8100

• UCREFRP Catalog Number: 8100
• Author: American Fisheries Society.
• Title: Proceedings of the 22nd Annual Meeting, Colorado - Wyoming Chapter, American Fisheries Society.
• USFW Year: 1987.
• USFW - Doc Type: March 11-12, 1987.
• Copyright Material: NO

RESULTS

Diet

From 11-26 fish were collected within each size class on the three sampling
occasions, July 12-13, August 9-10 and September 20-21, 1985. No young-of-the-
year brook trout were included in the analysis. The mean number of recognizable
prey items/stomach ranged from 5.2-42.1 in trout 5. 150 mm and from 2.1-18.2 in
trout > 150 mm. A seasonal decl ine in the number of prey/stomach was observed
for fish> 150 mm, but not in fish 5. 150 mm.

Differences in composition of the diet of brook trout 5. 150 mm and> 150 mm
on the three sampling occasions was observed (Table 1). The smaller size class
of fish tended to utilize small prey such as Diptera, especially Chironomidae
larvae. The larger size class tended to consume larger prey, especially
Plecoptera, Trichoptera and terrestrial insects. The proportion of terrestrial
insects in the diet was 1.8-9.0% for fish < 150 mm and 2.9-36.2% for fish> 150
mm TL over the three sampling occasions. Terrestrial insects were most abundant
in the diet of both size classes of fish in September.

Dri ft

The abundance of organisms in the drift samples declined from 4,474 (249/hr)
in July, to 1,589 (88/hr) in August, to 1,036 (58/hr) in September. Composition
of the drift samples on the three sampling occasions differed (Table 1). The
drift was domi nated by Ch i ronomi dae, Ephemeroptera and Pl ecoptera. Terrestri a 1
invertebrates comprised 4.1-8.8% of the drift, with the largest proportion
occurring in September.

Selectivity

The composition of the stomach contents and drift samples were taxonomically
s imil ar, with some exceptions. Taxa present in the drift, but not in the
stomachs, included Copepoda, Cladocera, Dixidae, Hemiptera, Lepidoptera and
Diptera of terrestrial origins. Taxa found in the stomachs, but not in the
drift, included Leptoceridae, Tabanidae and Orthoptera.

Selectivity by brook trout was evaluated for the five dominant orders of
aquatic insects, as well as for terrestrial insects found in both the stomachs
and drift sampl es (Tabl e 1). Sel ect i vity was observed for Tri choptera and
Coleoptera prey on all three sampling occasions. Terrestrial insects were
selected by fish> 150 mm in August and September. Ephemeroptera and Diptera
tended to occur in lower proportions in the diet than in the drift samples.

,.

DISCUSSION

Temporal trends in the abundance and composition of the diet items and
macroinvertebrate drift were observed over the three sampling occasions from July

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