Unconfounding the effects of climate and density dependence using 60 years of data on spiny dogfish (Squalus acanthias)

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Authors: Taylor, Ian G., Gallucci, Vincent F.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2009
• Subjects: Aquatic Science; Ecology, Evolution, Behavior and Systematics; spiny dogfish; Squalus acanthias
• Online Access: http://dx.doi.org/10.1139/f08-211; http://www.nrcresearchpress.com/doi/full-xml/10.1139/F08-211; http://www.nrcresearchpress.com/doi/pdf/10.1139/F08-211

The confounded effects of changes in climate and density on a population’s demography are hard to separate for long-lived species because demographic traits are usually the aggregated result of conditions faced over years. Demographic parameters are compared for spiny dogfish ( Squalus acanthias ) in the Northeast Pacific, the longest lived and latest maturing of all sharks, using samples from the 1940s and 2000s. This 60-year interval has seen ocean temperatures rise by almost 1 °C and dogfish harvests peak above 50 000 tonnes (t)·annum –1 and then drop below 50 t·annum –1 . Over this period, the age at 50% maturity for dogfish declined from 43 to 32 years, while the estimated average number of embryos per litter for a 100 cm dogfish increased from 5.9 to 6.7. Growth parameters changed significantly, with faster growth to a smaller size. Leslie matrix analysis showed that these changes could lead to an increase in population growth rate of about 1%. Comparison with published demographic parameters from the 1970s and 1980s indicated that the greatest change in demographic parameters occurred between the 1940s and 1970s, prior to the largest changes in ocean temperatures. The implications for fishing on long-lived populations during times of rapid environmental change are explored.