[ASC-media] CSIRO: Removing predators could offset seabird 'bycatch' losses
Rebecca.Eveleigh at csiro.au
Rebecca.Eveleigh at csiro.au
Thu Jul 19 07:20:22 CEST 2007
19 July 2007
Removing predators could offset seabird 'bycatch' losses
Removing invasive predators from island breeding colonies could save
more seabirds for less cost than reductions in fishing, a study of
Australia's Eastern Tuna and Billfish Fishery (ETBF) has found.
According to one of the authors of a paper on the findings in the August
edition of Frontiers in Ecology and Environment, CSIRO scientist Dr
Chris Wilcox, a major challenge for fisheries worldwide is to reduce
their impact on 'bycatch' species such as seabirds.
"Australian Commonwealth fisheries have made strong efforts towards
reducing bycatch, including modifying fishing gear and restricting areas
and periods of fishing, but these measures are not always effective,
leading to costly interventions such as fishery closure," Dr Wilcox
"While the priority should always be for fishers to avoid bycatch, they
could also 'offset' the bycatch that does occur by funding conservation
measures that tackle other, often greater, threats to bycatch-affected
Dr Wilcox and C. Josh Donlan of Cornell University explored the offset
approach in a study of flesh-footed shearwater bycatch in the ETBF,
which targets yellowfin and bigeye tuna, albacore and billfish.
Practices used in the ETBF to reduce the capture of seabirds on
longlines are costly and not always effective for all species. A species
of concern is the flesh-footed shearwater, which in eastern Australia
breeds only on Lord Howe Island where rats are potentially a major
Dr Wilcox and Mr Donlan compared the potential impact of fishing with
that of rat predation on Lord Howe Island flesh-footed shearwater
populations, and the costs and benefits of rat control and fishery
They found that banning fishing in a 750-kilometre radius of the island
would result in a six per cent increase in growth rate of the shearwater
population, at a cost of about A$3.5 million. The eradication of rats
would result in a 32 per cent increase in the population growth rate, at
a cost of about A$580,000.
Rat eradication therefore could yield a conservation return on
investment 23 times greater than a fishery closure, and could have
broader ecosystem benefits.
"Vessel levies could be set at the cost of offsetting their bycatch," Dr
Wilcox says. "As well as funding actions that effectively offset the
bycatch, the levy would encourage fishers to seek innovative ways of
He says environmental groups have made great strides in drawing
attention to the bycatch problem. Fishers, technologists and scientists
in turn have reduced bycatch substantially through fishing-method
"For fisheries to have a zero impact on bycatch, however, they will need
to use the full suite of cost-effective tools available, in a
responsible and integrated way," Dr Wilcox says.
Dr Wilcox and Mr Donlan believe that given the number of seabirds and
other mammals affected by fisheries and invasive species, the offset
approach could prove effective in many scenarios worldwide.
Dr Chris Wilcox, CSIRO Marine and Atmospheric Research 0448 349 465;
Chris.Wilcox at csiro.au
Bryony Bennett, CSIRO Marine and Atmospheric Research (03) 6232 5261;
Bryony.Bennett at csiro.au
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Island conservation shows promise for bycatch
A major challenge for fisheries worldwide is to reduce their impact on
non-target or bycatch species. Traditional methods of bycatch reduction
include modifying fishing gear and restricting the areas fished and
periods of fishing.
Gear modifications such as the use of turtle exclusion devices have
effectively reduced the capture of some bycatch species. In other cases,
avoiding unacceptable mortality levels has been difficult, leading to
costly interventions such as fishery closure. High-value fisheries that
have been closed due to their impact on endangered marine vertebrate
species include New Zealand's squid fishery and Hawaii's pelagic
For many bycatch species, however, fishing is not the only cause of
mortalities, and a redirection of resources to alleviate a greater
threat could prove a more effective means of conservation. This 'offset'
approach, known as 'compensatory mitigation', will be outlined in a
paper by Chris Wilcox of CSIRO and C. Josh Donlan of Cornell University
in the journal Frontiers in Ecology and Environment in August 2007.
Wilcox and Donlan evaluate the potential costs and benefits of
compensatory mitigation using the case study of seabird bycatch in
Australia's Eastern Tuna and Billfish Fishery (ETBF). They conclude that
bycatch offsets, in conjunction with direct bycatch mitigation efforts,
are an effective, enforceable, and cost-effective approach to seabird
Invasive mammals a greater threat
Many bycatch species spend part of their life on land where they are
subject to predation by invasive mammals. Predation by invasive mammals
on islands is the cause of the majority of vertebrate extinctions in the
past six centuries.
Predators such as feral cats and rats have decimated seabird breeding
colonies worldwide, preying on eggs, chicks, and adults of many species.
Three-quarters of seabirds listed by the World Conservation Union, or
IUCN, are threatened by invasive species, compared with less than half
threatened directly or indirectly by fisheries.
Given this situation, the removal of invasive predators from island
breeding colonies may save more seabirds for less cost than a reduction
in fishing pressure. The relatively low cost and high impact of predator
control at key seabird breeding colonies suggests that it might be a
feasible offset for fisheries bycatch, in cases where it is difficult to
reduce bycatch by the more direct means of avoidance or gear
A study in compensatory mitigation
Wilcox and Donlan tested the concept of bycatch offsets in the ETBF, a
longline fishery that extends from Cape York, Queensland, to the South
Australian/Victorian border. The fishery targets billfish along with
yellowfin, bigeye, and albacore tunas in the Australian fishing zone and
adjacent high seas.
Seabird capture is a major issue for the ETBF and mitigation measures
include prohibiting the setting of longlines during daylight, mandatory
use of heavily-weighted lines, and fisheries closures. But some of these
measures are thought to be costly, difficult to enforce, and in the end
may not provide adequate protection for some species.
While effective in reducing albatross bycatch, Australian operated
vessels have been reported to kill 1800-4500 flesh-footed shearwaters
(Puffinus carneipes) annually. With the entire eastern Australian
population breeding on Lord Howe Island and evidence of a decline,
fishery closures are possible.
However, fishing is not the only threat to flesh-footed shearwaters.
Other threats include habitat loss, predation by invasive predators
including rats and ingestion of plastic.
Wilcox and Donlan used annual population growth rates of flesh-footed
shearwaters and estimates of rat consumption of shearwaters on Lord Howe
Island to compare the impact of predation by rats with that of fishing.
They also compared the expected cost and conservation benefit of rat
control and fishery closures.
Their analysis showed that the closure to fishing of a 750-kilometre
radius around Lord Howe Island resulted in a 6% increase in population
growth rate of the shearwater population, at a cost of about A$3.5
million. Eradication of rats resulted in a 32% increase of population
growth, at a cost of about A$580,000.
Rat eradication from Lord Howe Island therefore could yield a
conservation return on investment 23 times greater than a fishery
Cost effective conservation
The ETBF example shows that bycatch offsets such as rat eradication
could achieve conservation benefits exceeding those of bycatch
Wilcox and Donlan believe that offsets, when used in the proper
framework, can constructively address a global conservation concern by
providing a mechanism for generating revenue for high-impact
conservation actions and forging alliances between conservation and
In the fisheries context, setting vessel levies at the cost of
offsetting their bycatch:
* creates individual incentives for fishers to avoid bycatch (and
to seek innovative ways of achieving this);
* avoids the "race to fish" prompted by fishery closures; and
* funds actions that effectively offset the bycatch that does
An important aspect of the approach though is to prioritise the
avoidance of impacts, and reduction of those impacts that do occur,
leaving offsets as the fallback tool where bycatch cannot be prevented.
An additional benefit is that suites of species, even ecosystems, would
benefit from the removal of invasive mammals and other on-island
Given the number of seabirds that are threatened both by fisheries
bycatch and invasive species, bycatch offsets are likely to prove
applicable and effective in many scenarios worldwide.
Offset approaches could re-establish seabird colonies on islands where
they have been extirpated, and be adapted to suit other species affected
For example, many endangered populations of sea turtles are affected by
factors such as human consumption of adults and eggs, nest predation by
invasive mammals, and fisheries bycatch from artisanal, in addition to
industrial fishing. Industrial fishing might be able to fund reductions
in these other threats, reducing the pressure on the turtles to a
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