Aerial high definition video surveys - an advanced method to monitor marine mammals and seabirds
2, Andy Webb2, Thilo Liesenjohann1, Ansgar Diederichs1, Felix Weiss1, Georg Nehls1
1BioConsult SH GmbH&Co.KG, 25813 Husum, Germany, 2HiDef Aerial Surveying Ltd, Cleator Moor, Cumbria, UK
Monitoring the abundance and distribution of marine animals (e.g. dolphins, whales and resting/migrating birds) has traditionally been conducted by conventional observer-based ship and low-flying aerial surveys. Both conventional methods cause strong responsive behaviour of the animals to the survey vessel or plane which results in biased estimates and affects the animals' distributions during the survey. Conventional methods are therefore replaced by an aerial high-flying survey technique which enables to video-survey at a resolution of two cm/pixel at ground level. During several investigations on offshore wind farms in the German North Sea, we used digital aerial video techniques to detect harbour porpoise (Phocoena phocoena), harbour seal (Phoca vitulina) and seabirds (e.g. Common Scoter, Melanitta nigra, and Red-troated Diver, Gavia stellata). Densities were compared between the former conventional visual survey method and the digital video technique.
The HiDef transect-based video-surveying technique works with four digital video cameras mounted on a Partenavia P68. At a survey altitude of 1800 ft, a total strip width of 544 m is covered at 2cm/pixel resolution at sea level with 9 pictures per second captured by each camera. This allows sampling of 120km2 per hour. Camera angels can be adjusted to avoid glare. Pictures are stored and a review and ID process is started to identify animals on species level.
For seabirds, our analyses suggested a substantial underestimation by traditional visual survey techniques, particularly for sensitive species such as the Common Scoter. Moreover, digital aerial video techniques provided additional data with insights on behaviour and the possibility to measure the animal sizes or sex ratios within larger groups of animals. As the detectability of small marine animals does not decrease with the distance from the transect-line, video-surveys offer accurate flock/pod counts without the need for distance correction. For the two marine mammal species, the videos provided high sighting rates of both surfacing and submerged animals allowing precise density estimates for marine mammals. The footage alse provides additional information on size (e.g., for identifying mother/offspring groups) or swimming direction of individual animals.
High definition survey techniques are efficient in covering large areas and are much safer compared to conventional low-flying surveys in areas with vertical structures like wind turbines. Video-survey data can be reviewed any time and a quality assurance process can be implemented. Additionally, digital surveys yield a better spatial resolution and additional information such as behaviour, size measurements and association to other animals without disturbing natural populations during sampling.
Aerial video surveys before, during, or after construction work produce reliable and reproducable data which can be reviewed by independent experts to provide environmental impact assessments. It is also an efficient method to study e.g., offshore birds or seals and thus give insight into biology and behaviour of species from which is little known so far.