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<br />Perspective <br /> <br />reduced about 25%. If the quota is taken from spawner <br />aggregations, all spawners will be removed and the stock <br />will be threatened with extiJ;lction. The risk to sustain- <br />ability (measured in terms of potential reductions in spawner <br />abundance) imposed by spawner targeting can only be <br />ameliorated by significant reductions in allowable harvest. <br />In our simple example, a 75% reduction in harvest would <br />be required to lower the risk imposed by spawner targeting <br />to that imposed by random selection. <br />Thus, when spawners are targeted for exploitation, con- <br />servation needs demand relatively low harvest levels and <br />strict harvest monitoring to keep the risk to stock sus- <br />tainability at an acceptable level. This requires informa- <br />tion-intensive management (i.e., accurate monitoring of <br />both stock abundance and harvest), which is extremely <br />expensive, and thus justifiable only for those stocks that sup- <br />port large, economically important fisheries. Many oceanic <br />stocks fall into this category (e.g., the cod stocks of the <br />east coast of Canada and the anadromous stocks of the <br />west coast of Canada). However, recent experience (e.g., <br />Finlayson 1994, on the demise of northern stocks of the <br />Atlantic cod (Gadus morhua)) suggests that the environ- <br />ments inhabited by such stocks are so vast and complex <br />that it is extremely difficult to get the precise information <br />needed to micromanage spawner-targeted fisheries effec- <br />tively, even when large amounts of money are set aside <br />to acquire that information. As Hilborn et al. (1993) point <br />out, uncertainty in stock assessment and risk in decision <br />making cannot be eliminated, although both can and must <br />be dealt with. <br />The west coast anadromous stocks spend much of their <br />life cycle in oceanic habitats so large that efficient har- <br />vesting is not possible. Only when they form natural aggre- <br />gations, just before spawning, are they sufficiently con- <br />centrated in space to be effectively harvested. The <br />abundance and economic value of these stocks justify large <br />expenditures for the assessment and enforcement activi- <br />ties necessary to restrict spawner-targeted harvests to lev- <br />els where the risk to sustainability is acceptable. How- <br />ever, despite large current expenditures on such activities, <br />many stocks are in decline (Nehlsen et al. 1991; Waples <br />1991; Hilborn and Winton 1993), thus suggesting that <br />effective micro management of these stocks may also cost <br />far more than is currently appreciated. <br />Among freshwater species, only a tiny percentage of <br />the millions of discrete stocks scattered throughout the <br />lakes and rivers of Canada are of sufficient economic <br />importance to support the information-intensive, micro- <br />management practices demanded by spawner-targeted har- <br />vesting. To subject such stocks to spawner-targeted har- <br />vesting, without escapement monitoring and absolute <br />abundance estimates, would expose the sustainability of <br />these stocks to risks that are both avoidable and unneces- <br />sary. In the vast majority of cases, the efficiency of mod- <br />ern fishing gear is high enough, and dispersal of indi vid- <br />uals low enough, to permit cost-effective harvesting of <br />these populations without targeting spawning aggregations. <br />Harvest theory points to the avoidable damage that <br />spawner targeting can inflict on stock sustainability. In <br />principle, this damage is reversible: a harvest moratorium <br /> <br />1591 <br /> <br />or harvest refuge (sensu Carr and Reed 1993) may allow <br />regeneration of a depleted stock. However, genetic con- <br />siderations point to long-term damage that is irreversible <br />(Soule 1987). When spawners are targeted, exploitation is <br />focused on the only natural measure of stock success, <br />reproduction: only those fish that survive to maturity and <br />are successful in reaching the spawning grounds are killed. <br />By imposing direct selection against successful reproduction, <br />deleterious changes in the population gene pool are likely. <br />Among species that home to specific breeding sites, selec- <br />tion will act against homing and imprinting abilities. Selec- <br />tion will also act against those genetic subgroups that use <br />the exploited spawning sites, leading eventually to elimi- <br />nation of those groups from the population. Among species <br />that have specific spawning periods, selection will act to <br />narrow the range of spawning times, typically favouring <br />spawning times that are later than normal. All such changes <br />reduce the ability of a stock to maintain itself in its natural <br />environment and thus damage stock sustainability. <br />Additional negative effects that accompany spawner <br />targeting include (i) increased risk of inadvertently exceed- <br />ing allowable harvest; increased risk stems from increased <br />vulnerability of spawning fish to capture: use of killing <br />gear (e.g., gill nets) exacerbates the problem because excess <br />harvest cannot be released alive; and (ii) habitat damage and <br />disruption of reproductive behaviour: spawning habitat <br />may be damaged by the placement and use of fishing gear; <br />activity accompanying placement and use of gear may also <br />disrupt the reproductive behaviour of the fish themselves; <br />both effects violate the principle of habitat protection. <br />The potential for undermining population sustainabil- <br />ity by targeting adults during their reproductive periods <br />is well recognized in conservation genetics (Lande and <br />Barrowclough 1987; Soule 1987). Experience in fresh- <br />water systems has shown that one of the most cost-effective <br />ways to contrQl nuisance or invading species is to focus <br />intense exploit,hion on their spawning aggregations. Small, <br />discrete spawning stocks are particularly vulnerable to <br />elimination caused by intense spawner exploitation and <br />genetic deterioration caused by moderate spawner exploita- <br />tion. Yet, stocks of this sort are important contributors to <br />the genetic diversity of individual populations and to the <br />biodiversity of the species as a whole. <br />From the arguments presented above, it is clear that, at <br />any level of exploitation, the targeting of spawning fish <br />imposes an additional risk to population sustainability. <br />While the risk may be partly ameliorated by quantitative <br />monitoring of stock abundance and harvest, this is usu- <br />ally practicable only for large populations with known <br />stock compositions. Such populations would have spawner <br />abundances ranging from several thousand to hundreds <br />of thousands of fish, and would include many oceanic, <br />anadromous species where the economic and social value <br />of the fisheries justifies the cost of information-intensive <br />management. <br />For smaller populations, with unknown stock compo- <br />sitions, such intensive management will rarely be practicable <br />and, where practicable, may not be particularly effective <br />because smaller populations are inherently less predictable <br />than larger populations (Weinberg 1975, p. 20). Such <br />