7332

• UCREFRP Catalog Number: 7332
• Author: Valdez, R. A., et al.
• Title: Final Report Habitat Suitability Index Curves for Endangered Fishes of the Upper Colorado River Basin.
• USFW Year: 1987.
• USFW - Doc Type: \
• Copyright Material: NO

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3. Strata. In only one case were the data partitioned by strata
(longitudinal regions of river). For nonspawning adult humpback chub, the
experts were unable to reach a consensus on pooling or separating data from
Black Rocks, Westwater Canyon, and Cataract Canyon of the Colorado River, and
so the data of each of these strata were tested in all combinations for the
experts to decide on pooling at workshop #2.

4. Year. In no case did the experts decide to partition data by a
particular year or set of years. The experts felt that no differences in
habitat use could be perceived by water year.

5. Gear. The discussion on partitioning by fish sampling gear was lengthy
and rather involved at times, but in all cases the data were partitioned by
gear to be tested for significance. In some cases, the data were to be pooled
if not significantly different ('test'), and in others, the experts reserved
the right to decide on pooling after examining levels of significance
{'decision/test'}. Sample gears were grouped into the following categories:
radiotelemetry, electrofishing, passive nets (gill/trammel), active nets
(seines), and other nets and gear types (angling, fyke nets, wire traps). In
most cases, particUlarly for the earlier life stages, separation of data by
gear was not an issue because only one type of gear was used, i.e., larvae and
YOY were almost always captured with seines. The experts agreed to not use
data from larval drift nets to describe habitat of larvae and YOY in nursery
areas because this gear captures fish being transported by the rive~. However,
for the larger fish, partitioning by gear type was always an issue. For
nonspawning adult razorback sucker and humpback chub, data from each gear were
tested within river systems and pooled if not significantly different. The
same was done for nonspawning adult Colorado squawfish (size 5) from the
Colorado River. However, data from this size 5 from the Green, Yampa, and
White rivers were to be tested but not pooled without further review by the
experts ('decision/test'). The reason for this difference in approach between
river systems was because the experts felt that the large volume of
radiotelemetry data on Colorado squawfish in the Green River subbasin and
previous comparions of gear types in that subbasin showed differences in
measurements of habitat use.

One expert felt that, for adult Colorado squawfish from the Green and
Yampa rivers, the use of habitat data from gear types should be prioritized as
(1) radiotelemetry, (2) electrofishing, and (3) gill/trammel nets. The expert
made this recommendation because he believed that radiotelemetry data provided
the most accurate information on habitat use, followed by electrofishing data,
and gill/trammel net data. He also expressed that only radiotelemetry data
should be used to describe egg deposition habitat used by squawfish in the
Yampa River for the same reason, and because the majority of data on spawning
fish was collected by radiotelemetry.

6. Time of Year. The experts decided that data for the razorback sucker
and Colorado squawfish should be partitioned by time of year because there were
perceived seasonal differences in habitat use by certain life stages of these
two species. The data on nonspawning adult razorback sucker were partitioned
into April-June (spring) vs. other times of the year, because concentrations of
adul ts are found in these spring months in unique habitats (mouths of

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