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(...published in the Halifax Chronicle Herald, March 30, 2005)

Predator-prey relationship not a simple equation

By DEBBIE MacKENZIE - Grey Seal Conservation Society (GSCS)

In your March 18 editorial, "Seal hunt foes lose their clout," you wrote that the seal hunt protest movement now seems to be a "fast-fizzling" bust.

This was thought to be "a comment on changing times, including improved methods of harvesting seals and wider recognition for and acceptance of a seal cull."

If only it were so simple, and if only the protest was all that is fizzling.

Media coverage of the seal hunt "debate" fails to include the broad-scale horrendous losses that have affected all sea life. Besides seal hunt protesters having "lost their clout," seals themselves have lost virtually their entire competition in the sea, as sharks and other big fish have disappeared en masse. Seals now swim alone as the sole surviving fish predator/scavengers in Atlantic Canada.

The vital "predatory" ecosystem service provided by seals and others is now much less available than it was decades ago, when their "prey" fish were healthier and far more numerous.

This has occurred despite recent increases in numbers of some types of seals, because seal numbers have not come close to making up for the loss of large predatory fish.

Natural predators work in ways that boost the physical health and growth of their prey. Should fish health start to fizzle, an increase in natural predators would be naturally beneficial.

The health of cod in Canadian waters has recently fallen to an all-time low as cod predators overall have disappeared. Could the loss of predators somehow be working to stifle fish stock recovery? Might the subtle "mutual support" aspect of the predator-prey relationship really have been that significant?

It certainly seems so. Newfoundland's Grand Bank was long dominated by large cod that preyed heavily on capelin. The simplistic line of "common sense" thinking about ocean predators that now allows "wider recognition for and acceptance of a seal cull," would predict that the bulk removal of the large Newfoundland cod should have resulted in a vastly increased abundance of uneaten capelin. However, what actually happened was the complete reverse: predatory cod disappeared and then the capelin stock, their prey fish, unexpectedly fizzled and collapsed behind them.

A series of developments similar to this has recently "baffled" DFO scientists, but it seems not to have alarmed them to the point where they refuse to condone the decimation of the last surviving natural marine predators, the seals.

Ominous losses known to DFO, but unknown to the "accepting" public, include a decline in resources crucial to the sustenance of fish: zooplankton abundance has fallen, as has the oxygen content of the water.

Part of the beauty of seals as fish predators lies in their ability to quickly transform weak or dying bottom fish into plankton-stimulating materials released in the surface water. As air-breathers, seals perform this vital predator/scavenger role while drawing no oxygen from the water themselves and this represents an important advantage today, especially in the Gulf of St. Lawrence where a large area of stagnant bottom water has become so oxygen-poor that cod can no longer survive there.

The worst thing that could be done, ecologically, in this situation, would be to cause a mass mortality of seals and then to dump their carcasses to rot on bottom, because this would predictably worsen the low-oxygen problem. All bottom life might fizzle.

On Tuesday, the harp seal hunt begins in the Gulf of St. Lawrence. Hundreds of thousands of fish predators will be killed, skinned, and their carcasses dumped to rot. If the public clearly understood what is wrong with this, we might just see a fizzling of the current apathetic acceptance of the seal hunt.

 

(GSCS)


Copyright 2005 The Halifax Herald Limited