Antarctic Whales: Insights from Decades of Research

Japan Forward

2 days ago

[SPONSORED] Japan's long-term surveys of whales in the Antarctic Ocean have deepened understanding of the region's whale populations. What scientists learned.
Humpback whales have seen a remarkable recovery in their populations in both the southern and northern hemispheres. (©Institute for Cetacean Research)
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Since 1987, Japan's Institute of Cetacean Research (ICR) has carried out long-term whale surveys in the Antarctic Ocean. Over the years, these efforts have deepened our understanding of whales and whale populations and the surrounding marine environment. This article offers a reader-friendly look at what the research has revealed so far.
Minke whales were once believed to be a single species found across the world's oceans. However, research from Japan's whale sampling program revealed that those in the Southern Hemisphere are genetically distinct. They are now classified as Antarctic minke whales.
These whales are widely distributed across the Southern Hemisphere. In summer, they migrate south to the Antarctic Ocean, where they feed on vast amounts of Antarctic krill to store energy for the year ahead.
They exist in multiple populations, each with its own breeding grounds. Japanese research identified two major populations between the Indian Ocean and western Pacific (35°E to 145°W), which intermingle in the central part of this range.
Historically, Antarctic minke whales reached sexual maturity at around 14 to 15 years of age. But after commercial whaling sharply reduced blue and other large baleen whales, krill became more abundant. This abundance allowed minke whales to mature earlier — now at just seven to eight years. That shift likely contributed to a population increase from around 100,000 to 515,000 individuals. Estimated Population of Antarctic Minke Whales in Area IV. (©Suisan Keizai Daily News)
Southern right whales can grow up to 18 meters long, while newborns measure between 4.5 and 6 meters. They are easy to recognize by their enormous heads — roughly a quarter of their body length — and the callosities (roughened patches) on their skin. Unlike many other whale species, they have no dorsal fin or throat grooves.
Pregnancy lasts about 12 months, and females give birth roughly every three years. Calving takes place in mid- to low-latitude coastal waters, including areas off southwestern Australia, New Zealand, South Africa, and both coasts of South America. After calving, the whales migrate to higher latitudes to feed.
Due to their slow swimming speed and tendency to float after death, southern right whales were among the first to be targeted by whalers. Intense hunting by European and American fleets from the 17th to 19th centuries led to a steep decline in their numbers. By 1920, their global population had fallen to an estimated 300 individuals — already considered rare when modern whaling began.
The species has been protected from hunting since 1937 and has now been under international protection for 86 years (as of 2023). Their original population is estimated at 55,000 to 70,000. In the Antarctic, they are mainly found in Area IV, where a 2007–08 survey estimated the population at 1,557 individuals, with an annual growth rate of 5.9%. Estimated Population of Southern Right Whales in Area IV. (©Suisan Keizai Daily News)
Fin whales are most commonly found between 40°S and 60°S, a region known for its strong westerly winds and rough seas. Some whales venture even farther south beyond 60°S, which contributes to year-to-year fluctuations in population estimates.
Commercial hunting of fin whales in the Southern Hemisphere was banned in 1976. As of 2023 — 47 years later — there are encouraging signs of recovery.
In the Southern Ocean south of 60°S, the Indian Ocean group (Areas III East and IV) was estimated at 3,087 individuals in 1995/96, but declined to 2,610 in 2007/08. In contrast, the South Pacific group (Areas V and western VI) grew dramatically from 1,879 to 14,981 individuals over the same period. These groups are now showing annual growth rates of 8.9% and 12%, respectively. Estimated Population of Fin Whales in the Indo-Pacific Region South of 60°S. (©Suisan Keizai Daily News)
In the Southern Hemisphere, adult humpback whales can reach about 16 meters for females and 15 meters for males. Newborns typically measure between 4.5 and 5.0 meters. Their most distinctive feature is their exceptionally long pectoral fins, which can stretch to one-third of their body length.Pregnancy lasts around 12 months. Calving takes place in warmer, low-latitude coastal waters, after which mothers and calves migrate to cooler, high-latitude feeding grounds south of 50°S.
From 1904 to 1963, humpbacks were heavily targeted by commercial whaling, and their numbers declined steeply. Hunting was banned in the Southern Hemisphere in the 1963/64 season and later extended worldwide in 1966.
When Japan's Antarctic Research Program for Whales (JARPA) began, humpback sightings were so rare that spotting just one became a highlight of cruise logs. But beginning in the late 1990s, researchers started to witness a remarkable recovery.
In the Indian Ocean sector of Antarctica (Area IV), humpbacks eventually became the dominant species by biomass south of 60°S during summer, overtaking Antarctic minke whales. Since the mid-1990s, the IWC Scientific Committee has raised questions about the reliability of JARPA's findings, prompting Japan to defend the credibility of its research.
In August 2008, the International Union for Conservation of Nature (IUCN) released an update: although some regional concerns remain, the global humpback whale population — including those in the Northern Hemisphere — had surpassed 60,000 and was continuing to grow. The IUCN reclassified the species from "Vulnerable (VU)" to "Least Concern (LC)" on its Red List.
Recent estimates put the population at 29,067 in Area IV and 13,894 in Area V, with both regions showing steady growth. Surveys conducted by Australia and New Zealand have also confirmed this upward trend. Estimated Population of Humpback Whales in Area IV. (©Suisan Keizai Daily News)
Visual surveys conducted in the Antarctic during the 1980s estimated the blue whale population at just 700 individuals, highlighting the species' critically endangered status at the time.
By the 2005/06 to 2007/08 surveys, the estimated number of blue whales south of 60°S in the Southern Ocean had increased to 1,223. The population is now believed to be growing at an annual rate of about 8.2%.
Even so, the numbers remain very low — just around 2% of the species' estimated original population of 250,000. Still, more than 60 years have passed since hunting was banned in the 1963/64 season, and there are now gentle signs that the species is on a slow path to recovery. Estimated Population of Blue Whales in the Indo-Pacific Region South of 60°S. (©Suisan Keizai Daily News)
This program was launched in response to the International Whaling Commission (IWC)'s 1982 decision to place a moratorium on commercial whaling. The IWC's main focus was the Antarctic minke whale.
Surveys focused on population size, natural mortality, recruitment rates, and the ecological role of whales in the Antarctic Ocean. Researchers also examined how environmental changes were affecting whale populations and studied the distribution of different whale groups across the region.
JARPA II expanded the scope of research to include not only Antarctic minke whales but also fin whales and humpback whales.
The program aimed to explore how different whale species interact with one another, monitor the broader Antarctic ecosystem, and develop models of ecological competition among whales.
In 2014, the International Court of Justice (ICJ) reviewed the program following a case brought by Australia. While the court acknowledged the scientific value of the research, it ruled that JARPA II did not fall within the scope of Article VIII, Paragraph 1 of the International Convention for the Regulation of Whaling. One of the reasons cited was the program's failure to meet its target sample size. As a result, JARPA II came to an end later that year.
NEWREP-A was developed in response to the ICJ ruling. The program was launched after expert review by the IWC and discussions within its Scientific Committee.
Its main goal was to improve the accuracy of biological and ecological data used to calculate catch limits for Antarctic minke whales under the Revised Management Procedure (RMP). It also aimed to deepen understanding of the Antarctic ecosystem through the development of ecosystem models.
This ongoing program continues Japan's long-term efforts to study whales in the Antarctic with a focus on sustainable use of marine resources. All research is conducted through non-lethal methods.
The survey looks at population size and trends among large whale species, as well as their distribution, migration patterns, and stock structure. Since the launch of JASS-A, no whales have been caught, and researchers are now working to update population estimates based on data from the 2010s and 2020s. Surveys are primarily being conducted in Areas IV and V. (©Suisan Keizai Daily News ) (Provided by the Institute of Cetacean Research)
(The report is published in cooperation with the Institute of Cetacean Research in Japan. A version of it was first published in Japanese in the Suisan Keizai Daily News on February 28, 2023. Let us hear your thoughts in our comments section.)
Author: Suisan Keizai Daily News
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