Distribution and life-history of spurdog (Squalus acanthias) along the Norwegian coast inferred from a five-year fishery-independent longline survey

Abstract Northeast Atlantic spurdog ( Squalus acanthias ) has recently shown signs of recovery from overfishing following international conservation measures. As the fishery slowly reopens, ensuring its sustainable long-term trajectory will require an understanding of its contemporary population structure, habitat use, and life-history traits across its distribution range. Here, we used biological data collected during an annual autumn (September–November) longline survey from 2021–2025 along the southwestern coast of Norway to investigate sex, maturity, and age-related distributions and life-history traits of spurdog in the region. Spurdog catches (N = 7,492) included a wide range of life-stages for both sexes, including juveniles and reproductively active adults, across the entire survey area from Rørvik (65°N, 11°E) to the Swedish border (59°N, 11°E). Spurdog catches were consistently higher in shallow waters (< 150 m) in the latitude bands 58–60°N and 61–63°N. Catches were frequently sex- and maturity-biased, often dominated by gravid females or reproductively active males. Survey coverage along the southeastern coast was more limited but also indicated potentially important habitats in the area. Growth and maturity parameters were within the ranges reported in other areas of the stock, and uterine fecundity was positively correlated to maternal size and age. We provide updated information on the fecundity-length relationship, which has historically fluctuated in response to density-dependent effects and fishing pressure. The survey establishes a new reference point for spurdog in a biologically productive region not covered by other surveys and provides a foundation for long-term monitoring of a historically important fishery resource.