Highlights of The SWSTU Guadalupe Habitat Study

GRTU has sponsored an ongoing research project at Southwest Texas State University for approximately three years. The purpose of the study is to examine the Guadalupe River as a trout habitat. Some of the activities in the project include sampling insect populations and the preferences of the trout for eating insect types. Project goals include developing stocking strategies and investigating methods for enhancing trout habitat.

At the January GRTU meeting, Thorpe Halloran delivered a research update on the project. A summary of the insect sampling study appears in this newsletter. Many were surprised by the preponderance of scuds and midges, which accounted for over 50 percent of the insects in the drift in the April 1998 sampling.

Here are some other facts that come from the report, some generated by our research and others from literature searches done by SWSTU on tailwater fisheries:

Alan Bray, Director, Ex-Officio


April 1998 Drift Samples from SWSTU Study

 

Noon-3 PM

3 - 6 PM

6 - 9 PM

Average

         

Scuds

43%

14%

22%

26%

         

Spiders, Beetles, Bees, Ants, Moths

4%

11%

5%

6%

         

Midges

       

Midge (Chironomidae)

0%

23%

15%

13%

Black Flies (Simuliums)

21%

15%

24%

20%

Total Midges

21%

38%

40%

33%

         

Crayfish

1%

0%

0%

0%

         

Mayflies

       

Blue Wing Olive (Baetis)

5%

9%

9%

8%

Tricos (Tricorythidae)

6%

6%

15%

9%

Caenis

0

0

1%

0%

Heptagenia

0

0

1%

0%

Isonychia

0

0

1%

0%

Total Mayflies

11%

15%

26%

17%

         

Snails

1%

0

0

0%

         

Dragon flies

1%

0

0

0%

         

Caddisflies

       

Speckled & Spotted Sedge (Helicopsyche)

7%

14%

7%

9%

Small Spotted Sedge (Hydropsyche)

3%

0

0

1%

Microcaddis (Hydroptilidae)

2%

0

0

1%

Long Horn Sedge (Leptoceridae)

1%

6%

0

2%

Brown Checkered Summer Sedge

1%

3%

1%

2%

(polycentropodidae)

       

Total Caddisflies

13%

23%

8%

15%

         

Flat worms

5%

2%

1%

3%

Notes:

  1. Scuds+Midges+Mayflies+Caddisflies = 91% of drift
  2. Mayflies and Midges are most common in the evening drift
  3. Caddisfly pupae and larvae are most common in mid-afternoon drift
  4. Scuds are most common in the early drift, but are available throughout the day
  5. Blue Wing Olives (#18) and Tricos (#24) are the most common Mayflies
  6. The Speckled and Spotted Sedge (#12 - #16) are the most common Caddis
  7. Midges (#18 - #24) are the most common insect in the drift