ANNUAL VARIATION IN PARENTAL CARE IN SMALLMOUTH BASS, MICROPTERUS-DOLOMIEU

An eight year field study is summarized outlining variation in parental care in a northern population of smallmouth bass. Nesting males ranged in age from 4 to 12 + years old and ranged in size from 21 cm to 40 + cm in fork length. The age and size distributions were skewed right when strong year-classes entered the nesting stock. Larger males had more offspring in their nests than smaller males. The year-to-year variation in the duration of care was large and appears to be related to two general effects of water temperature. First, there was a significant positive relationship between the variation in spring spawning date and variation in the duration of parental care prior to swim-up of the larvae. This reflects the general effect of spring warming rate on the timing of nesting in each year. Second, in most years, there was a significant positive relationship between male size and the duration of parental care prior to swim-up. This reflects the consistent inverse relationship between male size and the seasonal timing of spawning in this population. The offspring of large males spawning early in a season take longer to develop than offspring of males nesting late in season. There is no relationship in most years between male size and duration of care after swim-up. Other factors unrelated to water temperature may be important in determining the duration of care after swim-up. In particular, ontogenetic changes in juvenile behaviour and energy depletion in nesters may be two important factors affecting care duration.