DIFFERENCES IN GROWTH AND MORTALITY OF JUVENILE PLAICE, PLEURONECTES-PLATESSA L, FOLLOWING NORMAL AND EXTREMELY HIGH SETTLEMENT

Abundance of juvenile plaice was quantified with a non-selective drop trap during two consecutive years (1991-1992) from time of settlement in late spring until start of emigration in late summer in a shallow ( 0-1 m) bay in the Gullmar Fjord, Sweden. Individual lengths were recor ded and otolith subsamples were examined to determine age distribution s (days after metamorphosis). Peak abundance reached 1.4 ind m(-2) in 1991 and 10.0 ind m(-2) in 1992. Settlement in 1991 occurred later tha n usual, possibly due to offshore winds during spring. Mean lengths at approximately one month after settlements were similar in the two yea rs. Later in the season, however, lengths at age were lower in 1992, i mplying density-dependent growth. In addition, analyses of individual cohorts demonstrated reduced growth of late settlers in 1992. Instanta neous mortality rates (d(-1)) did not differ between the two years. Co ntrol of population number in 1992 must have been governed by density- independent factors (e.g. larval supply) shadowing or decoupling a den sity-dependent regulation. Biomass of one major epibenthic predator Cr angon crangon was equal in the two years, but that of another Carcinus maenas was higher in 1992 than in 1991. Thus, a functional response a nd/or other sources of mortality must be assumed to account for the hi gher numbers of plaice eaten in 1992.