Variability in total egg production and implications for management of the southern stock of European hake

Stock recruitment (SR) relationships aim to predict the recruitment based on a given level of reproductive stock. Though the spawning stock biomass (SSB) is commonly used to fit such SR models, there is increasing evidence that the total egg production (TEP) is a more relevant stock reproductive potential index. Indeed, the TEP takes into account both the size-dependent capacity of females to produce eggs and the demographical structure of the spawning stock. This paper presents a method to assess the TEP based on the fecundity and egg quality based on the age as well as spawning fraction for the southern stock of European hake (Merluccius merluccius). The fecundity and egg quality increased significantly as the female size increased. The spawning fraction also increased with female size. Larger females concentrated their reproductive period during the first quarter of the year, whereas smaller ones spawned throughout the year. The stock's demographic structure showed a clear increase in the proportion of younger females and a reduction of older ones through the 1982–2007 time-series, which led to a decrease of egg production per unit of female SSB. Our results showed a significant contribution of older individuals to the reproductive output. The relevance of using TEP as an index of stock reproductive potential is discussed.