Fisheries Management and Ecology最新文献

Stocking of marine fish into coastal systems to augment natural recruitment is a growing practice adopted by fisheries managers around the world. Releasing fish directly into well-resourced nursery grounds greatly increases survival and retention of stocked individuals but requires an understanding of juvenile habitat requirements. In eastern Australia, the dusky flathead (Platycephalus fuscus) is a highly regarded recreationally targeted species and the focus of an emerging stock enhancement programme, although little is known of their specific nursery habitat. Using acoustic telemetry, hatchery-reared juveniles were monitored in Lake Macquarie to quantify habitat use and dispersal. Sandy areas adjacent to edges of seagrass beds were favoured, likely as foraging habitat. Within 5 weeks after release, fish were detected 5 km from the release site, but only at locations containing seagrass beds, so stocked fish likely disperse around estuaries to regions with suitable habitat. Future releases of dusky flathead should target areas containing patchy seagrass-sand to optimise stocking outcomes. Beyond fisheries enhancement programmes, our findings highlight the importance of structured habitat, such as seagrass beds, for juvenile fish.

Accurate information on population structure is essential for effective fisheries management. Greenland halibut (Reinhardtius hippoglossoides) in the North Atlantic is managed as four separate offshore stocks. We use Multivariate Autoregressive State-Space (MARSS) models to assess population structure by means of abundance and biomass trends in four regions (Norwegian Sea, Iceland, Southeast Greenland, and Northwest Atlantic) where three offshore stocks are recognized: (1) Baffin Bay–Davis Strait (Northwest Atlantic stock), (2) Southeast Greenland and Iceland (West Nordic stock (WNS)), and (3) the Barents and Norwegian Seas (Northeast Arctic stock). We formulated model alternatives, using bottom trawl survey data from each region for 1996–2019, to evaluate support for different population structures. Abundance and biomass observations from each region were linked to growth rate parameters in MARSS models and the impact of climate (North Atlantic Oscillation Index) and fishing (commercial catches) on stock dynamics was investigated. Top models identified the Northwest Atlantic as an independent population. Best-fit models treated Greenland halibut in the WNS as two independent populations (east and west), with potential connections between eastern Iceland and the western Barents Sea. These results suggest a mismatch between current stock perception and management boundaries in the Northeast Atlantic.

Evaluating population trends in dynamic estuarine environments can be challenging, especially when survey data include a high percentage of zero observations. In fishery-independent surveys, zeros that come from reduced susceptibility to sample gears and reduced availability of the population to the survey impact survey catchability and negatively bias relative abundance indices. A zero-inflated negative binomial model was used to standardize a juvenile Atlantic Sturgeon (Acipenser oxyrinchus oxyrinchus) relative abundance index (Hudson River, New York) that included a high proportion (42%) of zero observations and intra- and interannually variable covariates. Reduced susceptibility was related to low water temperature, with the percentage of zeroes increasing rapidly below 7°C. Availability was influenced by temperature and distance to salt front, as catch rates increased with temperature and peaked in mesohaline waters ~27 km downstream of the predicted salt front. An alternative index suggested significant population growth (r = 0.15; p-value = 0.007) occurred from 2004 to 2015. The zero-inflated model helped better understand Hudson River juvenile Atlantic Sturgeon ecology and relative trends in abundance, to better inform future management and monitoring decisions along the Atlantic Coast.

Size-based indicators are appropriate for monitoring status and guiding management of multi-species, multi-gear fisheries, such as coral reef fisheries. From May 2018 to April 2019, size distribution and composition of coral reef fish catches were monitored through a participatory landing survey in southwestern Madagascar. Fishers targeted a large diversity of fish taxa (75 families) and range of sizes (1.6–86 cm). Five predominant gears accounted for most of the catch (1360 [±39] t), including mosquito net trawl (27.7%), beach seine (26.8%), speargun (7.2%), gillnet (30.6%), and handline (7.1%). Due to widespread use of gears made from mosquito nets, 75% of fishes smaller than 9 cm and 47% of juvenile fishes were represented in the total catch number. Large-size taxa (Scaridae, Lethrinidae, Siganidae, Acanthuridae, Synodontidae, Mullidae, and Labridae) were mostly harvested as juveniles. Catches varied by 8%–70% throughout the year. Size of coral reef fish, annual catches, and catch rates all declined since the 1990s.

Groupers are apex predators that are believed to play crucial roles in ecosystems, so any loss or decline of these species in coral reefs can adversely affect ecosystem stability. Epinephelus fuscoguttatus is currently categorized as vulnerable (VU) from its previous near threatened (NT) category. Information about their biological and ecological status is limited to assist in formulating management plans for the species in Kenya. Therefore, we aimed to provide baseline scientific information on the biology of E. fuscoguttatus, to enable formulation of sustainable management strategies. Sampling was conducted for 1 year at two fish landing sites along the Kenyan coast: Shimoni and Mayungu. Exploitation rate, size at maturity (L₅₀), GSI, and fecundity were estimated. We found that E. fuscoguttatus was currently exploited above an optimum level, (E = 0.9). Length at maturity L₅₀ was 59.50 cm for males and 48.2 cm for females, and mean fecundity was 509,121 eggs/female/year. The gonadosomatic index was highest in June and December, but ripe females were identified in several months to suggest a protracted spawning period. The exploitation rate of E. fuscoguttatus was not sustainable. Consequently, we recommend reducing fishing effort to biologically sustainable levels to enhance recovery.

Fish are ubiquitous in pumped artificial drains but channel maintenance exposes fish to high flows and predators, and fish communities may experience population-level threats if they are unable to access refuge during extreme flood-relief pump operations. We assessed the impact of an extreme flood-relief pump operation and effects of artificial habitat introduction on a resident fish community in an artificial drain in Great Britain using side-scan and multi-beam sonar. Sonar surveys before the flood found abundant aggregations of resident fish, whereas no fish were found after the flood, which suggested flood-relief pump operations significantly altered resident fish populations. Fish abundance near artificial habitats monitored before the flood were highest during crepuscular periods and was similar among three different artificial habitat designs. Our findings improve the understanding of extreme flood impacts on fish in artificial drains and demonstrate the usefulness of sonar techniques for surveying abundance and spatial distribution of fish populations before and after floods.

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.