MEPS 338:169-181 (2007)  -  doi:10.3354/meps338169

ABSTRACT: We explored how size class distributions for 4 important groundfish species, Atlantic cod Gadus morhua, haddock Melanogrammus aeglefinus, spiny dogfish Squalus acanthias and silver hake Merluccius bilinearis, are related to depth, temperature, substrate and time-block for the fall and spring of a 35 yr time period in the Gulf of Maine – Georges Bank region. We examined the relative importance of each factor and how relative importance changes with season. Size increased with depth during both seasons for G. morhua and for M. aeglefinus during the fall, but decreased with depth for M. aeglefinus during the spring. Haddock size class distributions in the spring were also related to bottom temperature, with smaller individuals generally occurring in the warmest waters. For S. acanthias, depth was also the primary environmental variable explaining size class distributions in the fall, although size decreased with depth for this species. In the spring, bottom temperature was more important for spiny dogfish with smaller individuals associated with warmer bottom waters. Similarly, bottom temperature had the most explanatory value for M. bilinearis during both seasons, with size increasing with temperature. Seasonal associations with depth and temperature are related to spawning migrations, thermal preferences and other ecological factors. Time-block accounted for a notable amount of variance, particularly for S. acanthias and M. bilinearis, and was reflective of how population size structure has responded to exploitation over the time series. The local-scale relationships between abundance and substrate previously established for some species were not strong at the broader spatial scale we examined. Understanding how habitat associations change with ontogeny will aid in refining spatial fisheries management approaches and in delineating essential fish habitat.

KEY WORDS: Life history · Spatial distribution · Northwest Atlantic · Fisheries · Environmental gradient