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- Using a modified Nordmøre grid for by-catch reduction in the Portuguese crustacean-trawl fisheryPublication . Fonseca, Paulo; Campos, Aida; Larsen, Roger B.; Borges, Teresa C.; Erzini, KarimBy-catch and discards are a common problem to all fisheries. Recent studies of the Portuguese crustacean-trawl fishery show that discards average 70% of the total catch. This situation poses a threat not only to the management of target and commercial fish by-catch species stocks, but also in terms of the ecosystem impact of the discarded species whose survival is generally low. Previous attempts to address this problem by using oblique separator mesh panels associated with square-mesh windows, or square-mesh windows alone, provided encouraging results, but these are unlikely to have commercial applicability at present. Therefore, we tested the efficiency of a modified Nordmøre grid in excluding some of the most captured non-commercial bycatch species, such as the blue whiting, Micromesistius poutassou, and the boarfish, Capros aper, evaluating simultaneously the losses of the crustacean target species (rose shrimp, Parapenaeus longirostris, Norway lobster, Nephrops norvegicus and red shrimp, Aristeus antennatus) and commercially valuable fish by-catch. A total of 41 valid hauls were carried out during 2001, and 15 in 2002 on board the R/V “Noruega”. Results from both years varied considerably, with higher by-catch exclusion rates, in weight, registered in the second survey (73–74 and 48–63% for blue whiting and boarfish, respectively). The corresponding percentage reduction for target species was 8–15% for the Norway lobster, 4–9% for rose shrimp and 7–10% for red shrimp. The level of exclusion of the non-commercial by-catch is encouraging, although short-term loss of Norway lobster, where the escapees comprised larger individuals, raises some concern with regards to fishers’ acceptance of mandatory use of grids.
- Modelling the impact of deep-water crustacean trawl fishery in the marine ecosystem off Portuguese Southwestern and South Coasts: I) the trophic web and trophic flowsPublication . Angeles Torres, Maria; Fonseca, Paulo; Erzini, Karim; Borges, Teresa C.; Campos, Aida; Castro, Margarida; Santos, Jorge Manuel Bastos; Costa, Maria Esmeralda; Marçalo, Ana; Oliveira, Nuno; Vingada, JoseThe concentration of the population in coastal regions, in addition to the direct human use, is leading to an accelerated process of change and deterioration of the marine ecosystems. Human activities such as fishing together with environmental drivers (e.g. climate change) are triggering major threats to marine biodiversity, and impact directly the services they provide. In the South and Southwest coasts of Portugal, the deep-water crustacean trawl fishery is not exemption. This fishery is recognized to have large effects on a number of species while generating high rates of unwanted catches. However, taking into account an ecosystem-based perspective, the fishing impacts along the food web accounting for biological interactions between and among species caught remains poorly understood. These impacts are particularly troubling and are a cause of concern given the cascading effects that might arise. Facing the main policies and legislative instruments for the restoration and conservation of the marine environment, times are calling for implementing ecosystem-based approaches to fisheries management. To this end, we use a food web modelling (Ecopath with Ecosim) approach to assess the fishing impacts of this particular fishery on the marine ecosystem of southern and southwestern Portugal. In particular, we describe the food web structure and functioning, identify the main keystone species and/or groups, quantify the major trophic and energy flows, and ultimately assess the impact of fishing on the target species but also on the ecosystem by means of ecological and ecosystem-based indicators. Finally, we examine limitations and weaknesses of the model for potential improvements and future research directions.
- Using a modified Nordmore grid for by-catch reduction in the Portuguese crustacean-trawl fisheryPublication . Fonseca, P.; Campos, Aida; Larsen, R. B.; Borges, T. C.; Erzini, KarimBy-catch and discards are a common problem to all fisheries. Recent studies of the Portuguese crustacean-trawl fishery show that discards average 70% of the total catch. This situation poses a threat not only to the management of target and commercial fish by-catch species stocks, but also in terms of the ecosystem impact of the discarded species whose survival is generally low. Previous attempts to address this problem by using oblique separator mesh panels associated with square-mesh windows, or square-mesh windows alone, provided encouraging results, but these are unlikely to have commercial applicability at present. Therefore, we tested the efficiency of a modified Nordmore grid in excluding some of the most captured non-commercial by-catch species, such as the blue whiting, Micromesistius poutassou, and the boarfish, Capros aper, evaluating simultaneously the losses of the crustacean target species (rose shrimp, Parapenaeus longirostris, Norway lobster, Nephrops norvegicus and red shrimp, Aristeus antennatus) and commercially valuable fish by-catch. A total of 41 valid hauls were carried out during 2001, and 15 in 2002 on board the R/V "Noruega". Results from both years varied considerably, with higher by-catch exclusion rates, in weight, registered in the second survey (73-74 and 48-63% for blue whiting and boarfish, respectively). The corresponding percentage reduction for target species was 8-15% for the Norway lobster, 4-9% for rose shrimp and 7-10% for red shrimp. The level of exclusion of the non-commercial by-catch is encouraging, although short-term loss of Norway lobster, where the escapees comprised larger individuals, raises some concern with regards to fishers' acceptance of mandatory use of grids. (C) 2004 Elsevier B.V. All rights reserved.