Whale Populations

Are there too many humpbacks? Why are there so many Humpbacks, and so few Southern right and sperm whales? Humpbacks were always naturally numerous and they were fast moving whales that yielded relatively little oil or bone. Right whales were the opposite and came very close inshore along the southern coast of Australia during winter and spring. They were easily hunted. By the turn of the century, southern rights were considered virtually extinct in Australian waters. It wasn’t until 1955 that there was a scientifically recorded right whale sighting for the Albany coast. The natural and unhunted number of right whales at the beginning of the 1800s is unknown. Its presumed natural population on the west coast was probably always relatively low, possibly between 2,000 and 3,000. WA Museum estimates now a west coast right whale population around 2,100 in the surveyed southern coastal area from Cape Leeuwin to Ceduna. Aerial survey logs show an estimated 7.5% annual growth rate in WA’s southern right whale population, similar to the humpback rate. The population is uneven with the Great Australian Bight being a stronghold. They haven’t repopulated the sheltered bays of the south east as noticeably. Here they were wiped out the most thoroughly, and are probably disturbed by noise pollution and other human interference in these usually heavily populated harbour areas. When right whales were exterminated, larger vessels were built to take to the high seas and find the more pelagic sperm whales which yielded good oil and valuable spermaceti. Once their aggregation patterns were understood they were hit hard. They were hunted again in the 20th century using motor vessels. Key localities for Sperm Whales in Australia include the area between Cape Leeuwin and Esperance, Western Australia, close to the edge of the continental shelf (averaging 20–30 nm offshore); the region southwest of Kangaroo Island, South Australia; deep waters off the Tasmanian west and south coasts; areas off southern NSW, including Wollongong; and the deep water off Stradbroke Island, Queensland. The overall sperm whale population halved between 1968 and 1977. In 1979, WA whalers reckoned that the number of exploitable males had fallen to 25% of the 1947 figures. Exploitable female numbers were close to zero by 1989. 6 No population estimates are available for Sperm Whales in Australian waters. It is likely that the total number of mature animals within Australian waters is less than 10 000. In the Antarctic a population estimate of at least 3200–14000 animals has been made. Global population appears to be slowly recovering, with reports indicating an increase in population size over the last 20 years. This hasn’t been noticed in WA, although sperm whales move around and sightings fluctuate from year to year. It seems then that sperm and right whales were always rarer than humpbacks and it is possible that earlier hunting is still distorting the populations. This requires a lot more study. The last commercial whale hunting off Western Australia stopped when the Cheynes Beach Whaling Company near Albany closed in 1978. By then, maybe only a few hundred humpbacks remained. Humpbacks are now thriving due to a fast population growth rate of 10 per cent each year, and they are considered no longer in danger. There are now about 30000 humpbacks travelling along the WA coast each year, and about 25000 on the east coast. Humpbacks spend the southern winter in semi-tropical waters and head to the Antarctic during the southern summer. In 2014, the former head of West Australia’s Environmental Protection Authority said there would soon be “too many” whales off the state’s coast. The environment could not support this ongoing rate of expansion and it will soon have to drop back to a more normal 2%. Eventually, either humpback birth rates will suddenly fall or death rates will spike. Already there are increasing reports of distressed and hungry juveniles being washed ashore. This might be due to changes in food supply caused by things like climate change, but we should also consider that while we may try to push them out to sea again, this mortality is normal in a healthy population.

Right Whales boom in the Bight This year’s count at the Head of Bight in South Australia has sighted record numbers of southern right whales. A team of researchers at the Head of Bight on the edge of the Nullarbor Plain have counted up to 172 whales including 81 mothers with calves on a single day. The record numbers were consistent with the expected 7 per cent growth rate. Their numbers are still very low compared to what they were prewhaling. At one point there was less than 300 southern right whales in the world and it’s only since the 1970s and ‘80s that we’ve seen the whales return to Australian waters. Curtin University Great Australian Bight Right Whale Study. There are an estimated 12,000 southern right whales in the world now with sub species in Australia, New Zealand, Argentina and South Africa. About 100,000 southern rights cruised the oceans before whaling but more than 75 per cent of them were slaughtered by 1845. Females give birth every three to four years and reach sexual maturity at nine years of age. Adults can grow up to 18 metres long, weigh 80 tonnes and are believed to live for about 80 years. The Head of Bight Visitor Centre at the 55m high Bunda Cliffs overlooking Head of Bight, has been inundated with about 250 whale watchers a day. The whales come very close to shore usually within a few hundred metres and sometimes as close as 60 metres. Its shallow, sandy bottom, protection from wind and its location within the Great Australian Bight Marine Park has helped Head of Bight become one of the largest southern right calving areas in the world. “The sanctuary zone here is really doing a good job of providing the protection that the whales need, which also encourages other animals into the area,” Dr Charlton said. “There’s a full vessel closure in whale season and a total exclusion zone – it’s something we should be really proud of here.” A BP proposal to drill for oil about 200km offshore from Head of Bight has sparked environmental concerns and prompted a visit to the area by marine activist group Sea Shepherd last month. It should be noted that the populations in the SE, which were hardest hit by hunting, and are now noisy developed areas with lots of boat traffic, are not showing noted recovery in southern right populations.