Diel Reproductive Periodicity of Haddock in the Southwestern Gulf of Maine

Abstract

AbstractWe studied a population of Haddock Melanogrammus aeglefinus in the Gulf of Maine to determine whether it exhibits diel spawning periodicity. Commercial fishing vessels were chartered for 25 dedicated long‐lining trips to collect sexually mature Haddock in the Stellwagen Bank National Marine Sanctuary at locations identified by commercial fishers as having spawning aggregations. In order to examine diel effects on Haddock reproduction, the changes in CPUE and percentages of male and female Haddock of all reproductive maturity stages, as well as gonadosomatic index (GSI), were observed across a 24‐h diel cycle. The comparison of diel patterns among different maturation stages was used to differentiate diel periodicity due to spawning from feeding behavior. Diel periodicity was observed for the proportion of males and females in the catch, the proportion and CPUE of male and female maturation stages most indicative of imminent spawning, and for female GSI. Although spawning occurred throughout the diel cycle, peak spawning of females occurred during the evening hours (1700–2100 hours) and gradually declined to low values during the day at 0900 hours. In an apparent contradiction male spawning stages were uniformly high except for lows during the night between 2100 and 0100 hours. We hypothesize that this pattern is consistent with lekking behavior where strong competition among spawning‐ready males during courtship would reduce their feeding activity during the peak spawning hours. Strong annual differences in diel periodicity may have resulted from different temporal patterns in the spawning season or density dependence, or both.