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Comparing Boat and Aerial Survey Methods
Comparing Boat and Aerial Survey Methods
We compared results from boat-based surveys and high resolution digital video aerial surveys for wildlife. Generally, boat-based surveys were better at detecting avian taxa while aerial surveys were better at detecting aquatic taxa such as sea turtles and rays. Together, the two methods provided a more complete understanding of the ecology of the mid-Atlantic than either method achieved alone.

Download Mid-Atlantic Wildlife Studies: Distribution and Abundance of Wildlife along the Eastern Seaboard 2012-2014. This 32-page summary publication explores aspects of the mid-Atlantic ecosystem; describes our survey and analytical approaches; and presents a range of results, featuring several case studies on specific species or phenomena.

The Executive Summary for the technical report is also available here.

 

Survey Findings and Observations

  • During both boat and digital aerial surveys, wintering scoters were the most abundant avian group observed. Gulls and terns were observed throughout the year, and collectively were the next most abundant group observed in boat surveys, followed by wintering Northern Gannets. Northern Gannets and loons were the second- and third-most observed avian groups in aerial surveys.
  • High resolution digital video aerial surveys recorded large numbers of animals that were present below the water’s surface. Rays were were the most common, making up 45% of all observations of animals. Fish were the next most commonly observed aquatic animals from the air, including large groups of forage fishes. Many more sea turtles were observed in digital aerial surveys than in boat surveys.
 

Comparing Survey Methods

The survey methods generally showed similar species-habitat relationships, though there were differences in detectability between the two survey types. Boat survey observers recorded more birds per unit area, likely because some species were more reliably detected and identified from the boat. HiDef Aerial Surveying’s digital aerial surveys were very effective at detecting many aquatic taxa including rays, fish, and turtles. While some of these animals were also observed in boat-based surveys, the digital aerial surveys provided an excellent platform for detecting and identifying animals in the upper reaches of the water column.

In addition to detection of animals, there were differences between survey types in observers’ ability to identify animals. Only 45% of aerial observations were identified to species, versus 72% of boat-based observations. Scoters, the most common avian group in both surveys, were more often identified to species from the air, however (27% boat, 52% aerial). Scoters are known to be disturbed by boats, which may have pushed them out of range for definitive identification by boat-based observers in many cases. Excluding scoters, the rate of definitive identifications during boat surveys was 97%.

The relatively low rate of species identifications in aerial video was likely due in part to variations in image quality, as well as difficulties differentiating small species with subtle distinguishing features. Video reviewers also had difficulty identifying Common Loons and Red-throated Loons due to the overlapping body sizes of birds wintering in the region. Identification rates for sea turtles were lower from the air than from the boat (21% aerial, 91% boat), but more species were observed in aerial data, and many more individuals were detected from the air.

 

Comparison Study

<p>This diagram shows the fields of view available during boat surveys and digital video aerial surveys. The combined strip width for all four video cameras is 200 m; the boat transect has an intended minimum strip width of 300 m, although observations of animals were made up to 1,000 m from the vessel. Apart from the experimental comparison (discussed below), the boat and plane followed different transect lines.</p>
<p>To understand the effectiveness of digital video aerial surveys, and the specific challenges faced in employing the technique in North America, we experimentally compared results from simultaneous boat and digital video aerial surveys off of Virginia in 2013. The methods had clear strengths and weaknesses. Overall, the boat-based survey provided better species identification for many species groups, but the boat also caused substantial disturbance for some taxa, complicating identification efforts and abundance estimation.</p>

This diagram shows the fields of view available during boat surveys and digital video aerial surveys. The combined strip width for all four video cameras is 200 m; the boat transect has an intended minimum strip width of 300 m, although observations of animals were made up to 1,000 m from the vessel. Apart from the experimental comparison (discussed below), the boat and plane followed different transect lines.

To understand the effectiveness of digital video aerial surveys, and the specific challenges faced in employing the technique in North America, we experimentally compared results from simultaneous boat and digital video aerial surveys off of Virginia in 2013. The methods had clear strengths and weaknesses. Overall, the boat-based survey provided better species identification for many species groups, but the boat also caused substantial disturbance for some taxa, complicating identification efforts and abundance estimation.

 

Conclusions

Boat-based and digital video aerial surveys each had specific advantages and disadvantages, but were largely complementary. Digital aerial surveys may be particularly useful for covering offshore areas at broad scales, where general distributions of taxonomic groups are a priority; boat surveys can provide more detailed data on species identities and behaviors, but are more limited in geographic scope due to their slower survey pace.
 

For More Information

For more information, see Chapters 13 and 14 in the technical report.
 

References

  • Gray CE, Paruk JD, DeSorbo CR, Savoy LJ, Yates DE, Chickering MD, Gray RB, Taylor KM, Long D, Schoch N, Hanson W, Cooley J, Evers DC (2014) Body Mass in Common Loons (Gavia immer) strongly associated with migration distance. Waterbirds 37:64–75
  • Schwemmer P, Mendel B, Sonntag N, Dierschke V, Garthe S (2014) Effects of ship traffic on seabirds in offshore waters: implications for marine conservation and spatial planning. Ecological Applications 21:1851–1860
 
Photo Credits: Header image © Romolo Tavani; Infographic Linda Mirabile/Glen Halliday
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