Fecundity variation in Icelandic summer-spawning herring and implications for reproductive potential

Abstract

Abstract An exploration of fish fecundity aimed at estimating the reproductive potential of a stock requires comprehensive and quantitative examinations of the influencing factors. Here, Icelandic summer-spawning herring (Clupea harengus) are used to quantify potential fecundity (FP, number of eggs) and relative fecundity [RFP = FP (body weight − ovary weight)−1] as functions of length (L) and weight (W) in mature prespawning herring. Using a coupled examination of atresia (oocyte degeneration in the ovary) and the maturation stage of oocytes as characterized by size, we show that atresia has no meaningful effect on fecundity estimates if determined near the spawning time. Among prespawning herring, FP is a strong function of L or W (r2 = 0.84 in either case). Fulton's condition factor K (=100WL−3) explains a trivial (1.5%) but significant (p < 0.0001) amount of the residual variation in FP, and appears to have the greatest effect among smaller length classes. RFP is also a function of L (r2 = 0.56), and oocyte diameter explains 36% of the residual variation (p < 0.001). Therefore, stock-specific total egg production in herring can diverge from the assumed proportionality between total egg production and spawning-stock biomass through variations in the length structure of the stock, and to a lesser extent through the condition of prespawning herring.