Bigmouth shiner (Notropis dorsalis) COSEWIC assessment and status report: chapter 9

• Previous page
• Table of contents
• Next page

Population Sizes and Trends

In the original status report on the bigmouth shiner, Tompkins (1985) extensively covered population size and trends in the United States’ portion of its range, and that information will not be repeated in this document. In summary, Gilbert (1980) suggests that 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, which will be addressed in more detail in the habitat section of this report. In Wisconsin, Lyons (1996) found that the percent occurrence of the bigmouth shiner in collections from the 1970s (23%) was slightly higher than in the 1990s (21%). When first reported in Tennessee in 1990, the bigmouth shiner was the most abundant species in Bear Creek. In three previous collections of Bear Creek between 1967 and 1986 the bigmouth shiner was absent (Etnier and Starnes 1993). Pflieger (1997) also reports that bigmouth shiner distribution and abundance in Missouri have both increased in the last 50 years.

Since the original status report, our knowledge of the distribution of the bigmouth shiner in Manitoba has been expanded greatly to include the Assiniboine River and several of its tributaries as well as the Roseau River. It is difficult to assess population size and trends in the absence of repeatable and quantifiable data. The low numbers of the bigmouth shiner that typically characterize collections in the Assiniboine and Shell rivers makes any analysis difficult. Other streams such as Oak Creek and Epinette Creek have been sampled too few times to determine population size and trends. In the Cypress River, repeated sampling in September using seines at the Highway 2 crossing produced 130 fish in 1986, 58 fish in 1987, 52 fish in 1991, 58 fish in 1992, and 60 fish in both 1993 and 1994 (Appendix 4 in McCulloch and Franzin 1996).