Movements of grey mullet Liza aurata and Chelon labrosus associated with coastal fish farms in the western Mediterranean Sea

P Arechavala-Lopez,Jt Bayle-Sempere,D Fernandez-Jover,R Nilsen,P Sanchez-Jerez,I Uglem

doi:10.3354/aei00012

P Arechavala-Lopez, Jt Bayle-Sempere + Show 4 more

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https://doi.org/10.3354/aei00012

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Abstract

Grey mullet occur in abundance around sea bream and sea bass farms where they for- age on waste fish feed, a behaviour that could modify their natural movement pattern and distribu- tion. In this study, we used visual census to record grey mullet aggregations at fish farms in the west- ern Mediterranean Sea. We also mapped the movements of 2 species (Liza aurata and Chelon labrosus) between farms and adjacent coastal fishing areas, using acoustic telemetry. Grey mullet were frequently observed in the vicinity of the aquaculture cages and represented an important abundance and biomass at the farms. The presence and swimming depth of the tagged mugilids at any of the farms were neither significantly related to the time of the day nor the feeding period, except for C. labrosus, which showed a tendency towards deeper waters (~15 m) during feeding peri- ods. Some of the tagged fish stayed in the vicinity of the farms for longer periods and also moved fre- quently to other farms and nearby commercial fishing areas. Other tagged fish remained at the release location for shorter periods, before they moved out of the study area or possibly were caught by local fishermen. This is the first study using acoustic tagging in wild fish around Mediterranean fish farms that demonstrates that offshore aquaculture farms and local fishing grounds in the western Mediterranean Sea are connected through movements of wild fish. These farms attract and affect large numbers of commercially important fish species; probably causing ecological changes not only in the immediate proximity of farms but also several kilometres away from the farms.

Highlights

A wide range of wild fish species are attracted to coastal aquaculture farms, where they shelter and/or feed on organic matter from cages and organically enriched sediments (e.g. Carss 1990, Dempster et al 2002, Tuya et al 2006)
Grey mullet occur in abundance around sea bream and sea bass farms where they forage on waste fish feed, a behaviour that could modify their natural movement pattern and distribution
Other tagged fish remained at the release location for shorter periods, before they moved out of the study area or possibly were caught by local fishermen. This is the first study using acoustic tagging in wild fish around Mediterranean fish farms that demonstrates that offshore aquaculture farms and local fishing grounds in the western Mediterranean Sea are connected through movements of wild fish

Summary

INTRODUCTION

A wide range of wild fish species are attracted to coastal aquaculture farms, where they shelter and/or feed on organic matter from cages (faeces and pellets) and organically enriched sediments (e.g. Carss 1990, Dempster et al 2002, Tuya et al 2006). Attracted marine fishes could move frequently and quickly among farms, visiting different facilities in the same area, as has been demonstrated for saithe Pollachius virens in Norwegian fjords (Uglem et al 2009) This behavioural pattern could make wild fish potential — and hitherto not recognised — vectors for transmission of diseases and parasites among farms or to wild fish stocks. We sought to (1) document grey mullet aggregations in close proximity to sea cages, (2) study the movement of mugilids among fish farms and to adjacent coastal fishing areas and (3) assess the presence at and pattern of association to the farms in relation to time of day and feeding time for 2 mugilid species, Liza aurata (Risso, 1810) and Chelon labrosus (Risso, 1827)

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DISCUSSION