spawning behavior of trout and utility of redd counts

Spawning Behavior of Trout and Utility of Redd Counts

Spring Creek Chapter of TUOctober 2016Bob Carline

U.S. Geological Survey (retired)

Spawning Behavior of Trout

Male brown trout are readily recognized by a hooked jaw, often called a kype.

Young males may be sexually mature but may not yet have a kype.

The lower jaws of females are shorter than those of males, and females do not develop a kype.

When a female begins to dig a redd, a male will take up a position downstream of her and defend this territory from other males.

• Usually just the male defends the spawning territory• In this instance both male and female brook trout appear to

attacking an intruder

The female digs by lying on her side and forcefully flexing her tail.

A digging female usually attracts several males.

When the female is ready to deposit her eggs, the male comes alongside of her and they both expel sex products.

Widely gaped mouths are a sure sign spawning is in progress.

In this lake-spawning scene, a dozen or more other males have charged into the spawning pair and are depositing their sperm.

As soon as egg deposition is complete, the female moves upstream and covers the eggs with gravel.

Why Make Redd Counts?

Why Make Redd Counts?

Advantages:– Annual or periodic redd counts are a relatively

inexpensive way to assess trends in numbers of adult trout.

– The survey typically encompasses the entire stream, unlike other survey methods, e.g., electrofishing.

Why Make Redd Counts?

• Advantages– Given enough people, the entire stream can be

surveyed in a single day. – Over 20 miles of Spring Creek can be surveyed by

16 people.

Why Make Redd Counts

• Advantages:In contrast, one would need 52 person-days to electrofish just 10% of the stream length.

Why Make Redd Counts?

Disadvantages:– One of the difficulties of redd counts is identifying

individual redds. – This survey method does not reflect the number

of immature trout in a reach.

It was probably constructed by a single female, although we cannot be certain.

This redd is about 3 feet long and 1 foot wide..

It is possible that these fish were not the first ones to spawn at this site

The cleaned areas within the yellow line have been recently dug by multiple spawning females.

To approximate the number of redds here, take the estimated number of square feet and divide by 3.

How has redd count data helped to better manage the watershed?

Bellefonte

Upper: Moderate Density

Middle: Low DensityMiddle

Lower: Moderate to High DensityLower

Upper: Moderate to High Density

Middle: Low Density

Lower: Moderate To High Density

Perceived Density of Trout by Anglers - 1987

See next slide for text

In 1987 I began a study to explain why densities of wild brown trout in Spring Creek varied considerably. This map shows the perceived densities of trout by anglers who fished the stream regularly. Electrofishing confirmed these observation.

The upper section extended from Oak Hall to Spring Creek Park. The middle section extended from the park to the upper end of Fisherman’s Paradise. The lower section extended from the Paradise to Milesburg.

Bellefonte

345-439/mile

64-68/mile

257-301/mile

Redd counts 1987 and 1988

See next slide for text

Redd counts in fall 1987 and 1988 were consistent with angler observations and electrofishing results. The upper and lower sections of Spring Creek had high numbers of redds, while the middle section had substantially fewer redds, hence, fewer mature trout.

In late winter 1988 and 1989, researchers sampled a small subset of redds to estimate embryo survival.

Live eggs are translucent, while dead ones are opaque.

In late February embryos are either in the eyed egg stage, or they have hatched and are sac fry or alevins.

Eyed Egg Sac fry, Alevin

Bellefonte

67%

28%

58%

Embryo survival1988-1989

See next slide for text

Embryo survival in the middle section was less than half of that in upper and lower sections of Spring Creek.

Electrofishing in late summer provides estimates of juvenile trout.

Bellefonte

326/ha

51/ha

208/ha

Age-O brown trout 1988-1989

See next slide for text

Density of age-0 (5 months old) brown trout was lowest in the middle section of Spring Creek and 4 to 6 times higher in the upper and lower sections.

What did we learn from the redd study?

• Redd counts were a good predictor of both juvenile and adult trout density

• Lowest redd numbers in middle section• Lowest embryo survival in middle section• Highest percentages of fine sediment in

middle section

Immediately after the fertilized eggs are buried, the substrate is rather porous and water can easily move through the redd. This water movement is essential for the embryos to develop. The incoming water brings in dissolved oxygen and carries away carbon dioxide and waste products such as ammonia.

If stream water is transporting much sediment, these fine particles settle to the bottom and begin to fill in the small openings within redds. If enough sediment is deposited, the inflow of fresh water will cease, and the eggs will essentially suffocate and die.

SOURCE - Base map and land use information; Centre County Planning Office, Geographic Information System (GIS) data.

Land Use

Slab Cabin Run

Cedar Run

Land use surveys revealed many unfenced pastures in Slab Cabin Run and Cedar Run basins.

Intensive grazing of livestock along streams can lead to unstable banks that are vulnerable to erosion.

Slab Cabin Run – 2.55 miles of unfenced pastures

Cedar Run – 1.55 miles unfenced pastures

Riparian Restoration Project

• TU Chapter provided >$40,000• Used as match for public funds• Voluntary participation by landowners• 10-year agreements – only

maintenance required

Riparian Restoration Project

Participating landowners had to allow construction of fences along the stream and installation of rock-lined stream crossings where needed. Landowners received grant funds from the U.S. Department of Agriculture (75%) and the Spring Creek Chapter provided the remainder (25%) of the funds. Landowners did not have to invest any funds into the project. They just had to agree to maintain all improvements for 10 years.

BEST MANAGEMENT PRACTICES IMPLEMENTED

Slab Cabin Run

Pre-treatment: 2.55 miles unfenced stream

Treatment: 17,300 ft . Stream bank fencing

26 stream crossings

1,900 ft . bank stabilization

Post-treatment: 1.6 miles fenced stream (61% of unfenced)

Cedar RunPre-treatment: 1.55 miles unfenced stream

Treatment: 4,000 ft . Stream bank fencing

7 stream crossings

400 ft . bank stabilization

Post-treatment: 1.5 miles fenced stream (98% of unfenced)

BEST MANAGEMENT PRACTICES IN SPRING CREEK WATERSHED

Pre-treatment monitoring (1991-1992)

Treatments (1992 – 1995): streambank fencing

stream crossings

bank stabilization

Post-treatment monitoring (selected years 2001-2007)

See next slide for text

The Spring Creek Chapter also funded projects downstream of Slab Cabin Run and Cedar Run on the main stem of Spring Creek. These projects were aimed at stabilizing stream banks and improving trout habitat.

Median Total Suspended Solids (mg/L) during Base Flow

1991-1992 2007-2008

Spring Cr. 4.0 1.0

Cedar Run 17.8 1.0

Slab Cabin Run

29.3 1.0

Part of the restoration project entailed monitoring of water quality before and after stream bank stabilization and fencing. In this study, a site on Spring Creek in Oak Hall just upstream of the confluence with Cedar Run was used as a control section. There were no restoration projects upstream of the Spring Creek site.

The previous slide shows the average sediment load in Spring Creek and the two treatment watersheds. Sediment load declined greatly during base flow after project completion and declines were even greater during storm flow, shown in the next slide.

Median Total Suspended Solids (mg/L) during Storm Flow

1991-1992 2007-2008

Spring Cr. 7.0 18.6

Cedar Run 29.4 9.7

Slab Cabin Run

62.1 9.0

The previous tables illustrated the reduction in sediment load from Slab Cabin Run and Cedar Run after restoration was completed. The primary reason for initiating this project was to try to reduce sediment loading downstream in the middle section of Spring Creek where redd counts were low.

1987 1988 1997 1998 1999 2000 2002 2004 2005 2007 2008 2009 2010 20150

100

200

300

400

500

600

Redds/mile - Upper Spring Creek

Redd counts in the upper section were variable, but there were no trends through time.

1987 1988 1997 1998 1999 2000 2002 2004 2005 2007 2008 2009 2010 20150

100

200

300

400

500

600

700

Redds/mile – Middle Section Spring Creek

In the middle section of Spring Creek, number of redds continually increased from pre-construction until the present time. By 2015, the number of trout redds increased by more than a five-fold.

1987 1988 1997 1998 1999 2000 2002 2004 2005 2007 2008 2009 2010 20150

100

200

300

400

500

600

700

800

Redds/mile – Lower Section Spring Creek

Redd counts in the lower section of Spring Creek also increased, but not nearly as much as in the middle section. It is likely that increases in redd counts in the lower section were related to habitat improvement projects and removal of the McCoy dam downstream of Bellefonte.

Bellefonte

1988 vs. 2000

Age 1+ Brown trout

Number per mile

402 vs. 440

320 vs. 721

1,106 vs. 1,742

See next slide for text

Electrofishing surveys have confirmed that the trout population in the middle section of Spring Creek has more than doubled since the riparian restoration projects were initiated.

Inferences from Redd Count Data

• Redd counts reflect trout population trends

Inferences from Redd Count Data

• Redd counts reflect trout population trends• Redd counts in middle section suggest positive

response to riparian restoration projects

Inferences from Recent Macroinvertebrate Surveys

• Stormwater runoff from the Centre Region is negatively influencing macroinvertebrate communities and trout density

Perhaps our biggest challenge is to find ways to reduce the impact of urban runoff on trout and macroinvertebrate populations in Spring Creek.