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British Columbia: No Link Between Over-Spawning and Stock Collapse In Pacific Salmon, Says Paper |
| June 8, 2004 |
Source: Vancouver Aquarium Marine Science Centre
By Andy Torr
AquaNews Staff Writer
 | Sockeye salmon in BC's Adams River display their characteristic red and green spawning colours.
Photo: Vancouver Aquarium |
A new technical paper prepared by the Pacific Fisheries Resource Conservation Council (PFRCC) has disproved the belief that excessive returns of Pacific salmon to their spawning grounds will lead to a collapse of subsequent salmon populations.
The paper addresses the issue of over-escapement (a surplus of spawning fish) and its potential impacts on subsequent generations of salmon. Arguments for higher catches are frequently based on an alleged link between over-escapement and stock collapse. According to the report, there is no evidence for such a link.
“This long-overdue paper brings much-needed science to the question of over-escapement and salmon stock collapse,” said the Honourable John A. Fraser, Chair of the PFRCC. “With evidence now in hand that there is no link between over-escapement and stock collapse, fisheries officials will in future be able to make sounder, science-based decisions on the management of the stock.”
A Complex Fish
The lifecycle of the five Pacific salmon species begins in freshwater, where juvenile fish spend up to the first year of life. They then migrate to the Pacific Ocean, where they spend most of their adult lives before returning to their native freshwater streams to spawn and die. This complex biology contributes to unpredictable numbers of spawning salmon, which in turn influences the restrictions placed on British Columbia salmon fisheries by fisheries managers.
Salmon fisheries may be restricted for a number of reasons. For example, stocks (salmon native to a particular river or lake) that have experienced high mortality at sea can benefit from decreased fishing activity. A reduced fishery can also help to protect weaker populations of salmon that migrate through fisheries at the same time as stronger ones.
In recent years, such restricted fishing activity has in some cases yielded the highest spawning levels seen for nearly 100 years, leading some fishermen to raise concerns about “over-spawning.” They argue that large numbers of spawners will compete against each other for nest sites, decreasing each salmon’s chances of successfully reproducing. Crowding caused by large numbers of late-spawning salmon, for example, could destroy the eggs laid by early spawners.
Economy vs. Ecology
Concerned that competition by a surplus of spawners has led to repeated collapses of salmon stocks in recent history, many fishermen advocate increased fishing quotas to reduce the excess spawning populations.
The PFRCC paper acknowledges that the fishing community has been correct in expressing concern about the reproductive efficiency of these surplus spawners, as well as the associated lost economic opportunities. While it disproves the claim that over-escapement will lead to the collapse of a particular stock, it does support previous findings that a large spawning population does not necessarily produce a large number of offspring. When very large numbers of salmon spawn, females typically produce fewer offspring and the size of the next generation does not increase in proportion to the large number of spawners. However, this does not mean that a collapse will occur.
Due to the important ecological role played by salmon in British Columbia, others have argued in favour of over-escapement regardless of the impact on commercial fisheries. Salmon carcasses feed dozens of marine and terrestrial animal species and act as a natural fertilizer for forest ecosystems. Large returns of spawners may also serve to conserve genetic diversity and to promote the reintroduction of salmon to streams that have lost their salmon populations.
In addition to their role in nature, salmon also support an important fishery that has a direct effect on British Columbia’s economy. By understanding the relationship between over-spawning and reduced productivity, papers such as the one published by the PFRCC help fisheries managers to set fishing quotas that strike a balance between sustaining the unpredictable populations of these important fish, and supporting the people who depend on them for food and livelihood.
The PFRCC is an independent organization created to advise the governments of Canada and British Columbia, as well as the Canadian public, on the conservation and environmental sustainability of Pacific salmon stocks and their freshwater and ocean habitat.
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