Cockle population dynamics: recruitment predicts adult biomass, not the inverse

Abstract

Bivalves are an essential component of marine ecosystems, playing an important role in community maintenance. The abundance of an exploited bivalve population depends on the balance between inputs (reproduction/recruitment and growth) and outputs (mortality and fishery removals). Reproduction and subsequent successful recruitment are crucial for population sustainability. In the present study, the reciprocal relationship between recruitment (operationally defined as retention on a 1-mm sieve) and adult stock size was studied using a 17-year database (1997–2014) on an unexploited Cerastoderma edule population in a national nature reserve in Arcachon Bay, France. Results showed that cockle recruitment in a temperate climate with mild winters is rather unrelated to temperature in the previous months, but depends on recruitment timing. When temperature reached 14 °C in May, stimulating early recruitment, recruit density was high (500–1000 ind m⁻²), and the resulting cohort had a relatively long lifespan (>1 year) with high associated secondary production. Conversely, when temperature reached 14 °C in June, recruitment occurred later (June), recruit density was lower (0–500 ind m⁻²), and the cohort had a shorter lifespan (<4 months) with a consequent low secondary production. Adult spawner biomass was not positively correlated with recruitment, and the spawner biomass at the time of recruitment did not negatively affect recruitment. More than previous studies, the present study showed that factors driving cockle recruitment success are highly site-dependent, temperatures at the site being only one component.