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. In very cold years on the Bank, they appear to delay migration onto the Bank thereby remaining in the warm offshore waters longer, resulting in faster gonad development and an earlier readiness to spawn. 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 fish ng 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.