OVERWINTERING OF ADULT NORTHERN ATLANTIC COD (GADUS-MORHUA) IN COLD INSHORE WATERS AS EVIDENCED BY PLASMA ANTIFREEZE GLYCOPROTEIN LEVELS

Adult Atlantic cod (Gadus morhua) are known to produce antifreeze glyc oproteins in response to cold temperatures. Our laboratory studies dem onstrated that blood plasma levels in adult cod were positively correl ated with the number of days they spent in subzero water. Between Apri l 1991 and lune 1993, we monitored concentrations of antifreeze glycop roteins in the plasma of late juvenile and adult cod in Trinity Bay, N ewfoundland, and used the results to estimate how long cod had been ex posed to low water temperatures. A consideration of these data in conj unction with detailed temperature profiles of the area taken over the course of the study allowed us to deduce the distribution of cod in re lation to the temperature field. This study provides evidence that (1) blood antifreeze glycoprotein levels can be used to deduce the recent thermal history of cod in the wild and (2) after their inshore summer feeding period, considerable numbers of adult cod overwintered inshor e in Trinity Bay in subzero water, producing antifreeze glycoproteins as temperatures fell below 0 degrees C. From May onwards, ''cold-adapt ed'' cod moved into warming surface waters, where they became availabl e to an early inshore trap fishery.