RECRUITMENT AND RECRUITMENT MODELS IN FISHERY SCIENCE

Recruitment and growth of individuals bring the most to enlargement of fish stock biomass. Recruitment can be independent on stock size during the development of the fishery, but experience has showed that many fisheries have come to the point when recruitment decreases due to over fishing. Large parental stock does not give large number of juveniles because large number of individuals influences survival of juveniles (competition for food). In period between 1984 and 1987 this phenomenon was recorded in sardine population in the Adriatic Sea, when large biomass of parental stock resulted in twice less recruitment. In the period between 1993 and 2000 there was no significant recruitment of the sardine population in the Adriatic Sea and it reflected on biomass of the sardine. Large recruitment was recorded in 2001 and 2002. There are numerous mathematical models which give relation between stock and recruitment. Beverton–Holt’s and Ricker’s models are usually used. Beverton–Holt’s model assumes that recruitment depends on the density of population. Ricker’s model is based on assumption that all resources are evenly distributed among the individuals; therefore the rise in density causes the exhaustion of resources. This model is suitable for species as the sardine, which migrates in the breeding area