Sex-specific temperature distribution of American plaice (Hippoglossoides platessoides) and its relation to age and abundance

Abstract

I examined variation in the temperature distribution of American plaice (Hippoglossoides platessoides) in the southern Gulf of St. Lawrence using data from bottom trawl surveys conducted each September since 1971. Plaice tended to select cold temperatures relative to those available. Temperature distribution was unrelated to age over the range 3-12+ years. Females tended to occupy warmer water than males, although the extent of this difference between the sexes varied among years. Annual variation in plaice temperature distribution was positively correlated with variation in the temperatures available. After accounting for annual variation in available temperatures, female temperature distribution was density independent but males tended to occupy colder water at higher levels of abundance. The median temperature occupied by both sexes tended to be warmer at higher levels of abundance of Atlantic cod (Gadus morhua), a competitor of plaice. The difference between the sexes in temperature distribution increased as cod abundance decreased or as plaice abundance increased (depending on the measure of temperature distribution used). The observed difference between the sexes in temperature distribution and its density dependence may reflect differences in foraging rate associated with differences between the sexes in the fitness benefits of growth.