 |
The oceans are the engine of the world. Oceans make up more than 70 percent of the planet’s surface. The marine environment is a crucial part of the global climate, as it absorbs carbon dioxide, and its currents move nutrients and influence weather patterns. The driver of deep water currents in the ocean is thermohaline circulation, which transfers the oxygen that sustains marine life, and also moves warm waters from the tropics to the poles. This conveyer belt moves because of cold water sinking to the depths of the ocean. This could be disrupted by freshwater from melting ice and increased rain at the poles, which could block the cold saline water that sinks downwards. If this occurs it would have an extremely negative impact on all marine life (WWF 2000). 
Seabirds in Western AustraliaSeabirds depend on the marine environment for their sustenance. Each seabird population operates like a fishery, defined by a catching method, target species and operating zones. The number of seabirds breeding at a colony depends on the availability of their target fish species. Seabird populations are inherently stable, so shifts in their distribution, or changes in their population may be a signal of a sea change. Warm and cool water sea birds share breeding islands off mid and south-western Australia. These birds include Shearwaters, Tropicbirds, Terns and Noddies. The overlapping of tropical and temperate species is due to the Leeuwin Current that runs down the Western Australian coast, from North West Cape to the Bight. The current’s sensitivity to the El Nino Southern Oscillation (ENSO) is known to be a major reason for variations in fisheries supply and distribution. There have been major changes in seabird breeding distribution since bird observations were first recorded in the late nineteenth century. At least eight species have formed new breeding stations well to the south of their historical range and/or have seen marked population increases at their more southerly colonies. The rate of establishment and/or growth of new colonies appears to have accelerated since the early 1980s. The factors that are driving the changes suggest that seabird fisheries and breeding declines during El Nino conditions in the northern tropical parts of their ranges, forcing southward dispersal in pre-breeders. The El Nino phase of the Southern Oscillation increased in frequency with every couple of decades of the 1900s. What was once an unusual climatic pattern became familiar in the last two decades of the century, with major events in 1982/83, 1987/88, 1991-1994 and 1996/97. Since the behaviour of the Leeuwin Current is strongly influenced by the ENSO it is likely that this is the cause of the shifts in the seabird fisheries and changing population dynamics. The bird’s eye view is one of a changing ocean climate. If the seabird fisheries are undergoing change then it is likely that commercial and recreational fisheries will also be affected by fluctuations in fish productivity and changes in the distribution of species. Human fishing communities are also located within operational distance of targeted fish stocks. Even in the absence of over-fishing, climate change is likely to produce greater fluctuations in the recruitment of target species and in the redistribution of fisheries. Species may become inaccessible or decline and new species may invade the fishing grounds. Climate change is likely to lead to unprecedented fisheries adjustment at considerable economic and social cost. By Dr. Nic Dunlop, reproduced from Western Fisheries magazine 
Whales off the coast of Victoria and South AustraliaSouthern Right Whales travel to the waters of South Australia each year to breed and calf. Hundreds make the journey from Antarctica to our southern coastline. Blue Whales travel to an area off the coast of Warrnambool in Victoria between November and April to feed in an upwelling area. This upwelling contains nutrients flushed up from the ocean depths, providing essential food for the plant plankton on which the animal plankton, including krill (small prawn-like animals), feed. Blue Whales, in turn, depend on the krill as their food. There are only about 8 places like this in the world outside Antarctica where Blue Whales gather (Gill 2001). Whales world-wide are vulnerable to climate change (McGarvin and Simmonds, 1996) and the whales that come to Australian waters may suffer because of climate change-induced decreases in the availability of their food. Whales find food in a patchy environment and shifts in food sources through the change in upwelling patterns may create difficulties in securing food (McGarvin and Simmonds, 1996). The rate of climate change is likely to be outside the evolutionary experience of existing whale species. Whales with complicated life cycles (e.g. long migration routes) are dependent on finding resources (which includes temperature regimes such as warmer waters for breeding) in particular locations. Changes in food distribution may mean that whales will have to use more of their energy finding food (Agardy 1996). Temperatures in the Antarctic have increased more than 2°C in the last 50 years and sea ice has been shrinking. A doubling of pre-industrial CO2 concentrations (likely by 2060) could reduce sea ice in the southern hemisphere by more than 40%. A reduction in sea ice means less of the algae that grows in the pack ice, which is the food for krill. Krill have already been declining as temperatures at the pole have increased (Burns 2000). Krill are the primary food for whales in the Southern Oceans, and given 90% of the world’s remaining great whales feed in this region, it has serious implications for populations in the region. Southern Right Whales may have difficulty making the journey to Southern Australia to breed and calve if their food supply is reduced. The economic importance of whales and whale related marketing to Warrnambool is in excess of $17 million per annum. In 2000, 77,000 visitors to the town participated in whale watching (Warrnambool City Council, 2001). Whale watching areas such as Victor Harbour in South Australia have become new tourism hubs, providing income and employment. During the whale watching season in June – August 2001 an average of between 1350 – 1900 people visited the Victor Harbour Whale Centre each week to ask for information about whales (Victor Harbour Whale Centre, 2001). By Mark Simmonds, Director of Science, The Whale and Dolphin Conservation Society
|
|
Marine ecosystems and species Blue Whale, Image courtesy of Mark Carwardine
|
|