Week 5: The Traveling Fish

June 20, Tuesday:

Today marked the completion of sampling the entire lake twice. In general, since beginning our data collection on the lake in late May, both recreational activity and the size of the Milfoil beds has increased with the warmer weather.

Pictured above is a "bed" of lose Milfoil at the surface of the lake. These floating beds can be found both in the lake's small coves and around marinas. As the Milfoil gets closer to the surface of the water and boat traffic increases, it becomes easier for boat propellers to chop up the tops of the Mifoil plants, creating loose segments that collect around the lake like in the image above. An unfortunate property of Milfoil, that many people are unfamiliar with, is the fact that these cut segments can eventually become new, individual plants. Visible in the above image are small, silvery roots that emerge from the central stem of the cut plant. These roots sprout in a few days time from being separated from the mother plant. The plant fragment can then sink, and a whole new plant grows, sometimes in a totally different location than the parent plant. This pattern of growth is what enables Eurasian Water Milfoil to be such a dangerous invasive species, especially in recreational lakes. Milfoil can take over a lake, depending on the size and the amount of activity in about two years through a combination of plant divisions and reseeding itself.

Below: a "fragment" of Milfoil. This segment has not yet grown roots.

On the bright side, today yielded some interesting news for the Triploid Grass Carp program, and confirmation that many of the fish are definitely alive and well. One fish in particular has provided us with an interesting case. It was first sited this year near the Sherman town park on June 1st, and then disappeared. The fish had not been seen anywhere else in the lake since that date, even though the entire Sherman Arm has been sampled twice since June 1st. Due to the fact that the fish had not been spotted in over two weeks time, it became clear that the fish had moved a great distance. We were interested in what motivated this fish to move, as the water off of Sherman Town Park is filled with Milfoil and the cove is sheltered from the majority of recreational activity due to the enforced no wake zone. To our surprise, the fish finally turned up today, twenty days, and nearly four miles away from where it was first seen on June 1st, near the tip of Vaughn's Neck.

Such behavior indicates that although the carp are sterile, they may still exhibit behavior seen in fertile carp during the breeding season. This conserved behavior can include swimming great distances to find a mate and spawn once the fish reach sexual maturity. We know from data collected during 2016, some of the other tagged carp introduced to the lake embarked on similar long journeys across the lake, perhaps for the same reason.

While collecting our data, we observed significant movement of two other fish that had been observed as recently as June 9th in other locations. One fish moved from the large weed bed at the mouth of the New Milford Arm of the lake to a weed bed near the Brookfield Town Park, a trip of about a mile and a half. We theorize that this fish may have been scared out of the bed in New Milford by boat traffic, as it is a popular place for fishermen. The fish then likely settled in the cove by Brookfield Town Park due to the large Milfoil bed located there.

Another carp, originally found near the cove by Brookfield Town Park on June 9th, pulled a similar act to the fish found in the Sherman Arm of the lake, and vanished. Throughout our sampling today, the signal for this fish was not heard at all. This fish could simply be too deep down for our receiver to pick up the frequency from its tag, or it too could be on the move for reasons unknown.

Such hypotheses regarding these unexplained movements by the fish are simply theories, however, they appear to be logical based on what we know about the nature and behavior of Triploid Grass Carp from other similar studies.

Special thanks to Dave for taking us sampling today!

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June 21, Wednesday:

With two sets of data collected from the entire lake, we now hope to complete one more round of data collection before boat traffic on the lake becomes steady with the beginning of the summer season. Today, we sampled the least active region of the lake for our fifty tagged carp. The lower mid section of the lake, including Echo Bay, does not have any stocking sites (points in which the carp were originally introduced to the lake) so we find few fish there, even with the abundance of Milfoil in Echo Bay and around many of the small islands.

Below: A ring of Milfoil surrounds one of the small islands behind Candlewood Isle.

Although we do not find very many of our tagged carp in these regions, there is no evidence that other Triploid Grass Carp are not located in these large beds. We only have the ability to see only 50 out of the almost 8,000 fish that are now in the lake. In addition, the new carp that were added in early June of this year were released at several sites not included in the original 2015 release; including Squantz Pond and further up the New Milford Arm of the lake. Not only are these additional fish needed for the carp program to make a significant dent in the Milfoil, but adding more stocking sites will help them to disperse evenly throughout the entire lake. Therefore, although we may not hear the signals of our tagged carp in many areas of the lake, it is very likely that unmarked carp are.

As we have still yet to find 10 out of our 50 tagged fish, we inspected this section of the lake very thoroughly, sampling in small coves that were not designated sites on the map. As seen with some of the fish that have disappeared and then reappeared in a completely different location without detection, finding some of these fish is simply about being in the right place at the right time. In a lake that is 11 miles long and 2 miles wide in some areas, searching for these remaining 10 carp is analogous to looking for a needle in a haystack. Hopefully in the remaining week and a half before the Fourth of July, we will be able to find at least a few more of these missing fish.

Until next week, enjoy the beautiful weather out on the lake!

Special thanks to Bill for taking us sampling today!