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, , FISHERIES MANAGEMENT-PERSPECTIVE . Large T I I - High - I I I I I I I - CII .... 'iij c o ".;j I\J -= C. o Q. .:z::: III ';: ..................................................... c o ':;: v C ':;: >< w Small Low Time Figure 1. The general relationship between population size and extinction risk illustrates the potential danger of fisheries manage- ment policies that consider conservation aquaculture as a last resort for recovering endangered populations. Such policies may dictate implementation of conservation aquaculture when a population has already entered an extinction vortex (shaded rectangle at right). This condition may limit the success of any population recovery effort. The dark vertical bar (far right) represents extinction. habitat to support a restored population. A second approach suggests that aquaculture is a necessary interim measure to maintain the viability of endangered popula- tions. Critics of this second approach suggest that risks such as catastrophic loss due to culture facility failure or fish loss resulting from disease outbreak may outweigh its intended benefits. Rather that debating the strengths and weaknesses of these two approaches, one should realize that the success of each approach may be jeopardized if either is implemented exclusively. With the exception of overharvest, fish population crashes are rarely univariate problems. Thus, univariate management solutions often have failed to restore fish populations due to unresolved underlying problems. Fisheries managers need to acknowledge that several conservation measures can be complementary, and should seek combined strategies to immediately address conservation of gene pools while reestablishing habitats to support restored populations. An inflexible fisheries management policy that consid- ers conservation aquaculture as a last resort for managing endangered fish populations can seriously jeopardize the potential for recovering wild fish populations and can increase the probability of serious or irreversible genetic bottlenecks. As population size decreases, so does its N" Depending on population age class structure or particular harvest regulations, N" may decline at a disproportionately higher rate than total population size. In some cases slot limits, designed to prohibit harvest of fish of a particular size range, have been implemented to reduce the chances of disproportionate reduction of effective population size. If population size decreases in a relatively linear fashion (e.g., due to recruitment failure and natural mortality), the risks of reduced population viability and persistence may increase exponentially as N,. declines (Figure 1). This phe- nomenon is referred to as an extil/ctiol/ vortex (Cilpin ilnd Soule 1(86). In this situiltion, risks tilke the form of reduced 30 . Fisheries or lost within-population genetic variation manifested by genetic drift and inbreeding in small populations. By applying this concept across the geographic range of a species with multiple populations, it becomes evident that demographic bottlenecking also can reduce among-popu- lation genetic diversity of the species as individual popu- lations are lost or substantially reduced. Without timely implementation of appropriate conservation aquaculture, fish managers may unintentionally reduce the probability of population recovery after allowing N" to fall to danger- ously low levels. This is generally true regardless of the recovery measures undertaken. The recovery process for the Kootenai River population of white sturgeon (Acipenser transmontanus) in Idaho, Mon- tana, and British Columbia provides a good example of fisheries management that simultaneously incorporates conservation aquaculture and ecosystem restoration. In response to general natural recruitment failure since the mid-1960s, this aging and declining population was listed as endangered in 1994 under the Endangered Species Act. Rather than using a large-scale production hatchery to supplement this population, a breeding strategy was devel- oped to preserve the population's remaining genetic vari- ability. This conservation aquaculture program provides a systematic approach to preserving the Kootenai River white sturgeon gene pool while management agencies work to restore river habitat conducive to natural spawn- ing, larval survival, and natural recruitment. Simultaneous research to determine the ecological factors contributing to natural recruitment failure has been ongoing since 1989. This research has primarily focused on white sturgeon life history and reproductive biology, river productivity, and fish community dynamics issues, as well as on alterations to the post-impoundment hydrograph, in an international- ly coordinated attempt to reestablish natural recruitment. In conclusion, it is absolutely critical to understand that persistence and viability of endangered fish populations are profoundly affected by the size and structure of the population, its genetic variability, and its adaptive poten- tial. Conservation aquaculture is by no means proposed as a panacea for recovering endangered fish populations. However, in certain situations it may be the only viable, immediate solution for maintaining adequate Ne and pre- serving within-population genetic diversity, two require- ments for long-term population persistence. Timely imple- mentation of appropriately designed conservation aquaculture programs can, in some cases, provide a suc- cessful alternative to demographic and genetic bottleneck- ing, inbreeding depression, and loss of unique and impor- tant locally adapted genes. Such programs ultimately may reduce the immediate threat of extinction for endangered fish populations. Conversely, aquaculture for any purpose, especially with small threatened and endangered popula- tions, is not risk-free. Therefore, the need for objective, case-by-case evaluation of conservation aquaculture is crit- ical (Anders 19(7). I suggest that a rationill approach to assessing the role of conservation ilquaculture is to under- stand that it is one component, with population-specific Vol. 23, No. 11 --