| Abstract |
Greece, Spain, Italy, Turkey and France are the major contributors to the total Mediterranean and European aquaculture. The main farmed species in the Mediterranean region are the gilthead sea bream (Sparus aurata) and European sea bass (Dicentrarchus labrax), while particularly in Greece their species make up for 95% of the total national fish production. With the recent tremendous growth of the Mediterranean fish industry during the last two decades, fish escape from sea cage facilities increases the pressure upon a forthcoming sustainable industry.
Fish escapes have been reported for almost all the European farmed species, including sea bream and sea bass. Fish escapes disclose a considerable socio-economic effect to the relevant countries, with additional disclosed ecological and genetic impacts on the marine environment. As a considerable indirect effect from fish escape is the reduction on the fame of the industry and of course the loss of money and also several conflicts with groups related with the protection of the environment. Additionally, as the last stage, consumers might pay more for a fish that has been mistakenly considered as fisheries. Further, interaction with the wild stocks, interbreeding, food and mate competition and transfer of pathogen and parasites are major examples of serious environment interactions. The main cause of fish escape is a combination of structural failure of equipment with severe environmental conditions, such as strong winds and storms. Predators and pelagic animals attacking the offshore farm facilities are also another cause for fish escape. Recently, species-specific behavioral attributes have been also correlated with a potential risk of escape. Indeed, fish farmers have widely documented interactions towards the net pen, concerning net inspection and bite, mostly regarding Atlantic cod (Gadus morhua) and sea bream. These interactions, also called “pre-escape” behavior disclose a potential risk of net damage and a creation of a hole that will eventually lead to fish escape. However, knowledge of the related factors, both biotic and abiotic, that affect sea bream and bass escape behavior as well as the relative net interactions that potentially lead to net damage is almost nonexistent until now.
The main objective of this thesis was to provide basic knowledge regarding the related factors that affect the escape behavior of the main Mediterranean farmed species. In addition, species-specific attributes that lure farmed fish to interact with the cage net, create holes on the surface and escape are discussed. Pre-escape behavior is further evaluated in accordance with the condition of the net pen, based on different nets commonly found in farm facilities. Simulated small-scale experiments in laboratory conditions were performed and specially developed video processing and image analysis systems were used so as to evaluate species-specific behaviors in aquaculture. Moreover, preventive measures and implementations to avoid large-scale events are discussed. […]
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