RECRUITMENT MECHANISMS IN FLATFISH - WHAT DID WE LEARN AND WHERE DO WE GO

This paper summarizes the developments in flatfish recruitment studies over the last decade with emphasis on the general patterns that have emerged from the contributions to the two Flatfish Symposia of 1990 an d 1993. Recruitment variability is largely generated by density-indepe ndent factors acting during the pelagic egg and larval phases. Effects of variability generating processes tend to be amplified towards the edges of the distribution range and appear to be related to abiotic co nditions. Density-dependent feedback processes occur in the demersal j uvenile phase, when flatfish become highly specialized benthic feeding fish. There is evidence that density-dependent feedback processes may also occur during the adult phase in not or lightly exploited populat ions. Areas of future research that emerge from this symposium are: 1. the classification of flatfish populations in 'ecological equivalents ', including the habitat requirements of the successive life history s tages; 2. comparative studies among species and populations of recruit ment processes; 3. analysis of environmental factors determining the s urvival of pelagic eggs and larvae; 4. density-dependent habitat selec tion of demersal juveniles in relation with growth and mortality; 5. a nalysis of the habitat characteristics of species for pelagic eggs and larvae, demersal juveniles and adults, including drift of eggs and la rvae, transport from spawning towards nursery areas and adult migratio n; and 6. simulation studies of relevant population dynamical processe s to explore quantitatively the importance of the various processes an d the necessary precision with which these should be known.