A COMPARATIVE-ANALYSIS OF RECRUITMENT VARIABILITY IN NORTH-ATLANTIC FLATFISHES - TESTING THE SPECIES RANGE HYPOTHESIS

The hypothesis that recruitment variation in flatfishes should be most variable at the northern edge of the species range, least near the ce ntre of the range, and intermediate near the southern limit was tested using stock and recruitment data generated from sequential population analysis for several different flatfish stocks involving four species (plaice Pleuronectes platessa, sole Solea vulgaris is from the easter n Atlantic, American plaice Hippoglossoides platessoides, and yellowta il flounder Limanda ferruginae from the western Atlantic). Several gro undfish species have been found to conform to this so-called species r ange hypothesis with the suggestion that density-independent processes predominate at the edges of the distributional range and density-depe ndent processes dominate in the centre of the range. Our results were generally inconsistent with thr hypothesis: the coefficient of variati on (CV) of recruitment for plaice in the eastern Atlantic was independ ent of latitude, the CV of recruitment For sole exhibited a dome-shape d relationship with latitude with the highest CVs occurring at the mid -point of the range, and the CV of recruitment for the western Atlanti c stocks exhibited a monotonic decrease with latitude. We extended our latitudinal analyses by assessing both the degree of dependency of re cruitment on spawning stock biomass and the spatial and temporal scale s of Variability in recruitment and pre-recruit survival for the easte rn Atlantic stocks. In general our analysis revealed no evidence of a strong stock and recruitment relationship for any of the stocks examin ed, and previously published analyses revealed no such patterns with l atitude. Analysis of both de-trended recruitment and pre-recruit survi val time series over the species ranges of sole and plaice revealed st rong positive correlations among adjacent stocks and inverse correlati ons among stocks at the extremes of the range. Recruitment variation i n the flatfish stocks examined appears to be dominated by density-inde pendent factors, operating at a local scale, on the egg and larval sta ges.