Effect of observer differences on abundance estimates of seabirds from ship-based strip transect surveys

Ibis ◽  
2008 ◽  
Vol 138 (3) ◽  
pp. 433-437 ◽  
Author(s):  
J. VAN DER MEER ◽  
C. J. CAMPHUYSEN
Keyword(s):  
Abundance Estimates ◽  
Strip Transect

Use of line transect methods to estimate abundance of benthic stream fishes

1995 ◽  
Vol 52 (1) ◽  
pp. 213-222 ◽  
Author(s):  
William E. Ensign ◽  
Paul L. Angermeier ◽  
C. Andrew Dolloff
Keyword(s):  
Distance Sampling ◽  
Line Transect ◽  
Strong Positive Correlation ◽  
Stream Fishes ◽  
Visual Estimation ◽  
Abundance Estimates ◽  
Benthic Stream ◽  
Roanoke Logperch ◽  
Strip Transect ◽  
Stream Salmonid

Visual estimation of stream salmonid abundance using strip transect sighting models has become commonplace. Application of visual estimation to other stream fishes, particularly benthic forms, has been limited. Examination of the distribution of sighting distances for the Roanoke darter (Percina roanoka), Roanoke logperch (P. rex), and black jumprock (Moxostoma cervinum) indicates that strip transect sighting models that assume probability of sighting remaining constant out to the limits of observer visibility are not appropriate for these benthic species. Our datasets indicate that distance sampling models that assume decreased sighting probability with increasing distance of the target from the observer provide a reasonable alternative to strip transect sighting models. There was a strong positive correlation between abundance estimates calculated using two alternative distance sampling models, as well as between the distance sampling model estimates and an estimate of abundance obtained with a backpack electroshocker.

scholarly journals Delphinid spatial distribution and abundance estimates over the shelf of the Bay of Biscay

2008 ◽  
Vol 65 (4) ◽  
pp. 656-666 ◽  
Author(s):  
G. Certain ◽  
V. Ridoux ◽  
O. van Canneyt ◽  
V. Bretagnolle
Keyword(s):  
Spatial Distribution ◽  
Large Scale ◽  
Bottlenose Dolphins ◽  
Shelf Break ◽  
Bay Of Biscay ◽  
Stenella Coeruleoalba ◽  
Abundance Estimate ◽  
Abundance Estimates ◽  
Common Dolphins ◽  
Strip Transect

Abstract Certain, G., Ridoux, V., van Canneyt, O., and Bretagnolle, V. 2008. Delphinid spatial distribution and abundance estimates over the shelf of the Bay of Biscay. – ICES Journal of Marine Science, 65: 656–666. The small delphinid community (bottlenose Tursiops truncatus, common Delphinus delphis, and striped Stenella coeruleoalba dolphins) of the Bay of Biscay (100 000 km2 of continental shelf along the French Atlantic coast) has been studied here by combining strip-transect aerial surveys conducted between 2001 and 2004 and ship-based surveys conducted between 2003 and 2006. Distribution was modelled spatially in relation to several large-scale descriptors of the environment. Highest densities of small delphinids were associated with the shelf break, in particular in two hotspots located in the north and the south of the bay. Using ship-based data, we found strong spatial segregation between common and bottlenose dolphins in spring, with common dolphins associated with coastal areas (and especially river plumes) and bottlenose dolphins on the outer shelf and the shelf break. Assuming a detection probability of 1, a strip-transect abundance estimate for the small delphinid community was obtained in August 2002 with 56 500 (95% CI 29 100–90 400), but relative abundance varied across months.

Abundance Estimates of Guiana Dolphins (Sotalia guianensis; Van Bénéden, 1864) Inhabiting an Estuarine System in Southeastern Brazil

2019 ◽  
Vol 45 (1) ◽  
pp. 56-65 ◽  
Author(s):  
Aline B. de Mello ◽  
Julia M. B. Molina ◽  
Maja Kajin ◽  
Marcos C. de O. Santos
Keyword(s):  
Southeastern Brazil ◽  
Estuarine System ◽  
Sotalia Guianensis ◽  
Abundance Estimates

Bridled Quail-dove Geotrygon mystacea population assessment after hurricanes Irma and Maria, St. Eustatius, Caribbean Netherlands

2021 ◽  
pp. 1-12
Author(s):  
FRANK F. RIVERA-MILÁN ◽  
HANNAH MADDEN ◽  
KEVIN VERDEL
Keyword(s):  
National Park ◽  
Food Limitation ◽  
Distance Sampling ◽  
Population Status ◽  
Management Actions ◽  
Abundance Estimates ◽  
Detection Mode ◽  
Limited Food ◽  
Seed Eating ◽  
Free Ranging

Summary Structural vegetation damage and food limitation are important effects of major hurricanes, particularly for fruit/seed-eating, forest-dependent Caribbean birds with restricted distributions and small populations, such as the Bridled Quail-dove Geotrygon mystacea. Motivated by the lack of abundance estimates, corrected for detection probability, we conducted distance-sampling surveys inside and outside the Quill National Park each May in 2016-2019. Detection mode was the most important covariate, with others receiving no support from the data. Detectability of available single individuals and clusters of individuals within 60 m of transect centrelines averaged 0.957 ± 0.114 standard error for audio detections, 0.434 ± 0.052 for visual detections, and 0.693 ± 0.064 for detection modes combined. Availability averaged 0.475 ± 0.138 and the product of detectability and availability averaged 0.329 ± 0.098. Density averaged 1.459 ± 0.277 individuals ha-1 and population size averaged 642 ± 122 individuals in 440 ha. Density did not differ along and away from forest trails, but was higher inside than outside the park and at elevations within 201-400 m than 100-200 m and 401-600 m. Density declined by 76% after hurricanes Irma and Maria in 2017. We suggest that major hurricanes together with free-ranging livestock overgrazing degraded foraging habitats, limited food supply, and caused a population bottleneck. Our methodology can be implemented across the distribution range to assess population status and trends and evaluate the result of management actions at key conservation sites. Bridled Quail-dove populations probably were declining on most islands before the 2017 hurricanes and population status warrants revision.

scholarly journals Temporal trends in stock origin and abundance of juvenile herring (Clupea harengus) in the Irish Sea

2009 ◽  
Vol 66 (8) ◽  
pp. 1749-1753 ◽  
Author(s):  
Nóirín Burke ◽  
Deirdre Brophy ◽  
Pieter-Jan Schön ◽  
Pauline A. King
Keyword(s):  
Temporal Trends ◽  
Clupea Harengus ◽  
Irish Sea ◽  
First Year ◽  
Juvenile Abundance ◽  
Abundance Estimates ◽  
Otolith Microstructure Analysis ◽  
Celtic Sea ◽  
The Irish Sea ◽  
First Year Of Life

Abstract Burke, N., Brophy, D., Schön, P-J., and King, P. A. 2009. Temporal trends in stock origin and abundance of juvenile herring (Clupea harengus) in the Irish Sea. – ICES Journal of Marine Science, 66: 1749–1753. Celtic Sea herring (Clupea harengus) larvae partly disperse into the Irish Sea, where they mix with the resident stock during their first year of life. This affects the reliability of the use of acoustic estimates of juvenile abundance on the Irish Sea nursery grounds as a recruitment index for use in stock predictions. Otolith microstructure analysis can be used to distinguish between autumn-spawned and winter-spawned individuals. Because winter spawners do not occur in the Irish Sea, this component can be assigned to Celtic Sea immigrants. We used this method to estimate the proportion of winter-spawned individuals in samples of age-1 herring from the western Irish Sea over a 10-year period (1993–2003), and subtracted a corresponding proportion from the acoustic age-1 abundance estimates. The adjusted index for autumn-spawned (supposedly Irish Sea) juveniles was significantly correlated with the abundance of age-3 fish from the same year class in commercial catches and in the acoustic surveys (p < 0.05 and <0.01, respectively), whereas the correlations for unadjusted indices were not significant. These findings are discussed in relation to the monitoring and assessment of herring in the two areas.

scholarly journals Boreal bird abundance estimates within different energy sector disturbances vary with point count radius

The Condor ◽  
2016 ◽  
Vol 118 (2) ◽  
pp. 376-390 ◽  
Author(s):  
Erin Bayne ◽  
Lionel Leston ◽  
C. Lisa Mahon ◽  
Péter Sólymos ◽  
Craig Machtans ◽  
...  
Keyword(s):  
Energy Sector ◽  
Bird Abundance ◽  
Point Count ◽  
Abundance Estimates

scholarly journals Estimation of harp seal (Pagophilus groenlandicus) pup production in the North Atlantic completed: results from surveys in the Greenland Sea in 2002

2006 ◽  
Vol 63 (1) ◽  
pp. 95-104 ◽  
Author(s):  
Tore Haug ◽  
Garry B. Stenson ◽  
Peter J. Corkeron ◽  
Kjell T. Nilssen
Keyword(s):  
North Atlantic ◽  
Barents Sea ◽  
Temporal Distribution ◽  
Harp Seal ◽  
Greenland Sea ◽  
The North ◽  
Pagophilus Groenlandicus ◽  
Pack Ice ◽  
Photographic Survey ◽  
Strip Transect

Abstract From 14 March to 6 April 2002 aerial surveys were carried out in the Greenland Sea pack ice (referred to as the “West Ice”), to assess the pup production of the Greenland Sea population of harp seals, Pagophilus groenlandicus. One fixed-wing twin-engined aircraft was used for reconnaissance flights and photographic strip transect surveys of the whelping patches once they had been located and identified. A helicopter assisted in the reconnaissance flights, and was used subsequently to fly visual strip transect surveys over the whelping patches. The helicopter was also used to collect data for estimating the distribution of births over time. Three harp seal breeding patches (A, B, and C) were located and surveyed either visually or photographically. Results from the staging flights suggest that the majority of harp seal females in the Greenland Sea whelped between 16 and 21 March. The calculated temporal distribution of births were used to correct the estimates obtained for Patch B. No correction was considered necessary for Patch A. No staging was performed in Patch C; the estimate obtained for this patch may, therefore, be slightly negatively biased. The total estimate of pup production, including the visual survey of Patch A, both visual and photographic surveys of Patch B, and photographic survey of Patch C, was 98 500 (s.e. = 16 800), giving a coefficient of variation of 17.9% for the survey. Adding the obtained Greenland Sea pup production estimate to recent estimates obtained using similar methods in the Northwest Atlantic (in 1999) and in the Barents Sea/White Sea (in 2002), it appears that the entire North Atlantic harp seal pup production, as determined at the turn of the century, is at least 1.4 million animals per year.

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