SEASONAL, INVERSE CYCLING OF LENGTH-AT-RECRUITMENT AND AGE-AT-RECRUITMENT IN THE DIADROMOUS GOBIES SICYDIUM-PUNCTATUM AND SICYDIUM-ANTILLARUM IN DOMINICA, WEST-INDIES

We report on an 18-month field study of temporal pattern and interrelationships of size-and age-at-recruitment (to fresh waters) for two diadromous hill-stream gobies in Dominica, West Indies (15 degrees 30'N, 61 degrees 25'W). Recruitment is panseasonal in Sicydium punctatum and Sicydium antillarum and supports a directed fishery similar to other goby fry fisheries. We found both size and age of recruits to vary seasonally, but the relationship of size to age is complex. Although positively related within lunar-monthly recruiting cohorts, the overall relationship of size and age was poor because seasonal variation in size is out of phase with age. Among recruiting cohorts, mean (or predicted) size and age are negatively correlated. Recruitment (fishery yield) also varies seasonally, in phase with size and out of phase with age. Peak fishery yields coincide with the youngest, but largest, recruits; low yields coincide with the reverse, implicating growth rate variations in fishery yield. This is the first such report of systematic seasonal variation in age-at-recruitment. Given these findings, size- and age-at-recruitment (here similar to settlement or metamorphosis) should not be assumed invariant, even for tropical fishes.