External scarring of whitefish, Coregonus nasus and C. clupeaformis complex, from the western Northwest Territories, Canada

Up to 40% of whitefish (Coregonus nasus and C. clupeaformis) sampled during spawning migrations from the area of the Mackenzie Delta, N.W.T., had external scars. Percent frequency of scarred individuals varied geographically from the Mackenzie mainstem and tributaries, where 20% were scarred, to Anderson river (2%), Cox Lake (16%), and Alaska (0–7%). Within the Mackenzie system fish captured at mainstem locations had approximately twice the frequency of scarring than did fish from tributary locations. Scars were classified as either slash or round type. Both scar types were located more frequently on the left side of the fishes and below the lateral line. Details of orientation and location on the body provided clues permitting the assignment of putative causation. Small round scars were restricted to locations with connections to the Arctic Ocean and were probably caused by the marine parasitic copepod Coregonicola or by Arctic lampreys (Lampetra japonica). Larger round scars were either the result of attacks by lampreys or by previous gill net capture. Unequal distribution and orientation on the body of slash scars indicated previous capture in gill nets or predation attempts by bears, birds, or piscivorous fishes.