Characterizing size-specific fecundity in crustaceans

Abstract

Studies of crustacean fecundity are compromised by the absence of a general model for estimating the relationship between fecundity and female size. Coefficients of determination (i.e. r2) of five different regression models were compared in analyses of 20 published data sets to determine if any one model of size-specific fecundity was superior. No one model was best, possibly because variability in fecundity increases with female size such that each model accounted for a similar amount of the total variance. Of these five, the allometric model of log fecundity and log size that is commonly used in fisheries biology was further examined to establish whether the allometric egg number (volume) -female size relationship was characterized by a slope of 3.0. The observed slope was not significantly different from the theoretical slope of 3.0 in 60% of the data sets. No consistent deviation from the expected value was apparent within taxa; however, the frequent occurrence of clusters of points representing size classes with possibly different size-specific fecundity may have affected these results. Although studies of crustacean life history recognize the importance of size at maturity and fecundity, the absence of a general model of size-specific fecundity limits broad comparisons. The allometric model is recommended because 1) analytical simplicity, 2) relative scale independence and 3) it provides two life-history parameters: the intercept (or adjusted mean) describing absolute size-specific fecundity, and the slope estimating relative size-specific fecundity. The existence of differences in size-specific fecundity among discrete size classes within populations suggests new directions for future studies of crustacean life history.