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Detroit River-Western Lake Erie Basin Indicator Project
INDICATOR: Hexagenia Density and Distribution in the Detroit River
Figure 8. Mean ±SE density of Hexagenia in the Detroit River between 1968 and 2004. The number of sites sampled each year is indicated. *Data compiled from Thornley and Hamdy (1984), Farara and Burt (1993), Wood (2004), and Ciborowski et al. (2006).
| Year | Number of Sites Sampled | Hexagenia Density [#/m2] |
|---|---|---|
1968 |
53 |
6.4 |
1980 |
59 |
119.4 |
1991 |
77 |
10.3 |
1999 |
150 |
28 |
2004 |
20 |
20 |
Riverwide Frequency and Abundance
Figure 8 summarizes the trends in Hexagenia abundance average across all samples for surveys conducted since 1968. Hexagenia mayfly nymphs were found in 70% of the 59 stations sampled in 1980 compared to only 26% of 53 stations in 1968 (Thornley and Hamdy 1984). The greatest changes in occurrence were along the Canadian shoreline. The mean density of Hexagenia in 2004 was 20 per square meter, but distribution was restricted to fewer locations than previously (Ciborowski et al. 2006), partly due to timing of sampling.
Figure 8. Mean ąSE density of Hexagenia in the Detroit River between 1968 and 2004. The number of sites sampled each year is indicated. *Data compiled from Thornley and Hamdy (1984), Farara and Burt (1993), Wood (2004), and Ciborowski et al. (2006).
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