fisheries Archives - EcoEvo@TCD

For decades, Irish fishermen have called for Irish seals to be culled. The call for a seal cull has been made especially vociferously in the west of the country, and has been brought into the national discussion when backed by politicians and highlighted by illegal acts of violence against seals. Just weeks ago, Michael Healy-Rae, Independent TD for Kerry, was in the media demanding a cull. Though many people perceive seals to compete with fishermen, any impact on fisheries is not well supported by the research. Studies have found that seals do not generally compete for the same fish resources as fishermen, and modelling has indicated that the presence or absence of seals has little impact on fisheries catches.

Stephen Leahy at the Guardian reports on a battle between science and politics which is worth highlighting. The Atlantic cod fisheries in the Atlantic collapsed during the 90s due to overfishing. They have yet to recover. The Atlantic cod is an apex predator and its decline effected a trophic cascade, which modified the original food web, perhaps irrevocably.

The Canadian government is holding the grey seal responsible for this. They argue that the seals, which are growing in number, are preventing the recovery of the stocks and are planning to kill 70,000 of them next year.

This has vexed a group of marine biologists at Dalhousie University so much that they wrote an open letter arguing that cod are rarely preyed upon by the seals. Instead, the cod’s main predators are other, larger fishes. And in actual fact, the seal preferentially feeds on these fishes. So any reduction in seal numbers will produce the opposite result to the one intended, seals will be killed, the predatory fish population will increase, and the cod population will decline even further.

Correlation does not imply causation. But perhaps, the view of the Canadian government is that of Winston Churchill who once remarked, scientists should be on tap, not on top. It will be interesting to see how this one plays out.

Author

Adam Kane: kanead[at]tcd.ie

Photo credit

wikimedia commons

Tag: fisheries

Is a seal cull needed to protect fish stocks?

Cod, correlation and causation