CONTENTS

A BRIEF OVERVIEW OF THE ‘STATUS’ OF WHALE POPULATIONS

It is well known that overexploitation by the whaling industry led to serious declines in many of the world’s populations of whales, although thankfully no species was brought to extinction and many are now in the process of recovering, although not all. One reason for this is the improved management of whaling that began in the mid-1970s, when management by population or stock was introduced. This led to the development of the present highly precautionary scientific ‘management procedure’ approaches developed by the IWC’s Scientific Committee for commercial and aboriginal subsistence whaling in order to ensure that past mistakes will not be repeated.

What is status?

Normally when considering ‘status’, one is interested in (a) where a population is now compared to where it was originally and (b) where it is going in the future. In other words one does not only need information on present abundance but also on trends in abundance. The importance of long-term monitoring cannot be over-emphasised and further details of monitoring and how we can achieve it for cetaceans can be found here.

Concurrent with improved management procedures, our ability to estimate the number of whales directly, using a range of techniques, has greatly improved (see summary on pages 166-171 in this paper). Below, we provide a general (and necessarily simplified) overview of the status of large whales by species and ocean basin. For some species/stocks there is sufficient information to assess the present abundance against unexploited population size. For others we have good estimates of present population size but not of past abundance, or of abundance estimates for only part of their range or, in a few cases, no estimates of present abundance. Estimating the number of whales in an area is not an exact science and, of course, estimates come with confidence intervals that reflect uncertainty. For the purposes of this very general overview, we have used what in common parlance is called the ‘best’ estimate by broad geographical areas. It is important to note that any scientific work associated with management and conservation must use rigorous abundance estimates and take fully into account any uncertainty surrounding abundance estimates and population structure.

Threats

Knowledge of status is important in terms of evaluating threats to populations, assigning priorities to mitigating those threats and evaluating the success of those mitigation measures. Threats to cetaceans can be said to incorporate two broad categories. The first are those that result in death in the short-term such as direct hunting (e.g. whaling) and accidental/incidental mortality (e.g. bycatches in fishing gear, ship strikes). At the level of the individual animal, this is of course always a problem; however, when considering conservation at the population level, this is not necessarily so (depending on the conservation objective chosen), provided that the level of mortality is sustainable.

The other category of threats is more difficult to identify and especially quantify – those that can be said to affect the ‘overall fitness’ of the population with respect to reproductive success and/or survivorship and that are generally related to environmental degradation. These include such factors as chemical pollution, noise pollution, overexploitation of prey, disturbance, climate change, etc. At the level of the individual animal these may not always appear to be a problem (for example a female whose reproductive ability has been impaired may seem perfectly healthy), but at the population level they may represent a serious threat. These environmental factors can affect populations of all species; indeed the most vulnerable populations to such threats may be those for which direct exploitation would not be allowed.

Species or population

Although often people request information on status at the species level, biologically it is more sensible to consider status at the population level (although determining stock structure, particularly for populations where the breeding grounds are unknown, is difficult). A perfect example of why this is the case is the gray whale; there is one healthy population (and thus the species is not endangered) but also one critically endangered population that therefore requires immediate conservation action (see below).  In fact only two species of large whales can be considered in danger of extinction, the North Pacific right whale and the North Atlantic right whale, both of which were severely depleted by pre-20th century whaling.

The information summarised below comes from papers and reports of the IWC Scientific Committee, marine mammal status reports published by the US
(www.nmfs.noaa.gov/pr/sars/) and documents produced for the IUCN Red List
(www.iucnredlist.org/), as well as other published scientific literature.

Blue whales including pygmy blue whales (protected worldwide since the 1960s)

Blue whales in the Southern Hemisphere were reduced to only a few percent of their unexploited stock size (which may have been as many as 200,000) by industrial whaling in the Southern Ocean, primarily from the 1920s-1940s. Although sadly they remain at very low levels (in the low thousands), encouragingly the available evidence reveals an increasing trend of around 8% per year in recent years.

Blue whales in the North Atlantic were also exploited heavily. A full assessment of present status has not been carried out. Encouragingly though, the available evidence suggests they are increasing, at least in the area of the central North Atlantic; at present, there are around 1,000 animals off Iceland and several hundred in the Gulf of St Lawrence. They remain rare in the northeastern Atlantic where they were once common.

Blue whales in the North Pacific were again heavily exploited. There are insufficient data available to comment on present status in most parts of the North Pacific although there is evidence of an increase rate of about 3% for the Gulf of California. Blue whales in the eastern tropical Pacific are thought to number around 3,000.

Humpback whales (protected worldwide since the 1960s although a few individuals are allowed to be caught by subsistence whalers)

Humpback whales in the Southern Hemisphere were heavily exploited by commercial whaling primarily from the 1920s-1950s in both their Southern Ocean feeding grounds and in their tropical breeding grounds. Thankfully, in most areas for which there are good data, humpback whales have shown evidence of strong recovery towards their unexploited size (which may have been 75,000-100,000 in total), with annual increase rates of about 10% being recorded in a number of areas including off Australia, Southern Africa and South America. However, there is no evidence of recovery for populations in some areas such as Oceania, where there may be as few as 2,000 animals. The total Southern Hemisphere abundance is probably at least 60,000.

Humpback whales in the North Atlantic were also heavily exploited but, at least in the central and western North Atlantic, have recovered to perhaps pre-exploitation levels and number over 12,000 animals. Less is known of the present or past abundance of humpback whales in the eastern North Atlantic but numbers are considerably less than in the western North Atlantic.

Humpback whales in the North Pacific were also heavily exploited and again have shown positive increase rates in most areas for which there are data (although abundance in the western North Pacific may be only about 1,000).The present abundance in the total North Pacific is estimated at over 17,000. A full assessment of the status of North Pacific humpback whales has yet to be undertaken.

Fin whales (protected in the Southern Ocean and North Pacific since the 1970s and in the North Atlantic by the moratorium from 1986; some special permit and commercial whaling under objection has occurred since)

Fin whale populations in the Southern Hemisphere were heavily exploited by industrial whaling in the Southern Ocean, especially between the 1930s and 1960s. The data do not exist to allow a full assessment of present status, as the surveys that have been undertaken (usually south of 60°S) do not cover all of their primary summer distribution but there is no evidence that they have recovered to anywhere near unexploited levels (which may have been around 200,000). The existing estimates from the limited parts of the range covered are of the order of several thousand animals.

Fin whale populations were exploited throughout the North Atlantic. Present total abundance in the North Atlantic is over 35,000 animals although not all areas have been surveyed. Assessments of the population status in the central North Atlantic and off West Greenland have shown populations there to be in a healthy state. The status of fin whales in other parts of the North Atlantic has not been fully assessed.

Fin whale populations were exploited throughout the North Pacific. There are insufficient data to undertake an assessment of their present status. However, partial estimates for the eastern North Pacific reveal around 10,000 animals with some evidence of annual increase rates of 4-5%.

Sei whales (protected since mid-1970s apart from in the central North Atlantic where protection came with the moratorium in 1986; some special permit catches occur)

Sei whale populations in the Southern Ocean were heavily exploited by industrial whaling after the decline in numbers of blue and fin whales, primarily from the mid-1960s to early 1970s. There are insufficient data to undertake an assessment of their status in the Southern Ocean. There are no good estimates of abundance since Southern Ocean surveys undertaken thus far cover primarily the region south of 60°S and thus do not include the primary distribution areas of sei whales that are much more northerly.

Sei whale populations in the North Atlantic were exploited by commercial whaling up until the 1970s; there are insufficient data to undertake an assessment of their present status. Surveys reveal little sign of recovery of sei whales in the northeastern Atlantic. Exploitation was much less severe in the central North Atlantic; a survey in part of their summer range revealed around 10,500 animals in 1989 since when there have been no catches. Sei whales were heavily exploited off Canada up until the 1970s but no recent abundance estimates are available.

Sei whale populations in the North Pacific were heavily exploited by commercial whaling. There are insufficient data to undertake an assessment of their present status. The only recent abundance estimate (around 7,700 animals in 2006/7) is from a part of their range in the western North Pacific.  

Bryde’s whales (protected since the moratorium apart from some special permit catches in the North Pacific)

Bryde’s whales prefer warmer waters and are generally found between around 40°N and 40°S. They have been subject to a shorter and less intensive history of whaling than the other baleen whales and primarily for this reason neither the species itself nor any population is considered endangered. The only region for which sufficient data exist to undertake an assessment is the western North Pacific; the most recent (partial) abundance estimate is around 20,500 for the year 2000. The only other reliable estimate of abundance (around 13,000 in the late 1980s) is for the eastern tropical Pacific.

Antarctic minke whales (protected since the moratorium apart from some special permit catches)

Commercial exploitation of Antarctic minke whales (the smallest of the large whales) began in the early 1970s, much later than the other large whale species. There are several hundred thousand Antarctic minke whales and thus they are clearly not endangered. However, there has been an appreciable decline in their estimated abundance between the multi-year circumpolar surveys conducted between 1982/83-1988/89 and 1991/92-2003/04. Present estimates of total Antarctic abundance range from around 460,000 – 690,000 (two methods); work continues to determine a final estimate and to determine whether the appreciable decline represents a real decline in abundance, changes in survey methods, changes in the number of animals available to be sighted due to presence within the ice or some combination of these.

Common minke whales (protected since the moratorium apart from commercial catches under objection and subsistence catches in the North Atlantic and special permit catches in the North Pacific)

Apart from the dwarf sub-species, common minke whales are only found in the Northern Hemisphere. There are no reliable data with which to assess dwarf minke whales.

Common minke whales were taken in most parts of the North Atlantic but these stocks are in a healthy state. Reliable recent abundance estimates exist for the northeastern and central North Atlantic and off West Greenland; these total over 180,000 animals.

Common minke whales have been primarily hunted in the western North Pacific. Difficulties in determining stock structure make firm conclusions on status difficult. As a species in the western North Pacific it is not through to be endangered but there is concern over the status of the ‘J-stock’ (whose range includes the Yellow Sea, East China Sea and Sea of Japan) and for which there is considerable bycatch in fishing gear. Abundance estimates for parts of the western North Pacific total over 25,000. The eastern North Pacific has been poorly covered by surveys.

Gray whales (protected since the 1930s apart from some subsistence whaling)

There are two populations of gray whales, both of which were severely depleted by pre-20th century whaling. Thankfully, the eastern North Pacific population has now recovered to around its pre-exploitation level of some 20,000 animals. By contrast the western North Pacific population probably numbers fewer than 130 animals and is critically endangered. Thus the gray whale as a species is in no danger of extinction but its western population is at a very low level and extremely vulnerable.

Bowhead whales (protected since the early 1930s apart from limited subsistence whaling)

The bowhead whale is an Arctic species. It was very heavily exploited by pre-20th century whaling but thankfully at least two stocks are in a healthy state. The Bering-Chukchi-Beaufort Seas stock numbered over 10,500 in 2001 and has been increasing at an annual rate of over 3% since 1978 when reliable census data were first collected; it may be approaching pre-exploitation levels. The eastern Arctic-West Greenland population numbers well over 3,500. There are no good estimates of abundance for the Spitsbergen and Okhotsk Sea stocks but they have shown no signs of significant recovery.

Southern right whales (protected since the early 1930s apart from some illegal whaling)

Southern right whales were severely depleted by pre-20th century whaling; there may once have been around 70,000-100,000. Thankfully, the breeding populations of Argentina/Brazil, South Africa and Australia have shown evidence of strong recovery with annual increase rates of 7-8% and together may now total over 16,000 if those increase rates have continued since the 1990s. Other populations (e.g. off the west coast of South America) have not shown similar signs of increase and remain small.

North Pacific right whales (protected since the early 1930s apart from some illegal whaling)

The North Pacific right whale was severely depleted by pre-20th century whaling and has shown little signs of recovery. It is one of the most endangered species of large whale. Few abundance estimates exist. There may be several hundred animals in the Sea of Okhotsk feeding grounds. There may be only tens of animals in the eastern North Pacific.

North Atlantic right whales (protected since the early 1930s)

The North Atlantic right whale was severely depleted by pre-20th century whaling and, like its North Pacific counterpart has shown little signs of recovery. It is one of the most endangered species of large whale.  In the eastern North Atlantic sightings are extremely rare. In the western North Atlantic, the population numbers around 300-350 with little sign of significant increase.