A statistical discrimination method using sagittal otolith dimensions between sibling species of juvenile codGadus morhuaandGadus ogacfrom the northwest Atlantic

Abstract

Greenland cod (Gadus ogac) and Atlantic cod (Gadus morhua) co-exist and are caught in the same fisheries in coastal waters off western Greenland and eastern Canada. Juveniles (<15–20 cm total length, TL) are similar in morphology and are not easily distinguished in fisheries research surveys or when examining stomach contents of common predators such as seals, small toothed whales, seabirds and gadoid fish. Often only the skeleton and otoliths remain in predator stomachs. Examination of variation in otolith length, width, height and weight in relation to body size and zoogeographic differences indicated otoliths of G. ogac are consistently larger and heavier than otoliths of G. morhua from Greenland and Canadian fish of both sexes and all sizes examined. Discriminant function analyses (DFA) was used to determine if otoliths removed from fish with known identity, can be individually discriminated based on otolith dimensions. Otoliths from the two species can be statistically discriminated based on otolith dimensions alone, primarily otolith length and height with relatively high certainty (71–80%). Discrimination certainty approaches 100% if body size is included. Simple additive statistical models with only a few descriptors and their discriminant functions with linear decision surfaces are provided and should simplify the identification of intact otoliths.