Reduction in size-at-maturity in unprecedentedly strong cohorts of redfish (Sebastes mentella and S. fasciatus) in the Gulf of St. Lawrence and Laurentian Channel.

Life-history traits, such as size-at-maturity, are key parameters to model population dynamics used to inform fisheries management. Fishery-induced evolution, density-dependent effects, and global warming have been shown to affect size- and age-at-maturity, and resulting spawning stock biomass (SSB) in a wide range of commercial fish stocks. Marked changes in redfish biomass and environmental conditions in the Gulf of St. Lawrence and Laurentian Channel over the past decade called for a review and update of size-at-maturity for commercially important deepwater redfish Sebastes mentella and Acadian redfish Sebastes fasciatus stocks. Following a 25-year moratorium, local redfish biomass has recently reached unprecedented levels, co-occurring with an overall warming of bottom water temperatures. Our objectives were (1) to perform a histological assessment of redfish reproduction stages, including the validation and fine-tuning of a robust visual chart to facilitate monitoring of size-at-maturity and SSB in a transforming environment, and (2) to evaluate changes in size-at-maturity in unprecedentedly strong cohorts of redfish, and consequences for stock status assessment and fisheries management. Each specimen was genetically identified to species, and gonad reproduction stages were determined by histology and macroscopic appearances. The present study enabled a robust visual chart for continued and cost-effective monitoring of redfish reproduction stages to be refined and validated, and has shown a large decrease in redfish length when 50% of the individuals are considered mature that led to an increase in estimates of SSB during the 2011-2021 period for S. mentella and S. fasciatus. These changes modified the perception of stock status, thus having significant implications for fisheries management. Given that fishery-induced evolution and community structure changes along with global warming are affecting numerous stocks worldwide, the present study outlines a major and global challenge for scientists and resources managers. As shown by our results, the monitoring and frequent updates of life-history traits in transforming environments are needed to provide reliable science advice for sustainable fisheries.

Traditional approaches to estimate length at first maturity (L50 ) retrieve better results than alternative ones in a Neotropical heptapterid.

Length at first maturity (L50 ) is an important tool for the management and conservation of fish populations. Traditional approaches based on macroscopic and microscopic maturity staging exhibit high accuracy and precision, while alternative approaches (e.g., Ig -based staging, stanza changing point) are less resource-demanding. Herein, we compare four approaches to estimate L50 in a population of the heptapterid Rhamdioglanis transfasciatus from Atlantic Forest streams. Fish were sampled monthly during a year by using electrofishing. We measured the length (cm), mass (g), and gonad mass (g) of each specimen, then classified their maturity status macroscopically and microscopically. Alternative approaches were strongly discordant from traditional ones. Logistic curves considering mature individuals as those displaying at least 1% of the maximum Ig in the sample greatly underestimated L50 for females and overestimated L50 for males. The stanza changing point derived from the polyphasic growth model underestimated L50 in both cases. Despite the increasing development of less onerous approaches, it seems that they are not suitable for all fish populations and the requirements to use such approaches demand further investigation.

Temporal changes in size-at-maturity of black dogfish Centroscyllium fabricii.

By examining the maturity of 283 black dogfish Centroscyllium fabricii from Greenland waters, a shift in size-at-maturity in both sexes over the past 25 years is observed. Size-at-first maturity decreased approximately 10 cm in both sexes, and L50 and L95 shifted similarly in males, but not in females. It is argued that bycatch in the Greenland halibut Reinhardtius hippoglossoides fishery has contributed to the observed shift, but also emphasised that such a distinct change could have a methodological component as well as being subject to effects of environmental change.

Reproductive biology and population structure of white warehou Seriolella caerulea and silver warehou Seriolella punctata in the austral zone off Chile.

Using an extensive database compiled by scientific observers aboard commercial fishing operations between 1984 and 2014, we describe the maturity and size structures of white warehou Seriolella caerulea and silver warehou Seriolella punctata from by-catch of the trawling industrial fisheries operating in the austral zone off Chile. Macroscopic maturity stages and gonadosomatic (IGS ) index show mature females throughout the year and a pronounced spawning period in both austral autumn and winter seasons, with an IGS peak in July for S. punctata and August for S. caerulea. Reproductive patterns in both species show an extended spawning season (July to September) across the area between 43 and 47° S. Length-mass relationships showed significant differences between sexes in both species, where females reach a larger size. Fork length at 50% maturity was 43.5 cm for S. caerulea and 37.2 cm for S. punctata. Female catch composition is dominated by adult fish (96% for S. caerulea and 86% for S. punctata). Currently, both species are exploited with no assessment and management-decision framework. Therefore, information regarding reproductive biology and demographic traits becomes an important baseline to ensure adequate fisheries management for both species.