Focus Issues: Aquaculture in Ocean Replenishment

Uncertainties about Stock Enhancement

Alternate views to the concept of marine stock enhancement can be expected from some conservation biologists, fishery scientists, and resource managers.  Opposition to stock enhancement is fueled by the current controversy over salmonid hatcheries in the Pacific Northwest, where concern has focused on potential damage to ESA-listed wild stocks from a hatchery system that presently produces fish that are captured in mixed stock fisheries containing wild and hatchery fish.  Hatchery fish are harvested at high rates, which cannot be sustained by wild populations. Additionally, many assume that density-dependent mortality of wild stocks is a likely response to increasing abundance by stocking. This is a key issue in stocking programs that can only be addressed by experimental stocking to evaluate effects on wild stocks and the effectiveness of hatchery releases in increasing population size and fishery yields.

Inbred or introduced strains of hatchery fish, when spawning with wild fish, will result in loss of wild-stock fitness.  And breeding too few parents can result in loss of wild-stock genetic diversity. It can be expected that these same legitimate concerns will be expressed as new proposals for marine stock enhancement appear.  More specifically, conservation biologists will be concerned that stock enhancement will disrupt natural evolutionary processes and result in loss of local adaptability in naturally spawning stocks.  Fishery resource managers may favor a science-based regulatory fishery management approach over the stocking of marine fish as a means to recovery.  The environmental community, on the other hand, may oppose the philosophy of marine stock enhancement on the basis that technological fixes for the depletion of fish stocks simply substitute one problem for another and divert attention from the real problem, the need for better management of wild stocks and their habitats.

All of these concerns need to be addressed by the fisheries management and fisheries-science communities. Environmentalists, conservation groups and other stakeholders need to be informed about the responsible approach to marine stock enhancement, which is expanding in use throughout the world, and included in the exploratory phase of decision making about planned use and regional expansion in the US of stock enhancement as a fisheries management tool. Stock enhancement is only at an intermediate stage of development. Adaptive management needs to be integrated into every stocking plan, so that critical uncertainties can be addressed and refinements made in response to new information gained from stocking.