The reason why southern and northern whales DON´T interbreed...

INSTRUCTIONS – Read the following text carefully and then choose the correct alternatives that answer the questions.

SOUTHERN HUMPBACK WHALE

INTRODUCTION

During the Australian winter, these ocean leviathans journey 3,100 miles north from their Antarctic feeding grounds to the warm tropical waters near Australia´s Whitsunday Islands. At the southern edge of the Great Barrier Reef, the 40-ton female humpbacks give birth to calves measuring 14 feet long and weighing over one ton. The Whitsundays´ sheltered bays keep the calves warm and safe from predators. During the next few months, the whales rest, sing, play and mate. The calves nurse, but the one thing the adult whales don´t do while in the tropical seas is eat. By winter´s end, adults are famished, and they head south.

This life cycle is repeated throughout the Southern Hemisphere: one group migrates along the western coast of Australia, others to southern Africa and South America.

SIGHT UNSEEN

Underneath the blue Australian ocean, film crews captured the elegant rituals of southern humpbacks as they swim, sing, nurse, and play. A mother humpback whale supported her young calf from underneath, so it could breathe easier near the surface. Calves drink 130 gallons of milk a day! While baby grows fat, the mother starves for five months, her blubber stores depleting daily. Unlike the cold Antarctic waters, the seas here don´t grow rich with krill that humpbacks filer through their baleen plates. But she provides her calf with rich milk that contains some of the highest fat content of any mammal´s milk – 45 percent.

UNIQUE BEHAVIOR

Humpback males sing a unique melody, full of high-pitched chirps and whistles interspersed with deeper gurgles and moans. Each male repeats his song for hours, which likely plays a role in courtship. The song may change over time, with males singing a modified melody in consecutive years.

Whale-watching tours take advantage of the humpback´s playful and curious nature. They often approach boats and put on quite a show. As whales journey south along the eastern coast of Australia, many stop in sheltered Platypus Bay around Fraser Island – a World Heritage Site – where they display the charismatic behaviors loved by whale-watchers. The crystal blue waters give a perfect window to watch the whales twist, roll and swim upside down, emerging to breathe, slap their tails or pectoral fins on the water´s surface. Breaching whales jump nearly all the way out of the water. “Spyhopping” means their head emerges, and they peer at the surroundings with their large eyes.

STATUS/CONSERVATION

Commercial hunting in the 19th and 20th centuries decimated most whale species. Because they migrate close to shore and swim slowly, humpbacks became a popular whalers´ target, and were hunted down to a few hundred animals in the Southern Hemisphere. The International Whaling Commission (IWC) implemented a moratorium on harvesting all species starting in 1986, and in 1994, declared Antarctica´s Southern Ocean a whale sanctuary. Now numbering over 10,000 in the Southern Hemisphere, humpbacks have shown incredible resilience, but their numbers still remain a fraction of their historic abundance. Recovery of regional populations varies, and the World Conservation Union (IUCN) lists the humpback as vulnerable.

Humpbacks also have two Northern Hemisphere populations that number around 11,500 in the North Atlantic and 6,000 in the North Pacific. Northern humpbacks are genetically differentiated from the Southern Hemisphere population, and have dark bellies, while the southern humpbacks have all-white bellies. They don´t interbreed, because while the southern populations are mating and calving in the warm tropical seas, northern populations are near the polar Arctic.

OUTLOOK

The International Whaling Commission (IWC) allows hunting by indigenous cultures but bans hunting of humpback whales. Japan has long engaged in IWC-sanctioned “scientific whaling” of minke and other whales, and plans to start hunting humpbacks in 2007. “We are all concerned about Japan´s plans to add this species to the scientific whaling quota”, says Dr. Scott Baker, a renowned cetacean conservation biologist. Iceland also just started commercial whaling in 2006.

Some Asian countries allow the sale of whale meat from incidental bycatch, and a whale´s value of $100,000 provides incentive for illegal harvest. Baker and colleagues used DNA to show that the whale meat being sold in South Korean shops did not match that reported to the IWC. Illegal harvest and sale of whale meat is occurring.

Australia and New Zealand have petitioned the IWC to create a South Pacific Sanctuary adjoining the Southern Ocean Sanctuary where whaling would be illegal. Thus far, it has not been approved by IWC.

http://dsc.discovery.com/convergence/planet-earth/animals/animals.html