Mark recapture distance sampling: using acoustics to estimate the fraction of dolphins missed by observers during shipboard line-transect surveys

Cetacean populations in coastal habitats are increasingly threatened by multiple anthropogenic impacts. Monitoring these populations to obtain robust estimates of abundance and detect trends over time is critical to achieve conservation goals. Here, we conducted a pilot study to evaluate the effectiveness of two commonly used abundance estimation methods: mark-recapture and distance sampling line-transect. Surveys were conducted to estimate the abundance of bottlenose dolphins in Laguna, southern Brazil. We implemented power-analysis models and compared both techniques in terms of cost, time and effectiveness to detect trends over a five-year period. Mark-recapture models were analyzed in MARK and resulted in an abundance of 50 individuals (CI = 39-64) with a coefficient of variation (CV) of 0.13. The line-transect models were implemented using the program DISTANCE and resulted in an estimate of 62 individuals (CI = 38-103), with a CV of 0.24. Comparing both approaches, mark-recapture resulted 1.30 time more expensive than line-transect for a single season of effort, but was twice as effective in terms of precision. As a consequence, the probability of detecting a 5% trend during a five-year period is 2.08 times higher with mark recapture. Conversely, the final cost to detect a trend with distance sampling is 1.19 time higher but considering six more years of effort. These results highlight the importance of selecting a-priori sampling design techniques that include developing pilot studies that evaluate the bias, precision and accuracy of estimates while considering costs involved. Considering the small population size estimated herein, the sensitivity of both approaches for detecting trends is not sufficient because the original population would be markedly reduced by the time a declining trend was detected. Thus, a precautionary approach is still imperative, even when robust estimates are obtained.

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Accounting for Lack of Independence and Partial Overlap of Observation Zones in Line-Transect Mark-Recapture Distance Sampling

Journal of Agricultural Biological and Environmental Statistics ◽

10.1007/s13253-015-0234-1 ◽

2015 ◽

Vol 21 (1) ◽

pp. 41-57 ◽

Cited By ~ 2

Author(s):

D. I. MacKenzie ◽

D. Clement

Keyword(s):

Distance Sampling ◽

Line Transect ◽

Mark Recapture ◽

Partial Overlap

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Getting the Most From Surveys: How Method Selection and Method Modification Impact Butterfly Survey Data

Annals of the Entomological Society of America ◽

10.1093/aesa/saab004 ◽

2021 ◽

Author(s):

Katherine C Kral-O’Brien ◽

Adrienne K Antonsen ◽

Torre J Hovick ◽

Ryan F Limb ◽

Jason P Harmon

Keyword(s):

Species Richness ◽

New Species ◽

Count Data ◽

Distance Sampling ◽

Line Transect ◽

Similar Species ◽

Method Selection ◽

M 10 ◽

Sampling Procedures

Abstract Many methods are used to survey butterfly populations, with line transect and area surveys being prominent. Observers are typically limited to search within 5 or 10 m from the line, while observers are unrestricted in larger specified search regions in area surveys. Although methods differ slightly, the selection is often based on producing defendable data for conservation, maximizing data quality, and minimizing effort. To guide method selection, we compared butterfly surveys using 1) line versus area methods and 2) varying width transects (5 m, 10 m, or unrestricted) using count data from surveys in North Dakota from 2015 to 2018. Between line and area surveys, we detected more individuals with area surveys, even when accounting for effort. However, both methods accumulated new species at similar rates. When comparing transect methodology, we detected nearly 60% more individuals and nine more species when transect width increased from 5 m to unrestricted, despite similar effort across methodology. Overall, we found line surveys slightly less efficient at detecting individuals, but they collected similar species richness to area surveys when accounting for effort. Additionally, line surveys allow the use of unrestricted-width transects with distance sampling procedures, which were more effective at detecting species and individuals while providing a means to correct count data over the same transect length. Methods that reduce effort and accurately depict communities are especially important for conservation when long-term datasets are unavailable.

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Harbor porpoise (Phocoena phocoena) recovery in the inland waters of Washington: estimates of density and abundance from aerial surveys, 2013–2015

Canadian Journal of Zoology ◽

10.1139/cjz-2015-0236 ◽

2016 ◽

Vol 94 (7) ◽

pp. 505-515 ◽

Cited By ~ 3

Author(s):

Thomas A. Jefferson ◽

Mari A. Smultea ◽

Sarah S. Courbis ◽

Gregory S. Campbell

Keyword(s):

Puget Sound ◽

Distance Sampling ◽

Line Transect ◽

Inland Waters ◽

San Juan ◽

Phocoena Phocoena ◽

Harbor Porpoise ◽

San Juan Islands ◽

Juan De Fuca ◽

Harbor Porpoises

The harbor porpoise (Phocoena phocoena (L., 1758)) used to be common in Puget Sound, Washington, but virtually disappeared from these waters by the 1970s. We conducted systematic aerial line-transect surveys (17 237 km total effort) for harbor porpoises, with the goal of estimating density and abundance in the inland waters of Washington State. Surveys in Puget Sound occurred throughout the year from 2013 to 2015, and in the Strait of Juan de Fuca and the San Juan Islands (and some adjacent Canadian waters) in April 2015. We used a high-wing, twin-engine Partenavia airplane and four observers (one on each side of the plane, one looking through a belly port, and one recording data). A total of 1063 harbor porpoise groups were sighted. Density and abundance were estimated using conventional distance sampling methods. Analyses were limited to 447 harbor porpoise groups observed during 5708 km of effort during good sighting conditions suitable for line-transect analysis. Harbor porpoises occurred in all regions of the study area, with highest densities around the San Juan Islands and in northern Puget Sound. Overall, estimated abundance for the Washington Inland Waters stock was 11 233 porpoises (CV = 37%, 95% CI = 9 616 – 13 120). This project clearly demonstrated that harbor porpoises have reoccupied waters of Puget Sound and are present there in all seasons. However, the specific reasons for their initial decline and subsequent recovery remain uncertain.

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The importance of survey design in distance sampling: field evaluation using domestic sheep

Wildlife Research ◽

10.1071/wr10234 ◽

2011 ◽

Vol 38 (3) ◽

pp. 221 ◽

Cited By ~ 6

Author(s):

Tom A. Porteus ◽

Suzanne M. Richardson ◽

Jonathan C. Reynolds

Keyword(s):

Population Size ◽

Survey Design ◽

Distance Sampling ◽

Field Evaluation ◽

Stage I ◽

Stage Ii ◽

Line Transect ◽

Domestic Sheep ◽

Management Decisions ◽

Mobile Species

Context Sampling methods to estimate animal density require good survey design to ensure assumptions are met and sampling is representative of the survey area. Management decisions are often made based on these estimates. However, without knowledge of true population size it is not possible for wildlife biologists to evaluate how biased the estimates can be if survey design is compromised. Aims Our aims were to use distance sampling to estimate population size for domestic sheep free-ranging within large enclosed areas of hill country and, by comparing estimates against actual numbers, examine how bias and precision are impaired when survey design is compromised. Methods We used both line and point transect sampling to derive estimates of density for sheep on four farms in upland England. In Stage I we used limited effort and different transect types to compromise survey design. In Stage II we increased effort in an attempt to improve on the Stage I estimates. We also examined the influence of a walking observer on sheep behaviour to assess compliance with distance sampling assumptions and to improve the fit of models to the data. Key results Our results show that distance sampling can lead to biased and imprecise density estimates if survey design is poor, particularly when sampling high density and mobile species that respond to observer presence. In Stage I, walked line transects were least biased; point transects were most biased. Increased effort in Stage II reduced the bias in walked line transect estimates. For all estimates, the actual density was within the derived 95% confidence intervals, but some of these spanned a range of over 100 sheep per km2. Conclusions Using a population of known size, we showed that survey design is vitally important in achieving unbiased and precise density estimation using distance sampling. Adequate transect replication reduced the bias considerably within a compromised survey design. Implications Management decisions based on poorly designed surveys must be made with an appropriate understanding of estimate uncertainty. Failure to do this may lead to ineffective management.

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The influence of animal mobility on the assumption of uniform distances in aerial line-transect surveys

Wildlife Research ◽

10.1071/wr07077 ◽

2008 ◽

Vol 35 (4) ◽

pp. 275 ◽

Cited By ~ 31

Author(s):

Rachel M. Fewster ◽

Colin Southwell ◽

David L. Borchers ◽

Stephen T. Buckland ◽

Anthony R. Pople

Keyword(s):

Survey Design ◽

Distance Sampling ◽

High Mobility ◽

Line Transect ◽

Transect Line ◽

Aerial Surveys ◽

Pack Ice ◽

Capture Recapture ◽

Distance Data ◽

Crabeater Seals

Line-transect distance sampling is a widely used method for estimating animal density from aerial surveys. Analysis of line-transect distance data usually relies on a requirement that the statistical distribution of distances of animal groups from the transect line is uniform. We show that this requirement is satisfied by the survey design if all other assumptions of distance sampling hold, but it can be violated by consistent survey problems such as responsive movement of the animals towards or away from the observer. We hypothesise that problems with the uniform requirement are unlikely to be encountered for immobile taxa, but might become substantial for species of high mobility. We test evidence for non-uniformity using double-observer distance data from two aerial surveys of five species with a spectrum of mobility capabilities and tendencies. No clear evidence against uniformity was found for crabeater seals or emperor penguins on the pack-ice in East Antarctica, while minor non-uniformity consistent with responsive movement up to 30 m was found for Adelie penguins. Strong evidence of either non-uniformity or a failure of the capture–recapture validating method was found for eastern grey kangaroos and red kangaroos in Queensland.

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Estimating abundance of the Endangered onager Equus hemionus onager in Qatruiyeh National Park, Iran

Oryx ◽

10.1017/s0030605311001827 ◽

2013 ◽

Vol 47 (2) ◽

pp. 266-272 ◽

Cited By ~ 3

Author(s):

Mahmoud-Reza Hemami ◽

Moslem Momeni

Keyword(s):

Growth Rate ◽

Protected Area ◽

National Park ◽

Natural Populations ◽

Distance Sampling ◽

Line Transect ◽

Management Interventions ◽

Equus Hemionus ◽

Wild Ass ◽

Semi Arid

AbstractHistorically, the onager or Persian wild ass Equus hemionus onager, endemic to Iran, was widespread on the arid and semi-arid central steppes but only two natural populations remain. We estimated the population density of the onager in Qatruiyeh National Park using line transect distance sampling. Transects were surveyed on three plains in the Park and the results compared with total counts conducted by the Department of Environment. Our estimate (109 onagers per 100 km2; 95% confidence interval 67–179) is similar to that obtained by the total counts (137 onagers per 100 km2). Distance sampling is therefore a promising method for estimating the abundance of the onager. Using the annual censuses performed by the Department of Environment over the last 13 years we estimated that the population has a growth rate of 0.09. During the same period the onager population in the Touran Protected Complex has experienced a severe decline. The high density of onagers within the National Park indicates the unsuitability of adjacent habitats, including Bahram-e-Goor Protected Area, for this species. Lack of sufficient security and poorly distributed water sources appear to be the main reasons discouraging onagers from entering the Bahram-e-Goor Protected Area. We recommend and describe management interventions that could potentially assist in maintaining the last surviving onager populations in Iran.

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Status of the relict population of the Critically Endangered Madagascar spider tortoise Pyxis arachnoides

Oryx ◽

10.1017/s0030605311001293 ◽

2012 ◽

Vol 46 (3) ◽

pp. 457-463 ◽

Cited By ~ 2

Author(s):

Ryan C. J. Walker ◽

Tsilavo H. Rafeliarisoa

Keyword(s):

Protected Areas ◽

Distance Sampling ◽

Habitat Destruction ◽

Species Range ◽

Line Transect ◽

Anthropogenic Pressures ◽

Community Based Conservation ◽

Relict Population ◽

Distance Model ◽

C 71

AbstractThe Madagascar spider tortoise Pyxis arachnoides is endemic to the coastal dry forests of south-west Madagascar. In recent years its range has been reduced by c. 71%, with the species now confined to eight fragmented populations occupying a total of 2,464 km2. These remaining populations are facing a significant threat of extinction because of habitat destruction and other anthropogenic pressures. We developed methodology for a line transect distance sampling survey and applied it systematically across the species' range. The resulting distance model estimated a mean density of 226.9 tortoises km−2 (95% confidence interval, CI, 168.1–306.3) and a total population of 664,980 (95% CI 492,680–897,550). Fragmentation of the species’ range suggests the current population could be <30% of the historical population. Of the remaining population 73.5% falls within protected areas. However, nine of these 12 protected areas are designated as IUCN category III, V or VI parks, allowing some extractive activities to be undertaken. The most effective strategy for the conservation of P. arachnoides would be to reduce the threats to this species and its habitat, and to develop and expand the current community-based conservation and poverty alleviation programmes in the region.

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Demographic decline of the last surviving Moroccan dorcas gazelles Gazella dorcas massaesyla in M'Sabih Talaa Reserve, Morocco

Oryx ◽

10.1017/s0030605312000506 ◽

2013 ◽

Vol 47 (4) ◽

pp. 578-583

Author(s):

Moulay Abdeljalil Ait Baamrane ◽

Mohammed Znari ◽

Chris Loggers ◽

Said El Mercht ◽

Mohamed Naimi

Keyword(s):

Distance Sampling ◽

Management Programme ◽

Line Transect ◽

Captive Population ◽

Genetic Management ◽

Single Population ◽

Catastrophic Event ◽

Feral Dogs ◽

Conservation Actions ◽

To Receive

AbstractThe formerly widespread but now Vulnerable dorcas gazelle Gazella dorcas has declined markedly during the last 2 decades. The semi-captive population in M'Sabih Talaa Reserve, west-central Morocco, is genetically distinct and may be the last remnant of the Moroccan dorcas gazelle G. dorcas massaesyla. The last estimate of the size of this population was c. 200, in 1996. To assess the current population we used line-transect distance sampling to survey this population over five seasons from April 2008 to August 2009. The estimated population declined from 113 to 87 individuals from April to November 2008, increased to 111 in February 2009 (primarily because of recruitment), declined to 99 from February to April 2009, and to 95 by August 2009. These results indicate a decline of nearly 50% in < 15 years. The main conservation actions required for this subspecies are the suppression of poaching and feral dogs, the creation of other reserves to receive dorcas gazelles from M'Sabih Talaa (to avoid loss of the single population from a catastrophic event), and the implementation of a genetic management programme.

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