Uninvited guests and permanent residents: long-term changes in the distribution and abundance of the five most common sharks in the northwestern Pacific

This study analysed long-term trawl survey data to investigate changes in the spatial distribution, range boundaries, and catch rates of the five most common shark species in the Russian waters of the northwestern Pacific. Significant alterations in the spatial distributions of these shark species were observed during the study period. The 1980s witnessed the most widespread distribution and maximum catches of salmon and blue sharks. In the 2000s, the North Pacific spiny dogfish exhibited its broadest distribution, with maximum catches recorded in the 1980s and 2010s. The Pacific sleeper shark exhibited its widest distribution in the 1980s, with maximum catches occurring in the 2000s. Shortfin mako were recorded within the study area only in the 1980s and 2010s, with maximum catches occurring in the latter period. Shifts in the range of boundaries during the study period exhibited different patterns among the species. Statistically significant shifts in boundaries were found for Pacific spiny dogfish, salmon sharks, and Pacific sleeper sharks. During the review period, salmon shark catches significantly decreased in Pacific waters and in the study area as a whole, but the reasons for this difference have not yet been determined. For the other shark species, statistically significant changes in catch size were not revealed. The observed significant changes in the spatial distribution and position of the boundaries of the ranges are likely due to both subjective reasons and climatic changes.