Estimates of the abundance of pilot and other species of whales in the North Atlantic have been based largely on sightings surveys conducted from ships and airplanes. The North Atlantic Sightings Surveys (NASS) provide a time-series of abundance estimates from 1987 to 2007, covering a large part of the North Atlantic. Norwegian “mosaic” surveys cover most of the Northeast Atlantic, surveying a portion of the area annually on a six year rotation. In addition the European CODA (Southern New England to Scotian Shelf Abundance survey) and American SNESSA (Southern New England to Scotian Shelf Abundance) surveys have contributed to our knowledge of pilot whale abundance and distribution.
The five NASS surveys covered substantially different areas and, not surprisingly, yielded different population estimates for pilot whales. Year-to-year shifts in distribution are apparent. The 1989 survey, conducted later in the summer than the other surveys, covered the largest area of potential pilot whale habitat (1,279,741 nm²) and yielded the most reliable total estimate of 778,000 (CV=0.295) for the northeastern North Atlantic Ocean, although small numbers occur outside the area considered (Buckland et al. 1993). No sightings were made in the area North and northeast of the area, thus indicating that the joint survey covered the northernmost areas of pilot distribution.
The table below gives the abundance of pilot whales for the five NASS surveys for the Faroese and Icelandic areas, as well as the northern area of CODA (CODA1), with all data re-analysed similarly (Pike et al. 2013). The 1989 estimate is significantly higher than the 1987, 2001 and 2007 estimates, but the 1989 survey had a substantially different timing and coverage (larger area, extending more to the south and west) than the others, with the possibility of more pilot whales having moved inside the area. The table also gives the first abundance estimate of pilot whales for West Greenland (Guldborg Hansen and Heide-Jørgensen 2013).
Abundance of pilot whales in the northern Northeast Atlantic, from NASS and CODA surveys.
FI, Faroe Island - Iceland area; WG, West Greenland area; CODA1, block 1 of the CODA survey.
The estimates obtained are not directly comparable to one another because of different survey extent. When the estimates are restricted to an index area covered by all five surveys (see also under 'Trends in abundance'), or the larger area covered by the three larger surveys (1989, 1995 and 2007), a decline appears to have taken place over the twenty year period. However, because of the high degree of uncertainty within survey estimates, this apparent decline is not statistically significant (Pike et al. 2013). The analysis of relative abundance in the index areas therefore provides suggestive but inconclusive evidence of a decline in the summer abundance of pilot whales in the area.
It is interesting to see how the size of the index area influences the results, with a high abundance in the 5-survey smaller index area in 1995, which does not appear in the 3-survey larger index area. This illustrates the difficulty in interpreting trends using relative abundance in an index area, when the proportion of pilot whales occupying this area may vary greatly from year to year, which could lead to spurious apparent trends in abundance.
5 and 3 Survey Index Regions and pilot whale abundance by areas (W, E, ALL) for combined platforms used on 1995-2007 surveys. Index Regions indicated on the 2007 survey coverage. In blue, the index area common to the five NASS surveys; In red, the index area common to the 3 largest surveys, 1989, 1995 and 2007 + CODA-1, in which the blue area is included.
An indication of long term historical trends in the abundance of pilot whales around the Faroe Islands can be gained from analysis of catch data. Catch records from the Faroes go as far back as 1584, and are unbroken since 1709 (Bloch 1994). Catch, corrected for hunting effort, shows a cyclic pattern with a period of 100–120 years, with peaks in catch occurring in 1720–1730, 1840–1850, and 1935–1985 (Hoydal and Lastein 1993). There is no long-term indication of declining or increasing abundance over the period (Bloch and Lastein 1995). The local availability of pilot whales to the Faroese may be related to changes in sea temperature and the abundance of their favoured prey. See under 'Life history and Ecology' for further detail.
Pilot whales are common in the offshore waters of the northeastern USA and Canada (Mercer 1975, Lynch 1987, Nelson and Lien 1996, Gannon et al. 1997a, 1997b, Waring et al. 1999, Garrison et al. 2011). However, the abundance and trends in abundance are uncertain, although several abundance estimates are available from selected regions for select time periods.
Long-finned and short-finned pilot whales overlap spatially along the mid-Atlantic shelf break between Cape Hatteras, North Carolina, and New Jersey. As the two species are difficult to distinguish at sea, sighting data during abundance surveys are reported as Globicephala sp. and thus combined abundance estimates for the two species have previously been derived from line-transect surveys. Sightings from shipboard and aerial surveys have been strongly concentrated along the continental shelf break; however, pilot whales are also observed over the continental slope in waters associated with the Gulf Stream.
The best available abundance estimates are from surveys conducted during the summer of 2004 (Waring et al. 2012). These survey data have been combined with an analysis of the spatial distribution of the two species based on genetic analyses of biopsy samples to derive separate abundance estimates. The best resulting abundance estimate for long-finned pilot whales in U.S. waters is 12,619 (CV=0.37).
Although there is no information on abundance trends, abundance is likely increasing because human-induced mortality has declined in recent years (Waring et al. 1999).
Pilot whales were subject to an intensive drive fishery in Newfoundland from 1947 to 1972, and this fishery apparently reduced the stock to very low levels (Mercer 1975, Hay 1982, Nelson and Lien 1996). Abundance at the onset of the fishery was likely about 60,000 animals (Mercer 1975). Hay (1982) conducted in 1980 an aerial survey in eastern Newfoundland and Labrador waters, and estimated 13,167 whales (95% C.I. 6,731 to 19,602, not corrected for diving whales or whales missed by observers). In July–August 2007, the Canadian Trans North Atlantic Sighting Survey (TNASS) covered the area from northern Labrador to the Scotian Shelf, thus providing full coverage of the Atlantic Canadian coast (Lawson and Gosselin 2009, 2011). This aerial survey generated an abundance estimate of 5,612 pilot whales (95% CI = 3,020-10,867, estimate not corrected for availability and perception biases).
Pilot whales in the North Atlantic. Photo: Nordlysid