Observations on the Ecology of the Pacific Cod (Gadus macrocephalus) in Canadian Waters

In Canadian waters, Pacific cod are close to the southern limit of their range and appear to inhabit depths where temperatures are between 6° and 9 °C. Seasonal variations in depth distribution are not as pronounced as those in the northwestern Pacific where there are much greater variations in the seasonal cycle of temperature.Relatively high temperature experience in Canadian waters appears to be responsible for a more rapid initial growth rate (instantaneous rate, g = 1.99 between ages I and II; 0.64 between ages II and III, decreasing to 0.19 between ages IV and V) and a much shorter life span than elsewhere. Estimates of L∞, the asymptotic length, range from 72.8 cm to 77.4 cm, while estimates of K, the rate at which growth approaches L∞, range from 0.56 to 0.71.Maturity is reached at two to three years of age—several years earlier than in colder regions of the North Pacific—and estimates of instantaneous total mortality rate range from 1.27 to 1.77 for fish of commercial size. Although these are probably overestimates, it is nevertheless apparent that total mortality rate is very high and that a large share is due to natural causes. Instantaneous-natural mortality rate possibly exceeds 0.9.