Bigmouth shiner (Notropis dorsalis) COSEWIC assessment and status report: chapter 2

Logo of COSEWIC

COSEWIC
Executive Summary

Bigmouth Shiner
Notropis dorsalis

Species Information

The bigmouth shiner has a distinctive body form, being slender, relatively flat-bellied and more hump-backed than other Notropis. The eyes appear to focus upward in fish greater than 1.5 cm total length when viewed from above, due to the pupil being skewed dorsally. The body colour is olive-yellow on the back and silvery on the sides and belly. A mid-dorsal stripe that runs along the top of the body is continuous around the dorsal fin base. In Manitoba, the bigmouth shiner, sand shiner (Notropis stramineus), mimic shiner (Notropis volucellus), and river shiner (Notropis blennius) are similar to one another in appearance. 

 

Distribution

The distribution of the bigmouth shiner includes the Hudson Bay (Red River), Great Lakes and Mississippi River basins from northern Michigan to southern Manitoba, and from eastern Illinois to the Platte River system, eastern Wyoming and northern Colorado. There are disjunct populations in western New York and Pennsylvania, western Michigan, northern Ohio, and northern West Virginia, and western Tennessee.

In Manitoba, the distribution of the bigmouth shiner includes the Cypress, Shell, Little Saskatchewan, and Assiniboine rivers, as well as Oak and Epinette Creeks, all of which are in the Assiniboine River drainage. The species also has been found in the lower Roseau River near its junction with the Red River (Red River Drainage) and the Woody and Roaring rivers (Lake Winnipegosis drainage).

 

Habitat

In Manitoba, the bigmouth shiner appears to favour small streams, up to 12 metres in width and one metre in depth, although presence in larger rivers such as the Assiniboine has been documented.

 

Biology

The bigmouth shiner is fast-growing, exhibits a variable growth rate, and has a maximum life span of three years. Adult fish ranged between 50 and 75 mm. Nothing is known about reproductive behaviour and spawning sites of the bigmouth shiner in Manitoba or elsewhere. Spawning occurs from late May to August depending on the location of the population

The bigmouth shiner is often associated with the sand shiner in Manitoba and the United States. In the smaller streams in Manitoba, they are collected with large numbers of common shiner (Luxilus cornutus) and creek chub (Semotilus atromaculatus).  Both the longnose dace (Rhinichthys cataractae) and western blacknose dace (Rhinichthys obtusus) often also form part of this assemblage. No information is available regarding bigmouth shiner movements in Manitoba. However, appearance of the bigmouth shiner in repeated fall collections at sites on the Cypress and Assiniboine rivers throughout the 1980s and 1990s suggests that some movement occurs. Elsewhere, the bigmouth shiner has been observed to migrate upstream during fall and winter, and return downstream in summer. Diel movements can involve movement into shallow water at night, likely to either avoid terrestrial predators and to take advantage of emerging insect larvae.

Little is known of the diet of bigmouth shiner. Specimens collected from the Cypress River in the fall of 1995 were feeding exclusively on water boatmen (Family Corixidae). Benthic fauna, including aquatic nymphs, plant material, and bottom ooze are commonly found in stomachs. Taste is likely more important in foraging than is vision. 

 

Population Sizes and Trends

Bigmouth shiner populations in the western part of its range are increasing, while those in the eastern part are decreasing. Increases in the west have been attributed to changes in habitat, specifically channelization of rivers. In Wisconsin, populations appear stable. Collections made in the Cypress River in Manitoba suggest that populations have been relatively stable.

 

Limiting Factors

Human disturbance, such as eutrophication from shoreline development, has resulted in decreases in bigmouth shiner populations. However, human disturbance to stream hydraulics through channelization has appeared to benefit the species. Reproduction might be affected by high water levels in spring, as preferred habitats, food sources, and spawning sites could be affected. In Ohio, decline in some bigmouth shiner populations has been attributed to competition with the invasive silverjaw minnow (Notropis buccatus). The recent invasion of the spotfin shiner (Cyprinella spiloptera) into the Hudson Bay watershed will not likely negatively affect the bigmouth shiner due to physical constraints on dispersal and differences in habitat preferences.

Two large-scale land uses that occur within the bigmouth shiner’s present distribution in Manitoba are agriculture and forestry. The presence of livestock in watercourses can result in accelerated bank erosion and increased siltation, both of which could be harmful to fish habitat. In forestry operations, several stream crossings can be installed every year depending on a company’s annual operating plan. Poorly installed culverts can prevent fish passage and increase siltation into the watercourse either directly, or from sediment runoff from road infrastructure.

 

Special Significance

The bigmouth shiner is native to the United States and Canada. In Ohio, it is presently listed as “threatened.” In Pennsylvania, the species has been recommended for “threatened” status.” Its status in New York remains unknown. In Manitoba, the bigmouth shiner has no direct economic importance. However, it is used as bait fish in several states. The three subspecies of Notropis dorsalis may be of interest scientifically, as they represent geographically isolated populations. 

 

Existing Protection and Other Status Designations

The bigmouth shiner is not protected in Canada, although the federal Fisheries Act prohibits destruction of fish habitat unless authorized by the Minister.

The bigmouth shiner was assessed by COSEWIC as a Species of Special Concern in Canada in 1985. In Manitoba, the Manitoba Conservation Data Centre (MBCDC) has ranked the bigmouth shiner as G5 (globally), and S3 (provincially). A global rank of G5 indicates that the species is “demonstrably widespread, abundant, and secure throughout its range” and “essentially irradicable under present conditions.” A provincial rank of S3 indicates that it is uncommon in the province with 21-100 occurrences.

As with several fish species, the bigmouth shiner is sensitive to sedimentation caused by road and other linear crossings, bank erosion and intrusion of livestock into waterbodies. In most of its range in Manitoba, agriculture and forestry are major land use activities.

Page details

Date modified: