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 11^th century^3,4. In the east, sightings are extremely rare⁵. In the west, the population numbers were estimated below 400 in 2019^6,7, with signs of decreasing since 2010. The main threats are entanglement and ship strikes^8,9. High mortality has been observed since 2017¹⁰.

North Pacific (Eubalaena japonica).

Very endangered with few signs of appreciable recovery and numbers are in the hundreds. In 2012 the population estimate for the northwest Pacific was around 1000¹¹. Sightings in the eastern North Pacific are rare^12,13,14; the current abundance is not expected to exceed ~30 individuals¹⁵.

Southern right whales (Eubalaena australis).

Pre-exploitation abundance is estimated at 70000-100000 animals^16,17,18. In 2009, there were around 14000¹⁸ distributed on calving grounds off Argentina/Brazil¹⁹, South Africa²⁰, New Zealand²¹ and Australia. Populations are recovering at different rates but low abundances persist in Brazil, SE Australia and Chile-Peru^17,22. Demographic changes of concern -including low numbers of cow-calf pairs and increased calving intervals - are observed in South Africa since 2015^23,24. The southwest Atlantic and Eastern Pacific populations are the subject of CMPs.

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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 2001²⁵. They remain rare in the northeast Atlantic^25,26 (refers to 2007 and 2015) where they were once common. Several hundred were seen in their summer feeding ground in the Gulf of St Lawrence^27,28,29,30.

North Pacific

Blue whales are sighted in surveys in the west North Pacific¹¹ but there are insufficient data to comment on their present status in the region. There are around 2,000 animals in the eastern North Pacific³¹. Under careful management, the population has reached levels close to recovery^32,33.

Southern Hemisphere

Pre-exploitation size of Antarctic blue whales (Balaenoptera musculus intermedia) may have been as many as 2-300000 whales³⁴. They are currently thought to exceed 2000 individuals (based on circumpolar estimates in the 1990s and early 2000s)^35,36. Although they have shown an increasing trend since the 1970s, their levels remain low compared to pre-exploitation³⁴. 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 distribution^37,38.

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Fin Whales (B. physalus)

Were heavily exploited across their distribution range during the 20th century³⁹.

North Atlantic

Total abundance, based on the most up-to-date estimates available, is around 74,000^25,39,40,41 whales although not all areas have been surveyed. Assessments show the Central and West Greenland populations to be in a healthy state. Recent catches in West Greenland do not exceed 8 whales per year (2017-2021). Their status in other areas has not been fully assessed but fin whales in the northern Gulf of St. Lawrence are showing signs of decline⁴². Ship strikes are one of the greatest threats for fin whales in the Mediterranean^{43,44,45,46,47}.

North Pacific

There are insufficient data to assess their present status. Partial estimates for the eastern North Pacific show around 3000 (2013)⁴⁸ whales in the Gulf of Alaska, 1000 (2010)⁴⁹ on the eastern Bering Sea shelf and around 400 (2009-2014) along the Canadian continental self⁵⁰, more than 8000 (2014)⁵¹ in California, Oregon, and Washington waters.

Southern Hemisphere

There has been no recent full assessment of the status. There is some evidence that populations summering in the Antarctic are increasing⁵² but abundance trends are unknown.

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Sperm Whales (Physeter macrocephalus)

Cosmopolitan species⁵³, heavily exploited, particularly during the 1960s⁵⁴. The IWC has no recently accepted reliable estimates of abundance because their estimation is complicated by their long dive times and their behaviour⁵⁴. Local surveys estimate 20000 (2015) whales in the central Atlantic²⁵, less than 4000 (2015) in the northeast Atlantic⁴⁰, and 10000 (2012) in the western north Pacific¹¹. Although not endangered the species has probably not recovered to pre-whaling levels⁵⁴. There have been no recent assessments of status by the IWC but plans are being developed to undertake an assessment.

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Gray Whales (Eschrichtius robustus)

Heavily exploited pre-20th century. They have been protected since the 1930s apart from some subsistence whaling. After the 2019/2020 unusual mortality event⁵⁵, the eastern North Pacific population abundance is around 20000⁵⁵ (2019/2020). The situation for the western North Pacific population is uncertain, and it is the subject of a CMP. Around 200 gray whales regularly feed off Sakhalin Island but numbers are increasing by 4%^56,57. Primary threats are entanglement and activities related to oil and gas. A basin-wide assessment is almost complete. In the Atlantic gray whales are considered extinct since the 1700s⁵⁸ but some recent sightings have been reported^59,60.

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Bryde’s Whales

Currently classified as Balaenoptera edeni but its taxonomy is reviewed⁶¹. They occur in warm, tropical waters⁶². They have not been heavily exploited and their populations are not endangered⁶³. In the western North Pacific, the 2011-2014 (partial) abundance estimate is 41000^64,65.

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Sei Whales (B. borealis)

were heavily exploited from the late1950s to the mid-1970s ⁶⁶.

North Atlantic

There are insufficient data to assess their present status. Surveys show little sign of an increase in the northeast Atlantic. There were less than 10000 whales in 2007 in the central region⁶⁷, 1500 and 700 in West and East Greenland respectively⁶⁸. No recent abundance estimates are available off Canada where few whales have been sighted⁶⁹.

North Pacific

Recent surveys indicate current abundance is over 30000^70,71. 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^72,73,74 and the Falkland Islands, where sei whales number around 700 individuals (2018)⁷⁵.

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Antarctic Minke Whales (Balaenoptera bonaerensis)

The exploitation of Antarctic minke whales began in the early 1970s⁷⁶. The most recent estimate (1998) of total abundance in the surveyed areas south of 60°S is higher than 500000⁷⁷. 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 concern⁷⁸.

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 200000 animals^{26,79,80,81,82}. The Canadian East coast stock numbers some 20000 whales⁸³.

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. Abundance estimates in the western North Pacific total 23000^{84,85,86,87,88}; Japan takes an average of 120 whales per year (2017-2021)⁸⁹. 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^{90,91,92,93,94}. In the eastern North Pacific, surveys do not cover the distribution of the species; partial estimates total 4000^{49,95,96,97,98} 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 are knowledge gaps regarding the biology, population structure and abundance of minke whales.

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Humpback Whales (Megaptera novaeangliae)

have been heavily hunted throughout their distributional range⁹⁹.

North Atlantic

In the northeast Atlantic, they number a little less than 25000 animals^25,26,40,100. Abundance estimates from surveys of the Canadian feeding ground are partial and estimate some 12000 whales in the area¹⁰¹. Less than 1000 individuals are estimated for west Greenland²⁶, where the population has been increasing^102,103. 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 shifts¹⁰⁰. They are vulnerable to entanglement.

North Pacific

During the period 2004-2006 humpback whales in the North Pacific numbered more than 21000 individuals¹⁰⁴. They have been increasing in most areas for which there are data¹⁰⁵, although abundance in their Asian wintering area may be only about 1000^106,107. A full assessment of status is underway.

Southern Hemisphere

Southern Hemisphere humpbacks were primarily exploited between 1904-1965 on both their Southern Ocean feeding grounds and low-latitude breeding grounds¹⁰⁸. In many areas, they have shown evidence of strong recovery with high annual increase rates (7-12%) recorded around the Antarctic¹⁰⁹, in the south-west Atlantic^108,110, off Australia^{111,112,113,114}, Southern Africa and South America^115,116. Population models predicted > 96000 in the southern hemisphere (2015)¹¹⁷. Estimates of abundance from the majority of the Southern Hemisphere breeding grounds can be found in literature^{111,113,118,119120,121,122,123,124,125}.

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Bowhead Whales (Balaena mysticetus)

Heavily exploited pre-20th century. The population in the Bering- Chukchi-Beaufort Seas has been recovering^126,127. In 2019 its abundance was 14000-17000 animals¹²⁸. The eastern Arctic-West Greenland population numbers 6500 individuals (2013)^129,130,131. The Okhotsk Sea stock amounts to 200 whales (in 2016)¹³² and the Svalbard stock 300 (in 2015)¹³³.

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