Observer precision and bird conspicuousness during counts of birds at sea

Ryan, Peter G.; Cooper, Jim

doi:10.2989/02577618909504567

Cited by 10 publications

(10 citation statements)

References 4 publications

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“…Changes detected in the amounts of debris are the balance between inputs and losses and do not necessarily reflect the efficacy of mitigation measures to reduce losses of plastics into the environment. Ryan & Cooper 1989), which needs to be addressed if multiple observers are used to monitor debris at sea. Counts of litter at sea can be used to provide an index of abundance (number of items per unit distance) or an estimate of abundance based on fixed-width or line transects.…”

Section: Surveys At Seamentioning

confidence: 99%

Monitoring the abundance of plastic debris in the marine environment

Ryan¹,

Moore²,

Franeker

et al. 2009

Phil. Trans. R. Soc. B

1,288

565

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Plastic debris has significant environmental and economic impacts in marine systems. Monitoring is crucial to assess the efficacy of measures implemented to reduce the abundance of plastic debris, but it is complicated by large spatial and temporal heterogeneity in the amounts of plastic debris and by our limited understanding of the pathways followed by plastic debris and its long-term fate. To date, most monitoring has focused on beach surveys of stranded plastics and other litter. Infrequent surveys of the standing stock of litter on beaches provide crude estimates of debris types and abundance, but are biased by differential removal of litter items by beachcombing, cleanups and beach dynamics. Monitoring the accumulation of stranded debris provides an index of debris trends in adjacent waters, but is costly to undertake. At-sea sampling requires large sample sizes for statistical power to detect changes in abundance, given the high spatial and temporal heterogeneity. Another approach is to monitor the impacts of plastics. Seabirds and other marine organisms that accumulate plastics in their stomachs offer a cost-effective way to monitor the abundance and composition of small plastic litter. Changes in entanglement rates are harder to interpret, as they are sensitive to changes in population sizes of affected species. Monitoring waste disposal on ships and plastic debris levels in rivers and storm-water runoff is useful because it identifies the main sources of plastic debris entering the sea and can direct mitigation efforts. Different monitoring approaches are required to answer different questions, but attempts should be made to standardize approaches internationally.

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Section: Surveys At Seamentioning

confidence: 99%

Monitoring the abundance of plastic debris in the marine environment

Ryan¹,

Moore²,

Franeker

et al. 2009

Phil. Trans. R. Soc. B

1,288

565

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“…The second potential source of error is the presence of the vessel influencing the behaviour at sea of the seabirds observed (Ryan & Cooper 1989). Some species are known to be attracted to vessels (e.g.…”

Section: Limitations To the Studymentioning

confidence: 99%

“…The first is that numerous observers collected the data used in this study. It is impossible to correct for inter-observer biases (Ryan & Cooper 1989), and particularly so in multi-decadal studies where there are numerous observers. To some extent this bias is mitigated by a majority of the seabird observations being collected by observers who were present on multiple voyages.…”

Section: Limitations To the Studymentioning

confidence: 99%

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Decadal-scale seabird assemblages in Prydz Bay, East Antarctica

Woehler¹,

Raymond²,

Watts³

2003

Mar. Ecol. Prog. Ser.

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A total of 26 species/taxa make up the seabird community of Prydz Bay, East Antarctica, of which 9 are resident breeding species. Analyses of almost 32 000 at-sea observations over 20 yr (1980/81 to 2001/02) identified 3 assemblages. Observations of Assemblage 1, which included the 9 resident species, were consistent with the influx, presence and departure of breeding birds to their colonies around Prydz Bay. Assemblage 2 was comprised of all seabird species/taxa reported from Prydz Bay and represented an overlap (in time and space) assemblage, being observed in late summer in central Prydz Bay. Assemblage 3 consisted principally of the non-resident species/taxa that visit Prydz Bay every summer from sub-Antarctic and temperate breeding localities. This assemblage was observed most frequently in mid to late summer and well offshore. Two species were found to be indicator species of all 3 assemblages; this is proposed to be a result of their Antarctic and subAntarctic breeding distributions that in turn produce broad ranges in their at-sea distributions in the Southern Ocean. Assemblage 1 is similar to the pack-ice associated seabird assemblage identified elsewhere around the Antarctic, differing only in species composition due to species' breeding distributions at regional scales. Analyses at finer temporal scales (decadal and semi-decadal) identified the same assemblages, indicating the stability of seabird assemblages over the 1980/81 to 2001/02 period within Prydz Bay.

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“…Conspicuousness can affect the detection and counting of animals along transects (Ryan & Cooper 1989, Spear et al 2004. Marine mammal surveys frequently incorporate correction factors for different species (Forney & Barlow 1998), but there are few published data on detection probabilities for seabirds other than marbled murrelets.…”

Section: Detection Of Seabirdsmentioning

confidence: 99%

Estimating seabird densities from vessel transects: distance sampling and implications for strip transects

Ronconi¹,

Burger²

2009

Aquat. Biol.

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Vessel-based transects have been a mainstay of seabird research for decades, yet there has been surprisingly little effort to evaluate the detectability of seabirds within strip transects. Distance sampling methods offer an opportunity to quantify detectability and assess the proportions of birds on the water that may be missed during strip transects. Three summers of line-transect surveys were analyzed using the program Distance to model detection functions of 6 seabird taxa (marbled murrelet Brachyramphus marmoratus, rhinoceros auklet Cerorhinca monocerata, common murre Uria aalge, pigeon guillemot Cepphus columba, pelagic cormorant Phalacrocorax pelagicus, gulls Larus spp.). We tested the effects of covariates (year, observers, sea state, and cluster size) on detection function estimation. Year and observer were the most important covariates for some but not all species. For a 300 m wide transect (150 m on either side), 20 to 80% of birds were detected, depending on species, year, and observer. Detectability was highest for cormorants (60 to 90%) and fairly similar among other species (typically 40 to 60%). Sea state had a significant effect on encounter rate for murrelets suggesting that g(0), detection probability near the transect line, may be <1 when wave height increases. These data emphasize that a high proportion of birds on the water remain undetected during strip-transect surveys. It is important that surveys develop independent estimates of detection probability to account for detectability among species, years, observers, vessel types/speed, and viewing conditions. The application of distance sampling to seabird surveys can provide more accurate abundance and population estimates, which can improve conservation and management efforts.

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Observer precision and bird conspicuousness during counts of birds at sea

Cited by 10 publications

References 4 publications

Monitoring the abundance of plastic debris in the marine environment

Monitoring the abundance of plastic debris in the marine environment

Decadal-scale seabird assemblages in Prydz Bay, East Antarctica

Estimating seabird densities from vessel transects: distance sampling and implications for strip transects

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