03 williams et al PROOF for pdf.indd

• Main Authors: R Williams, G N Tuck, A J Constable, T Lamb, Doro
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2002
• Subjects: Heard; Heard Island; Indian; Kerguelen; McDonald Islands; Southern Ocean
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1038.277; http://archive.ccamlr.org/ccamlr_science/Vol-09-2002/03williams-etal.pdf

Abstract Stocks of Patagonian toothfi sh (Dissostichus eleginoides) in different sectors of the Southern Ocean are considered to be genetically distinct. However, in the Indian Ocean, it is largely unknown whether stocks are separate between shelves and banks separated by deep water. More particularly, the separation of stocks on the Kerguelen Plateau has not been investigated. This paper examines the assumptions of stock separation using tagged fi sh from the fi shery around Heard Island and McDonald Islands (HIMI) in the Australian Exclusive Economic Zone (EEZ). Movement, growth and trends in fi sh abundance are examined using these data. The bulk of the data show that fi sh disperse only a very short distance, up to 15 n miles in most cases, from their point of release. This may be explained in part because of the concentration of fi shing in the established grounds, which makes recaptures more likely in the same place as marking. The concentration of effort should also result in a high probability of detecting fi sh movements between grounds, if they occur, but so far no such movement has been detected. It appears that fi sh tend to be locally resident during their phase in the depth range of the fi shing grounds, but they move on once they approach maturity at about 850 mm total length and become unavailable to the fi shery. Four fi sh have been recorded as moving a long distance, and thus provide contradictory evidence. Three fi sh moved from ground B of HIMI to Crozet and were all within the size range normally found in the Heard Island fi shing grounds, and so appear to be behaving differently from those fi sh that follow the normal pattern of residency in the grounds. One fi sh has been recorded as moving from ground A to Kerguelen and was at the upper end of the size range normally found on the grounds. These four long-range movers provide the fi rst documented direct evidence of toothfi sh moving such distances and of fi sh moving from one fi shery to another. The signifi cance of this is discussed. ...