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 eastern North Pacific, but critically endangered in the west.

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 not easy to accurately estimate the number of animals in any population because they are constantly moving, often over large areas. 
• Whales present even greater challenges because they spend most of their time deep under water and many inhabit the world’s most remote regions.
• Assessing the health of a population requires an understanding of the original, undisturbed size of a population prior to human activity, predominantly industrial whaling.  This 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. 

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 Summaries - by Population

Right Whales

All three species were heavily exploited pre-20th century and substantially reduced¹.

North Atlantic (Eubalaena glacialis).

One of the most endangered species of whales² hunted since at least the 11th century³,⁴. In the east, sightings are extremely rare⁵. In the west, the population numbers were estimated below 400 in 2019^6,7 and 360 in 2022⁸, with signs of decreasing since 2010. High mortality has been observed since 2017⁹. Extinction risk has been linked to entanglements and vessel strikes^{10, 11}, ¹². 

North Pacific (Eubalaena japonica).

Endangered with few signs of appreciable recovery and numbers are in the hundreds. There is no reliable population estimate for the Northwest Pacific but it is believed to be between 400 and 1,100 individuals¹³. Sightings in the Eastern North Pacific are rare¹⁴; the current abundance is not expected to exceed ~30 individuals¹⁵, ¹⁶; the current abundance is not expected to exceed ~30 individuals¹⁷, ¹⁸, excluding the Gulf of Alaska.

Southern right whales (Eubalaena australis). 

Pre-exploitation abundance is estimated at 70000-100000 animals¹⁹, ²⁰, ²¹. In 2009, there were around 14,000²¹ individuals distributed on calving grounds off Argentina/Brazil²², South Africa²³, New Zealand²⁴ and Australia. Populations are recovering at different rates but low abundances persist in Brazil, SE Australia and Chile-Peru²⁰, ²⁵. Demographic changes of concern - including low numbers of cow-calf pairs - have been observed in South Africa since 2015²⁶, ²⁷. Increased calving intervals are observed in South Africa and the southwest Atlantic. The southwest Atlantic and southeast Pacific populations are the subject of CMPs (See Conservation below). Salmon farming, noise and vessel strikes pose threats to the Southeast Pacific population²⁸. 

Blue Whales (Balaenoptera musculus)

Were severely exploited across their distribution range. 

North Atlantic 

Present status has not been fully assessed, but encouragingly, evidence suggests they were increasing, at least in the central area. There were 3000 animals in central N. Atlantic (in 2015) particularly in the west and north of Iceland, showing a significant increase since 2001²⁹. They remain rare in the northeast Atlantic²⁹, ³⁰ (reference years: 2007 and 2015) where they were once common. Several hundred were seen in their summer feeding ground in the Gulf of St Lawrence³¹, ³², ³³, ³⁴.

North Pacific 

There are insufficient data to comment on their present status in the central and western North Pacific although they are sighted in surveys in the western North Pacific³⁵. There are around 2,000 animals in the eastern North Pacific³⁶, where the population has reached levels close to recovery³⁷, ³⁸.

Southern Hemisphere

Pre-exploitation size of Antarctic blue whales (Balaenoptera musculus intermedia) may have been as many as 2-300,000 whales³⁹. They are currently thought to exceed 2,000 individuals (based on circumpolar estimates in the 1990s and 2000s)⁴⁰, ⁴¹, ⁴². Although they have shown an increasing trend since the 1970s, their levels remain low compared to pre-exploitation³⁹, ⁴³. There have been no assessments of the pygmy blue whale (Balaenoptera musculus brevicauda) to date but efforts are made to separate the two subspecies in terms of historical catch and distribution⁴⁴, ⁴⁵ and to separate stocks within pygmy blue whales. 

Fin Whales (B. physalus)

Were heavily exploited across their distribution range during the 20th century⁴⁶.

North Atlantic 

Total abundance, based on the most up-to-date estimates available, is around 74,000^{29, 46}, ⁴⁷, ⁴⁸ 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 but fin whales in the northern Gulf of St. Lawrence are showing signs of decline⁴⁹. Fin whales in the Mediterranean are believed to be declining with ship strikes being one of the threats⁵⁰, ⁵¹, ⁵², ⁵³, ⁵⁴.

North Pacific 

There are insufficient data to assess their present status. For the eastern North Pacific, partial estimates show around 3,000 (2013)⁵⁵ whales in the Gulf of Alaska, 1,000 (2010)⁵⁶ on the eastern Bering Sea shelf, around 400 (2009-2014) along the Canadian continental shelf⁵⁷, more than 8,000 (2014)⁵⁸ in California, Oregon, and Washington waters.

Southern Hemisphere 

There has been no recent full assessment of the status. There is some evidence that populations in the Antarctic are increasing⁵⁹. 

Sperm Whales (Physeter macrocephalus).

Cosmopolitan species⁶⁰, heavily exploited, particularly during the 1960s⁶¹. The IWC has no recently accepted reliable estimates of abundance because their estimation is complicated by their long dive times and their behaviour⁶¹. Although not endangered the species has probably not recovered to pre-whaling levels⁶¹, ⁶².

North Atlantic

Local surveys estimate 20,000 (2015) sperm whales in the central Atlantic²⁹, less than 4,000 (2015) in the northeast Atlantic⁴⁷. The Mediterranean sperm whale population is genetically distinct from the Atlantic populations with fewer than 3000 individuals⁶³, ⁶⁴

North Pacific

In the western North Pacific sperm whales are estimated at 10,000 individuals (2012) ³⁵. The IWC plans to assess eastern North Pacific sperm whales.

Southern Hemisphere

Circumpolar abundance estimates of sperm whale males, based on IDCR/SOWER data, exceed 8,500 (1997/98) males⁶⁵  

Gray Whales (Eschrichtius robustus)

Heavily exploited pre-20th century. They have been protected since the 1930s apart from some subsistence whaling. After the 2019-2023 unusual mortality event⁶⁶, the eastern North Pacific population abundance is around 20,000⁶⁷ (2024). The status of the western North Pacific population is endangered; the population is subject to a CMP. Around 200 gray whales regularly feed off Sakhalin Island, Russia; although population numbers have slowly increased by 4% since the 1990s ^{68, 69}, the low numbers of individual whales observed in 2022-2023 raise concern⁷⁰. Primary threats are entanglement and activities related to oil and gas. A basin-wide assessment is almost complete. In the Atlantic, gray whales have been considered extinct since the 1700s⁷¹ but some recent sightings have been reported^{72, 73}. 

Bryde’s Whales

Currently classified as Balaenoptera edeni but its taxonomy is reviewed⁷⁴. They occur in warm, tropical and warm-temperate waters⁷⁵. They have not been heavily exploited – except in the western North Pacific - and their populations are not endangered⁷⁶. In the western North Pacific, the 2011-2014 (partial) abundance estimate is 41,000^{77, 78} where they are currently hunted in the Japanese EEZ.

Sei Whales (B. borealis) 

They were heavily exploited from the late 1950s to the mid-1970s ⁷⁹.

North Atlantic 

There are insufficient data to assess their present status. Surveys show little sign of an increase in the northeast Atlantic. There were just under 10,000 whales in 2007 in the central region⁸⁰, 1,500 and 700 in West and East Greenland respectively⁸¹. The average abundance estimate (2010-2013) is 6,300 from Nova Scotia, Canada to Florida⁸².

North Pacific

Recent surveys indicate current abundance is over 30,000^{83, 84}. An assessment of North Pacific sei whales is underway. 

Southern Hemisphere 

Little information is known about their abundance and trends. Anecdotal and opportunistic reports allude to increasing occurrence in the coastal waters of southern South America^{85, 86, 87} and the Falkland Islands, where sei whales number around 700 individuals (2018)⁸⁸. 

Antarctic Minke Whales (Balaenoptera bonaerensis). 

The exploitation of Antarctic minke whales began in the early 1970s⁸⁹. The most recent estimate (1998) of total abundance in the surveyed areas south of 60°S is higher than 500,000⁹⁰. However, there has been an appreciable decline in estimated abundance between the 1985/6-1990/91 and 1991/92- 2003/04 circumpolar surveys. Work continues to determine whether this decline is real or an artefact. Climate change has been a concern⁹¹.

Common Minke Whales (Balaenoptera acutorostrata).

North Atlantic (B. acutorostrata acutorostrata)

These stocks are in a healthy state. Recent reliable abundance estimates for the north-eastern and central North Atlantic and off West Greenland total around 200,000 animals^{92, 93, 94, 95}. The Canadian East coast stock numbers some 20,000 whales⁹⁶. Since 2017, increased mortality of minke whales has been observed along the US East coast¹

North Pacific (B. acutorostrata scammoni)

They were heavily hunted in the western North Pacific. Stock structure complexity makes conclusions on status difficult. There is no estimate for the entire North Pacific. Partial abundance estimates in the western North Pacific total 23,000^{97, 98, 99, 100, 101}; Japan takes an average of 120 whales per year (2017-2021)¹⁰². 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^{103, 104, 105, 106, 107}. In the eastern North Pacific, surveys do not cover the distribution of the species; partial estimates total 4,000^{108, 109, 110, 111} individuals. A new assessment is underway. 

Southern Hemisphere

The dwarf minke whale (B. acutorostrata unnamed subs.) typically occurs from the Equator to the Antarctic. There is insufficient information on the biology, population structure and abundance of the subspecies to assess status. 

Humpback Whales (Megaptera novaeangliae)

have been heavily hunted throughout their distributional range¹¹²

North Atlantic

In the northeast Atlantic, they number a little less than 25,000 animals^{29, 30, 47, 113}. Abundance estimates from surveys of the Canadian feeding ground are partial and estimate some 12,000 whales in the area¹¹⁴. Less than 1000 individuals are estimated for West Greenland³⁰, where the population has been increasing^{115, 116}. Increasing or stabilising trends are observed for most North Atlantic regions but it is not clear whether they can be attributed to population growth or distributional shifts¹¹³. They are vulnerable to entanglement. Since January 2016, high mortalities have occurred along the US East Coast². An assessment is expected within the next few years.

North Pacific 

During the period 2004-2006, humpback whales in the North Pacific numbered more than 21,000 individuals¹¹⁷. They have been increasing in most areas for which there are data^36,118. Abundance in their Asian wintering area may be about 1,000^{119, 120}. An IWC assessment of status was completed in 2024 and indicated a strong overall recovery since the mid-1960s, with the population reaching a peak in 2014¹²¹. After 2014 regional declines have been linked to an extreme marine heat wave¹²²,¹²³.

Southern Hemisphere 

Southern Hemisphere humpbacks were primarily exploited between 1904 and 1965 on both their Southern Ocean feeding grounds and low-latitude breeding grounds¹²⁴. In many areas, they have shown evidence of strong recovery with high annual increase rates (7-12%) recorded around the Antarctic¹²⁵, in the south-west Atlantic^124,126, off Australia^{127, 128, 129, 130}, Southern Africa and South America^{131, 132}. Population models predicted > 96,000 in the Southern Hemisphere (2015)¹³³. Estimates of abundance from the majority of the Southern Hemisphere breeding grounds can be found in literature^{127, 129, 134, 135, 136, 137, 138, 139, 140, 141}. 

Bowhead Whales (Balaena mysticetus). 

Heavily exploited pre-20th century. The population in the Bering- Chukchi-Beaufort Seas has been recovering^142,143. In 2019 its abundance was 14,000-17,000 animals¹⁴⁴. The eastern Arctic-West Greenland population numbers 6,500 individuals (2013)^{145, 146, 147}. The Okhotsk Sea stock amounts to 200 whales (in 2016)¹⁴⁸ and the Svalbard stock 300 (in 2015)¹⁴⁹. 

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