Temporal patterns of sex-specific size at maturity of porbeagle sharks (Lamna nasus)

Abstract

Examining population dynamics within fisheries science is an effective way to investigate the size and age structure of a given fish population, and to understand how that stock might change over time. Porbeagle sharks are an endangered, pelagic shark species, for which there was an active Canadian food fishery until 2013. The objective of this research is to conduct a temporal study of size and maturity of porbeagle sharks before and after the fishery closure. Using longline fishing equipment at approximately 50 locations in the Northwest Atlantic Canadian waters, the sharks were caught, and body size and maturity were measured. Comparing length at maturity data from 1999-2001 (before fishery closure) and 2017 (after fishery closure) has provided insights into the changes that have occurred in the last 16 to 18 years. I used generalized linear models to analyse changes in size at maturity, and in body shape, and body size. I found that maturity was influenced by fork length, year, and sex. The difference among years may be due to a lack of data collected during some years of the study. In addition, body shape was affected by sex alone, whereby the relationship between fork length and interdorsal length was steeper for males than females. Overall, our results indicate that there has been a temporal change in life history traits of porbeagle sharks.