Wednesday, December 5, 2007
On BBC news this morning there was a marvellous news item about the cleverness of Amazon River Dolphins. Some males carry objects in their mouths such as weeds, sticks and clay as symbols of courtship and sexual display.
After a three year study of over 6000 dolphins, scientists found that there is a relationship between object carrying dolphins and aggression. They explained that such aggression is linked to those males who produce the most offspring.
This latest study adds to the research data on the tenacity of dolphin culture. For example, in Shark Bay in Western Australia, researchers found that dolphins use tools such as sponges to rest on to protect their bodies when they are foraging for food amongst sharp and rocky terrain.
Clever dolphins like the Amazon River Dolphins and other fresh and salt water dolphin species across the globe are sadly under threat from deforestation and habitat degradation. Research from the World Wildlife Fund (WWF) states that threats to the Amazon River Dolphins are also due to their use as bait for destructive commercial fishing practices in Colombia.
This year the Yangzte River Dolphin known as the Goddess of that river has become extinct. And at the 10th International Riversymposium & Environmental Flows Conference held in Brisbane in September, scientists spoke of the dangers to river dolphins in other parts of Asia, especially along the Mekong in Cambodia, the Ganges in India and the Indus in Pakistan.
At the Symposium, speakers from the WWF explained that dolphins are the watchdogs of river quality, pointing out that a decline in river dolphin numbers represents a decline in water quality (increasing polluition and toxicity) which affects both water creatures and humans alike in terms of health, wellbeing and live-ability.
The Brisbane River is home to a number of dolphins. Recently the Brisbane Times reported that there is anecdotal evidence that imroved water quality in the river over the past few years has led to an increase in dolphin numbers along the river and in Moreton Bay. But little research in being undertaken on these local dolphin species, although it's suggested that 'the relatively timid Indo-Pacific humpback dolphin, one of the two species of dolphin found in Moreton Bay, could also be susceptible to urban development.'
It's been estimated that there are about 160 Indo-Pacific hump-backed dolphins in the Moreton Bay region (Hale et al 2004). According to whale and dolphin researcher Dr Mike Noad from the University of Queensland, dolphins have been coming up river possibly because of the higher levels of salinity in the river. Increasing saltiness of the river is linked with reduced fresh water run-off and low rainfall.
Scientists have been working to improve water quality in catchment areas and local streams and rivers but currently these areas in SE Queensland are suffering from damaging drought conditions. The Brisbane Times article went on to say that those 'streams that are degraded by poor riparian and catchment land-uses appear less resilient under drought conditions and therefore show declines ... [which have led] 'to high nutrient and sediment loads and low dissolved oxygen levels'. In contrast, earlier this year, the Courier Mail reported that 'Brisbane River is at a crossroads – 30 years of conservation work is finally bearing fruit – and marine biologists say it is in its best shape in years.' That's excellent news.
Hale, P, Brieze, I, Chatto, R & Parra, G, 2004, Cetaceans: Whales and Dolphins. In National Oceans Office. Description of Key Species Groups in the Northern Planning Area. National Oceans Office, Hobart, Australia.