Rapid widespread declines of an abundant coastal shark

Lindsay N.K. Davidson, Philina A. English, Jacquelynne R. King, Paul Grant, Ian G. Taylor, Lewis Barnett, Vladlena Gertseva, Cindy A. Tribuzio, Sean C. Anderson 

Determining population trends is challenging for marine species with transboundary ranges, but increasingly important given the redistribution of species across international borders with climate change. Here, we use spatiotemporal models fit to data from 10 scientific surveys to evaluate trends in biomass, abundance, and distribution for Pacific Spiny Dogfish (Squalus suckleyi) across their entire eastern North Pacific Ocean range. We find a coastwide 51% (95% CI: 38%–61%) decline in Dogfish biomass from 2003–2023. Regional declines were steepest for the US West Coast and Canada: 79% (95% CI: 71%–85%) and 72% (95% CI: 58%–82%), respectively, while Alaskan declines were less steep at 37% (95% CI: 13%–54%). Mature females and immature Dogfish had the largest proportional declines. We find a deepening distribution on the US West Coast and Canada and an increase in the biomass-weighted temperature across most maturity groups on the US West Coast, but these patterns do not explain the overall declines. Contrary to prior hypotheses, we find no clear shift in biomass northward to Alaska. Further work investigating causal mechanisms of the decline is needed.