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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. 

IWC Scientific Committee: Status of Stocks Initiative (new text - not published)

The Scientific Committee uses computer models to compare current population size to a chosen point in the past (e.g. prior to commercial whaling) and predict where is it likely to go in the future (e.g. increasing, decreasing, remaining the same). These models combine multiple direct abundance estimates with other information over many years to track population abundance over time (‘trajectories’). Thus, model estimates of abundance for a particular year may differ from the ‘best’ estimate from any individual survey.

The Scientific Committee has been developing and refining these modelling approaches for many years, producing assessments in support of a range of core, long-standing tasks including ensuring sustainable limits for aboriginal whaling and development of the Revised Management Procedure

The Scientific Committee Status of Stocks Initiative aims to present its stock assessments in a format that is both detailed and clear.  Additional assessments will be added annually, as they completed and endorsed by the Committee.  

These assessments represent the Scientific Committee’s best judgment about the status of whale stocks and provide a unique, quantitative view of status.

 

Types of status assessment

To follow: paragraph on the different types of assessment used by IWC. To cover the following points as simply/succinctly as possible:

Different types of assessment undertaken by IWC and IUCN

What different types of assessment are used for (different aims/purposes)

Accounting for Uncertainty

To follow: paragraph on scientific uncertainty.
Why there is always an element of uncertainty.

How it is measures, accounted for and factored into assessments

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.    

Read more

links to new sections:

Short status summaries
Status of Stocks Tables by relative abundance and 20 year change
Assessments of individual whale stocks

Information about the methods used by IWC to assess status
Glossary

[separate contents below onto new page]

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 20196,7, with signs of decreasing since 2010. The main threats are entanglement and ship strikes8,9. 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 rare12,13,14; the current abundance is not expected to exceed ~30 individuals15.

Southern right whales (Eubalaena australis).

Pre-exploitation abundance is estimated at 70000-100000 animals16,17,18. 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-Peru17,22. Demographic changes of concern -including low numbers of cow-calf pairs and increased calving intervals - are observed in South Africa since 201523,24. 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 Atlantic25,26 (refers to 2007 and 2015) where they were once common. Several hundred were seen in their summer feeding ground in the Gulf of St Lawrence27,28,29,30.

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 recovery32,33.

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 distribution37,38.

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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 74,00025,39,40,41 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 Mediterranean43,44,45,46,47.

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.

Click for more information about sperm whales.

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 reported59,60.

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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 4100064,65.

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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 3000070,71. 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 America72,73,74 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 animals26,79,80,81,82. 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 2300084,85,86,87,88; 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 gear90,91,92,93,94. In the eastern North Pacific, surveys do not cover the distribution of the species; partial estimates total 400049,95,96,97,98 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 animals25,26,40,100. 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 increasing102,103. 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 1000106,107. 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 Atlantic108,110, off Australia111,112,113,114, Southern Africa and South America115,116. 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 literature111,113,118,119120,121,122,123,124,125.

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Bowhead Whales (Balaena mysticetus)

Heavily exploited pre-20th century. The population in the Bering- Chukchi-Beaufort Seas has been recovering126,127. 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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