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

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-October) 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 all life-stages for both sexes, including juveniles and sexually active adults, across the entire survey area from Rørvik (65°N) to the Swedish border. Spurdog abundance was consistently higher in shallow waters (< 150 m) off the coasts of Rogaland (58–60°N), northern Vestlandet and Møre og Romsdal (61–63°N) counties, where we encountered sex- and maturity-biased aggregations often dominated by gravid females or sexually active males. Survey coverage in the Skagerrak was more limited but also indicated potentially important habitats to the east. 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. The fecundity-length relationship, which has historically fluctuated in response to density-dependent effects and fishing pressure, was indicative of a recovering stock. The survey establishes a new reference point for spurdog in a biologically productive region that has not been covered by other surveys, and provides a foundation for long-term monitoring of a historically important fishery resource.