An Evaluation of Steelhead Habitat and Population in

the Gabilan Creek Watershed

Julie HagerCapstone Project

5/24/01

State Water Resource Control Board

Primary Objectives

Is there suitable habitat for steelhead in the Gabilan Creek watershed?

Have populations existed there in the

past?

Do populations currently exist, and if not, why?

Overview

Steelhead life cycle and characteristics

Reconnaissance survey

Spawning and rearing habitat

Population survey

Limiting Factors

• Temperature (Preferred 7.3 -14.6 ° C)

• Dissolved Oxygen (Criterion >7.8 mg/L)

• Suspended Sediment (Criterion <25 mg/L)

• Cover (overhead and escape)

• Food (aquatic insects)

• Lack of Pools and Sufficient Flow

• Migration Barriers

• Substrate for Spawning (diameter .6-10.2 cm)

• Pollution

• Overfishing

Gabilan Creek Watershed

Reach 1

Reach 2Reach 3

Phase 1: Reconnaissance Survey

perennial water

obstructions

creek pattern, profile, and roughness

important features:• pool/riffle sequences• dominant substrate• bank condition• riparian vegetation• pollution sources• adjacent land use• fish and frog sightings• estimates of bankfull width and depth

Reach 1Location Perennial

WaterPools LWD Overhead

CoverErosion Bank

VegetationSubstrate Fish & Amphibian

SightingsAdjacent Land Use

Section 1 Yes - - - + - sand, silt Common Carp row crop agriculture

Section 2 Yes - - - +

sand, silt California Roach row crop agriculture

Section 3 Yes - - - + - silt, clay Common Carp row crop agriculture

Section 4 Yes - - - +

silt, clay California Roach row crop agriculture,industrial

(-) very little to none ( ) moderate (+) abundant

Reach 2Location Perennial

WaterPools LWD Overhead

CoverErosion Bank

VegetationSubstrate Fish & Amphibian

SightingsAdjacent Land Use

Section 1 Yes - - + sand Pacific Treefrog residential

Section 2 No - +

sand Western Toad row crop agriculture,

grazing, residentialSection 3 No - - - + - sand none row crop agriculture

residential

(-) very little to none ( ) moderate (+) abundant

Reach 3

Location PerennialWater

Pools LWD OverheadCover

Erosion BankVegetation

Substrate Fish & AmphibianSightings

Adjacent Land Use

Section 1 Yes + + + - + cobbleboulder

Rainbow Trout grazing

Section 2 Yes + + + - + bedrockboulder

none grazing

Section 3 Yes + + + - + cobbleboulder

Bullfrog grazing

(-) very little to none ( ) moderate (+) abundant

Phase 2: Detailed Habitat Assessment

Section Length(m)

Avg. CobbleAbundance

Avg. CobbleEmbeddedness

Average PoolDepth (m)

RearingIndex

Density(fish per meter)

Habitat 1 44.00 18% 21% .24 4182 1.58

Habitat 2 14.00 14% 30% .16 1767 2.02

Habitat 3 12.85 23% 35% .34 1121 1.47

Habitat 4 21.90 33% 26% .22 1300 1.08

Habitat 5 24.60 24% 18% .31 2525 1.72

•Rearing Index for Young-of-

Year

•length, width,& depth

• velocity & embeddedness

•rate cover and roughness

• # fish per meter

•suspended sediment, DO, &

temperature

Monitoring

Location Mean SummerTemp (C)

Reach 1 20.75

Reach 2 21.0

Reach 3 12.93

Above Preferred Range

RainEvent

Range of Suspended SedimentConcentration (mg/L)

Reach 1 Reach 2

Jan 7-13 29 - 913 0-1904

Jan 23-26 47 -1928 7.8-6714

Feb 9-12 No Data 302-5884

Feb 18-19 33-1321 2.5-6812

Can Prevent Migration

Phase 3: Population Assessment

Electrofishing was not conducted due to lengthy ‘take’ permit process

During ~400 visits, zero steelhead were observed

Local residents reported 20 inch steelhead catch ~10 years ago

Is there suitable habitat for steelhead in the Gabilan Creek

Watershed?

Suitable rearing and spawning habitat exists in the headwaters

Watershed has potential to support 30,000 young-of-the-year

Reclamation Ditch and lower reaches are problematic for migration:• lack sufficient cover

• lack woody debris

• uniform flow structure lacking pools and riffles

• high summer temperatures

• high suspended sediment concentrations

YES

Have populations existed there in the past? Maybe

One interview reported a catch 10 years ago

zero positive steelhead observations (lack of rainfall and flow)

16 Rainbow Trout were observed in headwaters

potential exists due to polymorphic life-history allowing resident trout to assume anadromy

Do populations of steelhead currently exist? No

Outcomes Prior to this study, there was no information on

steelhead habitat or population in Gabilan Creek

Increase awareness within management, local agencies, & community about the potential for a steelhead run in Gabilan Creek

Address problematic areas in the lower reaches (restoration, education, sustainable land use practices)

RDIPAC

Continue studies on steelhead habitat and population in the Gabilan Creek watershed

Acknowledgements

• Dr. Fred Watson

• Joel Casagrande

• Wendi Newman

• Thor Anderson

• SSS Team

• Dr. Lars Pierce

• Dr. Bob Curry

• Marc Angelo

• Dr. Doug Smith

• Scott Hennessey

• David Dettman

• Jennifer Nelson

• Joy Nguyen

• Cheri Everlove

• Dave Rosenow

• SWRCB: 9-168-130-0