Understanding recruitment patterns of historically strong juvenile year classes in redfish (sebastes spp.): the importance of species identity, population structure, and juvenile migration

Genetic analyses were undertaken on archived otoliths from juveniles representing historically strong year classes of northwest Atlantic redfish (Sebastes spp.) and on tissue samples from adults of known species and population of origin. The results indicated that the species composition of a year class is key information for understanding recruitment dynamics, with redfish species having distinct population-associated patterns of spatial dispersion. In the Gulf of St. Lawrence--Laurentian Channel area (GSL-LCH), the last strong year class (which supported the fishery for more than 30 years) belonged to Sebastes mentella and originated from the area. In contrast, four year classes that appeared abundant at young ages in research surveys in GSL-LCH but contributed only marginally to the adult population and the fishery of the region belonged to Sebastes fasciatus and carried the genetic signature of the adult population from the slope of the Newfoundland Grand Banks. Ocean currents and spatiotemporal trends in abundance-at-length suggest that the latter population uses the Gulf of St. Lawrence as a nursery area, with larvae and early juveniles drifting toward the Gulf of St. Lawrence and older juveniles migrating back to the slope of the Grand Banks after about 5-6 years. It is suggested that juvenile migration behaviour is a postsettlement process that plays an important role in redfish recruitment dynamics and carries both demographic and evolutionary implications. Des analyses genetiques ont ete realisees a partir d'otolithes archives appartenant aux juveniles de fortes classes d'age historiques de sebaste (Sebastes spp.) du nord-ouest Atlantique et d'echantillons de tissu preleves sur des adultes d'espece et de population d'origine connues. Les resultats ont montre que la composition specifique d'une classe d'age constitue une information clef pour la comprehension de la dynamique de recrutement, en revelant que les especes de sebaste ont des patrons de dispersion spatiale distincts et propres aux populations. Dans la region du Golfe du Saint-Laurent et du chenal Laurentien (GSL-LCH), la derniere forte classe d'age (qui a supporte la peche pendant plus de 30 ans) appartenait a Sebastes mentella et etait originaire de la region. Par contre, quatre classes d'age qui semblaient abondantes a un jeune age dans les releves de recherche du GSL-LCH, mais qui ont contribue seulement marginalement a la population adulte et a la peche de la region, appartenaient a Sebastes fasciatus et portaient la signature genetique de la population adulte distribuee le long de la pente des Grands Bancs de Terre-Neuve. Les courants oceaniques et les tendances spatiotemporelles d'abondance en fonction de l'age suggerent que cette derniere population utilise le Golfe du Saint-Laurent comme zone de nurserie; les larves et jeunes juveniles deriveraient vers le Golfe du Saint-Laurent puis, 5 a 6 ans plus tard, les juveniles plus ages retourneraient vers la pente des Grands Bancs. Il est suggere que le comportement migratoire des juveniles joue un role significatif dans la dynamique de recrutement du sebaste et possede des implications aux niveaux demographique et evolutif.
Introduction Episodic recruitment is commonly observed in long-lived marine teleost species, such as Sebastes spp. (Longhurst 2002; Love et al. 2002; Planque et al. 2012; Ralston et al. 2013). The [...]