Lack of life history change in two over-exploited haddock (Melanogrammus aeglefinus) stocks

Abstract

Concomitant with declines in abundance, many commercially exploited marine fishes have undergone significant life history changes that are critically important as they impact population growth rate and, thus, recovery rate of depleted stocks. By examining data collected as part of offshore surveys conducted during 1971–2012, we evaluated whether there have been changes in growth rate and size at maturity for haddock on Grand Bank and St. Pierre Bank, two over-exploited stocks at the northern extremity of the species range in the western Atlantic Ocean. Contrary to expectation, we found no evidence for change in either growth or maturity since 1971. However, there were differences in life history characteristics between the two stocks, as well as between males and females. Although no difference in growth was observed between sexes, differences in maturation were evident with 50% of males maturing at ∼40cm and 50% of females maturing at ∼48cm. Haddock from Grand Bank were larger than haddock from St. Pierre Bank at ages 8 and 10 by 4.4% and 7.6%, respectively. We also found that haddock on Grand Bank matured at smaller sizes (length at which the probability of maturity was 50% was 38.2cm for males and 46.3cm for females) than those from St. Pierre Bank (42.1cm for males and 49.9cm for females). The haddock fishery off Newfoundland developed rapidly from 1945 but collapsed within less than two decades. Available information suggests that while fishery exploitation rates were undoubtedly high, haddock on Grand Bank and St. Pierre Bank may not have been exposed to sufficient multigenerational fishing pressure to generate decreases in growth and maturity timing as seen in other over-exploited stocks and appear to have maintained historic life history characteristics.