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.

Functional anatomy of the female reproductive system of the American lobster (Homarus americanus).

Light microscopy studies of the female American lobster Homarus americanus reproductive system are essentially nonexistent or outdated. Based on samples taken in the spring, summer, and autumn from the southern Gulf of St. Lawrence between 1994 and 2014, and using a combination of histological and scanning electron microscope techniques, we propose an ovarian cycle with 10 stages, identifying for the first time a recovery stage. Also, an atypical resorption stage, characterized by massive reabsorption of mature oocytes, is occasionally observed during summer months. The oviducts are composed of connective tissue (elastic and collagen fibers) with no muscle or secretory activities. Their epithelium shows a cyclic pattern and phagocytosis activities linked to spawning. Although the role of the seminal receptacle is to store and protect semen, free spermatozoa (i.e., without the spermatophoric wall and the acellular gelatinous substance that constitute the semen) were also observed in its posteriolateral grooves immediately prior to spawning, which is consistent with an external fertilization mechanism at the seminal receptacle. Unexpectedly, free spermatozoa were observed externally near two pore-like structures located on the gonopore's operculum, not at the seminal receptacle, after spawning; hence, more work is needed to fully understand the fertilization mechanism for the American lobster.

Functional anatomy of the male reproductive system of the American lobster (Homarus americanus).

Despite supporting a valuable fishery, the reproductive system of the male American lobster (Homarus americanus) is poorly understood. The elongated H-shaped testis is responsible for spermatogenesis and is composed of follicles, a common collecting duct with interlaced scattered striated muscles, and a serosa as an external wall. Sertoli cells are associated with the spermatogenesis that produces spermatozoa, which are transferred to the collecting duct through a temporary passageway. Spermatogenesis is asynchronous between follicles and occurs on a continuous basis. The anterior and posterior lobes of the testes are independent and connect to the vasa deferentia through the Y-shaped collecting tubules that have a different cell anatomy and function than the two organs they connect. The vas deferens is divided into four regions. Spermatophores, produced in the proximal vas deferens, are packets of spermatozoa encapsulated in a single layer-the spermatophoric wall, which is composed of mucopolysaccharide acid. Large dense ovoid granules and the seminal fluid, composed of acidic sulfated mucosubstances, are secreted in the median vas deferens. Spermatophores within these secreted substances (i.e., semen) are stored in the distal vas deferens that, with the spermiduct (last region of the vas deferens), is responsible for the extrusion of the semen by striated muscle contractions. Smooth muscles suggest a peristaltic movement of the spermatophores within the vas deferens. Finally, the gonopores and the first pair of pleopods (i.e., gonopod) move the semen to the female seminal receptacle during copulation.