Lees Ferry Trout Fishery Status and Tr

January 2006

January 25, 2006 

Technical Work Group

Bill Persons, Scott Rogers

Arizona Game and Fish Department
Update:

• Electrofishing catch rates 1991-2• Size distributions• Condition Factor 1991-2005• Discussion of possible flow, foo

water quality effects
Electrofishing catch/minute 1991-N

SIZE: 1 < 152 mm TL

Year Month

OCT 

JUN 01

JUN 00

SEP 99

APR 98

APR 97

MAR 96

JUL 94

MAY 93

MAY 92

FEB 91

95% CI Catch Per Minute

6543210

-1-2
Electrofishing catch/minute 1991-N

SIZE: 2 152 - 304 mm TL

YRMO

OCT 

JUN 01

JUN 00

SEP 99

APR 98

APR 97

MAR 96

JUL 94

MAY 93

MAY 92

FEB 91

95% CI CPE

76543210

-1
Electrofishing catch/minute 1991-N

SIZE: 3 305-405 mm TL

YRMO

A

JUN 0

JUN 01 SEP 00 DEC 99 MAY 99 APR 98 AUG 97 AUG 96 DEC 95 JUL 94 SEP 93 NOV 92 FEB 92 FEB 91

95% CI CPE

6543210

-1
Size Distributions 1991-2005

100400

Count

1991 1992 1993 1995 1996 1997 1999 2000 2001 2003 2004 2005

100400

Count

100400

Count

0 2

0

4

0

6

0

Length Interval

100400

Count

0 2

0

4

0

6

0

Length Interval

0 2

0

4

0

6

Length Interval
Size distributions 1997-2005

100200300400500

Count

1997 1998 2000 2001 2003 2004 

100200300400500

Count

0

20 40 6

0

Length Interval

100200300400500

Count

0 2

0

4

0

6

0

Length Interval

0

Len
Condition Factor

SIZ

E: 3 305

YR

M

O

JUL 

SEP 93

NOV 92

FEB 92

FEB 91

95% CI WR

100

90807060

SIZ

E: 2 152 - 304 m

m T

L

YR

M

O

NOV 05

NOV 04

NOV 03

OCT 02

JUN 01

SEP 00

DEC 99

MAY 99

APR 98

AUG 97

AUG 96

DEC 95

JUL 94

SEP 93

NOV 92

FEB 92

FEB 91

95% CI WR

110100

908070

Possible flow effects:
Difference between SEPT maximum 

minimum discharge

-2000

0

2000400060008000

10000120001400016000

1990 1995 2000 
Jan Feb Mar Apr May Jun Jul Aug Sep O

6°C7°C8°C9°C

10°C11°C12°C13°C14°C15°C16°C17°C18°C

Temperature (°C)

Temperature Patterns below Glen Canyon Dam

1988 to January 19, 2006 °C

Daily Mean Temperatures for 2003-2005

2005

2

1988-2002 Trendline

2006
Jan Feb Mar Apr May Jun Jul Aug Sep O

2.03.04.05.06.07.08.09.0

10.011.012.0

Dissolved Oxygen(mg/L)

Dissolved Oxygen:

Dam: July 1992 to 2004

2005 Lees Ferry

2005 below Dam

2005 ins

Lees Ferry

i

05

de Dam

Annual Dissolved Oxygen & pH Patterns below Glen Canyon Da

July 1992 to December, 2005 Glen Canyon Dam Tailrace & Lees Ferry

2005 values are daily means 

Hypoxia
Possible Temperature -

Oxyge

•

Increased temperature = increase

metabolic demand, more food nemaintain fish

•

Low oxygen = fish get lethargic, 

feeding, may die or move downsAffects larger fish more than smbecause of higher metabolic demlarger fish.
Possible foodbase cha

•

New Zealand Mudsnail?

• Changes in species composition 

community structure of invertebr

(Gammarus chironomids)

• Changes in community structure 

plants 

(Cladophora

Æ Oscillatoria & B
New Zealand MudSna

Discovered in 2000 least as early as 19has been labeled a other systems.
New Zealand Mudsn
Summary:

• Catch rates and condition of larg

classes of fish decreased significNovember 2005.

• Anglers report very slow fishing• Anglers report little or no spawn

– No sexually mature fish were obse

November 2005, a time when fish beginning to spawn.
• Lee’s Ferry density and condition have dec

– Why?

• Increased temperature and metabolic demands by • Change in food base• Introduction of New Zealand mud snails 

• We have seen evidence of decreasing recru

past two years and during our November saevidence that we may have another poor spto think about stocking again??? Will this hseeing the effects of a changing food base afood limited response by rainbow trout??
Mean KnL and sample 

KNL YRMO Mean N Std. Devia

March-00 76.9159 1070 

June-00 82.3385 1012 

September-00 76.0251 919 

December-00 73.9698 700 

April-06 75.4272 796 

June-06 79.7062 1107 

October-06 76.5032 860 

June-06 80.1323 1015 

October-06 80.2139 952 

April-06 82.8185 322 

August-06 79.1251 193 

November-06 73.7174 47 

April-06 80.5129 456 

July-06 79.9892 663 

November-06 79.0824 520 

April-06 80.9924 242 

June-06 81.1652 666 

November-06 76.7528 528 

Total 80.3195 38003