In theory I’m still on sabbatical and this blog should be dormant, but I just can’t help myself. I have to climb on my soap-box and open my big aquatic scientist mouth.

So what’s got me worked up enough to break my self-imposed silence? The imminent arrival of the FV Margiris, the world’s second-largest trawler, currently on its way to Tasmania to take up a licence for fishing jack mackerel (Trachurus declivis & Trachurus symmetricus) & and redbait (Emmelichthys nitidus).

There’s been a lot of noise in the media about this “super-trawler”, reflecting a lot of unhappiness in the community at large. Despite the promise of much-needed jobs in northern Tasmania, the local community is strongly opposed to the Margiris’s arrival, fearing devastating impacts on local fish stocks and the long-term sustainability of the local fishery. It’s not often you see environmentalists and fisher-folk standing arm-in-arm in Australia (just look at the debate over marine reserves), but right now common concerns are bridging the historical divide.

The 142 m long ship can process over 250 tonnes of fish per day, towing a 300 m net through the water. It’s a pelagic trawler, which means the net doesn’t scrape the bottom, but rather scoops through open waters, funnelling fish and other marine animals through its 2 800 m² mouth. The operators, Seafish Tasmania, claim the trawl net is fitted with proven marine mammal exclusion devices and that by-catch is minimised. I can only hope they’re right.

The Margiris holds a licence for an 18 000 tonne* quota of jack mackerel and redbait to be fished over the Australian Small Pelagic Fishery Area. How many fish is this? Given rough estimate of 1 kg per fish (based on size to weight ratios), that’s 18 000 000 fish per year!

Opponents are worried about both whole-of-fishery and local-scale stock depletion: that the Margiris will take more fish than the ocean can sustain. The quota has been set by the Australian Fisheries Management Authority, in theory based on sound science, but there’s no great surprise that the community is sceptical. AFMA doesn’t have the best track record in accurately estimating sustainable yields and no-one in Tasmania has forgotten the near-extinction of the orange roughy, so let’s take a look at the science behind the Margiris’s quota: AFMA admits that the data used to calculate sustainable catch levels is 8 years old. Given the age of the data and the fact that it wasn’t collected for quota-determination purposes, it’s fair to question the reliability of the data. AFMA claims to have taken this uncertainty into account by setting the quota at the most conservative level of for sustainability derived from the data set. But is this good enough?

The truth is we can’t honestly model the impacts of fishing at this scale on the ecosystem. Modern science simply doesn’t have enough information or understanding of the complex factors and interactions involved in moderating marine ecosystems. There are incredibly complex food webs involved, a lack of information on fish movements, genetic exchange and breeding patterns, and huge gaps of our understanding of the impacts of weather and climate on breeding and survival rates. Fish stocks vary in response to many factors including climate cycles (El Niño versus La Niña years), water quality and chemistry, terrestrial run-off, predator pressure, habitat quantity, quality and connectivity and a multitude of other factors. The inter-relationships and feedback loops between these factors are complex and poorly understood. To add to the uncertainty, eight years is a long time in fishery population terms and we have no information on recruitment rates since the data was collected. Much could have changed in that period of time.

Add to that the impacts of a changing climate. Ocean temperatures and currents are changing and no research has been done on the impact of these changes on redbait & jack mackerel stocks. The climate will continue to change and we have no way of accurately predicting the future impacts of these changes on our fisheries. Given the high level of uncertainty, taking the lower yield estimate from eight-year-old data can hardly be called the conservative approach! To truly apply the precautionary principle I think it would be fair to initially harvest half the current quota, and to put in place a monitoring program to verify the impacts on the fishery over several generations and recruitment events.

Word is, however, that reducing the Margiris’s quota would make the venture financially unviable. So we have a fishery that’s only marginally profitable – given a pretty liberal estimate of fish stocks and a large quota – in an area with strong community opposition and significant concerns over local environmental, social and economic impacts. That really doesn’t sound like a sustainable business to me!

I don’t think the Margiris belongs in Australian waters under its planned operational regime, and I’d question the viability of super-trawler fishery operations anywhere on this watery planet. We already have a sad legacy of collapsed fisheries around the world; please don’t risk plundering our waters for short-term profits and a lack of rigorous science.

For balanced, fact-based information about the super-trawler debate, check out the following references and make up your own mind:

• ABC 7:30 Report investigation
• ABC Background Briefing coverage 
• Seafish Tasmania FAQ page
• Australian Fisheries Management Authority Margiris FAQ page
• Department of Environment & Heritage: Australian small pelagic fishery report
• Australian Small Pelagic Fishery Management Plan (2009)

If, like me, you still think the Margiris is a bad idea, add your voice to the protest over at stopthetrawler.net