Aquatic Species at Risk - The Hickorynut

Hickorynut

Hickorynuts

SARA Status: Under consideration
COSEWIC Status: Endangered

Region: Ontario and Quebec

Region: Ontario

Did You Know?

Hickorynut shells were considered valuable for the pearl button industry in the early 20th century, and were harvested for these purposes in the United States.

Freshwater mussels are molluscs, soft-bodied animals without a skeleton (invertebrates) that live on the bottom of streams, rivers, lakes and ponds. They use a muscular foot to burrow and crawl and have a pair of hinged shells.

The suspected host fish for this mussel in Canada is the Lake Sturgeon (Acipenser fulvescens). Lake Sturgeon in the Great Lakes-St. Lawrence region was assessed as Threatened by COSEWIC in 2006.

Related Information

COSEWIC Assessment and Status Report on the Hickorynut Obovaria olivaria in Canada (2011)

Description

The Hickorynut is one of Canada’s 54 freshwater mussel species and one of only two mussels in the genus Obovaria found in Canada. Also known as the Olive Hickorynut, this small-to-medium sized mussel is easily recognized by the following features:

  • nearly oval-shaped shell, no longer than 7.5 cm;
  • shell colour is green to yellowish-brown, turning dark brown with age;
  • thin, greenish coloured rays can often be seen on juvenile shells;
  • inside of shell (nacre) is usually bright white and often iridescent towards the back (posterior);
  • shell is thicker in the front (anterior) and thinner at the back (posterior);
  • posterior of the shell is broadly pointed in males and rounded in females;
  • beaks are elevated, raised above the hinge line and set towards the extreme anterior of the shell; and
  • hinge teeth are complete, thick and well defined.
Image of inside and outside of the Hickorynut mussel shell.

Image of inside and outside of the Hickorynut mussel shell. - Photo credit: Environment Canada

Habitat

Map showing the distribution of Hickorynut in Canada

Historically, the Hickorynut was widely distributed along the large river bottoms of the Mississippi River drainage system and the Great Lakes-St. Lawrence basin. While still broadly distributed in the Mississippi drainage of the United States, the Hickorynut is imperiled or lost from most of the American Great Lakes states.

In Canada, current populations are now only found in certain rivers and their tributaries within the Great Lakes-St. Lawrence drainage system, from Lake Huron in southern Ontario to Quebec City in the east. Rivers include the Mississagi River, Ottawa River, St. Lawrence River and the Saint Francois River.

Hickorynut are typically found in the sandy bottoms (substrates) of large, wide and deep rivers (2–3 metres or deeper) with moderate to strong currents. They are fairly long-lived mussels, with a lifespan between 7 and 14 years.

Like all species of freshwater mussels, the Hickorynut filters its food from the water. Bacteria and algae are its primary food sources.

The Hickorynut is considered a long-term brooder; spawning happens in the fall and the larvae (glochidia) are released the following summer. Like most other freshwater mussels, Hickorynut glochidia are parasitic on fishes—the glochidia attach to and feed off the gills of a host fish until they reach their juvenile, free-living stage and drop off to burrow in the substrate below. Adult Hickorynut are essentially sessile and may move only a few meters along the substrate the entire rest of their lives.

Threats

The introduction of Zebra and Quagga mussels in the 1980s and 90s wiped out the Hickorynut in the Detroit and upper St. Lawrence rivers. The invasive mussels attach to Hickorynut shells by the hundreds, preventing them from eating, breathing, moving and reproducing, and continue to threaten the remaining Hickorynut populations. Dams along the large river habitats of the Hickorynut are another serious threat, as its suspected host fish, the Lake Sturgeon, are unable to traverse them. With fewer hosts, the chances of enough larvae reaching their free-living stage to maintain the population are greatly reduced. Pollution from industry and agriculture also threaten the Hickorynut and its host by decreasing the water quality of the habitat.

Further Information

The Hickorynut has been designated as endangered by the Committee on the Status of Endangered Wildlife in Canada. Public consultations regarding the addition of this population to the List of Wildlife Species at Risk were held from April 9 to June 9, 2014. The Governor-in-Council’s listing recommendation will published in the Canada Gazette Part I (Government of Canada newspaper where laws and regulations are published) and on the Species at Risk Public Registry.

If listed under the Species at Risk Act (SARA), a recovery strategy and action plan will be developed to prevent the loss of the Hickorynut in Canada, involving research, land and water stewardship, monitoring and awareness activities. Critical habitat for the Hickorynut will also be identified under SARA, allowing for greater protection and recovery of its habitat.

Provincially, the Hickorynut is listed as endangered under Ontario’s Endangered Species Act, 2007 and is anticipated for listing under Quebec’s Act respecting Threatened or Vulnerable Species.

For more information, visit the SARA Registry.

Text Sources: COSEWIC assessment and status report on the Hickorynut in Canada, 2011; Metcalfe-Smith et al. Photo Field Guide to the Freshwater Mussels of Ontario, 2005. Fisheries and Oceans Canada, Canadian Science Advisory Secretariat, Recovery Potential Assessment of Hickorynut (Obovaria olivaria) in Canada, 2013.

Scientific Information:

Scientific Name: Obovaria olivaria
SARA Status: Under consideration
COSEWIC Status: Endangered (May 2011)