MPA Perspective: Existing Small Marine Reserves Can Indicate Whether a Larger Network Is Feasible - Case Study from the West Coast of the United States

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Editor's note: Mark Hixon, author of the following perspective piece, is a professor of marine ecology and conservation biology at Oregon State University (USA). Hixon excerpted this piece from a report he prepared for the Oregon Ocean Policy Advisory Council and the California Fish and Game Commission. His full report, entitled Fishery Effects of Existing West Coast Marine Reserves: The Scientific Evidence, can be obtained via e-mail directly from Dr. Hixon. The report contains full citations for studies mentioned in the following piece.

By Mark A. Hixon

Two of the greatest concerns of the fishing community regarding fully protected marine reserves are, first, whether reserves will work in their particular part of the ocean, and second, whether a network of reserves would truly help to replenish and sustain fisheries. Such issues are critical in regions such as the US West Coast, where an ongoing fishery crisis has resulted in closure of a substantial portion of the continental shelf [see "Notes and News" in this issue - Editor]. As in many regions worldwide, the difficulty of addressing fishermen's concerns is that existing reserves are much too small and too few to benefit fisheries in ways that are directly detectable statistically. Indeed, there are only about a half-dozen fully-protected reserves in Washington (all in Puget Sound, accounting for only about 0.003% of state waters), only 1 in Oregon (about 0.003% of state waters), and 11 scattered along the California coast (about 0.2% of state waters). Ultimately, the effectiveness of a network of reserves can be tested rigorously only after implementation. However, it is nonetheless possible to use existing reserves as indicators of whether a scaled-up network would provide fishery benefits.

The predicted fishery benefits of fully-protected reserves are twofold: (1) the "seeding effect," whereby reserves function as a source of eggs and larvae that replenish fish and shellfish populations outside reserves via dispersal in ocean currents, and (2) the "spillover effect," whereby reserves function as a source of juvenile and adult emigrants that literally swim or crawl out of reserves into adjacent fished areas. The seeding effect occurs only if the number and especially the size of organisms inside reserves is substantially greater than outside, so that abundant eggs and larvae produced inside reserves can effectively seed a large area outside. The spillover effect occurs if (a) the number of mobile animals inside reserves becomes great enough that crowding occurs and a substantial number of animals consequently emigrates to adjacent fished areas, or (b) the life history of mobile animals is such that they gradually move from habitat to habitat as they grow, so that the early stages of the life history can be protected within reserves, and older animals later move into fished areas. Thus, comparisons inside vs. outside reserves provide indicators of whether seeding and spillover effects are probable, and examination of movement patterns can further suggest whether spillover is likely.

There have been scientifically rigorous comparisons inside vs. outside about a dozen existing reserves in Washington, Oregon, and California that were studied at least 10 years after the reserves were established. In all studies - which span unpublished graduate theses and technical reports to articles in peer-reviewed journals - SCUBA divers compared areas inside and outside reserves in similar seafloor habitat by visually censusing plots or transects. Compared indicators included the number and size of fish and shellfish, and sometimes calculated egg production. Egg production is well-documented to increase dramatically with body size in these fish and invertebrates, so areas with high abundance and large sizes of animals clearly produce numerous eggs that may contribute to the seeding effect.

A total of 22 species-specific comparisons involving 17 fished species (red sea urchin, red and pink abalone, and 14 species of fish, mostly rockfishes) were conducted among 13 reserves. Considering cases where statistical differences were detectable, in 15 of 17 comparisons (88%), animals were more abundant inside reserves than outside. In 12 of 15 comparisons (80%), animals were larger inside reserves than outside. In 15 of 17 comparisons (88%), animals were inferred to produce more eggs inside reserves than outside. The exceptions may be cases of smaller species that are out-competed or eaten by more abundant or larger fish inside reserves, although there are presently no definitive data.

A variety of studies have also examined movement patterns of West Coast groundfishes using tag-and-recapture methods. A common life history of species such as lingcod, rockfishes, and some flatfishes is that juveniles live in shallow water, then slowly migrate to deeper water as they grow, eventually living within relatively limited home ranges as adults. Published movement distances suggest that these fishes could spillover from marine reserves of substantial size. Exceptions include exclusively shallow species that inhabit coastal rocky reefs for their entire juvenile and adult life.

Overall, for a broad variety of fished species along the U.S. West Coast, available data indicate that the existing few and small marine reserves are effective in supporting substantially more abundant, larger, and more fecund animals (i.e., more eggs) than comparable fished areas outside. Moreover, many groundfish move sufficiently during their lifetimes to allow for spillover to occur from reserves of substantial size. These results are consistent with the prediction that a scaled-up network of numerous larger reserves would produce detectable fishery benefits via both the spillover and seeding effects.

For more information:
Mark Hixon, Department of Zoology, Oregon State University, Corvallis, OR 97331-2914, USA. Tel: +1 541 737 5364; E-mail: hixonm [at] bcc.orst.edu

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