Patchiness of eggs, larvae and juveniles of European hake Merluccius merluccius from the NW Mediterranean

Abstract

We estimated patchiness for different life stages (egg, larvae and juveniles) of European hake (Merluccius merluccius) from two ichthyoplankton surveys (September and November 1999) and four bottom-trawl surveys (November 1998, February, June and September 1999). Lloyd’s patchiness P=1+1/k, where k is the dispersion parameter of the negative binomial distribution, was calculated. Juveniles showed lower indices of patchiness than early ontogenetic stages. In juveniles, patchiness was highest for smaller size classes (3.5–5 cm TL) settling to their near-bottom habitat and was very low for those larger than 5 cm up to the 30–35 cm size class (approximately 3 yr of age, 50% mature individuals). Patchiness of settling juveniles was especially high in the June and September surveys, coinciding with peak recruitment to the bottom. Both eggs and yolk sac larvae showed patchiness values <10, increasing in flexion stage larvae from 12 to 20. This pattern is different to that observed in other studies for pelagic species, where patchiness of early-stage eggs is very high, but coincides with results obtained for other demersal species with pelagic eggs. Factors that may explain these patterns are discussed in light of oceanographic conditions, adult distribution and larval ontogenesis.