SEX-SPECIFIC TEMPERATURE DISTRIBUTION OF AMERICAN PLAICE (HIPPOGLOSSOIDES-PLATESSOIDES) AND ITS RELATION TO AGE AND ABUNDANCE

I examined variation in the temperature distribution of American plaic e (Hippoglossoides platessoides) in the southern Gulf of St. Lawrence using data from bottom trawl surveys conducted each September since 19 71. Plaice tended to select cold temperatures relative to those availa ble. Temperature distribution was unrelated to age over the range 3-12 (+)years. Females tended to occupy warmer water than males, although t he extent of this difference between the sexes varied among years. Ann ual variation in plaice temperature distribution was positively correl ated with variation in the temperatures available. After accounting fo r annual variation in available temperatures, female temperature distr ibution was density independent but males tended to occupy colder wate r at higher levels of abundance. The median temperature occupied by bo th sexes tended to be warmer at higher levels of abundance of Atlantic cod (Gadus morhua), a competitor of plaice. The difference between th e sexes in temperature distribution increased as cod abundance decreas ed or as plaice abundance increased (depending on the measure of tempe rature distribution used). The observed difference between the sexes i n temperature distribution and its density dependence may reflect diff erences in foraging rate associated with differences between the sexes in the fitness benefits of growth.