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Trends in bycatch rates of cetaceans in the north-west Iberian Peninsula between 1999-2008.

Read F L1,2, González A F1, Goetz S2, Ferreira M3, López A4, Martinez Cedeira J4, Santos M B2 & Pierce G J2,5

1Instituto de Investigaciones Marinas (C.S.I.C), Eduardo Cabello 6, 36208 Vigo, Spain

2Instituto Español de Oceanografía, Centro Oceanográfico de Vigo, PO Box 1552, 36200, Vigo, Spain

3 CBMA/SPVS, Departamento de Biologia, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal

4 CEMMA, Apdo. 15, 36380, Gondomar, Spain

5School of Biological Sciences (Zoology), University of Aberdeen, Tillydrone Avenue, Aberdeen, AB24 2TZ, United Kingdom

The north-west Iberian Peninsula is one of the world’s main fishing regions and cetaceans are very abundant in the area. A previous interview survey of fishermen suggested a high and potentially unsustainable cetacean by-catch rate (up to 1700 animals per year). Since 2008, 553 further interviews have been conducted concerning marine mammal-fisheries interactions. Trawl and gillnets have the highest reported rate of cetacean mortalities, almost entirely of Delphinus delphis. Most interviewees said that interactions with cetaceans are not problematic and that the economic effects of interactions, e.g. damage to nets, are negligible. Delphinus delphis are commonly sighted offshore and Phocoena phocoena coastally. Evidence of fisheries interactions was found in 60% of ‘fresh’ stranded D. delphinus. In Galicia, 42% of ‘fresh’ P. phocoena strandings have indications of by-catch, increasing to 58% in northern Portugal due to the use of beach seines. Age, maturity and pregnancy data from stranded animals are used to construct life tables and to estimate overall mortality and reproductive rates. By-caught animals were significantly younger than non-by-caught animals. Estimated annual mortality rates were 12% and 15% in the D. delphinus and P. phocoena populations respectively, and necropsy data suggest almost half of this mortality is attributable to fisheries interactions. This would give annual mortality rates due to fisheries greatly in excess of the 2% limit set by ASCOBANS.

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