Escapement of Eggs from Farmed Cod Spawning in Net Pens and Offspring Intermingling with Natural Spawned Larvae

Interbreeding between wild fish and escaped farmed fish (or deliberate releases in enhancement/ranching) could result in genetic changes in the wild populations that reduce overall fitness and productivity (Utter et al. 1993; Utter 1998). Although this problem has been discussed for a long time (e.g. Hindar et al. 1990; Skaala et al. 1990) experimental evidence of harmful effects from interbreeding between cultured and wild stocks has been limited. Recently, however, new knowledge has been established especially for Atlantic salmon (Einum & Fleming 1997; McGinnity et al. 1997; Fleming et al. 2000). A comprehensive 10-year study in Ireland (McGinnity et al. 2003) measured the lifetime fitness of offspring from various crosses between farmed and wild salmon, carried out over two generations. The data obtained demonstrated a dramatic reduction in the lifetime success of the offspring of farmed and hybrids compared to wild salmon offspring.