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North Dakota Fisheries Investigations

Methods

In 1994, an effort was made to review all recent and historical fish surveys. As a result, a species checklist was developed which included individual status determinations for all fish species in North and South Dakota. One of the results of this effort was a brochure produced jointly by the Dakota Chapter of the American Fisheries Society and the North Dakota Game and Fish Department (Fishes of the Dakotas 1994).

For this 1994 effort, information used for determining species status in North Dakota was assembled from 62 river/stream surveys conducted from 1950 through 1994 with site (referenced sampling stations) specific data. These surveys were conducted by the North Dakota Game and Fish Department, other governmental agencies and various universities. River/stream surveys were reviewed because, compared to lake/reservoir surveys, they provided a more diverse assemblage of fish species. For example, only 29% of all lake/reservoir's surveyed (other than the Missouri River system¹) from 1968 to 1978 produced more than five fish species (Fig. 1).

Fish abundance indices such as catch rates derived from previous river/stream fish surveys were reviewed in order to determine if population trends for each species of native fish was possible. However, due to inherent differences in historical sampling techniques (e.g. electrofishing vs. sodium cyanide vs. seining) as well as the various presentations of data (e.g. differing catch per unit of effort), abundance indices could not be used. Instead, the 62 river/stream surveys were analyzed based on frequency of occurrence per station and subsequently species status was determined based on the following categorizations: rare (collected at 0.1-2% of the stations), infrequent (3-9%), occasional (10-35%), and common (36-100%). Species of concern for North Dakota, as listed in Fishes of the Dakotas (1994), were ascertained either by a noticeable downward trend in their frequency of occurrence (e.g. common to infrequent) or long-term scarceness.

Figure 1. Number of native fish species found during lake/reservoir (1968-1978) and river/stream (1950-1993) fish surveys conducted throughout North Dakota.

In addition to the above evaluation, another twelve fish surveys conducted in various rivers/streams throughout the state between 1995 and 1997 were reviewed for either presence or absence of new species and/or substantiation of a decline in population status.

¹Sixty-two fish species have been documented from the North Dakota's Missouri River system including 57 species in 1994 alone (Hendrickson et al. 1995).

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