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Line-transect abundance estimates of False killer whales (Pseudorca crassidens) in the pelagic region of the Hawaiian exclusive economic zone and in the insular waters of the northwestern Hawaiian Islands
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  • Description:
    "Three stocks of false killer whales (Pseudorca crassidens) can be differentiated within the U.S. Exclusive Economic Zone of the Hawaiian Islands (Hawaiian EEZ): an insular main Hawaiian Islands stock, a dispersed pelagic stock, and a newly recognized Northwestern Hawaiian Islands stock. Current abundance estimates are needed for the pelagic and Northwestern Hawaiian Islands stocks. To this end, a ship-based line-transect survey of the Hawaiian EEZ was conducted in the summer-fall of 2010, resulting in 6 systematic-effort visual sightings of pelagic (n = 5) and Northwestern Hawaiian Islands (n = 1) false killer whale groups. These sightings were combined with data from multiple sources and analyzed within the conventional linetransect estimation framework, although the detection function, mean cluster size, and encounter rate were estimated separately so as to appropriately incorporate data collected using different methods. Unlike previous line-transect analyses of false killer whales, subgroups were treated as the analytical unit instead of groups because subgroups better conform to the specifications of line-transect theory. Bootstrap values (n = 5000) of the line-transect parameters were randomly combined to estimate the variance of stock-specific abundance estimates. Hawaii pelagic and Northwestern Hawaiian Islands false killer whales were estimated to number 1503 (CV = 0.66) and 552 (CV = 1.09) individuals, respectively. These estimates can be considered positively biased to an unknown extent due to the effect of vessel attraction"--Abstract.
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