Loading...
Publication
Estudo do devir das rejeições ao mar com um veículo de operações remota (ROV)
| Name: | Description: | Size: | Format: | |
|---|---|---|---|---|
| 5.61 MB | Adobe PDF |
Authors
Advisor(s)
Abstract(s)
A pesca de arrasto de crustáceos é uma actividade piscatória que produz grandes quantidades de descargas ao mar - rejeições, constituídas por espécies sem valor
comercial. Sabe-se que o volume do material rejeitado é muito elevado, mas pouco ou nada se sabe quanto ao seu devir a partir do momento em que “desaparece” na coluna de água.
É de esperar que uma grande proporção deste material morto atinja o fundo, ficando
disponível para os necrófagos bentónicos, não se conhecendo os seus efeitos sobre as
comunidades bentónicas.
Pretendeu-se com o presente trabalho estudar o devir do material rejeitado ao mar pela
pesca industrial de arrasto de crustáceos, utilizando uma abordagem em situação real,
através da simulação, em condições controladas, da largada ao mar de material “rejeitado” e seu fornecimento às comunidades bentónicas, em áreas alvo de arrasto de crustáceos.
A utilização de um veiculo de operação remota (ROV - “Remoteiy Operated Vehicie”)
permitiu um estudo directo e em tempo real, pois está equipado com uma câmara de vídeo, ligada, através de um umbilical à unidade de superfície, onde as imagens são visualizadas.
Com o objectivo de estudar o processo de afundamento do material rejeitado, foi efectuado um conjunto de experiências de acompanhamento com o ROV do afundamento de simulacros de rejeição, desde o momento em que foram largados à superfície. Em 19 casos foi possível fazer o seu acompanhamento até profundidades superiores a 50 m e em 6, até ao fundo - a profundidades entre 95 e 213 m.
A considerable portion of the catch of crustacean trawl fisheries, mainly species with no commercial value, is discarded overboard. Little is known of the fate of this bycatch from the moment that it “disappears” in the water column. lt is expected that a large number of dead individuals will reach the bottom becoming available to benthic scavengers, with unknown effects on the benthic communities. The main objective of this work was to study the fate of the commercial crustacean trawl fisheries discards. The experimental setup consisted of Simulation, in controlled situations, of the discarding of material and also its introduction to the bottom communities targeted by crustacean trawling. The use of a remotely operated vehicle (ROV) allowed for a direct and real-time approach, since it is equipped with a video camera connected through an umbilical to a surface unit where images can be watched. In order to understand the sinking process of discarded material, several experiments were conducted: dead individuals were discarded and followed with the ROV through the water column. In 19 experiments, individuals were followed the discards down to more than 50 m; in 6 down to the seafloor, at depths ranging from 95 to 213 m.
A considerable portion of the catch of crustacean trawl fisheries, mainly species with no commercial value, is discarded overboard. Little is known of the fate of this bycatch from the moment that it “disappears” in the water column. lt is expected that a large number of dead individuals will reach the bottom becoming available to benthic scavengers, with unknown effects on the benthic communities. The main objective of this work was to study the fate of the commercial crustacean trawl fisheries discards. The experimental setup consisted of Simulation, in controlled situations, of the discarding of material and also its introduction to the bottom communities targeted by crustacean trawling. The use of a remotely operated vehicle (ROV) allowed for a direct and real-time approach, since it is equipped with a video camera connected through an umbilical to a surface unit where images can be watched. In order to understand the sinking process of discarded material, several experiments were conducted: dead individuals were discarded and followed with the ROV through the water column. In 19 experiments, individuals were followed the discards down to more than 50 m; in 6 down to the seafloor, at depths ranging from 95 to 213 m.