Aquatic Environment and Biodiversity Annual Review 2012

AEBAR 2012: Non-protected bycatch
to seabirds, especially setnet. For each taxon, the risk was assessed by dividing the estimated number
of potential fatalities by an estimate of Potential Biological Removals (PBR, after Wade 1998). This
index represents the amount of human-induced mortality a population can sustain without
compromising its ability to achieve and maintain a population size above its maximum net
productivity (MNPL) or to achieve rapid recovery from a depleted state. In the risk assessment, PBR
was estimated from the best available information on the demography of each taxon (Figure 5.13).
Because estimates of seabirds’ demographic parameters and of fisheries related mortality are
imprecise, the uncertainty around the demographic and mortality estimates was propagated through
the analysis. This allowed uncertainty in the resulting risk to be calculated, and also allowed the
identification of parameters where improved precision would reduce overly large uncertainties.
However, not all sources of uncertainty could be included, and the results are best used as a guide in
the setting of research and management priorities. In general, seabird demographics, the distribution
of seabirds within New Zealand waters, and sources of cryptic mortality were poorly known.
Amongst the 64 studied taxa, black (Parkinson’s) petrel (Procellaria parkinsoni) clearly stood out as
at most risk from commercial fishing activities within the New Zealand Exclusive Economic Zone
(estimated annual potential fishing-related fatalities almost 10 times higher than the PBR, Figures
5.14 and 5.15). Seven other taxa had estimated annual potential fatalities with 95% confidence
intervals of their risk ratios completely above one. These were grey-headed albatross, Chatham
albatross, Westland petrel, light-mantled albatross, Salvin’s albatross, fleshfooted shearwater, and
Stewart Island shag. For a further 12 taxa, the confidence interval of the risk ratio included one.
Small inshore fisheries, especially trawl fisheries targeting flatfish, and small bottom and surface
fisheries, were associated with the highest estimated risk to seabirds. This was due to a combination
of low observer coverage, high effort, and overlap with the distributions of many seabirds. In fisheries
where there were few observations, the number of potential fatalities was estimated in a precautionary
way, with the estimates being biased toward the high end of the range of values that were consistent
with the observer data. In these poorly observed fisheries, the risk estimates are often primarily
associated with the lack of information. Of the taxa that had a risk ratio greater than one, the risk for
four of them (grey-headed albatross, Westland petrel, Chatham albatross, and light-mantled albatross)
was associated with low observer coverage in inshore fisheries that overlap with the distribution of
these birds. Increasing the number of observations in inshore trawl and small vessel longline fisheries,
especially in FMAs 1, 2, 3, and 7, would increase the precision of the estimated fatalities. The risk
was estimated independently for each fishery, and it was assumed that the vulnerabilities of seabirds
to capture in different fisheries were independent. This has the consequence that birds (such as lightmantled
sooty albatross) may be caught infrequently in well observed fisheries, but still have high risk
associated with poorly observed fisheries.
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