Friday, May 19, 2006
Another Invasive Species for the Don
School of goldfish in Brick Works pond (click to expand)
Goldfish (or koi or carp) have been present in the Brick Works ponds for a number of years, but this spring there appears to have been a population explosion. This is likely due to the mild winter we experienced so it looks like more than the usual number survived. I took these pictures last week and there were hundreds of goldfish.
The problem of people dumping goldfish has always been a problem in urban ponds and wetlands. I am not sure why people do it- maybe they think a pond isn't complete without a few goldfish. I've also heard that for some Asian people, releasing goldfish into the wild is a way of increasing your luck or good fortune.
Whatever the reason, it is bound to cause ecological chaos for the ponds. These fish will grow very large and will likely outcompete native fish. They are also bottom feeders so they stir up the mud and make the ponds cloudy and dull.
Getting rid of them is a big problem. One fisheries management tool is electrofishing. Basically you stick a cattle prod like device in the water and send out an electric charge. This stuns any fish in the vicinity and they float to the surface. You can then scoop them out easily. Another option is to drain the pond. This is more drastic and will harm other fish species as well. This actually happened a couple of years ago at Riverdale Farm Ponds. The lower pond dried up and this solved the koi problem there. However the Brick Works have a steady supply of water so it is unlikely to happen.
Fortunately for the goldfish, nothing is likely going to happen until a new management plan for the quarry ponds is finished. At that time they may decide to do something. Until then we are left contemplating a pond full of scum sucking goldfish.
A closeup view (click to expand)