Biocomplexity in a demersal exploited fish, white hake (Urophycis tenuis): depth-related structure and inadequacy of current management approaches

Understanding the factors generating patterns of genetic diversity is critical to implementing robust conservation and management strategies for exploited marine species. Yet, often too little is known about population structure to properly tailor management schemes. Here we report evidence of substantial population structure in white hake (Urophycis tenuis) in the Northwest Atlantic, perhaps among the highest levels of population structure exhibited by a highly exploited, widely dispersed, long-lived marine fish. We show that depth plays a role in this extensive and temporally stable structure, which does not conform to previously established fisheries management units. Three genetically distinguishable populations were identified, where all straddle several management divisions and two (Southern Gulf of St. Lawrence and Scotian Shelf) overlap in their range, coexisting within a single division. The most highly exploited population in the Southern Gulf of St. Lawrence was also the most isolated and likely the smallest (genetically effective). This work shows that conservation and management priorities must include population structure and stability in establishing effective species recovery strategies.