May 11, 2008 In the Ebro River delta, the fishing of elver (Anguilla anguilla) leads to the accidental capture of other fish species, with the capture of one ton of elver possibly resulting in the capture of up to 8.2 tons of accompanying species. Researchers from the Institute for Agro-Food Research and Technology (IRTA), who have assessed the effects of this method of fishing and identified the most fragile species, propose improvements in current methodologies.
With the capture of elver, eel (Anguilla anguilla) fry, scientists have identified up to 17 fish species, apart from the eel, which on average die in 36.5% of cases. The “dramatic” situation of accompanying ichthyofauna (fish captured with elver), which represents 43% of the various types of species in the area studied (350 Km²), may lead to ecological imbalances since it is the smallest specimens that are most likely to die when captured.
Enric Gisbert, main researcher of the study, explained that improvements are necessary in fishing methods to “reduce the mortality of accompanying ichthyofauna associated with capture processes and initial elver selection, as well as increase the sustainability of this activity.”
Fish species accidentally affected by elver fishing in the estuaries and coastal lagoons of the Ebro delta include mullets (fish normally found in ports or estuaries) and, in particular, the fry of Liza ramada, Liza aurata and Mugil cephalus, species which, according to the research, share part or their entire recruitment calendar with the elver fishing season.
In addition, researchers have shown that “the impact of elver fishing is not only on migratory species but might also ultimately affect resident species, as well as other strictly limnetic species.”
According to the data obtained for the two-year project, it has been determined that for every one ton of elver captured, 8.2 tons of other fish species are accidentally fished too, without taking into account illegal fishing which could make up between 20% and 25% of captures.
Gisbert puts the mortality of species captured during the elver manual selection process down to “not very careful or delicate handling by the fishermen, i.e. excessively harmful, worsened by the effects of prolonged immersion that causes lack of oxygen (anoxia) in fish.”
More sustainable fishing methods
The study shows the need to consider the impact of elver fishing at a population, trophic and ecosystem level. The IRTA researcher, together with Miguel Ángel López from the Department of the Environment at the Generalitat de Catalunya (Catalan autonomous government), pointed out to SINC that “actions which promote the reduction of the collateral effects of fishing and the selection of elver must be introduced.”
Among the most relevant actions, “informing fishermen so that they are aware of the impact of their activity appears to be a priority.” Researchers also stress that “methodological and procedural changes should be introduced in elver handling and selection tasks.” In this case, scientists suggest that a reduction in handling time and maximising care in selecting fish could avoid the death of many fish captured by accident.
In addition, an improvement in the design of fishing nets used for “highly” selective fishing might be another solution as this would “only target the species to be fished”, said Gisbert. According to the researcher, this method has been proved “experimentally” in situ, with “very promising” results. A simple alteration was made in the design of the fishing net, which significantly reduced the handling and selection time of elver, accidental captures, number of accidental species rejected during fishing and, naturally, deaths.
This work could “serve as a basis to the administration for implementing measures which guarantee a far more sustainable exploitation of this natural resource”, concluded Gisbert and López.
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- E. Gisbert, M. A. López. Impact of glass eel fishery on by-catch fish species: a quantitative assessment. Hydrobiologia, 2008; 602 (1): 87 DOI: 10.1007/s10750-008-9284-5
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