(An over-extrapolation of my beach sample.)
Jim Alseth, Long Lake - Park Rapids, MN
The Long Lake Association AIS representatives dropped by a few weeks ago to install a zebra mussel sampling device on my dock. In our conversation I said I should “do the math” on a sample of clams I took this spring as I raked a small swim lane at our newly placed dock and
posted earlier on the “Long Lake Leisure” FB site. This was May 15th, before the lush grass bed forms, and it was just a matter of removing the sticks that are annoying under foot.
While this year appeared to be a good one for lake clams, I recalled that when the “banded snails” moved in about a decade to 15 years ago, I believed there was a big drop in the number of clams. Encouragingly I have seen underwater sand tracks of clams regularly at our beach this year.
This is entirely anecdotal, but as a teen (I’m 60 now), I used to think nothing of scooping up a clam, cracking it open, and “hand feeding” sunnies as I put my arm in the water from the dock. They would congregate once they heard me crack it open underwater and pick away at
the meat as I held the shell in my hand. I no longer use a clam up like this. I never before found a banded snail in the sand that had a live mussel and their shell does not lend to cracking it open, so I never got to see if a banded snail was of interest to the fish.
- Note: This behavior is probably illegal now. The DNR’s site on clams(aka) freshwater mussels (https://www.dnr.state.mn.us/minnaqua/speciesprofile/freshwater_mussels.html) states that 28 of the state's 50 species are now listed as either extirpated, endangered, threatened, or of special concern.
- Most of the data on clams is focused on river populations, as these filtering animals probably thrive in water that is naturally moving by. In this manner, one would expect most of our clams to live in shallow lake water where wave action could provide the same benefit.
- I found out there is a Minnesota State Wide Mussel Survey associated with the information above, and if they have such data on Long Lake, it costs a minimum of $90, filling out a four-page form, and submitting a graphic in specified format of the area of concern. It’s called the DNR's Natural Heritage Information System (NHIS). So, I’ll live with my numbers for now, or maybe there’s a way I can assist science in the future.
- I “discovered” a couple of live mature banded snails (4 to 5 turns on the shell) as I raked, thinking they might have been small clams. So, I believe they live their lives in the weed bed, die once mature, and their shells wash up on the shore -- all the while competing with the clams for resources.
- Another discovery was the egg mass I found on one of the large clams. (See the photo above.) Since the algae-covered portion of the clam is affected, it looks like something took it for a semi-permanent object on which to lay its eggs.
So here is my effort, utilizing the faded 1941 CCC survey map above, a tape measure, and the little data I have from a 15’ wide (sandy shoreline) by 30’ long (underwater length) area. Like the paneling behind it, the map has been on that wall since the 1970’s. We really should colorize the topographic lines on it, or something! Consider this as exhibit 1 of my wife’s contention our lake home exists as the “Alseth Museum.” This is highly contested, but too many artifacts exist for an outright denial of the hypothesis.
The stamp above left appears to lend some gravitas to my effort, being the map is “designed to provide basic information for scientific fish and game management when used with biological, physical and chemical survey data”....so there!
The legend above right notes that the survey by CCC camp S-144 includes bottom types, so I proceeded to measure the lineal length of “sand” at the shoreline around the lake. I came up with 86.5”. The scale is 500’ to an inch, which works out to a little over 8 miles of sand shoreline around the lake (43,250’). Our factor to multiply each clam by is then:
- 43,250 divided by 15 = 2883.33 (Sand shoreline/shoreline length of “sample”)
- 2 large (>4”) 5,766
- 7 medium (2”-4”) 20,183
- 18 small (<2”) 51,900
- TOTAL 77,849
- So, this could be approximately how many clams live in sand within 30’ of the shore of our lake in 2021.
- With only 2 live mature banded snails found, that gives them a paltry 5766 individuals, but I suspect that I missed any smaller examples and they may be teeming throughout the underlying stick layer of the lake.
- I look forward to learning more about clams as “indicator species”.
- Primary predators of freshwater mussels are muskrats, otters, raccoon, geese, ducks, flatworms (on juvenile mussels), fish, and humans.
- Their life cycle includes the attachment of larvae to freshwater fish gills, and eventually getting free somewhere else to live. One species even “baits” largemouth bass with a fake “minnow” to get them to chomp on the larvae sack that then coats their gills...wow.
- So check out: https://www.dnr.state.mn.us/minnaqua/speciesprofile/freshwater_mussels.html
I’ll probably keep this going and see how we do in future years!