A rapid assessment of the impacts of the Montara oil leak on birds, cetaceans and marine reptiles

EXECUTIVE SUMMARY

• On 24th September 2009, Dr James Watson of the University of Queensland was commissioned by the Department of the Environment, Water, Heritage and the Arts (DEWHA) to lead a rapid survey of the ‘megafauna’ (defined as cetaceans, birds and marine reptiles, i.e. turtles and sea snakes) in the Montara oil spill region. He solicited the help of Dr Liana Joseph (University of Queensland) and Dr Alexander Watson to conduct these tasks.
• The rapid survey, conducted on board the boat Sea Sprint, departed Darwin in the evening of Friday 25th September and returned the morning of Sunday 4th October.
• Five days of transects (incorporating 279 10-minute strip transects) were conducted at sea, covering a distance of 668.5 nautical miles (1,238 km) and a total survey area of 99,040 ha. In these surveys, a total of 124 (44%) 10-minute strip transects were in waters that were visibly affected by oil.
• The surveys at sea revealed a high level of diversity and abundance of birds (number of individuals (NI) = 2801, number of species (NS) =23), cetaceans (NI= 462, NS= 4), turtles (NI=25, NS=2) and sea snakes (NI=62, NS=4), in the region of the Montara oil spill.
• A further three days of land-based surveys were conducted on the three permanent islands (East, Middle and West Islands) of Ashmore Reef. The surveys on land found 35 bird species of which 10 species were in a stage of breeding.
• The presence of one dying Common Noddy (Anous stolidus) and one dead Horned Sea Snake (Acalyptophis peronii) floating in oil affected waters indicates that some species are negatively affected by the oil spill. The Noddy died within 12 hours of its capture. A further 17 adult dead birds found on the islands of Ashmore Reef appeared to have died of unknown causes, with at least four having large amounts of oil residue on parts of their body. These birds are undergoing toxicological testing to establish cause of death.
• During the surveys at sea, five seabird species were found only in transects where oil was not observed. These species may be avoiding the oil slick region when feeding. However, a number of bird, cetacean and sea snake species were found in higher numbers in oil affected waters than in non oil affected waters. Our observations suggest that response to the oil slick is species-specific and the presence of oil in the water is affecting some species’ behaviour.
• We believe that the only way to ascertain the true impacts of the Montara oil spill on the region’s biodiversity is to conduct a systematic, long-term monitoring effort. This effort should include long term monitoring on all seabird and turtle breeding islands in the region as well as permanent transects along the reef itself to ascertain the impacts of the oil slick on fish and sea snake populations. Further long term monitoring at sea is also needed to ascertain if the oil spill has affected species behavior and population dynamics for both species breeding in the region and migratory species visiting the region. Toxicological studies of all ‘megafauna’ species (birds, mammals and reptiles) as well as fish are recommended to assess if toxic chemicals are present in the tissue of the animals.

Download file here