Aspects of reproduction of striped venus Chamelea gallina in the Gulf of Cádiz (SW Spain): Implications for fishery management

Abstract

This study analyzes the main reproductive aspects of a natural population of Chamelea gallina on the SW Spanish coast (Gulf of Cadiz): gametogenic cycle, size at first maturity, size at sexual differentiation and partial fecundity. Methodology involved the use of standard histological techniques, image analysis and the assessment of the variation of gonadal growth.Monitoring throughout one year (May 2010–April 2011) identified 5 gametogenic developmental stages and evidenced the existence of a long reproductive period between March and September. In May 70% of individual were in stage 4, reproduction period (sub-stages 4A: maturity and 4B: partial emission), whereas in June most individuals were partially emitting gametes (4B). An important peak of gamete emission took place between June and July, after that recovery stages were detected (sub-stage 4C). In September most of individuals were in stage 5 (spent). It was not possible to define a single spawning event, but signs of partial spawning of greater or lesser intensity were identified throughout the whole reproduction period. This period was followed by a short period of sexual rest (stage 1; October), before beginning a new gametogenic cycle and of energy storage processes in November. Most of the individuals remained in a pre-active stage (stage 2: initiation of gametogenesis) until February, although advanced gametogenesis stages (stage 3) were also observed in January. The size (shell length) at first maturity was estimated for males (8.41mm), females (10.29mm) and the whole population (9.34mm) using standard histological techniques.For the range of shell lengths studied (20–30mm), between 40% and 60% of the visceral mass of C. gallina was devoted to reproduction. Gonadal volume was dependent on shell length and was between 37.25 and 205.95mm3. Gonadal volume and oocyte volume fraction were the most decisive factors in estimating fecundity. C. gallina is a multiple partial spawner and partial fecundity values were estimated and comprised between 76,835 and 797,424 oocytes per female. Partial fecundity was linearly related with both shell length and live weight. Since the oocyte output highly varies as shell length increases, reducing the minimum legal catch size (25mm) or overfishing legal size classes (>25mm) could diminish the total oocyte output and, consequently, affect the recruitment and the size structure of the population. Therefore, fishery management decisions must be taken carefully.