Redd Counts Track Bull Trout Abundance

SEELEY LAKE - Every fall Montana Fish, Wildlife and Parks (FWP) fish biologists complete bull trout redd counts, tracking the abundance of the trout spawning nests. A redd is an area on the stream bottom that trout prepare as their spawning nest.

The redd counts is an index for spawning activity and adult abundance. FWP Fisheries Biologist Ladd Knotek said that monitoring bull trout as the keystone species is a good indicator because they are the most sensitive species to disturbance and they cover a large geographic area because they are migratory.

FWP extensively surveyed for bull trout and bull trout spawning activity on all major tributary streams from 2000-2007. Bull trout have a high site fidelity meaning they typically relocate and spawn in the area where they were hatched. Bull trout select sites based on substrate size, gradient and flow level. Most importantly, these areas have high levels of groundwater inflow that keep eggs oxygenated and ice-free over the winter, as well as suitable juvenile rearing habitat (complex and cool habitat) in adjacent reaches. Because the number and location of stream reaches that have all these qualities is limited (combined with high site fidelity), spawning areas tend to be in discrete and consistent locations.

Redd count 'Index' sections were selected based on the distribution of observed spawning and the specific habitat requirements for bull trout

"We see over 90 percent of the redds because we have done it repeatedly, we know what they are looking for and we know where they came from," said Knotek.

Today FWP surveys the West Fork of the Clearwater, Morrell Creek and smaller populations in Marshall Creek and the East Fork of the Clearwater. Knotek said populations on Deer Creek are also recovering due to restoration work.

This year they counted 22 redds on the West Fork, 14 on Morrell Creek, seven on Marshall Creek and only a couple on the East Fork of the Clearwater.

"Numbers were below average everywhere, likely due to extended period of very low flow conditions," said Knotek. "Lower water conditions prevent assess and increase mortality."

According to Knotek, the counts work really well because the adults are large and they have discrete spawning area. While only two adult fish create a redd, Knotek said that statistically one redd represents about 3.2 adults due to mortality and other factors in the population.

Bull trout spawn between Aug. 20- Sept. 15 in the Clearwater Valley streams. Bull trout first spawn when they are four to six years old.

Bull trout are capable of spawning multiple times once they reach adulthood. However, many bull trout in the Clearwater Basin only spawn once due to challenging conditions they encounter spawning in the fall. In particular, surface flow levels often drop in lower portions of spawning tributaries, making it impossible for adults to exit the tributary after spawning until winter or the following spring. In addition, early migration timing and long periods in small tributaries (i.e. all summer) is very stressful for adults, exposes them to predators longer (including humans) and contributes to high mortality rates.

"If you have a healthy population it can easily buffer that if you have connectivity and consistent year classes," said Knotek. "If you start taking away some of those components things fall apart."

While redd counts are designed to monitor the number of adult spawning, FWP conducts electrofishing surveys to monitor the number of juveniles produced and the relative number of juveniles produced relative to juveniles of other species in the same drainage. The adult and sub-adults are monitored using the gill net series in the lakes.

"They go up here and spawn [as close to the headwaters of the West Fork of the Clearwater as possible]. The juveniles rear in the stream that was worked on. Then they go back past the barriers that were removed and into the lake," said Knotek. "Their life cycle ties all the work together that has been done over the past 10 years. The idea is if we are taking care of bull trout we are probably taking care of cutthroat trout and other aquatic species."

Bull trout redd counts in the Clearwater and Blackfoot watersheds indicate stable or increasing population trends for the major spawning populations, and relatively stable numbers in main stem lake and river system over the past 10-20 years. However, many other smaller populations are struggling or have disappeared altogether.

Thirty-50 percent of the viable tributary populations that were present 75 years ago are now no longer viable or completely gone. Similarly, the geographic distribution of spawning populations in tributary streams is also much smaller. The amount of suitable habitat is shrinking due to both habitat degradation and long-term temperature changes.

"It is really important for these streams to have these intact head waters," said Knotek. "We want to extend that down to at least where all the native trout are spawning. At the same time those are also the key elk, lynx and grizzly bear areas. It's all complimenting and makes sense at a landscape scale."