<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
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