Changes in catch rates and length and age at maturity, but not growth, of an estuarine plotosid (Cnidoglanis macrocephalus) after heavy fishing

The intense harvesting of a fish stock can be accompanied by changes in certain life history traits of that stock. For example, after heavy exploitation, Atlantic cod (Gadus morhua) in the northwestern Atlantic and haddock (Melanogrammus aeglefinus) on the Scotian Shelf matured at smaller sizes and younger ages (Olsen et al., 2004, 2005; Neuheimer and Taggart, 2010). Because earlier maturing individuals are more likely to reproduce before capture than late maturing individuals, such changes could have been the result of selection for the genotype for maturation at a smaller size or younger age (Marshall and Browman, 2007). It is relevant, however, that the results of simulation studies indicated that, although the harvesting of both immature and mature individuals and also only immature individuals of a stock leads to selection for a reduction in length and age at maturity, the restriction of harvesting to only mature individuals produces the reverse effect (Law and Grey, 1989; Heino, 1998; Ernande et al., 2004). Laboratory studies have shown that extreme selective harvesting of the largest individuals of Atlantic silverside (Menidia menidia) over four generations led to a reduction in growth rate (Conover and Munch, Changes in catch rates and length and age at maturity, but not growth, of an estuarine plotosid (Cnidoglanis macrocephalus) after heavy fishing