Biology and Management of Dogfish Sharks

7. Trends in Abundance of Spiny Dogfish in the Strait of Georgia, 1980–2005

Jackie R. King and Gordon A. McFarlane

doi: https://doi.org/10.47886/9781934874073.ch8

Abstract.—Spiny dogfish Squalus acanthias have been an important component of the Strait of Georgia fisheries from the late 1800s to the late 1940s, when the fishery collapsed owing to overfishing and changes in market demand. The stock population levels have sustained a commercial fishery of approximately 2,000 metric tons since 1978. Recent concerns regarding the status of dogfish stocks worldwide have reprioritized the status assessment of dogfish in British Columbia. Longline research surveys were conducted for dogfish in the Strait of Georgia in 1986, 1989, and 2005. Additional sources of information are catch and effort data collected through logbook records from the commercial longline fishery. Recent improvements in gear configuration resulted in a switch in the mid-1990s from traditional J hooks to circle hooks, which makes direct comparison of catch rates difficult. In November 2004 a calibration experiment using J hooks and circle hooks demonstrated that, overall, spiny dogfish catch per unit effort (CPUE) for circle-hook gear was 1.6–1.7 times higher than that for J-hook gear. After applying this conversion to the commercial longline CPUE data available for 1980–1984 and 2000–2004, no significant trend in catch rate over time was detected. The catch rate observed in the longline research survey actually increased in 2005 compared to 1986 and 1989. In both fisheries and research data, the proportion of smaller spiny dogfish in the size distribution has increased, reducing the overall mean size. The decline in mean size is probably due to an increase in recruitment of juvenile fish. However, caution in management of this stock is warranted given that the current commercial fishery is now landing a large proportion (estimated 80%) of immature fish. Increased fishing pressure on juveniles could have implications for the abundance of mature fish in upcoming decades.