Predation on hatchery-reared lobsters released in the wild

Predation on hatchery-reared lobsters (Homarus gammarus) in the wild was st udied in order to identify predators in southwestern Norway on rocky and sa ndy substrates in winter and summer. Lobsters of 12-15 mm carapace length w ere tagged with magnetic microtags. About 51 000 juvenile lobsters were rel eased on 10 occasions at three locations. Predator samplings were by tramme l nets, eel traps, and videorecordings during the 24 h immediately followin g the releases. In summer, loss to predators occurred on both rocky and san dy substrates. The loss was lower in winter when lobsters were found as pre y in predators caught on sand. The risk of fish predation was highest in th e first hours after release, when the lobsters were out of shelter. The wra sses Labrus bergylta and Labrus mixtus were the major predators of lobsters , while Atlantic cod (Gadus morhua), shorthorn sculpin (Myoxocephalus scorp ius), and crab (Cancer pagurus) were mainly winter predators. Winter predat ors were never as abundant as summer predators. To minimise predatory loss of reared and costly lobsters, they should be released onto rocky substratu m in winter. Due to the damage to the predated lobsters, it was not possibl e to correlate survival against lobster size.