In the Northwest Atlantic, the largest cod are found on Georges Bank with a 4-year old fish being, on average, five times bigger than one off Labrador and Newfoundland. Temperature also affects the reproductive cycle of fish and shellfish. These fish reside in warm offshore waters and move onto St. Pierre Bank prior to spawning. Temperature is one of the primary factors, together with food availability and suitable spawning grounds, in determining the large-scale distribution pattern of fish and shellfish. This recent shift appears to be part of a larger scale ecosystem change.
Recruitment is a measure of how many young survive long enough to potentially enter the fishery.
Understanding recruitment variability has been the number one issue in fisheries science this century. Evidence of changes in fish abundance in the absence of fishing suggests the likelihood of environmental causes. Since the advent of intensive fishing, it has become increasingly difficult to sort out the relative importance of fishing versus environment as the cause of recruitment variability. At the same time, as previously mentioned, cod moved further southward. Atlantic salmon, unlike their Pacific cousins, are multi-year spawners.