Posts Tagged ‘Sable Island’

Culling Seals

Wednesday, April 24th, 2013
Cape Fur Seals breed on the coast of Namibia, where the annual 'hunt' removes about 90,000 seals, most of them pups (africareview.com)

Cape Fur Seals breed on the coast of Namibia, where the annual ‘hunt’ removes about 90,000 seals, most of them pups (africareview.com)

The Canadian government has approved a cull of 70,000 Grey Seals over the next four years to protect cod (guardian.co.uk)

The Canadian government has approved a cull of 70,000 grey seals over the next four years to protect cod (guardian.co.uk)

Seals of course eat fish. As opportunistic feeders, they’ll eat any fish they can catch.

When those fish decline in numbers or fail to recover when fishing is curtailed, a natural response has been to blame the seals.

Culling seals to protect fish populations of interest to human fishermen has been going on for more than a hundred years – California Sea Lions, Ringed and Grey Seals in the Baltic Sea, Harbor Seals in both BC and along US East Coast, Grey Seals on the US East Coast, Iceland, Norway, and the UK, and currently Cape Fur Seals in Namibia. In all cases seal populations experienced huge declines.

Culling, as opposed to harvesting, refers to killing the seals without intent to market them in some way. Though the market for seal parts is now close to non-existent, Canada considers its annual Harp Seal hunt to be harvesting, not culling.

Grey Seals on Sable Island: are they really responsible for failure of cod to recover? (truenorthimages.com)

Grey seals on Sable Island: are they really responsible for the failure of cod to recover? (truenorthimages.com)

But have the culls resulted in increased fish stocks for human fishermen? Oddly enough, nobody actually knows! There simply are no data, no experiments, nothing to indicate whether culling is effective or not. If anything, almost all of the examples suggest that no particular impact occurred on the target fish species.

Is there then any evidence we can point to indicating an effect of culling? This is of current concern, for Canada has approved a cull of Grey Seals to encourage the recovery of cod, and the Baltic States are considering a cull for the same reasons.

Fishermen want the cull, politicians are sympathetic, and marine scientists are unanimous in opposing culling. This is a familiar stand-off. What’s needed is evidence.

And now there is some, and it illustrates just how complicated ecosystem dynamics are.

Sable Island is an arc of sand on the Scotian Shelf, where Grey Seals breed in large numbers, in a region where cod were once abundant (oceantrack'org)

Sable Island is an arc of sand on the Scotian Shelf, where Grey Seals breed in large numbers, in a region where cod were once abundant (oceantrack’org)

It involves cod. Following the moratorium on fishing North Atlantic Cod following the collapse of stocks in the early 1990s, everyone assumed the stocks would recover. They didn’t. But Grey Seal numbers exploded to around 400,000, particularly those breeding on Sable Island on the Scotian Shelf, near one of the past major cod stocks. That seems to indicate that seals have suppressed cod recovery, and therefore culling ought to help.

475 ships have wrecked on Sable Island since the 17th Century. Feral horses are the only permanent residents (getimage.php)

475 ships have wrecked on Sable Island since the 17th Century. Feral horses are the only permanent residents (getimage.php)

Instead the story goes like this. When the Scotian Shelf populations of cod and haddock, both large bottom predators, crashed from overfishing in the early 90s, the result was a major restructuring of the food web, a ‘regime change’ of the sort we have now learned to expect to occur. With the loss of the cod and haddock, planktivorous fish like herring, capelin and sand lance, as well as macro-invertebrates like Northern Shrimp and Snow Crabs became abundant instead – hugely so in some cases, and they have supported alternative fisheries. A new and stable balance of species seemed to have developed, with cod and haddock unrecovered. Grey Seals numbers increased greatly during this time.

Herring exploded in numbers, but have now crashed (fisherycrisis.com)

Herring exploded in numbers, but have now crashed (fisherycrisis.com)

But this was not in fact a stable system. The biomass of fish in the system increased to an estimated 10 million tons, where carrying capacity is estimated to be less than half of that amount. The fish ran out of food – the zooplankton abundance crashed, the herring and capelin starved, and their populations crashed.

And then, with the herring and capelin gone as predators on cod and haddock larvae, cod and haddock have begun to recover. Particularly haddock. A return to the earlier food web appears to be underway, though how far it gets is unknown, for of course so much else is also involved, such as the impact of climate change, pollution, and continued fishing.

Cod show signs of some recovery (fisherycrisis.com)

Cod show signs of some recovery (fisherycrisis.com)

Haddock recovery is greater (fisherycrisis.com)

Haddock recovery is greater (fisherycrisis.com)

The really good news is that ‘regime changes’ can reverse back to what previously existed. And in this case, in this ecosystem, the evidence indicates that Grey Seals, though obviously eating fish, are not responsible for preventing the recovery of the cod over the past two decades.

Since culling seals probably has no impact on the recovery of overfished populations, decisions to cull them anyway are then political, disregard science, and are so unfortunate.

Grey Seals, Sable Island, waiting to be culled (theglobeandmail.com)

Grey Seals, Sable Island, waiting to be culled (theglobeandmail.com)