Ecological indicators and gear-based management of Algarve coastal fisheries

Conduto, Telma Lúcia Pereira dos Santos Coelho

http://hdl.handle.net/10400.1/636

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Authors

Conduto, Telma Lúcia Pereira dos Santos Coelho

Advisor(s)

Erzini, Karim

Abstract(s)

A number of ecological indicators were used to study the impact of fishing gear on the Algarve marine ecosystem. Catch composition, species richness, diversity, mean length, trophic level, percentage of mature and optimum sized fish and percentage of megaspawners were determined for the fish catches of each gear type. Four types of static gears (gill nets, trammel nets, bottom longline and semi-pelagic longline) with different mesh sizes or hook sizes represented the small-scale fisheries and were studied using data from experimental fishing trials, while commercial catches of two trawling types, crustacean trawling and fish trawling exemplified the industrial fisheries. Different species dominated the catches of the different main gears. Gill nets were clearly differentiated by the low trophic levels. Semi-pelagic longline caught larger fish with high trophic levels. Trammel nets also had high percentage of mature individuals in the catches, but also more non-target species. The trawlers affected juveniles of many species. Larger mesh sizes caught larger individuals, though not necessarily mature. The ordination procedure revealed how gear catches are best characterized by the different indicators and catch composition. Technical interactions were apparent when some gears affected juveniles of target species of other gears. Management recommendations such as minimum legal size, closed areas, gear restrictions and modifications are provided. Fishers participation in management can be enhanced by explanations of these simple indicators. Public participation can be extremely important for supporting unpopular management measures.