Recruitment of cod and haddock in the North Atlantic: a comparative analysis

We examined recruitment patterns of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) from eight regions in the North Atlantic (Georges Bank, Browns Bank, the Eastern Scotian Shelf, the Faroe Plateau, Iceland. the Barents Sea. the North Sea, and West of Scotland). The selection was based on the availability of contemporaneous estimates of stock and recruitment for both species within each location. We considered the following metrics for both species by region: recruitment variability (measured as absolute numbers at age I and as deviations from a fitted stock recruitment curve), the rate of recruitment at low spawning stock sizes (the maximum reproductive rate. a measure of resilience of the stock to exploitation) and autocorrelation in recruitment adjusted for spawning stock size. We also examined the correlation of cod and haddock recruitment within regions. Differences in recruitment variability and resilience between cod and haddock in paired comparison tests were highly significant. Haddock consistently exhibited higher recruitment variability and lower resilience than cod. Autocorrelation in recruitment of the two species within region was related possibly indicating serial correlation in forcing mechanisms affecting both species. Cod and haddock exhibited moderate synchrony in recruitment patterns within regions. In six out of the eight regions, the correlation between recruitment (adjusted for spawning stock size) was similar to0.5. suggesting that common environmental conditions experienced by both species did affect recruitment. Research-vessel survey information available for three of the regions (North Sea, Barents Sea, and Georges Bank) and one additional location (Gulf of Maine) were analyzed for evidence of density dependence and for levels of post-larval abundance variability, Cod exhibited stronger density-dependent mortality in three out of four regions. Post-larval abundance variability was not different between the two species.