PREY SELECTION BY INEXPERIENCED PREDATORS - DO EARLY JUVENILE SNAILS MAXIMIZE NET ENERGY GAINS ON THEIR FIRST ATTACK

Through encounters with prey, a predator may learn to become more sele ctive and thus forage more efficiently. This is the case for several m uricid gastropods. When searching for their first prey, however, early juveniles have no such foraging experience. Prey species and prey siz e preferences of inexperienced Nucella emarginata (Deshayes) hatchling s from Barkley Sound, British Columbia, Canada, were therefore examine d to determine if selective feeding occurs in the absence of foraging experience and, if so, whether the preferences are consistent with the energy maximization hypothesis of optimal foraging theory. When given a choice between 5 prey species (small Mytilus spp., Balanus glandula (Darwin), Chthamalus dalli (Pillsbury), Pollicipes polymerus (Sowerby ) and Lasaea spp.), 80% of the hatchlings attacked Mytilus spp On thei r first attack. When offered 5 size classes (1, 2, 3, 4 and 5 mm shell length) of Mytilus spp., approximate to 73% of the hatchlings attacke d 1-mm or 2-mm size classes. Hatchlings were, in fact, more selective than late juveniles and adults. Hence, strong prey species and size pr eferences can exist without prior foraging experience even in species which use such experience later in life to make foraging decisions. Bu t hatchlings feeding on Mytilus spp. for 25 days did not grow faster t han hatchlings feeding on Balanus glandula or Chthamalus dalli, and th ere was no difference in energy content between Mytilus spp. and Chtha malus dalli. Thus, the strong preference for small Mytilus spp. can no t be explained by considerations of energy gain. In the field, small M ytilus spp. are mostly located in microhabitats which provide hatchlin gs with substantial protection from mortality factors. The preference for small Mytilus spp. should keep the young snails within protective microhabitats once these sites have been reached, and might be an adap tation to help the hatchlings locate these havens from a distance, in an otherwise highly dangerous environment.