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The white-chinned petrel Procellaria aequinoctialis is one of the most frequently observed seabird species captured in fisheries bycatch, yet some populations remain virtually unstudied. The size of the breeding population on the sub-Antarctic Auckland Islands, New Zealand, is unknown. Disappointment Island is thought to be the main white-chinned petrel breeding site in the Auckland Islands, and maybe also in the New Zealand region, and has never had introduced mammalian predators. We estimated the white-chinned petrel breeding population size taking into account the detection probability of burrows via distance sampling and the burrow occupancy rate. Eighty line transects were distributed over the island, with a total line length of 1600 m. Burrows were patchily distributed and most abundant in dense megaherb communities. White-chinned petrel burrow density D^D^ was 654 burrows/ha (95 % CI 528–809 burrows/ha), with burrow detection probability p^p^ varying among vegetation communities from 0.28 ± 0.02 to 0.43 ± 0.02 (±SE). Mean burrow occupancy was 0.73 ± 0.03. We document an estimated total of 155,500 (125,600–192,500) breeding pairs of white-chinned petrels on Disappointment Island during mid incubation in early January 2015. The relatively high occupancy and density of burrows suggest that Disappointment Island is a key breeding site for white-chinned petrels.
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ORIGINAL PAPER
White-chinned petrel population estimate, Disappointment Island
(Auckland Islands)
Kalinka Rexer-Huber
1
Graham C. Parker
2
Paul M. Sagar
3
David R. Thompson
4
Received: 20 March 2016 / Revised: 1 August 2016 / Accepted: 22 August 2016 / Published online: 2 September 2016
ÓSpringer-Verlag Berlin Heidelberg 2016
Abstract The white-chinned petrel Procellaria aequinoc-
tialis is one of the most frequently observed seabird species
captured in fisheries bycatch, yet some populations remain
virtually unstudied. The size of the breeding population on
the sub-Antarctic Auckland Islands, New Zealand, is
unknown. Disappointment Island is thought to be the main
white-chinned petrel breeding site in the Auckland Islands,
and maybe also in the New Zealand region, and has never
had introduced mammalian predators. We estimated the
white-chinned petrel breeding population size taking into
account the detection probability of burrows via distance
sampling and the burrow occupancy rate. Eighty line
transects were distributed over the island, with a total line
length of 1600 m. Burrows were patchily distributed and
most abundant in dense megaherb communities. White-
chinned petrel burrow density
^
Dwas 654 burrows/ha
(95 % CI 528–809 burrows/ha), with burrow detection
probability ^
pvarying among vegetation communities from
0.28 ±0.02 to 0.43 ±0.02 (±SE). Mean burrow occu-
pancy was 0.73 ±0.03. We document an estimated total of
155,500 (125,600–192,500) breeding pairs of white-chin-
ned petrels on Disappointment Island during mid incuba-
tion in early January 2015. The relatively high occupancy
and density of burrows suggest that Disappointment Island
is a key breeding site for white-chinned petrels.
Keywords Procellaria Burrow density Abundance
Population size Distance sampling
Introduction
Over the last two decades, oceanic seabirds have become
more threatened and have deteriorated in status faster than
other bird groups (BirdLife International 2013). This is
linked to their accidental bycatch in fisheries and predation
by introduced mammals at breeding sites. Globally, seabird
bycatch is highest in sub-Antarctic waters (Lewison et al.
2014) and introduced mammals occur on about 33 % of
sub-polar seabird islands (from data in TIBD 2012; Bird-
Life Datazone 2015). Population estimates underpin spe-
cies status and trend assessment as well as management
action, yet accurate and precise estimates are relatively rare
for burrow-nesting seabird populations (Barbraud et al.
2009; Parker and Rexer-Huber 2016).
White-chinned petrels Procellaria aequinoctialis breed
at a number of sites around the Southern Ocean. In the
Pacific sector, they breed on the sub-Antarctic Auckland,
Antipodes and Campbell groups, but very little is known
about any aspect of these white-chinned petrel populations.
Taylor (2000) suggested that the Auckland and Antipodes
islands may each support around 100,000 pairs, although
these figures should be considered intuitive guesses. Initial
quantitative estimates from Antipodes Island indicated that
the breeding population was more likely to be between
59,000 and 91,000 pairs (Sommer et al. 2010,2011),
considerably fewer than previously suggested (Taylor
2000). In the Auckland Islands group, white-chinned
&Kalinka Rexer-Huber
kalinka.rexerhuber@gmail.com
1
Department of Zoology, University of Otago, 340 Great King
Street, Dunedin, New Zealand
2
Parker Conservation, 126 Maryhill Terrace, Dunedin, New
Zealand
3
National Institute for Water and Atmospheric Research,
P.O. Box 8602, Christchurch, New Zealand
4
National Institute for Water and Atmospheric Research, 301
Evans Bay Parade, Hataitai, Wellington, New Zealand
123
Polar Biol (2017) 40:1053–1061
DOI 10.1007/s00300-016-2031-x
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... Small, fixed sampling plots were used instead of line-transect distance sampling (e.g. Rexer-Huber et al. 2017) because preliminary survey showed that transects on some shelves did not encounter sufficient burrows for distance sampling. Furthermore, small fixed-point plots were considered safer and more reliable in steep terrain, with less time spent looking for footing and more looking for burrows. ...
... Caved-in burrows were accounted for in occupancy sampling (included in the burrow correction b). Occupancy was stable across the three study years but differed between islands, with higher occupancy rates at Disappointment (73%; Rexer-Huber et al. 2017) than at Adams (59%). These whitechinned petrel burrow occupancy rates of 59-73% are similar to occupancy on Kerguelen and on Crozet (60-70% of burrows occupied; Barbraud et al. 2008Barbraud et al. , 2009, and also similar to that of the closely related spectacled petrels (Procellaria conspicillata) on Inaccessible Island (81% of burrows occupied; Ryan & Ronconi 2011). ...
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In New Zealand's subantarctic Auckland Islands, the island-wide population size of white-chinned petrels (Procellaria aequinoctialis) is unknown. On ten islands in the group, surveys for burrow distribution were followed by whole-island burrow counts or stratified random sampling of white-chinned petrel habitat. White-chinned petrel burrow density, burrow occupancy, and slope-corrected surface areas were used to calculate the breeding population size. Burrows were patchily distributed and most abundant in dense megaherb communities. White-chinned petrel burrow density at Adams Island was 701 burrows/ha (95% CI: 480-803 burrows/ha). Burrow occupancy was 0.59 ± 0.02 (mean ± se) at the start of incubation. An estimated 28,300 (10,400-44,800) white-chinned petrel pairs breed on Adams Island. Including the small colonies on Ewing, Monumental, and Enderby Islands (together c. 100 pairs) and the estimated 155,500 breeding pairs on Disappointment Island, the Auckland Island group has an estimated 184,000 (95% CI: 136,000-237,000) pairs of breeding white-chinned petrels. Rexer-Huber, K.; Thompson, D.R.; Parker, G.C. 2020. White-chinned petrel (Procellaria aequinoctialis) burrow density, occupancy, and population size at the Auckland Islands. Notornis 67(1): 387-401.
... About 155 500 (125 600-192 500) pairs of White-chinned Petrels have been recorded in mid-incubation on Disappointment Island which represents the majority of the population that visits Australian seas (Rexer-Huber et al. 2017). The total New Zealand population is estimated at 1.3 million individuals (0.9-2.1 million; Richard et al. 2017) with a global population of three million estimated in 2012. ...
... or by providing estimates of potential biological removal to help inform harvest and fisheries management (Defos duRau et al., 2015;Newman et al., 2009;Rexer-Huber et al., 2017), many did not. For these cases we cannot determine whether a population estimate was the best way of achieving the desired outcome. ...
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Population estimates are commonly generated and used in conservation science. All estimates carry inherent uncertainty, but little attention has been given to when and how this uncertainty limits their use. This requires an understanding of the specific purposes for which population estimates are intended, an assessment of the level of uncertainty each purpose can tolerate, and information on current uncertainty. We conducted a review and meta‐analysis for a widespread group of seabirds, the petrels, to better understand how and why population estimates are being used. Globally petrels are highly threatened, and aspects of their ecology make them difficult to survey, introducing high levels of uncertainty into population estimates. We found that by far the most common intended use of population estimates was to inform status and trend assessments, while less common uses were trialling methods to improve estimates and assessing threat impacts and conservation outcomes. The mean coefficient of variation for published estimates was 0.17 (SD = 0.14), with no evidence that uncertainty has been reduced through time. As a consequence of this high uncertainty, when we simulated declines equivalent to thresholds commonly used to trigger management, only 5% of studies could detect significant differences between population estimates collected 10 years apart for populations declining at a rate of 30% over three generations. Reporting of uncertainty was variable with no dispersion statistics reported with 38% of population estimates and most not reporting key underlying parameters: nest numbers/density and nest occupancy. We also found no correlation between uncertainty in petrel population estimates and either island size, body size or species threat status – potential predictors of uncertainty. Key recommendations for managers are to be mindful of uncertainty in past population estimates if aiming to collect contemporary estimates for comparison, to report uncertainty clearly for new estimates, and to give careful consideration to whether a proposed estimate is likely to achieve the requisite level of certainty for the investment in its generation to be warranted. We recommend a practitioner‐based value of information assessment to confirm where there is value in reducing uncertainty. Population estimates are commonly generated and used in conservation science. All estimates carry inherent uncertainty, but little attention has been given to when and how this uncertainty limits their use. This requires an understanding of the specific purposes for which population estimates are intended, an assessment of the level of uncertainty each purpose can tolerate, and information on current uncertainty. We conducted a review and meta‐analysis for a widespread group of seabirds, the petrels, to better understand how and why population estimates are being used. Globally petrels are highly threatened, and aspects of their ecology make them difficult to survey, introducing high levels of uncertainty into population estimates. We found that by far the most common intended use of population estimates was to inform status and trend assessments, while less common uses were trialling methods to improve estimates and assessing threat impacts and conservation outcomes. The mean coefficient of variation for published estimates was 0.17 (SD = 0.14), with no evidence that uncertainty has been reduced through time. As a consequence of this high uncertainty, when we simulated declines equivalent to thresholds commonly used to trigger management, only 5% of studies could detect significant differences between population estimates collected 10 years apart for populations declining at a rate of 30% over three generations. Reporting of uncertainty was variable with no dispersion statistics reported with 38% of population estimates and most not reporting key underlying parameters: nest numbers/density and nest occupancy. We also found no correlation between uncertainty in petrel population estimates and either island size, body size or species threat status – potential predictors of uncertainty. Key recommendations for managers are to be mindful of uncertainty in past population estimates if aiming to collect contemporary estimates for comparison, to report uncertainty clearly for new estimates, and to give careful consideration to whether a proposed estimate is likely to achieve the requisite level of certainty for the investment in its generation to be warranted. We recommend a practitioner‐based value of information assessment to confirm where there is value in reducing uncertainty. Uncertainty when estimating population sizes may limit the utility of the estimates. We reviewed published population estimates for a threatened seabird family, the Procellariidae, to identify the motives behind them and the level of uncertainty reported. Estimates were most commonly intended to detect trends, but uncertainty suggests they are unlikely to be able to do this reliably in most cases.
... The ongoing presence of predators on Auckland Island limits the gains from the Crown's investment in seabird bycatch reduction, through negative impacts on the breeding success of already threatened species 1 . Accidental bycatch is highest in the subantarctic region 41 and Gibson's albatross/toroa, white-capped albatross and white-chinned petrel (Procellaria aequinoctialis) in particular have been significantly impacted through bycatch 42 . The presence of pests on Auckland Island reduces the safe breeding habitat for these vulnerable species by 420%. ...
... Defos du Rau et al., 2015;Newman et al., 2009;Rexer-Huber et al., 2017), many did not.Brooke et 316 al. (2018) used monitoring data, including population estimates, to derive seabird population trends 317 in response to invasive species eradication. Such syntheses provide an important evidence base for 318 conservation interventions. ...
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... The nominate subspecies comprises some 681 000 breeding pairs on South Georgia (Martin et al. 2009), 36 000 on the Prince Edward Islands (PEI; Ryan et al. 2012), 23 600 on the Iles Crozet (Barbraud et al. 2008), 234 000 on the Iles Kerguelen , and < 100 pairs on the Falkland Islands (Reid et al. 2007). Population estimates of P. a. steadi are less accurate, but they are thought to number 153 000 pairs on Disappointment Island (Rexer-Huber et al. 2017), 22 000 on Campbell Island (Rexer-Huber et al. 2016) and 59 000-91 000 on the Antipodes (range of two estimates; Sommer et al. 2010Sommer et al. , 2011. Populations on a number of breeding islands are thought to be decreasing, including those on South Georgia and Ile de la Possession in the Iles Crozet (Berrow et al. 2000a, Barbraud et al. 2008). ...
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The white-chinned petrel (Procellaria aequinoctialis) is the seabird most often killed on longlines in the Southern Ocean and is listed as vulnerable to extinction. We estimated the population breeding at the Prince Edward Islands, the last breeding site for the nominate subspecies that lacks a recent population estimate. White-chinned petrel burrows are largely confined to deep, muddy soils, usually on slopes below 200 m, but locally up to 420 m. After correcting for count bias, Marion Island has an estimated 29,900 nests (95 % CI 27,700–32,400). Burrow occupancy rates at the start of the incubation period were 65 % during one-off surveys, but repeat surveys found that at least 73 % of burrows were occupied and 87 % of burrows showed signs of occupancy. This suggests that there were roughly 24,000 occupied nests on Marion Island (95 % CI 20,000–28,000). A more cursory survey on Prince Edward Island yielded 14,700 burrows, suggesting that there are 9,000–15,000 occupied nests. The nominate subspecies of white-chinned petrel occupies approximately 974,200 nests (95 % CI 678,000–1,286,000), with the Prince Edward Islands, the third most important breeding site, after South Georgia and Kerguelen. Assuming that populations breeding at islands in the Atlantic and Indian Oceans winter in different regions, the impact of fishery bycatch is likely to have had a greater impact on the Indian Ocean population. The Marion Island survey provides a baseline against which future population changes can be assessed.
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In adaptive cluster sampling designs, an initial probability sample is selected and, whenever the observed value of the variable of interest satisfies a given condition, units in the neighborhood of that observation are added to the sample. In this paper, the initial design is selected in terms of primary units, while subsequent sampling is in terms of secondary units. Such initial designs include systematic sampling, strip sampling, and other forms of classical cluster sampling. But because of the subsequent addition to the sample of secondary units in the neighborhood of any (secondary) unit that satisfies the condition of interest, the final "clusters" of units obtained through the procedure may be quite different in shape from the initial primary units. The methods described in this paper apply to such sampling situations as whale surveys in which the research vessel temporarily leaves the selected transect to close in on sighted whales, surveys of rare bird species in which initial observations are made at systematically selected sites and additional observations are made in the vicinity of any site at which sufficiently high abundance is observed, and aerial walrus surveys in which the aircraft searches to either side of the preselected transect line whenever a congregation of animals is encountered. Because conventional estimators of the population mean and total are biased with such a procedure, estimators that are unbiased under the adaptive designs are presented in this paper. Variance formulae and unbiased estimators of variance are also given. The designs are illustrated using a point pattern representing locations of individuals or objects in a spatially aggregated population; for such a population, the adaptive designs can be substantially more efficient than their conventional counterparts.