Population dynamics of spiny dogfish, Squalus acanthias, in the NW Atlantic

Dynamics of the NW Atlantic population of the spiny dogfish are investigated. The population underwent a three-fold increase in abundance since the early 1970s. This study aims to gain understanding of the underlying population dynamics of spiny dogfish, and the possible changes of some critical life-history parameters through time, that might explain the overall increasing trend in abundance. The first step consisted of estimating the abundance of the different life-stages of the population. The pre-adult female, adult male and adult female life-stages were identified and decomposed from length frequency modes. Area was then used for stratification of the log-transformed abundance estimates of each life-stage. MULTIFAN was used to assess differences in the growth of juvenile spiny dogfish. The growth rate was shown to increase from 1968-1971 to 1976-1979 and then decrease to 1988-1990. The hypothesis that these changes were density-dependent was tested and, with the exception of age-2, mean lengths at ages 1 through 5 were significantly correlated with the indices of abundance of the juveniles. Fecundity and size at maturity were also investigated. Literature data from samples collected since 1942 was re-analyzed and compared with more recent data collected during the 1980s and 1991. Significant negative correlations were detected between fecundity and abundance for most size-classes considered, and positive, mostly non-significant correlations were found between fecundity and mean weight. Changes in size at 50% female maturity were also detected and were suggested to be the result of density-dependent changes in juvenile growth. Several recruitment-stock relationships were investigated. Biomass estimates for females were smoothed using an ARIMA time series model on the logarithm of the indices of abundance. A Ricker model, with a temperature-dependent correction, was accepted as the best predictor of recruitment. A Leslie matrix model incorporating density-dependent sub-models for growth, fecundity and recruitment was used to model changes in reproductive dynamics. The model suggested that the observed increase in abundance is at least partially explained by changes in juvenile growth observed during the early-1970s. These changes later resulted in increased mean size at maturity, and subsequent fecundity