Abstract
A geostatistical approach was used to pinpoint the main nursery areas of demersal resources and define their persistence by means of direct estimation of fish densities. The European hake (Merluccius merluccius Linnaeus, 1758), one of the most important demersal resources inhabiting the whole Mediterranean from 30 metres (m) to almost 1000 m depth, was used as a case study to locate their recruits and check their stability using geo-spatial methods and common criteria. Data were collected during trawl surveys carried out in the late-spring and autumn from 1994 to 2006 in seven geographical sub-areas (GSAs) including Italian waters in the Western and Central Mediterranean. Indicator kriging was applied to locate the sites where number of recruits exceeded, at a given probability, a conditioned threshold value. The temporal persistence of high-density patches of recruits was then evaluated by means of an index of spatial persistence. Hake recruits showed patchy distribution with several denser areas showing a high temporal persistence. The main nursery areas were identified in the Central Adriatic Sea (GSA17), northern Tyrrhenian–Ligurian seas (GSA 9) and Sardinia (GSA 11). Important nurseries occurred also in the Strait of Sicily (GSA 16), South Adriatic Sea (GSA18) and North Ionian Sea (GSA19).