Log-linear modelling of age-structured abundance in terms of recruitment and survival for two bivalve species, the cockle Cerastoderma edule and the Baltic tellin Macoma balthica

Long-term series of almost 50 years of seasonal age-structured abundance data of two bivalve species are summarized by fitting a series of generalized linear models, all assuming a Poisson process generating the counts, but varying from a simple model assuming constant recruitment and survival to a most complicated model in which recruitment is year-dependent and survival is both year-, season-, and age-dependent. The best fitting model for both species showed that recruitment, summer survival, and winter survival are all year-dependent, but that all age classes, apart from the first winter, showed a similar survival chance. The decomposition of the trends in abundance in terms of trends in recruitment and trends in juvenile and adult survival may provide a basis for further explorations of the steering mechanisms.