Friday, December 13, 2013

December Mystery of the Month

Which fish is which?

Above are two ~3” long fish that were pulled from Markham Pond. As you can see they are very similar in appearance. They are also very similar in their dining habits. So who is who in this round-up of benthic feeders?

1 fish, 2 fish, 5700 goldfish!

The answer to the question is the fish on the left is a goldfish, and the fish on the right is a young-of-the-year common carp. The differences between young carp and goldfish are fairly subtle, although much easier to discern when you have them side by side. First and most obviously is the golden cast to this goldfish – this is not always a reliable characteristic, as the color of goldfish in the wild varies. Another difference is the size of the scales and the eyes, relative to body size; goldfish scales and eyes are larger. Again, this is easiest to spot when you are looking at both. A more reliable characteristic is the presence of 2 sets of barbels (whiskers) near the mouth on the common carp; goldfish have none. And though they are there, you can’t actually see them on either fish in the photo above!

Several young-of-year carp and goldfish were visible on one side of the
draw-down net.  The net was set up to keep adult carp from swimming
downstream.  These little guys, however, swam upstream and were trapped.

The fish above were pulled from Markham Pond. Markham Pond is a 13 acre shallow pond in Hazelwood Park in Maplewood. Markham is a part of the flow path for the Phalen Chain of Lakes and is connected to Kohlman Lake through Kohlman Basin and Kohlman Creek. Markham serves as a carp ‘nursery’; a spot where conditions occasionally allow a large number of carp eggs to hatch and young-of-the-year to thrive. There is also a large resident population of goldfish. A 2010 capture/mark/recapture study of fish in Markham Pond by a U of M graduate student found an estimated 21,000 goldfish along with 35,000 young-of-the-year carp.
Large adult carp swim in the shallow Markham Pond near the outflow pipe
while thousands of young carp and goldfish swim between the net and the outflow pipe.

Removal involved only a few staff with nets.
As a step in the ecological restoration plan for Markham Pond, RWMWD and Maplewood staff are in the midst of conducting a drawdown of the pond, to reduce or eliminate the carp and goldfish population and help clear the water. During the early stage of the draw down, District staff removed 6,600 small fish from Markham. Upon close examination, it appears about 86%, or 5700 are goldfish, and about 900 are young of the year carp. We will be writing more about the Markham Pond ecological restoration plan in next month’s Ripple Effect.

Approximate size range of those removed from Markham Pond.  With your new
knowledge, can you tell which fish is which in the photo above? 



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