Dolphins have a reputation of being smarter than your average mullet. After all, you can’t get to the top of the food chain on good looks alone. But being big in fishworld has its downside. You have to do what it takes to find a feed…. sometimes in dodgy waters.
My notes on dolphins in the north of the Bay (recorded between 1988 and 2009) show almost all occurred between June and December, with two thirds between July – September. The two pictured here were snapped in the Yarra just north of Westgate Bridge in early September 2009, while the Coza Zaanen was dredging just 200m downstream.
One theory, which seems to make sense, is that dredging creates a short term smorgasbord for predator species, as smaller marine organisms that normally live in the seabed are thrown up into the water column. The problem is that these same organisms have often swallowed heavy metals and other toxins that have been flushed into the river from stormwater drains.
Due to the gradual accumulation of toxins, it takes time for animals to be affected. Meanwhile, perhaps the Dolphins are also wondering why all the Yellow-eyed Mullet disappeared during the EPA’s 2009 Lower Yarra Fish Study?