Estimates of the abundance of fin 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. Variation in distribution from year to year is incorporated into the variance of the resultant abundance estimate (Skaug et al. 2004). 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 fin whale abundance and distribution.
This number is based on the results (Figure below) of the most recent summer surveys, conducted in 2007 as a trans-Atlantic cooperation – SNESSA, T-NASS and CODA. See under T-NASS for more information on this trans-Atlantic exercise under the NAMMCO umbrella.
The components of the overall survey do not overlap in space, thus the surveys are additive and the estimates from each area can simply be summed. A simple sum of the estimates for CODA, Iceland-Faroes, Greenland and Canada yields a total estimate of 42,119 (CV = 0.15) (Pike and Víkingsson 2009, Heide-Jørgensen et al. 2010, Lawson and Gosselin 2011). To this may be added the estimate for the Norwegian survey area in the period 1996-2001 of 6,409 (CV = 0.18) (Øien 2009) and recent estimates from the American eastern seaboard of about 3,000 (Palka, pers. commn.). All of these estimates are negatively biased to a greater or lesser degree by uncorrected perception, availability and/or other biases (see under Abundance surveys for more information on biases). Therefore the total number of fin whales in the North Atlantic must exceed 50,000 (NAMMCO 2011ac).
Distribution of fin whales sightings during the 2007 T-NASS, CODA and SNESSA surveys. Full survey effort shown in red, partial "extension" effort shown in blue.
The NASS and T-NASS surveys were conducted primarily from ships, but coastal Iceland (where few fin whales were found), West Greenland and Eastern Canada were surveyed by plane. See under Abundance surveys for more details on specific surveys, including timing and procedures.
Some available abundance estimates by stock area are listed in the table below. All the estimates listed have been endorsed by the NAMMCO Scientific Committee.
All estimates are likely underestimates, as the entire area of fin whale distribution was not covered in the surveys, and the estimates are not corrected (except indicated) for whales that were diving when the survey ship passed nor whales that were missed by the observers. Estimates for other areas are either not available or have not been compiled by stock area.
Surveys: 1987, 1989, 1995, 2001 and 2007 are NASS Surveys. 1988 is a combination of the 1987 and 1989 NASS surveys. 1996-2001 and 2002-2007 are the Norwegian NILS mosaic surveys. 95% CI is the confidence interval of the estimate, or the interval in which there is a 95% chance to find the true estimate. References give the reference of the report from the international organisation (s) which has/have endorsed the estimate.
The NASS-TNASS series shows relatively rapid changes in the distribution and abundance of fin whales in Central North Atlantic but not in the Eastern Atlantic (Víkingsson et al. 2009).
The area to the west of Iceland (WI), between Iceland and East Greenland, in the EGI stock area, holds the most dense summer concentration of fin whales in the North Atlantic (Figure below, left) Abundance estimates for this area shows an increasing trend of about 12% annually from 1987 to 2001 (Figure below, right). However the estimate from 2007 is similar to that for 2001 for a similar area, so the increase observed over the period 1987-2001 has apparently ceased. The area west of Iceland (WI) includes the former whaling grounds and recovery from whaling explains part of the increase in abundance. The growth in the population greatly exceeds, however, the numbers that were taken by whaling and other factors are also likely involved. These factors may include immigration from other areas and changes in carrying capacity.
Smaller numbers of fin whales are present off North Norway, where there is no indication of any trend in abundance. The numbers off West Greenland, where the surveys did not cover the entire distribution area of fin whales, show an apparent positive trend. A more thorough analysis is needed to confirm this.
Distribution of fin whales during the NASS-TNASS surveys. The reference area used for trend analysis is indicated in yellow.
Trend in abundance in the reference area to the west of Iceland.
Shifts in distribution and abundance of important prey species in the area might be a contributing factor to the observed trends, perhaps as a result of changes in sea temperature. The Figure below sets in parallel changes in sea temperature (200 m depth) between 1994 and 2003 and changes in the distribution of fin whales between 1989 and 2001. The extension of the whale distribution to the south and centre of the area seems to develop in parallel with the extension of the warmer waters (Pike and Víkingsson 2009).
|Changes in sea temperature (200 m depth) between 1994 and 2003 and changes in the distribution of fin whales between 1989 and 2001.The temperature gradient goes from blue through green to red with increasing temperature.|