Probability of Detecting Harbor Porpoise from Aerial Surveys: Estimating g(0)

Laake, Jeffrey L.; Calambokidis, John; Osmek, Steven; Rugh, David J.

doi:10.2307/3802415

Cited by 140 publications

(197 citation statements)

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“…Sum of distances r 1 and r 2 divided by aircraft speed (v) define w(x), the amount of time that segment of sea surface at perpendicular distance x is in observer's view subsection), a group was detected when 1 or more dolphins in the group were at the surface. Therefore, in agreement with Laake et al (1997), the length of time the dolphin groups were at or near the surface was measured by combining all intervals with surfacings of 1 or more dolphins less than 30 s apart as a surface interval, and longer intervals, with all dolphins underwater, as dives. To determine these periods, the groups were closely followed for periods lasting 30 min to nearly 4 h. Total observation time was 18 h 05 min.…”

Section: Methodsmentioning

confidence: 96%

“…Aerial surveys are affected by visibility bias, caused by undercounting animals missed because they are diving (availability bias), and by factors affecting perception (perception bias), such as cloud cover, sea state or observer fatigue (Laake et al 1997 and references therein). To address availability bias, data on dive and surface times were collected during boat surveys to study bottlenose dolphin distribution and movements around the Balearic Islands, in June 2003.…”

Section: Methodsmentioning

confidence: 99%

“…Following Laake et al (1997), at an observed perpendicular distance x, dolphin detection was defined by the function g(x|S,Z), conditional on the event S that was the occurrence of 1 or more dolphins in a group at or near the surface, and additional perception covariates Z (see below). Dolphin availability, a (S,x), was defined as the probability that a dolphin group at perpendicular distance x was at the surface and within the observer's field of view.…”

Section: Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Bottlenose dolphin abundance in the NW Mediterranean: addressing heterogeneity in distribution

Forcada¹,

Gazo²,

Aguilar³

et al. 2004

Mar. Ecol. Prog. Ser.

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Line-transect estimators were developed to assess abundance of coastal dolphins Tursiops truncatus and Stenella coeruleoalba encountered in low densities during aerial sighting surveys. The analysis improved on conventional approaches by objectively combining data from different species, survey areas and other covariates affecting dolphin detectability. Model selection and multimodel inference allowed robust estimates of precision in accounting for covariate selection uncertainty. These methods were used to estimate bottlenose dolphin abundance in NE Mediterranean waters that included a putative subpopulation in the Balearic Islands. . The results do not support an exclusively coastal Balearic Island subpopulation, but they strongly indicate that the islands contain critical habitats required for the conservation of the species. Given the observed decline of the species during the last few decades, conservation-oriented management should focus on reducing or eliminating adverse fishing interactions while key areas are protected from encroachment produced by human development.

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Section: Methodsmentioning

confidence: 96%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Bottlenose dolphin abundance in the NW Mediterranean: addressing heterogeneity in distribution

Forcada¹,

Gazo²,

Aguilar³

et al. 2004

Mar. Ecol. Prog. Ser.

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show abstract

“…Aerial surveys for harbour porpoises require specialised methods (e.g. Hammond et al 2003, Laake et al 1997) that were not applied in these surveys. For example, a dedicated harbour porpoise survey would likely have been flown at lower altitude, and effort would have been restricted to even better weather conditions than on these surveys.…”

Section: Harbour Porpoisesmentioning

confidence: 99%

Trends in the distribution and abundance of cetaceans from aerial surveys in Icelandic coastal waters, 1986-2001

et al. 2009

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Aerial surveys were carried out in coastal Icelandic waters 4 times between 1986 and 2001 as part of the North Atlantic Sightings Surveys. The surveys had nearly identical designs in 3 of the 4 years. The target species was the minke whale (Balaenoptera acutorostrata) but all species encountered were recorded. Sighting rate and density from line transect analysis were used as indices of relative abundance to monitor trends over the period, and abundance estimates corrected for perception biases were calculated for some species from the 2001 survey. More than 11 species were sighted, of which the most common were the minke whale, humpback whale (Megaptera novaeangliae), dolphins of genus Lagenorhychus, and the harbour porpoise (Phocoena phocoena). Minke whales and dolphins showed little change in distribution or abundance over the period. There were an estimated 31,653 (cv 0.30) dolphins in the survey area in 2001. Humpback whales increased rapidly at a rate of about 12%, with much of the increase occurring off eastern and northeastern Iceland. In 2001 there were an estimated 4,928 (cv 0.463) humpback whales in the survey area. The relative abundance of harbour porpoises decreased over the period, but estimates for this species were compromised by uncorrected perception biases and poor coverage. The ecological and historical significance of these findings with respect to previous whaling activities and present-day fisheries is discussed.

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“…Standard methods for surveying harbor porpoises should be employed (e.g., Barlow and Hannan 1995;Palka 1995;Polacheck 1995;Laake et al 1997;Hammond et al 2002). Concurrent with these activities, a systematic study of the threats facing harbor porpoises in the Black Sea should be conducted.…”

Section: Assess Abundance and Threats To Survival Of Harbor Porpoisesmentioning

confidence: 99%

Dolphins, whales and porpoises : 2002-2010 conservation action plan for the world's cetaceans

Reeves¹,

Smith²,

Crespo³

et al. 2003

228

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Probability of Detecting Harbor Porpoise from Aerial Surveys: Estimating g(0)

Cited by 140 publications

References 0 publications

Bottlenose dolphin abundance in the NW Mediterranean: addressing heterogeneity in distribution

Bottlenose dolphin abundance in the NW Mediterranean: addressing heterogeneity in distribution

Trends in the distribution and abundance of cetaceans from aerial surveys in Icelandic coastal waters, 1986-2001

Dolphins, whales and porpoises : 2002-2010 conservation action plan for the world's cetaceans

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