Comparing productivity of North Atlantic cod (Gadus morhua) stocks and limits to growth production

Data from stock assessments were used to compare stock biomass, annual growth (Gs) and surplus production per capita (TSPc) and per unit biomass (TSPb) among 15 cod ( Gadus morhua) stocks in the North Atlantic. TSPc ranged from 99 to 1012 g per fish among stocks and averaged 448 g per fish. TSPb ranged from 140 to 469 g kg(-1) among stocks and averaged 294 g kg(-1). Gs varied considerably with low growth production associated with low surplus production. On average, cod produced 724 g per fish in growth annually with cod in the least productive stock producing 7.2 times less than in the most productive stock. The stocks divided into four clusters reflecting four levels of production. Celtic Sea, Irish Sea and West Scotland cod showed the highest levels of production whereas Eastern Scotian Shelf, Northeast Arctic, Northern Grand Bank, Northern and Southern Gulf of St Lawrence showed the lowest levels. Surface and bottom salinity and temperature differed significantly among clusters in a canonical discriminant analysis. Temperature and salinity correlated with the first and second canonical variates, respectively. The most productive stocks were associated with higher bottom salinity and temperature. None of the stocks, including stocks with a fast growth rate and living at higher temperatures, had a specific growth rate (SGR) close to the maximum rate observed in laboratory experiments. The difference between observed and maximum SGR decreased at temperatures above 6 degreesC. Very cold temperatures resulted in smaller cod also achieving SGR values closer to the maximum. Temperature is a major determinant of stock production.