Research Document - 2001/124
Initial evaluation of community structure in goose barnacle (Pollicipes polymerus) and sea mussel (Mytilus californianus) beds off the west coast of Vancouver Island, British Columbia
By Jamieson, G., Dixon, S., Lauzier, R.
Abstract
Goose barnacles (Pollicipes polymerus Sowerby, 1833) have been harvested off the west coast of Vancouver Island since 1985. However, following rejection of approval to establish a sea mussel (Mytilus californianus) fishery because analysis indicated that harvesting this species would likely have significant negative ecological impacts, attention was directed to the possible effects of the existing commercial goose barnacle fishery. Since the ecological role of this species was also structural and its fishery implications had not previously been thoroughly investigated, the commercial goose barnacle fishery was closed in May, 1999, until appropriate evaluation studies could be done. Such studies were initiated in 2000, with objectives to: 1) evaluate the ecological role of goose barnacles in the exposed rocky intertidal; 2) to conduct goose barnacle biomass estimates in limited areas; and 3) to make management recommendations from an ecological perspective on how a commercial goose barnacle fishery, if reopened, should proceed. Here, we present initial results from our analysis of goose barnacle/sea mussel community structure and initial ecological observations of how experienced fishers harvest goose barnacles.
Species diversity within the exposed rocky intertidal zone is complex and is correlated with matrix thickness (the combined layer of living animals, dead shells and associated debris). Following screening with a 1.0 mm sieve, 142 species were identified in our samples. Species predominating numerically (>1000 individuals/species collected, 85% of all individuals found) in the samples were Mytilus californianus, Cirolana harfordi, Petrolisthes cinctipes, Corophium sp., Hyale sp., Lacuna vincta, Pollicipes polymerus, Semibalanus cariosus, Cucumaria pseudocurata, and Lottia alveus, respectively. Species observed consisted of gastropods (40%), marine arthropods (20%), annelids (16%), echinoderms (7%), molluscs (5%), cnidarians (3%), unknowns (4%); and insects, chordates, and sipunculas (5%). Sea mussels and goose barnacles predominated at an intertidal elevation of 2 to 4 m.
Experienced fishers typically harvest fist-sized “colonies” of goose barnacles from a sea mussel or acorn barnacle matrix, prying each colony off with a long flat steel bar. This harvest method produces divot holes in the mussel matrix layer or patches of bare rock in acorn barnacle areas. Three months after harvesting, the holes created in sea mussel areas had largely filled in through realignment of nearby sea mussels. Bare rock was still evident in acorn barnacle areas. Reduced community biomass at areas intensively harvested, anecdotally reported to be due to the actions of inexperienced harvesters in previous year(s), was visible at most sites.
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