Enhancing the reproductive potential of local populations of coastal Atlantic cod (Gadus morhua)

Abstract

We investigate the feasibility of enhancing the reproductive potential of northern Atlantic cod (Gadus morhua L.) populations resident in Newfoundland and Labrador bays by "catch, grow out, and release". This entails trapping juvenile and young adult fish from the local population, increasing their growth, maturation rate, and potential fecundity by feeding them a natural diet in net pens, and then returning the fish to their natal bay habitat to spawn. To determine whether multiyear farming affects spawning success, we determined the spawning period and egg quality of cod held in captivity for three growth seasons. Farmed cod spawned in a net pen concurrently with wild cod in Trinity Bay during 1995 and produced fertilized eggs from which viable larvae hatched. Sonic tracking showed that cod farmed for 3 years and then released reintegrated with wild cod aggregations over known spawning grounds. Recaptures of tagged fish several years after release suggest that farmed fish remained in the bay as members of the resident population. Fishing mortality (bycatch in coastal fisheries for lumpfish (Cyclopterus lumpus) and winter flounder (Pseudopleuronectes americanus)) of released farmed cod was not negligible, emphasizing that any enhancement effort must be carried out under a complete fishing moratorium.Résumé : Nous avons examiné la possibilité d'accroître le potentiel reproducteur des populations de morues franches (Gadus morhua L.) du nord de l'Atlantique vivant dans les baies de Terre-Neuve et du Labrador par la méthode de « capture, engraissement et libération ». La méthode consiste à capturer de jeunes poissons et de jeunes adultes dans la population locale, à augmenter leur croissance, leur taux de maturation et leur fécondité potentielle en les soumettant à un régime naturel dans des enclos en filet, puis de retourner les poissons dans leur baie d'origine pour la fraie. Nous avons déterminé la période de fraie et la qualité des oeufs de morues gardées en captivité pendant trois saisons de croissance pour voir si un élevage de plusieurs années affectait le succès de la fraie. Les morues de Trinity Bay en élevage ont frayé dans un enclos en filet à la même période que les morues sauvages et elles ont produit des oeufs fécondés d'où sont sorties des larves viables. Le dépistage par méthode acoustique a démontré que les morues mises en élevage pour trois ans avant d'être relâchées se sont intégrées aux rassemblements de morues sauvages sur les sites de fraies connus. La capture de poissons marqués plusieurs années après leur libération laisse croire que les poissons mis en élevage demeurent dans la baie comme membres de la population résidante. La mortalité due à la pêche des morues gardées en élevage (comme prises accessoires dans la pêche côtière à la lompe (Cyclopterus lumpus) et à la plie rouge (Pseudopleuronectes americanus)) n'est pas négligeable; il est donc essentiel que tout effort d'amélioration se fasse dans des conditions de moratoire complet de la pêche.[Traduit par la Rédaction] Wroblewski and Hisc...

Dispersal of wild and escapee farmed Atlantic cod (Gadus morhua) in Newfoundland

“…Farmed cod dispersal rates after release were similar to previous work; however, wild cod dispersal rates were slower (12 h for 90% dispersal compared with only 3 h for 100% dispersal observed by Wroblewski and Hiscock (2002)). Differences in seasonal activities such as migration and feeding may affect dispersal rate, as cod released in August dispersed more slowly than those released in October, and both dispersed more slowly than the cod released in late April and early May by Wroblewski and Hiscock (2002) (wild juveniles reared in captivity for 3 years prior to release). Furthermore, we detected few fish from December until April, suggesting that during winter the cod were avoiding the cold shallow coastal waters Fig.…”

“…Few studies have quantified the recapture rate of escaped farmed cod; however, results from an acoustic telemetry study in Norway (Uglem et al 2008) as well as from stock enhancement studies (Svåsand et al 2000;Skilbrei and Jørgensen 2010) suggest that the incidental recapture rates may be high (30%-44%) with even a modest fishing effort. While there was no dedicated recapture fishery near Bay Bulls, rates of incidental fishery recaptures did not differ between escapee farmed (11%) and wild cod (10%; similar to Brattey et al 2008), in contrast with previous studies (Wroblewski and Hiscock 2002;Uglem et al 2008). The timing and recapture locations in this study reflect the pattern of seasonal (i.e., summer) small-scale fisheries (recreational, sentinel, and commercial) at the mouth of Bay Bulls and off Petty Harbour.…”

“…Intentionally released farmed cod dispersed away from the farm more slowly than wild cod, as seen previously in Newfoundland using juvenile wild cod reared in captivity for 3 years prior to release (Wroblewski and Hiscock 2002), as well as in other species that show a high degree of site fidelity to sea cages (Bridger et al 2001;Arechavala-Lopez et al 2011. Farmed cod dispersal rates after release were similar to previous work; however, wild cod dispersal rates were slower (12 h for 90% dispersal compared with only 3 h for 100% dispersal observed by Wroblewski and Hiscock (2002)).…”

“…Previous studies have observed escapee farmed cod remaining in the local area in Norwegian fjords; however, population differences in dispersal and migration may occur between the east and west North Atlantic, as well as between bay systems (Uglem et al 2008. For example, wild juvenile cod reared in a farm setting in Newfoundland for 3 years prior to release traveled up to 170 km from the release site (Wroblewski and Hiscock 2002), overlapping the movements of local wild cod. The movements of escapee hatchery-reared cod in the Northwest Atlantic have to our knowledge not been studied previously.…”

Sonic tracking of wild cod, Gadus morhua, in an inshore region of the Bay of Fundy: a contribution to understanding the impact of cod farming for wild cod and endangered salmon populations

“…Similarly, Wroblewski and Hiscock (2002) demonstrated that wild cod held in cages for several growing seasons would reintegrate into wild populations in spawning areas when returned to the wild. However, these ''farmed'' cod were slower to disperse from the release point and were caught at higher rates in fisheries than wild cod.…”