Tuesday, September 22, 2009

What is success in sustainable fishing?

New Zealand hoki is a shining example of success or failure in fishery management, depending on who you ask. Mostly because of a decline in catch in the last decade.

There are other issues that matter, like bycatch of sharks and seabirds, and habitat impacts from trawling. But the most interesting part of the success/failure argument is the significance of the decline in hoki catch that happened in the last decade.

What does it mean when we see a decrease in the amount of a fish caught? Is this a sign of a collapsing fishery? Or is it a sign that managers are doing the right thing? People will claim both, and it's important to look at the details.

When a fishery is virtually unregulated, then declining catches are likely a sign of problems, such as a collapsing fish population. But when less fish are caught because managers reduce fishing limits, in response to scientific advice, then the shrinking catch may be a signal that sustainable management is responding to changing conditions.

A story in the New York Times presents a case for failure, but the Sustainable Fisheries Partnership presents a case for success. All based on the same set of facts about hoki.

Rather than speculate, I'll wait another year to see if hoki numbers increase or decrease. If the fishery is failing, then we should see further declines in the amount of fish. If management is sustainable, then the fishing decline should allow the fish to rebuild.

The latest sign is that managers claim hoki have already recovered to healthy levels. If that's true, then I lean more towards success as the correct story for hoki.


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Claire said...

If the catch limit is revised in response to scientific advice, that's evidence of responsive management, certainly. But isn't one of hallmarks of sustainable fishing that the population remains stable? Of course humans don't know everything and will have to revise fisheries strategies from time to time. My concern is fisheries managers who will say that they are being responsible by cutting catch numbers by some amount year after year, but not by enough to keep populations from continuing to decline. And in doing so push the species closer to the brink, yet making a nice show for the public so the extent of the problem is not realized until it's too late. I'm thinking of bluefin tuna here.

I suppose that I'm just skeptical that the reduction in hoki hasn't come about as a result of catch limits that were set very high before there was enough information to back them up - seems a common occurrence in fisheries management. Which to me is not a sustainable way to go about things. I guess we'll see.

Mark Powell said...

Claire, Good questions, and I think there's an answer. The science has been good for hoki, and managers largely followed scientific advice. For bluefin the situation is different, managers have largely ignored the scientific advice.

Decline in catch needs to be considered in light of the scientific advice and management response before a claim can be made about sustainability or lack of sustainability.

Hoki management has been much, much, much better than management of bluefin tuna, so the decline in catch for hoki means something different.

And no, sustainable management does NOT mean that stocks will be stable. Fish fluctuate naturally, and they often fluctuate dramatically from natural conditions. We know this from studies of fish stocks that were unfished by humans.

Claire said...

Mark, thanks for your reply. I suppose even if hoki isn't being overfished, I still am not really a fan of calling any fishery that uses bottom trawling and has so much bycatch "sustainable." I really think MSC needs to revise its standards to include bottom trawling as a destructive fishing practice.

Fishyfellow said...

There is an eastern and a western hoki stock. The eastern looks like it is doing ok, but the western went down to the Overfished or Depleted Zone in the recent period during which it was deemed sustainable by MSC, but has show a small increase in the recent period and is now at the bottom of the target zone. You can see the zones in a figure from the NZ Ministry of Fisheries that I posted on my blog http://fishyfellow.blogspot.com

It worries me a bit that the Target Zone and the Depleted Zone are so close for this stock. This is because of the high steepness in the stock-recruit curve which pushes the Bmsy to a low fraction of B0, the unexploited biomass.