North AtlanticNorth Atlantic fin whales were comprehensively assessed by the International Whaling Commission (IWC) Scientific Committee (SC) in 1991 (IWC 1992), and an update for the northern part of the region was undertaken in 2006 in a joint workshop with the North Atlantic Marine Mammal Commission (NAMMCO) (IWC 2007a). North Atlantic fin whale stocks had previously been assessed by the IWC Scientific Committee in 1976 (IWC 1977).
Based mainly on past whaling operations, the IWC recognizes seven management areas in the North Atlantic: Nova Scotia; Newfoundland-Labrador; West Greenland; East Greenland-Iceland; North Norway; West Norway-Faeroe Islands; British Isles-Spain-Portugal. Based on genetic evidence, it is now considered more likely that there are from two to four breeding stocks, which use these seven management areas in different proportions (IWC 2007a).
The best available estimates of recent abundance accepted by the IWC Scientific Committee (IWC 2007c) are: 25,800 (CV 0.125) in 2001 for the central North Atlantic (East Greenland-Iceland, Jan Mayen (Norway) and the Faeroes (Denmark)); 4,100 (CV 0.21) in 1996-2001 for the northeastern North Atlantic (North and West Norway); 17,355 (CV 0.27) in 1989 for the Spain-Portugal-British Isles area (Buckland et al. 1992); and 1,722 (CV 0.37) for West Greenland in 2005 (IWC 2007b) There are no complete estimates for the western North Atlantic , but partial estimates are 1,013 (95% CI 459-2,654) for Newfoundland in 2002-3 (IWC 2007a), and 2,814 (CV 0.21) for the east coast of North America from the Gulf of St Lawrence southward (Anon. 2005a).
Subject to a caveat concerning the different dates of the surveys, these figures can be summed to provide a rough total estimate of about 53,000 around the year 2000.
No significant trends were found in the total abundance for any of the above areas, but when the area west and southwest of Iceland was singled out, a significant increasing trend was found (IWC 2007a).
Fin whales were heavily exploited in the late 19th and early 20th centuries, starting in 1876, particularly off Norway, Iceland, the Faeroes and British Isles. Whaling then spread to Spain, Greenland and eastern Canada, and exploitation continued at a lower level until the 1980s.
Catch statistics for the early years are probably incomplete, and a large number of whales were killed but lost, due to lines breaking, etc., perhaps up to one-half in the first 20-25 years and one-third in the next 15-20 years (Tønnessen 1967). The IWC Scientific Committee added 50% to recorded catches up to 1915 to allow for this (IWC 2007a): recorded catches up to 1915 total 15,315 fin whales plus 29,024 unspecified whales of which about half may have been fin whales, thus the total kill may have been about 45,000 up to 1915. The total recorded catch post-1915 has been about 55,000 fin whales. The approximate figures by area are: Canada 12,000; Norway 10,000; Iceland 10,000; Faeroes 5,000; Greenland 1,000; British Isles 3,000; Spain and Portugal 11,000; and pelagic operations 3,000.
The behaviour evident for the various North Atlantic fin whale populations following earlier reductions by whaling differs. It ranges from clear evidence of recovery to no firm indications of any increase. An estimated 14,000 fin whales were killed off northern Norway during 1876-1904, and a further 1,500 during 1948-71, but fin whales are rare there now (although quite abundant off western Spitsbergen, where about 1,500 whales had been killed during 1904-11) (Øien 2003, 2004). An estimated 12,000 fin whales were killed off Iceland during 1890-1915, until whaling was suspended partly due to concerns about the reductions in the stocks, but the modern abundance data suggest that the there has been a recovery in the population that may still be continuing, particularly west of Iceland, despite catches during 1948-89 averaging about 220 per year (Branch and Butterworth 2006). An estimated 10,000 fin whales were taken from the Faeroes, but about 25% of these were actually caught off eastern Iceland (IWC 2007a). Whaling from the Faeroes and West Norway petered out during the 1960s as whales became scarce (IWC 1977), but catches had apparently been mainly of migrating whales rather than whales belonging to local populations. The impact of catches on the fin whale stocks in the Northwest Atlantic is unclear (Mitchell 1972).
Mediterranean
Catches of about 7,000 fin whales taken near the Straits of Gibraltar in the 1920s apparently reduced the local abundance, and fin whales are still rare there today, but this did not seem to affect the abundance of fin whales off northern Spain, where catches continued until 1985. Within the Mediterranean, the population was estimated in 1991 from surveys covering much of the western basin at 3,583 (CV 0.27) (Forcada et al. 1996). It is likely, but not certain, that the historical catches near the Strait of Gibraltar were from the North Atlantic rather than from this population (Sanpera and Aguilar 1992). Palsbøll et al. (2004) found that Mediterranean fin whales probably have a small but non-zero genetic exchange with fin whales elsewhere in the North Atlantic. The Mediterranean subpopulation contains fewer than 10,000 mature individuals and is subject to ongoing threats that may be causing a decline, but data on trend in abundance are insufficient to determine this (Reeves and Notarbartolo di Sciara 2006).
North Pacific
North Pacific fin whale stocks have not been assessed in depth by the IWC Scientific Committee since 1973, when the assessment by Ohsumi and Wada (1974) was accepted, and that was updated by Allen (1977). The stock in the western North Pacific was estimated to have declined from an “initial level” of 44,000, to 17,000 in 1975. The figures refer to the “exploitable” population, above the minimum allowed size at capture. However, these assessments were based on indices of catch-per-unit-effort (CPUE) and sightings-per-unit-effort (SPUE) that did not meet modern requirements for the analysis of such data (e.g. IWC 1989), although there is no doubt that the populations had declined to some unknown extent.
The current abundance of fin whales in the North Pacific is not well known, because survey coverage has been patchy, and not all available data have been analyzed. Current estimates indicate a population of 5,700 whales in the Bering Sea, coastal Aleutian Islands and Gulf of Alaska (Moore et al.2002, Zerbini et al. 2006). Zerbini et al. (2006) estimated a trend in abundance of 4.8%/year with a nominal CV of 0.15 for fin whales in the northern Gulf of Alaska from 1987 to 2003, but recalculation of the variance from the data indicates low precision (95% confidence limits -1.6-11.1%).
Based on surveys conducted in 1996 and 2001, an estimated 3,300 (CV 0.31) fin whales occur in summer/autumn off the west coast of the US (Barlow 2003a). Apart from a small population in Hawaiian waters (estimated 174 animals, CV 0.72; Barlow 2003b), there are no recent estimates of fin whale abundance in the remainder of the North Pacific. Some relevant data exist, including data collected under the Japanese Research Programme in the North Pacific (JARPN) (Tamura et al. 2005), but these do not appear to have been analysed with respect to fin whale abundance. Fin whales seem to be abundant in the central offshore part of the Okhotsk Sea, based on Japanese surveys conducted in 1989, 1990, 1992, 1999, 2000 and 2003, but no abundance estimate has been calculated (Miyashita 2004).
Given the lack of a comprehensive recent estimate, the estimate of 17,000 in 1975 from the earlier assessment is used for this assessment, but the global assessment is not particularly sensitive to the figure used for the North Pacific.
Over 74,000 fin whales are recorded caught by modern whaling in the North Pacific during 1910-75, plus about 20,000 unspecified whales during 1900-30, of which a substantial proportion may have been fin whales. Fin whales were protected by the IWC from whaling in the North Pacific from 1976 onwards, but small Korean catches continued until the early 1980s.
As to whether fin whales recovered from exploitation in the North Pacific, the evidence is, as for the North Atlantic, mixed. Over 24,000 fin whales are recorded caught off coastal Japan and the Korean peninsula from 1910 onwards; annual catches peaked at over 1,000 whales in 1915 and declined steadily thereafter. Fin whales appear to be rare there now (Miyashita et al. 1995, Kim et al. 2004). Similar patterns of apparent exhaustion of stocks occurred elsewhere. For example, about 4,000 fin whales were taken by stations in British Columbia, western Canada, until catches ceased in 1967, with signs of rapid decline in the last 10 years of operation (Gregr et al. 2000).
Gulf of California
This genetically isolated subpopulation was estimated in 2004 from a mark-recapture analysis of photo-identification data at 613 (CI 426-970) (Díaz-Guzman 2006). There are no data on population trend for this subpopulation. Telemetry information shows an all-year residency in the Gulf of California with seasonal latitudinal movements by these whales (Urbán et al. 2005).
East China Sea
There do not appear to be any current or historical estimates of abundance for fin whales in the East China Sea.
Southern Hemisphere
Along with other baleen whales, the IWC has traditionally managed Southern Hemisphere fin whales on the basis of six management areas, Areas I through VI, which are longitudinal pie slices 50°-70° wide. The areas were originally chosen as putative management stocks for humpback whales, and later used for all baleen whales, with little or no biological support (Donovan 1991).
Over 725,000 fin whales have been recorded caught in the Southern Hemisphere during 1905-76 (IWC 2006b). There was a series of assessments in the 1970s, including a synthesis by Chapman (1976) which was reassessed by Breiwick (1977), and updated (for Areas II-VI) by Allen (1977). A reassessment of Area VI fin whales was inconclusive (IWC, 1980).
These assessments were based on a combination of evidence, including trends in CPUE by whaling fleets, sighting rates by Japanese scouting vessels, and inferences on recruitment and mortality rates from age and length data. Their reliability is questionable on various grounds. For example, the IWC Scientific Committee subsequently determined that CPUE data should only be used for stock assessments when the nature of the whaling operations is fully described (IWC 1989). A reanalysis of the historical data using modern methods and insights is warranted.
Less indirect estimates are available from sightings data for more recent times. IWC (1995) gives estimates of 18,000 (CV 0.47) using data from 1966-79 and 15,000 (CV 0.61) using data from 1979-88 for the total population of fin whales south of 30°S in summer. These are obtained by extrapolating abundance estimates for the area south of 60°S from the International Decade of Cetacean Research (IDCR) international surveys, to the area south of 30°S using Japanese scouting vessel data. A slightly finer stratification of the same data yielded estimates of 8,387 for 1966-79 and 15,178 for 1979-88 (IWC 1996; no variances given). Despite their low precision, these estimates suggest that the previous assessments of the populations were seriously over-optimistic. Best (2003) suggested a similar conclusion, based on declines of fin whale catch and sighting rates of 89-97% on the former South African winter whaling grounds during 1954-75.
The most recent estimate of 15,178 for 1979-88 is used for the purpose of this assessment and referred to the year 1983, the middle of the period to which it refers. Use of updated results from subsequent IDCR surveys (Branch and Butterworth 2001) would lead to an estimate of 38,185 referenced to the year 1997 (Mori and Butterworth 2006), but use of this for the population trajectory computation would hardly affect the results because the predicted trajectory passes close to this value anyway. (The trajectory shown in Fig.1. is for the mature population, and hence not directly comparable).
Biological parameters and assessment
The generation time for a non-depleted fin whale population is estimated to be 25.9 years (Taylor et al. 2007). The time period of three generations is 1929-2007.
Estimates of age at sexual maturity for female fin whales, based on observed proportions mature by age, are 6-7 years in the Southern Hemisphere from British catches in the 1960s (Lockyer 1972) and Japanese catches in the 1960s and early 1970s (Mizroch 1981), but these values are likely negatively biased due to selection against smaller animals. For the North Atlantic, Gunnlaugsson and Víkingsson (2006) estimated an average of 8.9 years from catches off Iceland during 1967-89, but with some indication of an increase over time from 7.5 years during 1967-78 to 9.25 years during 1979-89. Aguilar et al. (1988) estimated 7.9 years using the same method from catches off Spain during 1979-84. Slightly different values are obtained using alternative methods. There do not seem to be any precise values for the North Pacific, but Kimura et al. (1958) estimated 8-12 years. For the purpose of this assessment, an age at maturity of 8 years is assumed, corresponding to an age at first reproduction of 9 years. The values of other biological parameters (age at first capture, net recruitment rate, and natural mortality rate) were taken from the previous Scientific Committee assessments (Allen 1977).
Because the available published assessments for this species are not up to date, an updated population assessment is conducted here to enable assessment of the population reduction over the period 1929-2007 relative to the A criterion. While the available data do not permit a scientifically rigorous estimation of the extent of population reduction, it is reasonable to use conventional population assessment methods to provide a crude indication of the extent of possible reduction relative to the criteria. A conventional deterministic age-structured model with an age at first capture (“recruitment”) (ar) and an age at first reproduction (am), and linear density-dependence was applied to the North Pacific, North Atlantic and Southern Hemisphere regions separately. The parameter values are listed in Table 1 in the attached PDF document (which forms an integral part of this assessment). The starting year was 1874 in the North Atlantic and 1900 in the North Pacific and Southern Hemisphere. The sex ratio of the population and catches is assumed to be 50:50. The results of this population assessments can be found in the linked PDF document, which forms an integral part of this assessment.
