Science does not support the super trawler!

Posted on 11. Sep, 2012 by in Advocacy, Research

One fish, two fish, red fish, blue fish: science doesn’t support the super trawler

By Jessica Meeuwig, University of Western Australia

This article was originally published at The Conversation.  Read the original article.

While fisheries science is more complex than Dr. Seuss’ iconic title implies, he had it right in two fundamental areas. We need to understand the species we are exploiting in our fisheries (red vs. blue) and we need to know how many there are. The science case for introducing a trawler to exploit southern small pelagics is weak in both these areas. As such, it does not support the introduction of super trawling in Australia.

The target species for this greatly expanded fishery include blue mackerel, jack mackerel, Peruvian jack mackerel and redbait. They are repeatedly referred to as “small pelagics”, “forage fish” , and “baitfish”.

Such labelling conjures teeming schools of Peruvian anchoveta and Atlantic herring associated with the highly productive waters of South American and South African western margins and of the North Sea. These recognised forage species share a set of life-history characteristics, such as high growth rates, low maximum age, and high reproductive output: they pursue the quintessential “live fast, die young” strategy. These characteristics increase their resiliency to exploitation, but aren’t enough to prevent their over-exploitation in the face of highly efficient industrialised fishing such as super trawling.

The “small pelagics” targeted by the super trawler do not share these resiliency characteristics. Our “small pelagics” are typically twice as large in maximum length as typical forage species (63 vs 33 cm), have a maximum life span 60% longer (21 vs 13 years), feed higher up the food chain, and grow 30% more slowly (0.17/year vs 0.62/year). Indeed, these characteristics make them statistically more similar to reef fish such as baldchin groper, recognised as over-exploited. It is unclear how the robust recommendations from the Forage Fish Task Force apply to non-forage species. We should not be treating these animals as a highly productive resource on which we experiment with super trawlers, but rather as valuable wildlife in Australia’s low-productivity southern oceans.

Some are concerned about the potential for localised depletions when super trawlers are active. To address those concerns, we need to understand how local populations are replenished by young fish across the region and whether adults can replenish depleted areas. There is increasing evidence that the adults of many species are not as mobile as previously thought.

But we are largely ignorant about the effective population structure of these species. Of the four species considered for exploitation, the population structure of blue mackerel is uncertain, and jack mackerel and redbait are believed to have eastern and western subpopulations. No dedicated population studies have been conducted on redbait nor is any information available for Peruvian jack mackerel. Moreover, little is reported about adult movements of any of these species except that larger jack mackerel are found in deeper waters.

The total allowable catch of approximately 18,000 tonnes is a 10-fold increase over previous years’ landings. In setting it, the Government is relying on its ability to determine the un-fished biomass; that is, its ability to count fish. But its estimates are generally based on old information (in the east, blue mackerel information is from 2004), inferred from other species (for jack mackerel in the east) or entirely absent (for jack mackerel in the west, Peruvian jack mackerel in the west, and redbait in the west). It is likely that biomass estimates (and associated quotas) are much more uncertain than is currently reported. Indeed, ABARES assessments of population status are based on fishing effort rather than actual population size.

Australia’s relatively strong fisheries management has been cited as a reason why this experimental fishery expansion should occur. This is despite our poor understanding of the species and the high uncertainty in population sizes. Fisheries scientists and managers around Australia are to be commended on the quality of their research, particularly given the large number of targeted species, the relatively low value of many of the fisheries, and the consequent budget constraints for research.

But we should also consider salutary lessons. For example, the Western rock lobster fishery experienced unexpected and unprecedented low levels of recruitment in 2008 and 2009, despite the wealth of research conducted on the species and despite its Marine Stewardship Council certification. Fisheries management is difficult and should be highly conservative in its approach. The proposed allowance of an 18,000 tonne annual quota is not.

There are many other reasons not to allow super trawling including concerns over bycatch in substantially larger nets, low economic returns (reportedly of $1/kg) for a valuable resource, uncertainty around the effects of a warming ocean on fisheries productivity, and dependencies of other wildlife on these species. But even at the most basic level, the scientific case is not strong enough.

The Conversation


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