Preliminary stock assessment of the Patagonian toothfish longline fishery around the Falkland Islands

Abstract

An experimental fishery for Patagonian toothfish Di,ssosfichus rlcginoides was opened in Falkland Island waters briefly in 1992 and then from April 1994. One to two longlines per vessel were usually deployed at night, mostly fishing for 12-30 h at depths between 600 and 2000 m. The characteristics of the vessel, gear, fishing activities and the data collection and analyses methods are described. An initial evaluation of the authors' current understanding of toothfish biology and population dynamics in Falkland Island waters is given. A first analysis of toothfish numbers caught in 1994 suggests that these are changing at rates faster than expected from simple demographic processes. Therefore, despite an intensive monitoring of catch and fishing effort of each vessel, it is still not possible to derive reliable estimates for the size of the toothfish population currently exploited around the Falkland Islands. Migration patterns in and out of' the fishery need to be understood before a reliable assessment of the fishery can be made. These results, together with current and future lines of research, are discussed in the light of ddtd available from other toothfish fisheries in austral waters.,V I996 The Fishcrics Socicty 01. tlic Britiali Isles

Allozyme and microsatellite DNA markers of toothfish population structure in the Southern Ocean

“…Few tagging studies have been carried out, but fish are known to move within the Kerguelen Plateau, and there may be local movements around the Falkland Islands (Des Clers et al, 1996). One long distance migrant was reported with a fish tagged off the Falkland Islands recaptured several …”

The Patagonian toothfish fishery in Falkland Islands’ waters

“…The authors found that in two time series longer than 30 weeks, catch rates increased dramatically after a period of steady decline which was used in the assessment, apparently contradicting the authors' assumption of a closed population in DeLury model. Eventually, it was concluded that the results of the investigation are encouraging but cannot be generalised, and a better understanding of toothfish migrations is needed to provide a sound basis for the fishery's management (des Clers et al, 1996). Since then little information about stock status and its changes during the last 10 years of fishery is available.…”

“…Reproduction of the Falkland population happens on the eastern slope of Burdwood bank and immature fish forage over the eastern Patagonian shelf edge and slope (Laptikhovsky et al, 2004, in press). An attempt to assess the Falkland Islands toothfish population using a DeLury depletion method for some localised areas was made by des Clers et al (1996). The authors found that in two time series longer than 30 weeks, catch rates increased dramatically after a period of steady decline which was used in the assessment, apparently contradicting the authors' assumption of a closed population in DeLury model.…”

Preliminary assessment of the Falklands Patagonian toothfish (Dissostichus eleginoides) population: Use of recruitment indices and the estimation of unreported catches

“…Many fish species found around the Falklands are shared stocks between Argentina and the Falkland Islands (Agnew, 2002). A clue to the apparent independence of toothfish in Falkland Island waters is given by the tendency of the species not to move very much as adults (Marlow et al, 2003;Williams et al, 2002), and the fact that two spawning and nursery areas are known; one around Staten Island (Prenski, personal communication) and one between the north eastern edge of Burdwood bank (des Clers et al, 1996) and the Falkland Islands themselves. Thus it seems quite likely that, in general, animals spawning in Falkland Island waters recruit in waters around the Islands, moving to deeper water off-shelf rather than along the shelf.…”

“…An unsuccessful attempt to assess the Falkland Islands toothfish population using a DeLury depletion method on very localised areas was made by des Clers et al (1996). At the time there were insufficient data to undertake an age-based, fishery-wide population model; a situation that has since been rectified.…”