On fish and uncertainty: more musings on the Margiris

The lovely Pauline Mak recently requested that I discuss the science behind my opposition to the FV Margiris “super-trawler” in a little more detail. Specifically, she quite rightly asked me to explain why I felt the quota was unsustainable given that respected fisheries scientists like Professor Colin Buxton and Dr Bob Kearney have spoken out in defence of the quota. If I’m going to cite my science degree to claim an informed perspective on the super-trawler issue I really ought to be backing it up with facts!

> You can read my original entry here.

First off, let me clarify that I am not a fisheries scientist. I’m an aquatic ecologist who specialised in freshwater systems and integrative ecology. Once upon a dim, dark undergraduate past I studied fisheries science before deciding that messing about in rivers was much more my thing. Fish ecology and aquatic ecosystems are, however, things I’m passionate about and I’d like to think I’m reasonably well-informed. Plus being a systems/integrative ecologist I’m trained to think in terms ecological interactions and broader ecosystem changes, which I think is relevant to the Margiris case.

So let’s get into it, shall we?

The quota currently set for the Margiris is 18 000 tonnes, or 7.5 % of the total estimated population of jack mackerel and redbait. Is this sustainable? My honest answer is: possibly.

7.5 % is a very conservative quota. For many fisheries a quota around 10 to 15 % is considered sustainable, and for some quickly reproducing species in productive waters, takes of up to 30 % may be managed. The species to be targeted – jack mackerel and redbait – are fairly short-lived species that do breed quickly and have bounced back from previous fishery activity, suggesting the populations are fairly resilient.  On the face of things, 7.5 % seems ok, but when I think about it a little more, concerns start to surface.

The first big worry is where the stock estimates come from. Some of the data used to set the fishery quota dates back to studies done in 2002-2004. Normally, the age of the data would not be a concern since there has been no commercial fishing activity in that time, thus no reason for fish numbers to have decreased. Normally: we’ve never really had to think about the impacts of climate change on fish populations before.

Recent CSIRO studies have revealed that fish populations in southern Australian waters are changing in response to climate change, and changing faster than predicted. The ranges of temperate species like jack mackerel and redbait are shrinking. On top of this, tropical species are shifting further south and no one knows yet how the changing species interactions are impacting on predator-prey relationships and marine food webs. Given this environment of rapid, unpredictable change, 8-year old data doesn’t really seem good enough.

Is 7.5 % of an estimated fish population sustainable, in light of the impacts of climate change on ocean ecosystems? Uncertain! We simply don’t have the data or ecological knowledge to say for certain, one way or another. Throw in the uncertainties around local fish depletion, the amount and species of by-catch and potential issues regulating the vessel and you start to understand why some scientists are concerned. Sure, the Margiris is unlikely to cause a catastrophic fishery crash but there’s enough uncertainty there to be questioning if the quota poses an acceptable risk.

So what is an acceptable risk? It all comes down to error: Type I or Type II.

We have 2 potential outcomes: the null hypothesis, that the quota is sustainable, and the alternative hypothesis, that the quota is not sustainable. The fisheries science to date suggests that the null hypothesis is correct, but there is a concerning level of uncertainty around that data. What are the consequences if we’re wrong?

  Null hypothesis is true:

Margiris quota is sustainable

Null hypothesis is false:

Margiris quota is unsustainable

Reject null hypothesis:

Stop the trawler

Type 1 error:

Fishery could have sustained quota but remains unfished

True positive:

Fishery unsustainable and trawler stopped

Accept null hypothesis:

Allow the trawler

True negative:

Fishery sustainable and successfully fished

Type II error:

Fishery exploited beyond sustainable yields

So, if my concerns are false but the trawler is stopped or the quota reduced, a Type I error has occurred, but the consequences of that error are pretty minor. SeaFish Tasmania loses some money, AFMA (www.afma.gov.au ) loses a contract and the Margiris’s European owners lose a potential market selling the catch to Africa. Forty theoretical Tasmanian jobs disappear.

If my concerns are true and the trawler fishery goes ahead as planned, a Type II error has occurred. The consequences here are a little uncertain but potentially much more serious. We could see local fish stock depletion, changes in marine food webs, loss of local predatory fish species, changes in fish communities and impacts on local fisheries. We could see jack mackerel and redbait numbers crash, with unknown ecosystem consequences. It’s not certain to happen. It may not even be likely to happen, but the uncertainty is high enough that I believe it’s a significant risk.

I don’t believe we’ll see an orange roughy scale disaster with the Margiris, but I do believe there are serious risks related to her operations and quota and think we should apply a precautionary approach. Personally, I’d like to see the quota lowered to 5 % with monitoring of fish populations over next 3 years to:

  1. Confirm stock estimates, including identifying any evidence of shifts in response to climate change;
  2. Confirm no evidence of localised depletion or loss of genetic diversity; and
  3. Confirm no resultant shifts in predator populations.

When I take into consideration my other concerns about the Margiris – that she and ships like her have been implicated in fishery collapse in European and African waters, that she is a vector for the spread of marine diseases and invasive species, and that the industrial nature of her operations means she’ll only provide employment for 40 locals – I believe the risks outweigh any potential benefits. Add to that the environmental impact of sending a ship from Europe to operate in Australia for fish to sell in Africa and it doesn’t look sustainable at all; environmentally, socially, financially or ethically.

This is why I still say no. Pauline, I hope this answers your questions!

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