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19510
Open
SC/68D/HIM/10
Iberian harbour porpoise - an update on fishery bycatch mortality
Graham J. Pierce, Marie A.C. Petitguyot, Paula Guti?rrez-Mu?oz, Diego Fern?ndez- Fern?ndez, Andrea Fari?as-Bermejo, Fiona L. Read, Camilo Saavedra, Alfredo L?pez, Jose Mart?nez-Cedeira
IWC
Several recent studies have suggested that the Iberian harbour porpoise is genetically and
morphologically distinct and may represent a separate subspecies. The main threat facing this
population is fishery bycatch. Recent data on porpoise bycatch are available from strandings
and on-board observations. Generally, more bycaught porpoises are recorded from strandings
than from on-board observations. Portugal has previously reported porpoise bycatches based
on on-board observation in Iberian waters, although Spain has consistently reported zero
porpoise bycatch Data from on-board observations of porpoise bycatch in Iberian waters
(2005-2021) submitted to ICES WKMOMA appear to be anomalous in that they apparently do
not include the majority of bycatch records previously submitted to ICES WGBYC. The
minimum annual estimate of bycatch mortality, consisting of documented bycatch mortalities
from strandings and observers in both Spain and Portugal, is around 0.5% (14 animals per
year). Both types of data can be used to estimate both total bycatch and bycatch rate, given
a population size estimate and (in the case of strandings) an overall mortality rate derived from
a life table. In both cases, it is necessary to assume that samples are representative in order
to scale up to the population level, and in both cases this is rather unlikely. Nevertheless, the
results from all data sources are remarkably consistent, suggesting an annual bycatch
mortality rate of no less than 8% (around 230 individuals) per year.
