Interpopulation differences in growth rates and food conversion efficiencies of young Grand Banks and Gulf of Maine Atlantic cod (Gadus morhua)

Abstract

Geographically separated Atlantic cod (Gadus morhua) stocks in the northwest Atlantic exhibit life history variation and have been shown to differ genetically. The genetic and environmental contributions to phenotypic differences, however, have not yet been measured. We used common environment experiments to evaluate the importance of temperature on the observed growth variation between Grand Banks (GB) and Gulf of Maine (GOM) cod stocks. Larvae from the GB grew faster than GOM larvae at both 7 and 12°C. Growth rates of juveniles were not different, but GB juveniles had higher food conversion efficiencies than those from the GOM (at both ambient and warm temperatures). The results indicate that faster growth of GOM cod in the wild is not due to a higher genetic capacity for growth rate in GOM than in GB fish. The findings give evidence of genetically based phenotypic variation, which is in agreement with molecular studies on population differentiation in cod, and support the theory of countergradient variation in growth rates of larval fish.Résumé : Des stocks de la Morue franche (Gadus morhua) du nord-ouest de l'Atlantique, provenant de régions géo-graphiques distinctes, ont des démographies particulières et possèdent des différences génétiques. Les contributions relatives des gènes et de l'environnement aux différences phénotypiques n'ont cependant pas encore été déterminées. Des montages expérimentaux classiques ont permis d'évaluer l'effet de la température sur les différences de croissance que l'on observe entre les stocks des Grands Bancs (GB) et ceux du golfe du Maine (GOM). Les larves GB croissent plus vite que les larves GOM tant à 7°C qu'à 12°C. Les taux de croissance des juvéniles ne diffèrent pas, mais les juvéniles GB ont une meilleure efficacité de conversion de la nourriture que les juvéniles GOM aussi bien aux tempéra-tures ambiantes que chaudes. Ces résultats indiquent que la croissance plus rapide des morues GOM en nature n'est pas due à une capacité génétique de croissance supérieure à celle des poissons GB. Il s'agit donc d'une variation phé-notypique qui est basée sur des facteurs génétiques; cela s'accorde bien avec les études moléculaires de différentiation des populations chez la Morue franche et confirme la théorie de l'existence d'une variation à contre-gradient des taux de croissance chez les larves de poisson.[Traduit par la Rédaction] 2229Purchase and Brown

Effects of food consumption and temperature on growth rate and biochemical-based indicators of growth in early juvenile Atlantic cod Gadus morhua and haddock Melanogrammus aeglefinus

“…, which agrees well with growth rates obtained in other laboratory studies using age-0 juvenile cod (Brown et al 1989, Folkvord & Otterå 1993, Otterlei 2000, Purchase & Brown 2000. For example, a G max of ~2.6 % d -1 was observed for 0.9 to 9.2 g juvenile cod feeding maximally at 9.5°C (Folkvord & Otterå 1993).…”

“…Edwards et al 1972, Jones 1978, Jones & Hislop 1978, Hawkins et al 1985, relatively little research has been conducted on this relationship in age-0 juvenile cod. Our understanding of the growth-feeding relationship in age-0 juvenile cod has been advanced by studies conducted at cold temperatures (Brown et al 1989) and maximal feeding levels (Otterlei 2000, Purchase & Brown 2000. Extending these analyses to include a wider range in both temperatures and feeding levels would provide additional ecologically relevant data, since age-0 juvenile cod are found over a wide temperature range (Fahay et al 1999) and feeding may be sub-maximal due to limited prey resources (Buckley et al unpubl.…”

Sub-populations of coastal cod with different behaviour and life-history strategies

“…Conover & Schultz 1995), it has been reported for several species including turbot (Scophthalmus maximus; Imsland et al 2001) and cod from separate populations on the coast of Canada (Purchase & Brown 2000). In the study of Purchase & Brown (2000), strains were kept in separate tanks and fed to satiation, thus reducing the need for competition. In the present study the focus was on behavioural adaptations of the strains.…”

“…Populations in warm water grow faster and mature earlier than those in colder water (Hutchings et al 1993, Brander 1994b. Previous studies have reported photoperiod affecting growth in cod larvae, with those in northern latitudes having a longer time for visual feeding during summer (Suthers & Sundby 1996), and higher food-conversion efficiency in northern cod compared with southern cod off the coast of Canada (Purchase & Brown 2000). Some of the units are heavily overfished and have collapsed; they have shown slow recovery even under a complete fishing moratoria (Hutchings 2000).…”

Possible countergradient variation in growth of juvenile cod Gadus morhua from the northwest Atlantic

“…growth rate) have successfully been used to test CnGV theory in fish populations (Conover & Schultz 1995). However, in Atlantic cod, studies of CnGV theory have been limited to 2 populations (Svåsand et al 1996, Otterlei et al 1999, Purchase & Brown 2000a,b, Salvanes et al 2004). Marcil et al (2006a) showed that laboratory reared juvenile cod from 2 regions of the NW Atlantic, 4X and 3L (Northwest Atlantic Fisheries Organization [NAFO] divisions), differed significantly in their body shape, yet no differences were found between the wild collected juveniles of the same origin.…”