8172

• UCREFRP Catalog Number: 8172
• Author: Jacobi, G. Z., J. E. Sublette, S. J. Herrmann, D. E. Cowley and M. D. Hatch.
• Title: Final Report
• USFW Year: 1998.
• USFW - Doc Type: Investigations of an Index of Biotic Integrity in New Mexico.
• Copyright Material: NO

elevation sites had an_ average of 5 species
of fish, which were designated a trout
stream assemblage in the cluster analysis of
fish presence/absence data. The sites at the
upper end of the distribution were generally
below reservoirs or were large river sites
(e.g., lower elevation, mainstream Rio
Grande sites). The histogram suggests that
in development of an IBI, separate indices
may --need to - be developed -for "trout
streams" and large river/reservoir tailwater
sites.
To explore further the relationship between
number of fish species and elevation, data
from the upper Rio Grande drainage were
compared with data from a study of the
fishes in the Black River, Eddy County,
New Mexico (Cowley, 1979; Cowley and
Sublette, 1987). The linear regression of
number of species onto elevation for sites
on the Black River are plotted together with
the upper Rio Grande data in Figure 27.
The individual regressions for upper Rio
Grande data and Black River data differed
significantly in slope and in intercept. This
indicated that substantially different
relationships between fish species number
and elevation can be expected in different
regions of the state. As a result, it will
probably be necessary to develop different
IBIs for different ecological regions of New
Mexico. The data also suggested that
elevation alone will be insufficient to
account for fish species diversity across a
large and physiographically heterogeneous
region such as New Mexico.
Finally, the potential utility of the distance
(km) from headwaters was investigated.
Here, number of species per site for Black
River was regressed onto distance of the site
from the headwaters (Figure 28). The
improved fit of the data (W=0.82), relative
to the comparable regression against
elevation, suggested that distance from
headwaters may have wider applicability
across different regions than elevation.
Discussion
Upper No Grande Aquatic
Ecoregions
The two aquatic ecoregions described in this
report have a boundary somewhere in the
vicinity of 7400 feet (Figure 6). This
elevational division is very close to the
ecoregion boundary in the upper Rio
Grande drainage that was described by
Omernik (1986, 1987; Figure 7). Omernik
described a Southern Rockies Ecoregion
that is consistent with Aquatic Ecoregion 1
defined through multivariate ordination and
clustering. Omernik's - Arizona/New
Mexico Plateau Ecoregion appears to be
reasonably consistent with Aquatic
Ecoregion 2 in the upper Rio Grande. The
aquatic ecoregions are less similar to
ecoregions defined by the Forest Service
(Bailey, 1994a,b; Bailey et al., 1994).
It is interesting to compare the results
obtained for the upper Rio Grande drainage
of New Mexico with studies conducted
elsewhere. The first multivariate
environmental factor obtained for upper Rio
Grande sites, elevation and variables that
vary inversely with elevation, is very
similar to the first factor obtained for
Arkansas streams (Matthews et al., 1992).
In a study of Swedish streams, the most
important environmental variables were
drainage area, elevation, alkalinity, color,
and phosphate. The most important
multivariate environmental factors for the
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