Exploring the life-history implications of colour variation in offshore Gulf of Maine cod (Gadus morhua)

The evolution of alternative life-history strategies in fish has largely been overlooked by fisheries managers, although differences in the biology of life-history variants can have important implications for the scale and productivity of fisheries. Cod display strikingly variable colouration in the Gulf of Maine, with redand olive-coloured cod found in close sympatry. Colour types from Cashes Ledge, a shallow, offshore ( 100 km) feature, are examined to see whether they differ in key life-history traits including diet, depth distribution, growth, and body morphology. Red cod consumed significantly more crabs, lobsters, and demersal fish, whereas olive cod consumed more shrimp. Stable carbon isotope signatures (dC) varied significantly among colour types, but are thought to reflect baseline differences in dC at Cashes Ledge (potentially useful for residence estimates). Red cod were confined to a small area of shallow water (,20 m) and were significantly smaller at age than olive cod. Body shape was used to classify colour types correctly with 84% accuracy; red cod had shorter snouts, deeper bodies, and more slender tails than olive cod. Collectively, the results suggest that red cod are resident at Cashes Ledge and represent a life-history strategy distinct from olive cod.