Blue Whale Encounters – by Mike Jacques Everyone knows they are the biggest animals on earth, even bigger than the biggest dinosaurs, other than that, confirmed facts about Blue Whales are slim pickings. We know there were a lot of Blue Whales around before commercial whaling started targeting them at the beginning of the twentieth century. There may have been 150,000 blue whales then and over the decades 350,000 were killed. The population figures now are a bit sketchy but is estimated at less than 20,000, with less than 1000 animals surviving in the southern hemisphere. These numbers haven’t appeared to recover much since the end of whaling. Even the species classification of blue whales is a bit confused. Blue whales in Australia are currently recognised as one species with two sub-species, True Blue Whales (Balaenoptera musculus musculus) and Pygmy Blue Whales (Balaenoptera musculus brevicauda). Recently it was decided that an estimated 6000 whales are from the separate pygmy blue subspecies. Most Australian sightings are likely to be of Pygmy blues, but it is very difficult to tell them apart visually Blue whales cover huge distances each year as they migrate warm waters, where they give birth in winter, and krill-rich polar regions in summer. They are usually solitary or seen in pairs, but may be found in larger groups in feeding areas. Blue whales live mainly in the open ocean but will periodically follow changes in the oceanic conditions that lead them to upwellings off the Australian coast. These upwellings support dense swarms of krill (tiny shrimp-like crustaceans). They also provide opportunities for whale watching encounters. Where to see them in Australia The Blue whale hotspots are Western Victoria and South east South Australia. The new Ngari Capes Marine Park, (between Busselton and Augusta WA) is also now believed to be a breeding area for the species. Big aggregations have been seen off Rottenest Island WA in an area known as the “Swan Canyon”. Off Victoria/SA, around one hundred blue whales visit the Bonney Upwelling each year, between November and May, to feed on large swarms of krill. Blue Whales have also been spotted feeding off Eden, during the humpback whale watching season (October to December), and between King Island and Tasmania, but these sightings are not as predictable as the ones in the Bonney Upwelling and it looks like the Hunter Island area is just the south-eastern extreme of the Bonney Upwelling during productive years. A helicopter/light plane is a good idea as there is a lot of ocean and not too many whales. It isn’t foolproof as blues don’t spend much time at the surface, so often you’ll fly over them without knowing they’re there. Page 10 If the winds that drive the upwelling are weak that year the nutrientrich water won’t always make it to the surface, which means there will be little surface krill and fewer visible whales. A whale will remain at the surface for a minute or so and then dive, disappearing for around 5 minutes. They can be difficult to track from a boat as they move on quickly, and that upwelling is caused by winds, bring the seasick pills. If you are broke like me, you might still get lucky closer to shore. According to the Portland tourist blurb, “Whilst blue whales rarely approach land very closely, their blows and backs can sometimes be seen at a distance off prominent headlands such as Cape Nelson and Cape Bridgewater. They generally arrive in November and remain off Portland until May. Their distinguishing features are a slender streamlined shape with a small dorsal fin towards the tail and a powerful, tall straight blow (exhalation of breath) that in good conditions can be seen at 10 kilometres and heard at 4 kilometres.” Boats should not approach closer than 100 metres to a whale. If you are in the water and a whale approaches, you must not initiate an approach closer than at least 30 metres from the whale. The importance of Upwelling Bonney Upwelling The South Eastern coast of South Australia and Western Victoria are renowned for having good fishing, millions of breeding seabirds, seal colonies. The area is also visited every summer and autumn by thousands of dolphins and whales, including Blue Whales. It boasts a distinct colder-water flora, and rich underwater gardens of sponges, bryozoans and corals. The key to all this life is a deep water upwelling bring nutrients to the surface from the deep waters adjacent to the continental shelf. The upwelling plays an important role in the life cycle of juvenile Bluefin tuna who feed on pilchards in the eastern Great Australian Bight during the upwelling season. Officially, its called the “Great South Australian Coastal Upwelling System”, but more commonly known as the Bonney Upwelling, although the one on the Bonney Coast is only one of three known upwellings. It is the deepest-reaching of our upwelling systems and percolates up from depths exceeding 300 m. The phenomenon can extend 800 km from Ceduna, South Australia, to Portland Victoria. Southeasterly coastal winds create the effect during the summer (December – April). Key upwelling centres form along the Bonney Coast (Robe, SA to Portland, Vic) and the southern tip of the Eyre Peninsula. A smaller upwelling also forms off the south-western coast of Kangaroo Island. In conservation terms these upwellings are considered as important as the Great Barrier Reef yet it is virtually unknown. We have known about it since 1998, but it was only properly mapped in 2004. The Bonney Upwelling area harbours 26 listed threatened species: one shark; 5 birds and 2 whales are listed as endangered; and 11 birds, 1 shark, 3 whales and 1 bony fish are listed as vulnerable. Page 11 If you want the Full Monty on how it forms, in layman’s terms water starts swirling around the deep submarine canyons of the Murray Canyon Group, on the continental shelf edge just south of Kangaroo Island. A pool of cold and nutrient-rich water is pushed to near the surface just west of Kangaroo Island. This provides the source waters for other nearby upwellings. Owing to the narrowness of the shelf along the Bonney Coast, upwelling there happens without a cold dense-water pool and is only wind-driven. Perth Canyon The Perth Canyon, known also as the Rottnest Trench or Swan Canyon, is a similar size to the Grand Canyon. Its a 15km cleft in the continental shelf starting at the 50 metre-deep water contour about 20 kilometres west of Rottnest Island. From there, it winds west for about 200 kms to depths of up to 4000 metres. The Perth Canyon, is a gorge formed after thousands of years of scouring by the ancient Swan River system. Back then the climate was wetter and nearly every river in Western Australia from North-West Cape to Eucla had an offshore canyon associated with it. There are huge canyons off Yardie Creek, the Murchison and Kalbarri. In terms of marine biodiversity, scientists have said that “nothing can match the productivity and biodiversity in this canyon”. Life in the canyon is fed by organic material from rivers. The small krill reach the nearsurface waters of the canyon in periodic upwellings between December and May. These deep ocean eddies are often spin-offs from the southward flowing Leeuwin Current. The canyon’s size and complexity mean that multiple eddies could form within it, taking nutrients to where marine life needs it. Blue whales use the Canyon for periods of between 2 to 4 weeks each year. It is only recently that we have recognized the Perth Canyon area as a major whale feeding area. Krill species in W.A. don’t come to the surface in daylight like the krill off Southern Australia. It is found during daylight hours at depths of 200-500 m, vertically migrating into surface waters only at night. The area’s blue whales can sometimes be seen circling on the surface before diving to the dark depths to harvest this krill. It is now understood that they circle to hold station over prey aggregations in deep water, while they regain their strength for another dive.