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Population Status

The IWC assesses cetacean status by population rather than by species.  This is because the majority of species exist in several different areas and groups.  Within a single species there may be one population that is feared to be close to extinction and one that is believed to be thriving.  A good example of this is the North Pacific gray whale, considered healthy in the western North Pacific, but critically endangered in the east.

Within a single whale population, groups are further broken down into 'stocks.' Even within a single population some stocks may be healthy whilst others are not.  For example, discussions are currently ongoing to decide whether there is cause for concern regarding one/some of the stocks that make up the population of common minke whales in the North Pacific.

In broad terms, the status of a population is assessed by comparing the current population size with its original, undisturbed size, and then predicting its future size based on identified trends and known threats.  In the case of cetaceans, the main historical 'disturbance' that impacted on population size was whaling activity.

Understanding population status is vital to understanding whether a population is ‘healthy,’ or whether conservation action is required and if so, whether those actions should be considered a priority.

Assessing population status is not straightforward.  There are a number of challenges to overcome, for example:

  • It is rarely easy to establish the number of animals in any population

  • Whales present even greater challenges because they spend most of their time deep under water and many inhabit the world’s most remote regions.

  • Understanding the original, undisturbed size of a population relies on historical data which may be incomplete or inaccurate.

  • Whales are long-lived, relatively late to reach maturity, and only have one calf every 1-3 years, so assessing population trends can only be accomplished with consistent monitoring over a long period of time.

  • Determining population structure, particularly for populations where the breeding grounds are unknown, is difficult.


The IWC’s Scientific Committee has developed a range of techniques and guidelines to handle these tasks consistently and with as much accuracy as possible. 

Click here to read the IWC Scientific Committee Handbook, which incorporates the various sets of guidelines and procedures.

Click here to read more about Population Estimates and see the latest IWC estimates for each population where the information required is available and it has been possible to calculate estimates.

Threats

Threats to cetaceans are categorised as either short-term threats with a direct impact on individual animals, for example whaling or bycatch in fishing gear, or longer-term threats which are more difficult to recognise and quantify, but may impact on the heath of an entire population, for example chemical pollution or climate change

Information about status is needed to evaluate threats to populations and decide the urgency with which conservation action is required.  A critically endangered population might struggle to survive the loss of just one mature female, but a thriving and abundant population will be more resilient and therefore less likely to require an immediate response, or possibly any human intervention at all.     

 

Status Summary - by Population

Minke Whales (two species)

Antarctic Minke Whales

Hunting of Antarctic minkes whales began in the early 1970s, much later than the other large whales.  The most recent estimate of total abundance in the surveyed areas is around 515,000 so the species is not endangered.  However a decline has been noted in abundance estimates calculated during circumpolar surveys in 1982/83, 1991/92 and 2003/04.  Work continues to determine whether the decline recorded in these abundance estimates is real.  Recent hunting is not at levels thought likely to cause declines.

Common Minke Whales

North Atlantic

These stocks are in a healthy state.  Recent reliable abundance estimates for the northeastern and central North Atlantic, and off West Greenland total around 180,000 animals.

North Pacific

These were heavily hunted in the western North Pacific.  Complexities in the structure of the population (which is divided into 'stocks') makes conclusions on status difficult.  Partial abundance estimates total over 25,000.  There is concern over the status of the 'J-stock(s)' whose range includes the Yellow, East China and Sea of Japan/East Sea, where there is considerable bycatch in fishing gear.  The eastern region has been poorly covered by surveys, but few catches have been reported here and a new assessment is underway.

Southern Hemisphere

The dwarf minke whale which is typically found from the Equator to the Antarctic, is believed to be either a Common Minke Whale or possibly a subspecies.  There are no estimates of abundance and catches have been low.

To read more about minke whales click here.

Humpback Whales

North Atlantic

In central and western areas, populations have recovered to perhaps pre-whaling levels and number over 12,000 animals.  Less is known about the abundance in eastern regions but almost 5,000 animals are estimated in the Norwegian and Barents Seas.  They have been increasing off West Greenland.  They are vulnerable to entanglement.

North Pacific

These have been increasing in most areas for which data exists, although abundance in the western North Pacific may be only about 1,000.  Total abundance is around 22,000.  A full assessment of status is now underway.

Southern Hemisphere

These were hunted primarily from the 1920s-1950s in both their Southern Ocean feeding grounds and tropical breeding grounds.  In many areas they have shown evidence of strong recovery towards their pre-exploitation population size (which may have been 75,000-100,000 in total) with annual increase rates of about 10% being recorded off Australia, southern Africa and South America.   However there is little evidence of recovery in some parts of Oceania.  The total Southern Hemisphere abundance is probably at least 80,000.

To read more about humpback whales click here.

Bowhead Whales

At least two stocks are now in a healthy state.  The population in the Bering-Chukchi-Beaufort Seas has been increasing annually at over 3% since the first reliable census in 1978 and may be approaching pre-exploitation levels.  In 2011 its abundance was nearly 17,000 animals.

The eastern Arctic-West Greenland population numbers around 6-8,000.  There are no good estimates of abundance for the Spitsbergen or Okhotsk Sea stocks but they show no signs of significant recovery.  

For more information about bowhead whales click here.

Sei Whales 

North Atlantic

Insufficient data exists to assess present status.  Surveys show little sign of increase in the northeastern Atlantic.  There were around 10,500 whales in 1989 in the central region where less hunting took place.  No recent abundance estimates are available off Canada where they were heavily exploited in the past.

North Pacific

Recent surveys indicate current abundance is over 35,000.  An assessment of North Pacific sei whales is underway.

Southern Hemisphere

The IWC has no recent accepted estimates of abundance or trends.  It is not possible to evaluate whether they have increased since protection from whaling, although in the absence of other major threats this seems likely.

To read more about sei whales, click here.

Right Whales (three species)

North Atlantic Right Whales

One of the most endangered species with little sign of recovery in most areas. In the east, sightings are extremely rare.  In the west, the population numbers around 500 animals with some signs of slow increase.  The main threats are entanglement and ship strikes.

North Pacific Right Whales

Also very endangered with few signs of recovery.  There may be several hundred animals in the Sea of Okhotsk feeding grounds and around 1,000 in the northwest Pacific, but only tens of animals in the eastern North Pacific.

Southern Right Whales 

There may once have been around 70,000-100,000 animals.  In 2009 there were around 14,000.  Off Argentina/Brazil, South Africa and Australia the populations are recovering strongly at 7-8% per year.  Other populations (e.g. off western South America) remain small.  The South Atlantic and Eastern Pacific populations are the subject of IWC Conservation Management Plans.

For more information about right whales, click here.

Blue Whales

North Atlantic

Present status has not been fully assessed but encouragingly, evidence suggests they are increasing, at least in the central area.  There are some 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.

North Pacific

Insufficient data exists to comment on present status in western areas.  There are over 2,000 animals in the eastern North Pacific and the population has almost recovered.

Southern Hemisphere

Pre-hunting population size may have been as many as 200,000-300,000 whales.  They were estimated to number around 2,300 in 1998 and to be increasing between 2.4-8.4% per year.  The IWC is undertaking an assessment of Antarctic blue whales at present.  There have been no assessments of the pygmy blue whale sub-species to date.

For more information about blue whales click here.

Fin Whales

North Atlantic

Present total abundance is over 75,000 whales although not all areas have been surveyed.  Assessments show the Central and West Greenland populations to be in a healthy state.  Their status in other areas has not been fully assessed.  They are vulnerable to ship strikes in the Mediterranean.

North Pacific

Insufficient data exists to assess their present status.  However partial estimates for the eastern North Pacific show around 10,000 whales with some evidence of annual increase rates of 4-5%.

Southern Hemisphere

There has been no recent full assessment of status.  There is some evidence that populations that spend summer in the Antarctic are increasing at a small but unknown rate.

For more information about fin whales click here.

Gray Whales

There are believed to have been two populations of gray whales.  A basin-wide assessment is underway in the North Pacific.  They have been protected since the 1930's apart from some subsistence whaling from the recovered eastern North Pacific population whose abundance is now around 27,000.

The situation for the western North Pacific population is uncertain and it is the subject of an IWC Conservation Management Plan. The feeding area off Sakhalin Island may contain both western and eastern animals.  Only around 200 gray whales regularly feed there but numbers are increasing at around 4%.  Primary threats revolve around oil and gas  industry related activities.

For more information about gray whales click here.

Bryde's Whales

Bryde's whales are found in warmer waters.  They have been subject to a shorter and less intensive history of whaling than other species and primarily for this reason no populations are considered endangered.  In the western North Pacific, the most recent (partial) abundance estimate accepted by the IWC is now around 26,000.  The only other reliable estimate of abundance (around 13,000) in the late 1980s) is for the eastern tropical Pacific.

For more information about Bryde's whales click here.