River Redhorse

(Moxostoma carinatum)

Status: Special Concern (ESA 2016, COSEWIC 2006)

Table of Contents:

Species Identification
Diet
Habitat and Range
Biology and Behaviour
Similar Species
Threats/Reasons for Being at Risk
Conservation and Recovery Strategies
How You Can Help

Photo by Dom Porcelli: https://www.inaturalist.org/observations/81250494

Species Identification:

The River Redhorse is a species of sucker that has a large, thick body of nearly 80 cm in length, and can weigh more than 5.5 kg. They have a large head with a flat top, a large snout, and a red tinted tail fin. Red Riverhorse also have a brown or olive back, yellow-green or copper sides, and a white belly. Males are generally shorter in length and lighter in colour than females.

Diet:

The River Redhorse’s diet consists of molluscs, aquatic insects and larvae. Juveniles will mostly feed on microcrustaceans, algae, and small invertebrates. They are a benthic species, which means they mainly feed off the bottom of water bodies using their sucker-like mouths.

Photo by Alexislifer: https://www.inaturalist.org/observations/91326446

Map taken from Government of Canada: https://www.sararegistry.gc.ca/virtual_sara/files/cosewic/sr_river_redhorse_e.pdf

Habitat and Range:

The River Redhorse is found in North America throughout the Mississippi River system and the Gulf Slope from Florida to Louisiana. They are also found in the Great Lakes basin and the St. Lawrence river. They are found in 24 U.S states as well as Quebec and Ontario. However, most populations have been dwindling over the past few years, and they are now mostly concentrated in Alabama, Arkansas, Kentucky, and Tennessee. Scattered populations are found in south-central Ontario and southern Quebec. They can be found in the southern region of The Land Between in the Trent River system, and the north-eastern region around the Madawaska River. This species prefers lakes and rivers with moderate to swift current and riverine habitat nearby for spawning. They also prefer clear water with coarse substrates like sand or gravel.

Biology and Behaviour:

River Redhorse are late to mature, but they are a relatively long lived species, with the oldest River Redhorse recorded at 28 years old. In more southern regions, River Redhorse can reach sexual maturity much earlier, between 3 and 5 years of age. In more northern regions, they can take up to 20 years. They are generally the last of the Redhorse species to spawn each year, heading to their river spawning areas in late May or early June. The female will lay eggs in a small depression while the males fertilize them immediately after. Females can lay anywhere between 9,000 and 50,000 eggs, which will hatch in about 5 days. Some River Redhorse may head back to lakes or deeper water to overwinter, but shallow fast moving rivers are crucial for spawning habitat. Predators include larger fish species and birds.

Photo by Bradley Rasmussen: https://www.inaturalist.org/observations/50500469

Similar Species:

The River Redhorse is one of seven Redhorse species in Canada. They are similar in appearance to the Shorthead Redhorse and the Greater Redhorse, but they can be distinguished by the size of their head and crumpled-looking lips.

Threats/ Reasons for being at Risk:

1. Turbidity: River Redhorse have very particular spawning requirements. They need riverine habitats with clear and moderate to quick moving water. This means that they are vulnerable to turbidity and water flow changes. Turbidity can be described as decreases in water clarity, and can be caused by water flow disturbances, pollution, development, and agriculture. These activities create and stir up sediments that pollute the water clarity.

2. Pollution: Contaminants like pesticides and fertilizers from agriculture, human waste and garbage, and increased nutrient levels can all impact the River Redhorse. Pollutants in the water not only are consumed by fish species, but they also pollute the clearness of the water which increases turbidity. Contaminants are ingested by this species if they find their way to the bottom of lakes and rivers, since River Redhorses are bottom feeders. Studies have shown that pollution is also negatively impacting the River Redhorse’s prey species as well.

3. Habitat fragmentation and degradation: Habitat fragmentation occurs through the creation of dams along our river systems, which can cut the River Redhorse off from important spawning habitat. Dams have also been known to change water flow, which can make old spawning habitats now unsuitable.

4. Recreational fishing: River Redhorse are at higher risk of injury and mortality from recreational fishing, especially when they head to their shallower spawning habitats. River Redhorse are not protected by catch limits or size restrictions, putting them further at risk. Quebec is the only exception to this threat, since all sucker species have been protected against recreational and commercial fishing.

Conservation and recovery strategies:

The River Redhorse and their habitat are protected under Ontario’s Endangered Species Act, and the federal Fisheries Act. However, there are currently no recovery strategies in place for this species, since this species is only listed as Special Concern. Conservation and recovery strategies should be put into place starting with increased research and creating a plan for recovery, which should involve protecting their habitat, but especially their spawning grounds. Dams should look into increasing the flow of water during spawning season, and providing fish with a way to cross them safely.

How can you help?

Report any sightings of the River Redhorse to The Land Between, iNaturalist, or the Natural Heritage Information Centre.
Keep the shoreline on your property natural and free of chemicals.
Get in touch with local organizations and government agencies to help protect your local watersheds.
Participate in citizen science shoreline and water rehabilitation projects with local organizations.
Do not release any invasive species into the wild, and make sure you are not relocating any aquatic invasive species when travelling from one area to another.

Quick Facts:

The River Redhorse was historically an important food source for Indigenous and European settlers
Like all sucker species, they play an important ecological role since they are nutrient cyclers. River Redhorse feed on species from the benthic food web, and transfer them to the pelagic food web when they are eaten by predators
They are one of the few freshwater species that have a preference for molluscs. In fact, molluscs make up about 25% of their diet, and they could possibly be used as a method of control for the invasive Zebra Mussel!

Additional Resources:

Government of Ontario River Redhorse Species at Risk page
COSEWIC 2006 Assessment and Report on the River Redhorse

Sources:

COSEWIC 2006. COSEWIC assessment and update status report on the river redhorse Moxostoma carinatum in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 31 pp. https://www.sararegistry.gc.ca/virtual_sara/files/cosewic/sr_river_redhorse_e.pdf

Government of Ontario. 2014. River redhorse. Retrieved from: https://www.ontario.ca/page/river-redhorse