North Atlantic Sightings Surveys (NASS) are a series of internationally coordinated cetacean surveys that have been conducted in 1987, 1989, 1995, 2001, 2007 (Trans-NASS (T-NASS)) and 2015. The main purpose of the surveys was and is to get quantitative information on the distribution and abundance of all cetacean species in the survey area, which encompasses much of the northern North Atlantic between Norway and North America. The NASS are perhaps the largest-scale wildlife surveys ever attempted, covering a maximum area of around 2 million square nautical miles, about the same size as Western Europe, and involving as many as 15 ships, 4 aircraft and 100 observers in a single survey. The distance covered by ships and planes while surveying has been as high as 40,000 nautical miles, a distance equivalent to about twice around the world. As many as 5,000 whales have been seen in a single survey. The long time span of the NASS make them ideal for determining abundance trends. Since 1995, the NASS have been planned and coordinated by the NAMMCO Scientific Committee.
The earliest surveys (1987and 1989) were the largest, involving the participation of 5 countries: the Faroes, Greenland, Iceland, Norway and Spain. By 1995, Spain and Greenland were no longer participating and the survey area was consequently smaller. After 1995, Norway began surveying a portion of their area annually on a 6 year rotation. As a result, the area covered by Norway in 2001 and later surveys was smaller than in previous years. In 2007, Greenland and Canada participated in the survey, and it was coordinated with simultaneous surveys in offshore European waters (CODA survey) and off the US eastern seaboard (SNESSA survey). This made the T-NASS 2007 one of the largest ever and the first to achieve trans-Atlantic coverage.
All species encountered are recorded on these surveys. However, each participating country has one or more target species: species which are of highest priority for the survey. This may be because the species is harvested or subject to indirect take, or because of other conservation concerns. For example, the minke whale is a target species for Norway because it is harvested there, while minke and fin whales are target species for Iceland for the same reason. The identification of target species influences survey design, in that the survey will cover only areas where the target species is expected to occur, and the stratification and effort allocation will be optimized for the target species.
Because of the huge area covered by the NASS, large ships are used to cover offshore areas. Ships can stay in the field for weeks at a time; the entire area takes as long as a month to complete. Some coastal areas, notably Iceland, West Greenland and eastern Canada, have been covered by aircraft.
Estimates of abundance have been produced for all target species and many non-target species from the NASS and T-NASS. In 2009, NAMMCO published Volume 7: North Atlantic Sightings Surveys: Counting whales in the North Atlantic, 1987-2001 of NAMMCO Scientific Publications devoted entirely to the NASS up to and including the 2001 survey. In addition, many estimates have been published elsewhere or produced as non-published working papers. These estimates have been used by the NAMMCO Scientific Committee, the Scientific Committee of the International Whaling Commission, and other agencies to provide advice on the conservation and management of many marine mammal stocks. Abundance estimates from the NASS are provided under the individual species pages, where applicable.