Are seals preventing the recovery of cod stocks?
A 1997 international scientific workshop on interactions between harp seals and fisheries - which included a number of DFO scientists - "accepted that it could not [on the basis of available information] assess the relative importance of predation by harp seals on the current status of the northern cod stock." The scientists concluded that they were "unaware of any evidence that harp seals have had a substantial effect on the abundance of northern cod since the collapse" (Anonymous 1997).
Seals, like all animals, must eat to survive. However, the perception of marine mammals as "gluttons" is entirely unfounded. Seals and whales have metabolic rates similar to terrestrial mammals of similar size. Those who support culling harp seals often refer to estimates of the annual consumption of fish by seals to support their demand for an increased seal kill. Claims that seals are eating "tens of thousands of tonnes" of commercially important fish may seem to support the conclusion that they are having a large impact on fisheries, but that conclusion may well be wrong.
Calls for culling seals to benefit fisheries are based on the idea that since seals eat fish, then "common sense" tells us that fewer seals mean more fish, and higher catches for fishermen. But comparisons made between the amount of fish consumed by marine mammals, and that taken in commercial fisheries, imply that if it were not for marine mammals, those fish would be available for human consumption. In reality, estimates of food consumption tell us little about whether seals are having direct or indirect effects on the abundance of various fish stocks, or on the catches of commercial fisheries.
Because seals are more visible than other predators, and are frequently seen as a nuisance because they damage fishing gear, solving the "seal problem" seems like an easy answer to restoring fish stocks.
Some argue that "common sense" tells us all we need to know, and the fact that seals eat fish somehow means that the impact on important fish stocks is obvious.
However, an equally "common sense" argument tells us that if seals eat predators of commercially important fish, then fewer seals would actually mean fewer fish for fishermen.
For example, harp seals in the Northwest Atlantic feed on squid, which are a predator of juvenile Atlantic cod. In this situation, a reduction in harp seals could lead to an increase in squid numbers, resulting in even greater predation on cod.
Clearly, it doesnt take a very large increase in complexity to see that a seal cull could actually result in a reduction in the abundance of commercially important fish.
It must be remembered that ocean ecosystems are actually much more complicated than either of the previous scenarios, and that there are many other predators in marine ecosystems.
Thus, any increase in the size of a fish stock as a result of culling seals is more likely to be eaten by other predators than it is to be caught by fishermen. Still others of the "saved" fish will die from other forms of natural mortality, e.g. disease, or, perhaps simply move beyond the range of the fishery.
Even in the still simplistic example shown here, the benefits of a seal cull to a fishery (if any) would be an extremely small proportion of the benefits originally estimated from simply examining the feeding habits of seals.
It is not surprising then, that the 1997 scientific workshop on interactions between harp seals and fisheries reached the conclusion that:
"It is not yet possible to predict the effects of an increase or a decrease in the size of the harp seal population on other ecosystem components, including commercially exploited fish populations, or on the yields obtained from them."
Analyses of the effects of seal culls in other parts of the world have only confirmed the uncertaintly in predicting the results of a seal cull. The most thoroughly analysed example of a proposed seal cull comes from the Benguela ecosystem off the southwest coast of South Africa, where, so far, it appears as though a cull is unlikely to be beneficial to fisheries. In fact, studies to date have indicated that a seal cull would most likely result in a decrease in fishery yields.
The Scientific Advisory Committee of the United Nations Environment Programmes Marine Mammals Action Plan has recently prepared a Protocol for the Scientific Evaluation of Proposals to Cull Marine Mammals (UNEP 1999). This Protocol provides a guideline to help decision makers determine whether a marine mammal cull should be undertaken in order to benefit fisheries. The scientific evaluation of a cull proposal is not a trivial exercise, and must consider the complexity of ecological interactions among the marine mammal population(s), the relevant fish stocks, and the fisheries which catch them. It is obvious that the decision to cull marine mammal populations should not, and can not, be based merely on "common sense."
Ultimately, it is politicians, not scientists, who determine fisheries and sealing policy. And politicians, ultimately, must answer to their constituents, many of whom see seals simply as a competitor for "their" fish. The Fisheries Resource Conservation Council (FRCC), a government advisory body, has advocated (among other measures) culling up to 50% of the seal population, and creating "seal exclusion zones." Some politicians feel that the FRCC doesnt go far enough in their recommendations to cull seals. On May 4, 1998, John Efford, the Newfoundland Minister of Fisheries and Aquaculture, told his legislature that: "I would like to see the 6 million seals, or whatever number is out there, killed or sold, or destroyed or burned. I do not care what happens to them... the more they kill the better I will love it."
Other politicians, such as the Hon. Herb Dhaliwal, Canadas federal Fisheries Minister, seem to show a greater appreciation of the complexity of marine ecosystems. In his Feb. 15, 2000, testimony to the Senate Standing Committee on Fisheries, Minister Dhaliwhal stated that: