Fieldwork spotlight: Minnow Trap Surveys

On a recent Wednesday, the sun-sparkled surface of the East Branch Ausable River was broken by some of our field staff as they waded into shady pools with a hiking stick and several minnow traps in tow. For several years, we have been learning more about fish communities in the Ausable River by collecting, studying, and releasing freshwater minnows. Read along as we guide you through a day in the field, minnow-trapping style.

_{Basket-style minnow traps are baited with dog food and submerged in ideal locations along the river.}

Minnow traps are one of several methods used by Ausable Freshwater Center staff to study fish communities, These are well suited for sampling swift riffles and deep pools. Each minnow trap consists of a hinged pair of rigid aluminum mesh baskets that are tied closed at the rims. We wade out into the river and place minnow traps in favorable locations along the stretch of river we're surveying. Attracted by a few pieces of dry dog food as bait, minnows swim into the trap through a narrow cone-shaped opening. Once inside, the shape of the trap makes it very difficult for them to swim out.

 _{An assortment of freshwater minnows from the East Branch Ausable River.} 

After several hours, we retrieve the traps. All the animals inside are transferred to a bucket of fresh river water. We determine the species of each minnow, tally them on our waterproof data sheet, and measure lengths and weights of a subset of all fish before returning them to the river. The minnows we catch typically range from 3.9 – 7 centimeters (~1.5 to 3 inches) and weigh 0.4 – 3 grams .

^{A blacknose dace gets a closer inspection and is measured for length.}

A variety of minnows live in the East Branch Ausable River. The most common species we encounter are Common Shiner, Blacknose Dace, Cutlips Minnow, and Creek Chub. Some of the less common species we have identified at our trap sites are Brook Stickleback, Tessellated Darter, Northern Redbelly Dace, and Longnose Dace.

^{Shown here are several types of fish we've caught in our minnow traps including a) Common Shiner, b) Cutlips Minnow, c) Blacknose Dace, d) Creek Chub, e) Tessellated Darter, f) Northern Redbelly Dace, g) Longnose Dace, and h) Brook Stickleback. Illustrations a-g by Ellen Edmonson and Hugh Crisp, for NYS Fresh Water Surveys (1926-1939). Illustration h: Iowa Department of Natural Resources.}

At times, we have also caught non-fish species in our traps, including freshwater crayfish, large dragonfly nymphs, and, very rarely, caddisfly larvae. All non-fish species are released directly back into the river.

^{Sometimes we catch surprise species, such as this crayfish, along with our minnows. No measurements for these feisty critters. They get released right back into the river.}

Minnow trapping is just one tool in our kit for understanding the local fish populations. We also employ other standardized fish survey methods including netting, backpack electrofishing, and snorkeling. It can be useful to combine methods in large, wide rivers to look for fish in different microhabitats. In one of our ongoing studies, we're combining multiple methods to track fish populations at eight study sites along the East Branch Ausable River, from the headwaters in Keene to the Stickney Bridge area near Au Sable Forks. This fall, we will compare all the data we've collected over the past three years and analyze it, looking for trends that will help us better understand the annual variability of fish communities in different sections of the Ausable and their response to restoration.

Stay tuned for reports of our results and more field work spotlights this fall and winter.