lake Sturgeon on the 653-km-long Nelson River, Manitoba. Tissue samples collected from 416 adults captured from 12 locations along the Nelson River, and from the Hayes and Churchill rivers that also empty into Hudson Bay, were sequenced using Illumina technology. A bioinformatics pipeline yielded 5637 high-quality filtered markers. Genetic differentiation (overall mean F_ST of 0.028; a range of means: 0–0.16) revealed spatial structuring among and within rivers. Two populations were found in the upper Nelson River, two more in the middle Nelson, and one in the lower Nelson. Discriminant analysis of principal components revealed first-generation migrants and a general lack of effective dispersal, which raises questions about historical versus contemporary influence. Lake Sturgeon stocking in northern Manitoba should avoid mixing among rivers and among Nelson River sections.

Stock assessments for Shovelnose Sturgeon have largely been limited to age and growth analyses using pectoral fin rays despite potential underestimation of age and lack of age validation. Fisheries stock assessments rely on accurate estimates of vital rates for effective fisheries management, within which fish age and lifespan are of primary importance. Age was estimated using pectoral fin rays and otolith sections, and bomb radiocarbon (¹⁴C) dating was applied to otolith cores to determine lifespan and validate ages. Age reading of fin rays was straightforward, whereas most otolith thin sections provided two age-reading scenarios: lumping (primary increments) or splitting (finer increments) presumed annuli. While fin-ray estimates led to a maximum age of 14 years, otolith estimates led to maximum ages of 27 and 42 years. ¹⁴C dating provided support for a combination of lumping early in life, to splitting in later years, and validation of a ~40-year lifespan. Age reading of otoliths was imprecise and resulted in ~40% of thin sections that were not age scoreable. However, scoreable otolith sections, coupled with ¹⁴C dating, resulted in growth and lifespan information that are the most accurate to date for Shovelnose Sturgeon and can be used as a baseline toward stock assessment refinements.

Age, growth, and maturity of the bluewing searobin Prionotus punctatus were studied to assess its stock status in southern Brazil. Total length compositions, weight, sex, and maturity stage were recorded from commercial landings, and ages were estimated from transverse sections of the sagittal otolith. The oldest observed specimen was a 12-year-old female. Females grew to a larger asymptotic length (L_∞ = 384.4 mm) than males (L_∞ = 311.7 mm) but at a slower instantaneous rate (k_females = 0.41 year⁻¹, k_males = 0.75 year⁻¹). Reproduction occurred from spring to early fall. Females size- and age-at-maturity was estimated at 246.8 mm and 1.66 years, while males were at 237.2 mm and 1.38 years. Based on a statistical catch-at-age stock assessment, the spawning biomass declined 84% from 1976 to 2000 being classified as overfished and suffering from overfishing (B/B_msy = 0.62; F/_Fmsy >1). P. punctatus was regularly discarded by industrial fisheries before 2000 but suffered from high exploitation in the last decades. These results highlight the need for the species to be included in Brazil's fishery management plans.

Atlantic salmon smolts are sensitive to disturbance during their migration and negative effects experienced in freshwater may carry over into the marine environment. In this study, smolts were PIT-tagged and detected during their subsequent spawning migration. A generalized linear model fitted to the return data predicted a return probability of 0.091 ± 0.0061 (±SE) for smolt that was released downstream of a hydropower dam. The additional effect of migrating through a Kaplan turbine associated with hydroelectric generation did not significantly reduce return rates, while the additional effect of being handled twice in a trap was significant and lowered the predicted return probability to 0.057 ± 0.0079 (±SE; model predictions from logistic regression). Catch-mark-recapture methods such as those using physical recapture of fish should be applied with great care to avoid multiple handling stress that may lead to reduced marine survival and biasing estimates intended to help monitor population statuses. Moreover, similar return rates in turbine and bypass migrating smolts emphasize that more knowledge is needed when evaluating mitigation actions for migratory fish at hydropower plants.

In five islands of Indian Sundarbans, issues were identified related to women fishers associated with small-scale fisheries (SSF) and strategies were formulated to address them in the context of “Voluntary Guidelines for Securing Sustainable Small-Scale Fisheries” formulated by FAO being followed by signatory nations. Women were actively involved in different fisheries-related sectors for earning their livelihoods. Despite the significant contribution of women in livelihood and nutritional security, their roles are often unrecognized leading to unfair distribution of benefits between men and women. The strategic and practical gender constraints were identified; “lack of awareness and low social participation” was the major factor as perceived by women fishers with the highest score (86.06). It was identified that gender-sensitive extension approaches, training methodologies, and region-specific appropriate technologies are to be applied to uplift the women members of the fishers' community associated with SSF. The aforesaid findings may be considered as precursors for formulating location-specific strategies to address the gender gap and to create gender equality in SSF that will lead to increased productivity and sustainability of SSF across the world.

In Salmonidae, infections with the parasite Tetracapsuloides bryosalmonae may lead to a temperature-dependent proliferative disease of the kidney (PKD). Trout that survive infection and recover become resistant to the disease. The use of this approach to improve brown trout (Salmo trutta) stocking success was tested in three PKD-affected streams in southern Germany. Fish were treated using local spores of the parasite and kept at low temperatures (14°C) to not develop the disease. Controls were similarly kept but not treated with spores. Independent of time of stocking (winter or spring), recapture rates for both control and parasite-treated stocked trout were very low (<1%). However, recaptured parasite-treated trout exhibited lower parasite prevalence than control and wild-caught trout.

Rights-based fisheries management (RBFM) seeks to create market incentives to reduce competition, avoid overexploitation, and increase economic efficiency. Particularly for artisanal fisheries, however, assumptions of RBFM may not be met and its use needs to be carefully considered. This study applies an existing tool (SEASALT) to evaluate the strength of RBFM based on attributes of security, exclusivity, fish mortality, scale, responsibility, limitations, and transferability. Results for 17 fisheries in Mexico show a positive (nonsignificant) relationship between the strength of RBFM and stock status, and no effect on prices or landed value. Real-world fisheries governance systems are much more complex than the simple linkages between attributes implied in SEASALT, but results highlight pre-existing monitoring and enforcement capacity as essential for successful RBFM. Transitions to RBFM may strengthen this capacity, but likely cannot create it where it does not already exist. Based on our findings, RBFM strategies may benefit from group quotas with limited transferability to avoid negative social outcomes from consolidation or rent capture by intermediaries; this could potentially build on the latent capacity of traditional community associations common in many artisanal fisheries.

Technical interactions (multiple fleets fishing multiple species with various gears, as either target or bycatch), bycatch regulations through a landing obligation, and biological and economic effects of climate change, affecting fisheries yield and profits, provide a challenge for demersal mixed fisheries of the North Sea. A multi-stock, multi-fleet, bioeconomic model was used to understand management options under these combined influences. Scenarios considered climate change effects on recruitment of three main gadoid stocks (cod – Gadus morhua, saithe – Pollachius virens, whiting – Merlangius merlangus), possible future developments of fuel and fish prices, and strict implementation of a landing obligation. The latter leads to decreased yield and profits in the short term due to increased choke effects, mainly of North Sea cod, being influenced by climate-induced productivity changes. Allowing fishing above F_MSY, but within sustainable limits, or limiting year-to-year quota changes, could help buffer initial losses at the expense of decreased profits in the mid- to long-term. Economic performance of individual fleets was linked to their main target's stock status, cost structure, and fuel and fish prices. The results highlight a need to consider both biological and economic consequences of climate change in the management of mixed fisheries.