Analysis and Interpretation of Freshwater Fisheries Data

4: Recruitment

Michael J. Maceina and Donald L. Pereira


Recruitment of young fish into catchable, harvestable, or adult size is necessary to sustain any population and fishery. Recruitment failure, due to overfishing, habitat alteration, or abiotic or biotic events, can lead to reduced adult abundance and reduced angler catch rates. If severe, recruitment failure can ultimately result in severe population declines and collapse of a fishery. However, larval, juvenile, and even adult fish can be stocked to augment a fishery or a population if natural recruitment is low or nil. Conversely, if recruitment is high, then catchable- size abundance and fishing success should be greater if density-dependent mortality and growth reduction are not excessive. Recruitment is typically the strongest determinate influencing populations among the three major factors affecting populations, that is, growth, recruitment, and mortality (Carline et al. 1984; Allen and Pine 2000).

Recruitment success typically varies from year to year in most populations due to a number of factors. Some species from certain water bodies may display fairly constant recruitment each year, whereas other species or populations display highly variable recruitment that will cause wide fluctuations in the number of fish reaching a certain age or length. In marine systems, recruitment rates tend to be lognormally distributed with many average and below average years interspersed with periodic strong year-classes (Hennemuth et al. 1980). Although a similar review has not been conducted for North American freshwater fishes, we suspect a similar pattern. Fecundity in fishes is typically high, and recruitment variability is often caused by density-independent factors, but density-dependent regulation can stabilize recruitment (Cowan et al. 2000). The processes and mechanisms that cause recruitment variation have been intensively investigated for many years (reviewed by Cowan et al. 2000). In this chapter, analysis of the effects of environmental factors and parental abundance on recruitment will be explored.