Environmental analysis of Atlantic cod (Gadus morhua) migration in relation to the seasonal variations on the Northeast Newfoundland Shelf

Abstract

Comparison of historical (1930-1989) and recent (1990-1993) oceanographic data from the Northeast Newfoundland Shelf reveals a significant phase lag in the normal seasonal cycle of temperature and salinity. Atlantic cod (Gadus morhua) migrating along hypothesized circular routes during the early 1990s experienced temperatures up to 1.0 °C below average, particularly at depths typical of the inshore cod fishery. Cod likely spent up to three times longer in subzero °C water during the early 1990s than was typical for the years 1930-1989. The time spent in subzero °C water during normal and warm years was relatively independent of timing of the migration, but even a delay of 1 mo during the early 1990s put cod in subzero °C water twice as long as normal. In contrast, no net salinity anomaly was experienced along the tracks. Temperatures experienced by cod along migration routes have a much larger range and a mean value up to 1.0 °C higher than the vertically averaged temperatures at Station 27. In addition, the interannual average temperature along the migration routes, while exhibiting similar trends, was up to an order of magnitude higher ( <3.0 versus <0.3°C) than the vertically averaged temperatures obtained from a fixed point on the shelf (Station 27).