MEPS 263:235-246 (2003)  -  doi:10.3354/meps263235

Controls on the distribution of Browns Bank juvenile haddock

David Brickman*

Ocean Sciences Division, Department of Fisheries and Oceans, Bedford Institute of Oceanography, PO Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada

ABSTRACT: A combination of biophysical modelling and data analysis is used to infer some important aspects of the southwest Nova Scotia (Canada)‹Bay of Fundy (BoF) ecosystem with respect to the first year of life of Browns Bank (BB) haddock. One of the main observations in this ecosystem is that adult fish found in the BoF region consistently exhibit a larger length-at-age than fish found in the BB region. This is generally thought to be due to drift and retention processes acting during the early life stages, with the larger fish assumed to be the result of settlement in a more favourable temperature and food environment downstream in the BoF. Also, while BB is considered to be an important juvenile nursery ground and the source for the smaller southwest Nova (SWN) fish, the existence of the larger BoF fish suggests a downstream nursery ground. To date, no analysis has been made regarding the whereabouts of such a nursery ground. The assumption of a favourable temperature and food environment in the BoF is investigated. The result of this analysis suggests that the small Œinshore¹ region off of Yarmouth, Nova Scotia, is the best settling ground. An Age-1 capture probability map is constructed from 30 yr of Canadian research vessel (RV) survey data. This map shows 3 regions where juvenile haddock are found‹BB, the inshore, and upstream (northeast) of BB. The average pelagic juvenile concentration field derived from the biophysical model predicts that BB and the inshore region are preferred settling grounds. A habitat suitability map, based on surficial sediment type, shows that the observed settling grounds coincide with preferred haddock sediment type. Finally, it is shown that the upstream Age-1 fish most likely come from larvae that drifted downstream from the Western Bank haddock spawning ground, and that BB likely acts as a potential source for the Georges Bank haddock stock. Thus, the combination of biophysical modelling and analysis of fisheries data provides evidence of the metapopulation structure of haddock stocks on the Scotian Shelf/Gulf of Maine.

KEY WORDS: Metapopulation · Haddock · Biophysical model · Scotian Shelf · Larval drift · Survival

Full text in pdf format