Navigation Links
Does fishing on drifting fish aggregation devices endanger the survival of tropical tuna?
Date:5/15/2008

Fishermen hold empirical knowledge that tuna aggregate under floating objects, such as lengths of old rope, pieces of wood, or even large marine mammals. There is still no full explanation for this aggregation behaviour, but the past 20 years have seen purse-seine fishery operators take advantage of the associated concentrations of fish. Fishermen cast off floating rafts equipped with buoys which act as FADs. An enormous purse-seine net, deployed in a wide arc on either side of the vessel, encircles the school of tuna that come to shelter under the FAD. The lower part of the net is tightened, enclosing the fish in a hemisphere large enough to entrap a mass of tuna.

A sudden growth in the size of tropical tuna catches taken from under these artificial drifting objects was observed for the early 1990s. This was true especially for juveniles. Between 1996 and 2005 the average annual catch taken on FADs reached 1 115 000 tonnes, nearly a third of the global figure for tuna, all species considered together. In Japan, the fish processing industry furthermore had long reported that the flesh from floating-object associated tuna was less plump than that of specimens caught from free schools. This prompted an IRD research team to investigate whether or not the practice of drifting FAD fishing could set up an ecological trap for the tropical tuna species.This trap concept is a notion from population biology used to describe situations in which the population falls following a sudden change in its environment, most often linked to human activity. An example is give by marine turtles which, after hatching on beaches, use the sparkle of moonlight on the sea surface to guide themselves back to the ocean. However, high light pollution levels on urbanized coastlines in certain regions disturbs their sense of direction. Young turtles therefore set off on a path that leads them to land, where they die from dehydration.

Over the past ten years, over 30% of world catches of skipjack (Katsuwonus pelamis), bigeye (Thunnus obesus) and yellowfin (Thunnus albacares) tuna, the three tropical tuna species which can be caught at drifting FADs, have been achieved using this fishing method. For the skipjack amounts taken under drifting FADs reached even as high as 72% of all catches. To check if the large-scale deployment of drifting FADs could present an ecological trap for these species, a range of biological (fish plumpness, growth rate, stomach fullness) and ecological (migration pattern and distance) indices were determined on yellowfin and skipjack captured under FADs in the Atlantic and Indian Oceans. Comparison was then made with data gathered from free-school caught individuals of these same species. A salient finding was that 74% of drifting FAD-associated skipjack had empty stomachs at the moment of capture compared with only 13% for those fished from free schools. Figures of the same order of magnitude were obtained for yellowfin, with proportions respectively reaching 49% caught on drifting FADs and 7% from free schools. The survey indicated that the tuna caught under the FADs fed less well than those fished from free schools. Moreover, the fact that for the same weight the FAD-associated specimens caught showed lower plumpness than the free-school ones could reflect a deficiency in energy-reserve accumulation in those that concentrated around the floating devices.

The research team also sought to find out if the large-scale deployment of drifting FADs could affect the migration patterns of these far-travelling fish species. Tagging surveys allowed comparison of the nature of migrations accomplished by fish moving with the drift of FADs with that of non-FAD-associated individuals. The migration directions and displacement rates in terms of daily distances travelled were indeed affected by the presence of artificial floating objects. Drifting FADs therefore appeared to act as super-stimuli, like strong magnets exerting a binding attraction that leads the tuna towards ecologically inappropriate waters with scarcer food supplies. This survey brought support for a body of reasonable assumptions regarding the tuna behaviour. However, it did not provide certain confirmation of drifting FADs negative impact on the entire life cycle of these tuna species and therefore of their possible role as a true ecological trap. Nevertheless, the biological effects observed indicated that it would be more reasonable to preclude deployment of drifting FADs near coasts where tuna juveniles aggregate. These young fish represent the future of the whole stock and such a restriction would be a way of avoiding their being led astray, away from the zones which are ecologically most favourable to them.


'/>"/>

Contact: Gregory Flechet
fichesactu@paris.ird.fr
33-014-803-7607
Institut de Recherche Pour le Dveloppement
Source:Eurekalert

Related biology news :

1. Can certain metals repel sharks from fishing gear?
2. Fishing throws targeted species off balance, Scripps study shows
3. Oceanic sharks worldwide at serious risk from high-seas fishing, rising demand for shark products
4. Small-scale fishing in Mexico rivals industrial fisheries in accidental turtle deaths
5. Research shows loggerhead sea turtles threatened by small-scale fishing operations
6. New Silex SX-560 Enables Enterprise 802.11 Wireless Connectivity for Battery Operated Devices
7. Childrens Hospital leads projects to develop nations first heart assist devices for young children
8. Better protection for biomedial devices could result from Rutgers-Camden research
9. MIT aids creation of neural prosthetic devices
10. IGERT fellows to design biodevices using flexible electronics
11. Great apes endangered by human viruses
Post Your Comments:
*Name:
*Comment:
*Email:
(Date:4/26/2016)... LONDON , April 26, 2016 ... EdgeVerve Systems, a product subsidiary of Infosys (NYSE: ... a partnership to integrate the Onegini mobile security ... (Logo: http://photos.prnewswire.com/prnh/20151104/283829LOGO ) The ... enhanced security to access and transact across channels. ...
(Date:4/15/2016)... CHICAGO , April 15, 2016  A ... companies make more accurate underwriting decisions in a ... offering timely, competitively priced and high-value life insurance ... health screenings. With Force Diagnostics, rapid ... and lifestyle data readings (blood pressure, weight, pulse, ...
(Date:4/13/2016)... -- IMPOWER physicians supporting Medicaid patients in Central ... in telehealth thanks to a new partnership with higi. ... patients can routinely track key health measurements, such as ... when they opt in, share them with IMPOWER clinicians ... retail location at no cost. By leveraging this data, ...
Breaking Biology News(10 mins):
(Date:5/3/2016)... , May 3, 2016  Dr. Thomas P. ... in The Woodlands, Texas , now ... percent of treated fat cells in just 25-minutes, leaving ... to 90 percent of Americans report feeling bothered by ... fat reduction procedures are a growing industry. This innovative ...
(Date:5/3/2016)... ... 03, 2016 , ... Nashville Fertility Center has joined a ... reproductive endocrinologists, including Dr. George Hill at Nashville Fertility Center, created ... build families. , Ovation Fertility is a nationwide network of leading fertility centers ...
(Date:5/2/2016)... Willoughby, Ohio (PRWEB) , ... May 02, 2016 ... ... website. Designed with its clients in mind, the fresh look and added functionality ... capabilities. , “Recent years have seen a dynamic shift in agriculture – from ...
(Date:5/2/2016)... PA (PRWEB) , ... May 02, 2016 , ... ... proud to report on the pre-launch success of their revolutionary, veterinarian-designed product for ... cats to stalk, trap, and play with their food the way nature intended. ...
Breaking Biology Technology: