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The Challenge of Preventing the Extinction of an Aquatic Species
Photo Credit: USFWS
One of the rarest freshwater mussels in North America, the purple cat's paw (Epioblasma obliquata obliquata) was widespread in the southern Ohio River and its larger tributaries before these rivers were dammed. The species was listed as endangered in 1990 when it was thought to be functionally extinct, meaning that some live adults existed in the wild, but these individuals did not appear to be producing any young.
In 1994, biologists discovered a breeding population in Killbuck Creek, Ohio, which renewed hope for the species' existence. However, water quality in Killbuck Creek has since degraded to such an extent that drastic measures are necessary to ensure the purple cat's paw mussel's survival.
Funded by U.S. Fish and Wildlife Service Preventing Extinction grants, surveys and efforts to collect purple cat's paw for captive propagation began.
After the 2006 survey, biologists found that safeguarding the species in captivity would be a challenge. The wild population had declined significantly, and only nine males were found after extensive surveying efforts. In 2007, three additional males were found, but no females.
In dire straits, the purple cat's paw could still survive if we could find at least one female. Propagation facilities can produce large numbers of juveniles from a single female. With successful captive propagation, additional recovery efforts become feasible, including reintroductions and habitat conservation and restoration. So, the search continued...
Photo Credit: USFWS
In 2012, much of the Midwest experienced drought. Ironically, this rainfall shortage provided exceptional survey conditions because Killbuck Creek is normally turbid with high flows that limit visibility and access. This survey yielded some encouraging findings: 15 males and 10 females from various age classes, including some only 3 or 4 years old. Surveyors placed these mussels into in-stream holding cages so they could be collected the following spring when females would likely be carrying mature larval mussels, called glochidia.
Earlier this year, biologist pulled the cages and transported the 10 female mussels to the Columbus Zoo and Aquarium's Freshwater Mussel Conservation and Research Center. At the zoo, biologists found that six of the mussels carried glochidia. The partners in purple cat's paw recovery1 hold the mussels at three separate propagation facilities2 to avoid a single accident or mistake wiping out the entire batch of glochidia.
Freshwater mussels have an unusual and complex method of reproduction. Female mussels release glochidia directly into the water and the glochidia must attach to the gills or fins of a specific host fish species to complete development. After attaching, glochidia transform into microscopic-sized juveniles within a few weeks and then drop off the fish.
At each propagation facility, biologists have extracted glochidia from the purple cat's paw mussels and placed them in containers with host fish. Biologists are now waiting to see if viable juvenile mussels drop from the host fish. The very existence of the purple cat's paw are riding on the success of this effort.
Angela Boyer, an endangered species biologist in the Service's Columbus, Ohio Ecological Services Field Office can be reached at angela_boyer @fws.gov or 614-416-8993, ext. 22.
1The U.S. Fish and Wildlife Service is working with many partners to prevent the purple cat's paw extinction, including the Columbus Zoo, Ohio Department of Natural Resources, Kentucky Department of Fish and Wildlife Resources, Center for Mollusk Conservation in Frankfort, Kentucky, and Ohio State University.
2Two females remained at the Columbus facility; two were transported to the Kentucky Department of Fish and Wildlife Resources' Center for Mollusk Conservation in Frankfort, KY; and the remaining two went to the U.S. Fish and Wildlife Service's White Sulpher Springs National Fish Hatchery in White Sulphur Springs, West Virginia.
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