Browsing by Author "Kirkman, Stephen P"

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    Open Access
    Accuracy of ARGOS locations of pinnipeds at-sea estimated using Fastloc GPS
    (Public Library of Science, 2010) Costa, Daniel P; Robinson, Patrick W; Arnould, John P Y; Harrison, Autumn-Lynn; Simmons, Samantha E; Hassrick, Jason L; Hoskins, Andrew J; Kirkman, Stephen P; Oosthuizen, Herman; Villegas-Amtmann, Stella
    BACKGROUND: ARGOS satellite telemetry is one of the most widely used methods to track the movements of free-ranging marine and terrestrial animals and is fundamental to studies of foraging ecology, migratory behavior and habitat-use. ARGOS location estimates do not include complete error estimations, and for many marine organisms, the most commonly acquired locations (Location Class 0, A, B, or Z) are provided with no declared error estimate. METHODOLOGY/PRINCIPAL FINDINGS: We compared the accuracy of ARGOS locations to those obtained using Fastloc GPS from the same electronic tags on five species of pinnipeds: 9 California sea lions ( Zalophus californianus ), 4 Galapagos sea lions ( Zalophus wollebaeki ), 6 Cape fur seals ( Arctocephalus pusillus pusillus ), 3 Australian fur seals ( A. p. doriferus ) and 5 northern elephant seals ( Mirounga angustirostris ). These species encompass a range of marine habitats (highly pelagic vs coastal), diving behaviors (mean dive durations 2-21 min) and range of latitudes (equator to temperate). A total of 7,318 ARGOS positions and 27,046 GPS positions were collected. Of these, 1,105 ARGOS positions were obtained within five minutes of a GPS position and were used for comparison. The 68 th percentile ARGOS location errors as measured in this study were LC-3 0.49 km, LC-2 1.01 km, LC-1 1.20 km, LC-0 4.18 km, LC-A 6.19 km, LC-B 10.28 km. Conclusions/Significance The ARGOS errors measured here are greater than those provided by ARGOS, but within the range of other studies. The error was non-normally distributed with each LC highly right-skewed. Locations of species that make short duration dives and spend extended periods on the surface (sea lions and fur seals) had less error than species like elephant seals that spend more time underwater and have shorter surface intervals. Supplemental data ( S1 ) are provided allowing the creation of density distributions that can be used in a variety of filtering algorithms to improve the quality of ARGOS tracking data.
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    Open Access
    Assessing the hunting practices of Namibia's commercial seal hunt
    (2010) Lavigne, David M; Kirkman, Stephen P
    Following mounting public concerns regarding the treatment of animals in recent years, there has been increasing interest in the development of science-based guidelines for animal welfare in industries such as agriculture and hunting.1,2,3 In the latter case, for example, the European Food Safety Authority (EFSA) was requested by the European Commission, in 2007, to issue a scientific opinion regarding welfare aspects of seal hunting and to assess the most appropriate killing methods, to reduce unnecessary suffering. As part of its assessment, EFSA's Scientific opinion4 compared seal hunting to the killing of livestock in abattoirs. It noted that while slaughter conditions vary considerably, the goal should be the same: to kill animals with the minimum amount of pain, distress and fear and without causing any avoidable suffering. The report concluded that there was strong evidence that effective killing is not always practiced during seal hunts and that unnecessary and avoidable pain and suffering occurs. Subsequently, Russia ended its commercial hunt for harp seals Pagophilus groenlandicus in the White Sea in February 20095 and banned the killing of all seals under the age of one year in March of 2009.6Two months later, the European Parliament voted 550-49 in favour of a resolution banning the importation of seal hunt products, which comes into effect in 2010.7 Canada and Norway have subsequently lodged challenges against the EU ban with the World Trade Organization.
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    Overlap in utilization of juvenile Cape Horse Mackerel by Cape Fur Seals and the purse-seine fishery in Namibia
    (Southern African Wildlife Management Association, 2007) Mecenero, Silvia; Underhill, Les G; Krakstad, Jens-Otto; Kirkman, Stephen P; Roux, Jean-Paul
    The Cape horse mackerel Trachurus trachurus capensisis one of Namibia's most valuable fish stocks, and an important component to the diet of Cape fur seals, Arctocephalus pusillus pusillus, off northern Namibia. The level of overlap in the utilization of this resource between seals and the purse-seine fishery was investigated using two overlap indices. For high overlap measures, seals and the purse-seine fishery utilized age-2 horse mackerel. For low overlap measures, seals mainly consumed age-0 fish whereas the fishery caught age-2 fish. Both indices were adjusted by the proportion of horse mackerel in the seal diet, with the assumption that the proportion consumed by the seals reflects the abundance of horse mackerel in the coastal waters of Cape Cross, Namibia. Both unadjusted and adjusted overlap indices showed that overlap between seals and the fishery in their utilization of juvenile horse mackerel was high only at times when horse mackerel abundance was high, and low when abundance was small. Confidence intervals and significance testing were included. Overall, there was little overlap between seals and the purse-seine fishery. This study provides important information that should be taken into account in the management of the horse mackerel resource.