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Effect Of Escapees On Wild Fish And MPAs

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Speaking at Aquaculture Europe 2011, Kilian Toledo Guedes from the University of Alicante looks at the effects escapees have on the environment and wild fish in Marine Protected Areas (MPAs). Charlotte Johnston, TheFishSite editor, reports.

The research was carried out at the Canary Island of La Palma.

The Canary Islands is the largest producer of seabass in Spain, said Mr Toledo - Guedes, with 30 per cent of Spanish production based in La Palma.

Bass and bream are both prominent species after being introduced in 2000, and are farmed in semi-exposed floating fish cages.

Between December 2009 and February 2010, two sea storms hit the island. With 4.6 m high waves, four sea cages were completely destroyed and many more seriously damaged.

Because of this, it is estimated that between 200 to 400 tonnes of bass and bream were released. Mr Guedes said that the number of escapees varies greatly depending on the source.

A MPA is situated 15 km south of the release point.

The two aims of the study were to monitor the temperature and spacial distributions of seas bass escapees on MPAs, and secondly to evaluate the influence on the captures of the artisinal fishing fleet on the island.

10 localities were identified, where samples would be taken, 60 km was the sample point furthest from point escapees. The size and number of escapees spotted were recorded. A total of 720 visual census of escapees were carried out. Moreover selling data by species and weight, declared by professional fishers from January 2009 to December 2010, were analyzed to reveal the impact of the massive escape on local fisheries.

The fish were easy to identify as escapees as they are not local to the area.

Escaped sea bass were found at all localities in each sample period. Escapees density varied greatly. The catches of aquaculture origin species never represented more than five per cent of total fish captured during 2009. However in January 2010, an increase of both aquaculture species and their relative importance is noticed.

A decrease trend of these values is observed through 2010, but catches were still higher than before the massive escape in December 2010.

The results show how massive escapes affect widely both shallow water ecosytems and fisheries dynamics. After the large escape mentioned above, sea bass were observed as much as 60 km away from the escape point.

As there is no fishing pressure in the MPA, escapees have higher resilience. On the other hand, fisheries are affected clearly by escaped fish, as some months after the escape, 38 per cent of fish caught were escapees.

Mr Toledo-Guedes said that the study highlighted the need of a complete risk assessment plan before the installation of new aquaculture facilities - with special attention given to the presence of MPAs.

He said that professional fishing seems an efficient way to remove escapees from the wild. With this in mind, Mr Toledo-Guedes suggests the development of emergency plans in close collaboration with local fishermen to minimise possible impacts, especially across the most sensitive areas.

Another suggestion that Mr Toledo-Guedes and his team came up with was for authorities to build up an adaptative management of the MPA and allow (under supervision) the fishing of escapees even in no-take areas of the MPA to mitigate the impact on native fish populations.

December 2011