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Windows of opportunity for Winged Mapleleaf Recovery
Midwest Region, September 29, 2017
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USFWS biologists Andrew Horton (MN WI Ecological Services Field Office), Megan Bradley (GNFH), and Nathan Eckert (GNFH) prepare to search for gravid winged mapleleaf mussels
USFWS biologists Andrew Horton (MN WI Ecological Services Field Office), Megan Bradley (GNFH), and Nathan Eckert (GNFH) prepare to search for gravid winged mapleleaf mussels - Photo Credit: Tamara Smith, USFWS
USFWS divers Nathan Eckert (left)and Megan Bradley (right), and prepare to search for gravid winged mapleleaf mussels
USFWS divers Nathan Eckert (left)and Megan Bradley (right), and prepare to search for gravid winged mapleleaf mussels - Photo Credit: Tamara Smith, USFWS

Every year just prior to Labor Day, the Service's Minnesota –Wisconsin Field Office, Genoa National Fish Hatchery, National Park Service, Minnesota Department of Natural Resource and other partners begin the every-other-day search for gravid (pregnant) female winged mapleleaf mussels to use in propagation efforts to aid the recovery of that species. This year’s efforts started with several days of no luck in finding gravid females, but one day, that changed.

We are not certain exactly what triggers the females to become gravid, but some theories include decreases in water temperature, changes in flow, changes in day length, or a combination of factors. Whatever it is, the period of gravidity typically passes fairly quickly - roughly in one to two weeks' time. This year we found the first gravid females on September 1 and the peak number of gravid females on September 11, and easily obtained the 10 gravid females that were needed for propagation.

When gravid, female mussels typically display a lure to attract their host fish – the winged mapleleaf’s host is the channel catfish. The lure is attractive to the fish and often mimics a minnow, worm or crayfish that the host may mistake as food. The winged mapleleaf lure - what the divers are looking for - is hard to describe: it resembles a zebra-striped blob. Catfish can’t see well, so it may be something other than a visual cue that is attracting them to the mussel lure. The host is a key part of the mussel’s life cycle – the host fish is attracted to the gravid mussel, she releases her glochidia (larvae) which attach to the fish’s gills and live for a short time until they transform and drop off as tiny mussels. Attaching to a host (which for some mussels is something other than a fish, like a mudpuppy) is a great venue for the mussel to travel upstream in its otherwise largely sedentary life.

After divers collect the gravid winged mapleleaf, they are transported back to the propagation facilities –either the Genoa National Fish Hatchery or Minnesota DNR’s mussel rearing facility in Lakeville, Minnesota – where waiting channel catfish are inoculated with the glochidia, and then brought back to the St. Croix River where they were originally captured. Because the timing varies from year to year, we strive to balance our collections to capture any genotypic variability that may be occurring in the wild (for example, individuals that become gravid early in the season vs. later in the season) with our competing needs to maximize genetic variability and produce as many progeny as possible. To capture that genotypic variability, we sometimes reserve a few catfish in case we find more gravid females later in the season, but we try not to reserve them for too long and miss out on our short window of opportunity. This year, we found that balance and hope that our propagation effort will result in many winged mapleleaf juveniles that we can reintroduce to the wild in a few years.


Contact Info: Tamara Smith, 612-725-3548 (x2219), tamara_smith@fws.gov
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