SPEARFISH (AP) – Researchers are studying if reducing the fish population in some areas of a western South Dakota creek will improve fish growth rates.

Researchers with the South Dakota State University and the state Game, Fish and Parks department are studying the densely populated Spearfish Creek, the Black Hills Pioneer reported.

The creek is full of brown, rainbow and brook trout.

"Spearfish Creek, especially in (Spearfish) Canyon, but in town too, we see slow growth rates of our older fish – 3 years old plus – a really diminished size structure. Densities are really high," said Travis Rehm, a graduate research assistant with the university.

The department removed half of the brown trout in seven of the 14 study areas in the creek in 2016. Brown trout are more aggressive so they were removed in an attempt to give rainbow trout a better chance of surviving.

Researchers have returned to the sites to study how the fishes' growth rates were impacted.

Initial findings have found that fish are larger, though it's too soon to officially draw any conclusions, Rehm said. This is only the second year of a three-year study.

The creek has a high population of fish in part because many anglers catch and release fish in the creek, Rehm said.

One section of the creek requires anglers to release any rainbow trout they catch. Beyond that section, anglers can catch up to five trout daily, and only one can be longer than 14 inches.