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Fisheries urged to diversify their 'take'


Can we have our fish and eat them too? (Source: iStockphoto)


Australian fisheries scientist Dr Tony Smith, of CSIRO's Wealth from Oceans Flagship in Hobart, and colleagues, lay out their argument for 'balanced exploitation' of the oceans in the Proceedings of the National Academy of Sciences this week.

"What we're looking for is a way to still be able to harvest from the sea but not have such large ecological impacts," says Smith.

"The 'balanced exploitation' approach is suggesting a lower overall exploitation rate - particularly with regard to some of the currently intensively fished species - with the trade off that you exploit a larger part of the ecosystem."

Traditionally, fisheries set quotas to ensure the survival of particular individual species.

But, says Smith, in the past 10 years, there has been a shift to what is called "ecosystem-based fisheries management" (EBFM).

This approach considers the interaction between fished species and other parts of the ecosystem.

For example, he says, in setting quotas for rock lobsters, consideration should be given to their interaction with sea urchins.

Rock lobsters can eat sea urchins, which if not kept in check can overgraze and prevent kelp forests from developing.

EBFM also tries to minimise the impact of fishing on bycatch, threatened species and breeding grounds, which can be destroyed by bottom trawling and dredging.

'Selective fishing'

Smith says that by and large, EBFM has been a "positive development".

But, he says, its frequent focus on selective fishing of particular species, particular sized fish, and particular areas could be a problem.

Smith and colleagues have pieced together growing evidence that shows more selectivity isn't necessarily better.

"There's now a fair bit of research to support the view that selective fishing can also have impacts on biodiversity and on marine ecosystems, and those need to be considered as well," says Smith.

For example, he says, one particular fishery may time their harvest to catch most of their target species before they reproduce.

But, in doing this, they will genetically select for fish that reproduce earlier or later than the majority, when conditions for survival are not optimal.

Another fishery may harvest more mature fish, but in doing so encourage reproduction by less mature fish, which may produce less viable eggs.

Smith says even protected marine areas can have an unintended negative side-effect, by putting more pressure on areas immediately outside the protected areas.

"A closure is usually brought in to protect biodiversity but can have unintended consequences on biodiversity, outside the closed area," he says.

'Balanced exploitation'

Smith and colleagues say humans should utilise a wider range of species to take pressure off those species that are being overfished.

He says, as well as broadening our palate we could avoid using fish we eat for dinner to feed agricultural animals and to produce fish oil.

"A lot of species lower in the food chain are not exploited at all the moment," says Smith.

But, he says, obviously there is a limit to how much can be consumed.

"Clearly the overall productivity of the oceans is limited by primary production so there is a finite limit to how much we can expect to harvest from the oceans."

Tags: oceans-and-reefs, fishing-aquaculture, fish