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North Branch Wiscoy Creek Habitat Enhancement Evaluation (2012)

Eighteen inch wild brown trout from North Branch Wiscoy Creek
Eighteen inch wild brown trout from
North Branch Wiscoy Creek.

In July 2012, Region 9 fisheries staff, USFWS personnel and angler volunteers conducted trout population sampling on the North Branch Wiscoy Creek (N. Branch). This sampling was the first year of a post-habitat enhancement monitoring on the stream. Trout population sampling had been conducted in 2010 and 2011 prior to a 2011 habitat enhancement project to compare with trout populations after completion of the project.

Habitat Enhancement Project

In July 2011, 57 "Lunker" structures (456 total feet) were installed along a 2,100 foot section of public fishing rights easements on the N. Branch (North Branch Wiscoy Creek Habitat Enhancement Project). This project was done to increase habitat for adult wild brown trout in this highly productive stream. Areas where the structures were installed were deepened to approximately 2 feet and the stream width was narrowed by 1/4 to 1/3. Prior to the work, this stream section was overly wide, shallow and overgrown with alder from past land use practices and held very few larger adult trout.

Post-Enhancement Assessment

Fisheries staff sampling fish on North Branch Wiscoy Creek.
Fish sampling on North Branch
Wiscoy Creek.

Trout population sampling was done on the entire 2100 foot habitat enhancement section (seven-300 foot sites) as well as one additional site on the N. Branch and one site on nearby Trout Brook to serve as "control sites." For all adult (yearling and older) wild brown trout, densities varied significantly at both the control sites and the habitat enhancement section from 2010-2012. Densities of brown trout >10", >12" and brown trout biomass declined from 2010 to 2012 at the two control sites. However, densities of brown trout >10", >12", >14", as well as brown trout biomass increased substantially in the habitat enhancement section from 2010 to 2012. It is likely that most of the larger fish moved into the habitat section rather than growing to a large size there in only one season. It is expected that in future years we will see further increases in both overall adult trout density and density of larger wild brown trout in the habitat enhancement section as the trout population fully occupies the enhanced habitat.

Lunker structures = larger trout

An indication of how effective the "Lunker" structures were as habitat for yearling and older trout in general and larger trout in particular can be seen in Table 1 below. Of the 609 total yearling and older trout captured in the 2100 foot long habitat enhancement section, 442 (73%) were found in the four 300 foot sections with Lunker structure and only 27% in the three 300 foot sections without Lunkers. Even more impressive, 97 of the 99 fish >10" and all of the fish >12" and >14" were in the sections with Lunkers. The two largest brown trout captured in the habitat enhancement section in 2012 were 17.0" and 18.0", while in 2010 they were 15.7" and 12.6". In 2011 they were and 13.9" and 12.6". The largest wild browns captured at the control sites on the N. Branch and Trout Brook were 12.8" and 18.1" respectively.

Angler fishing along Lunkers on North Branch Wiscoy Creek.
Angler fishing along Lunkers on
North Branch Wiscoy Creek.

Young-of-year abundance

The increased abundance of larger adult trout does not appear to have negatively affected reproduction in the habitat section, as we found substantially more young-of-year (YOY) trout in the habitat section of the N. Branch in 2012 than in 2010 (Sampling in 2011 was done too early in the summer to effectively estimate YOY densities). Substantially higher numbers of YOY were also found in the control sites than in 2010, thus it appears that the greater number of YOY in the habitat section is not due to more large, spawning size trout in that section.

Table 1. Comparison of the number of yearling and older (adult) wild brown trout (# adult, # >10", # >12" and # >14") in each 300 foot reach sampled within the habitat enhancement section on N. Branch Wiscoy Creek in 2012.
Section Lunkers present Feet of Lunkers in site # adult brown trout # >10" # >12" # >14"
2100' - 1800' Y 168' 115 32 6 2
1800' - 1500' N 0 62 0 0 0
1500' - 1200' Y 72' 121 23 5 1
1200' - 900' N 0 36 1 0 0
900' - 600' Y 104' 106 24 7 2
600' - 300' N 0 69 1 0 0
300' - 0' Y 112' 100 18 5 2
Total - 2100' - 456' 609 99 23 7