Environmental variability, mortality of fish larvae and recruitment

Abstract

       Over the past few decades, larval fish studies have been successful in relating certain aspects of recruitment to environmental factors, but without any convincing predictive capability. For exam­ple, in a SARP project on sardine (Sardina pilchardus) off the Atlantic coast of Spain, although there was some relationship between food availability and potential larval survival, as measured by a range of condition indices, ultimately it was advection of larvae into relatively unproductive deep water that was the main determinant of recruitment success. Similarly, more detailed studies on anchovy (Engraulis encrasicolus) in the northern Adriatic have shown how wind mixing can affect feeding conditions for the larvae, but their adaptation to spawning in the well stratified waters of the River Po outflow counteracts any simple relationship between food availability and the detri­mental effects of adverse weather.

       The potential of simulation modelling for investigations of larval survival and recruitment is described in relation to studies on blue whiting (Micromesistius poutassou) and mackerel (Scomber scombrus) in the eastern North Atlantic. The blue whiting transport model addressed the variabili­ty of advection of the planktonic stages under different wind regimes, while for the mackerel vari­ous additional biological attributes are incorporated in a bio-physical transport model, these being principally growth and mortality in relation to the biological and physical environment.