Effects of piscicides on American Dippers Lecture by Dr. Roarke Donnelly

I recently attended a lecture by Dr. Roarke Donnelly on the effects of piscicides on American Dippers (Cinclus mexicanus). A piscicide is a chemical that can be added to a water body to kill fish and is typically used to remove non-native fish. They are used all over the world in a variety of systems. The American Dipper looks like a songbird but hunts for its prey underwater, they are the only aquatic songbird in North America. They are considered a symbol of western birding and are quite interesting to watch! It consumes benthic macroinvertebrates.


American Dipper swimming Cornell Lab of Ornithology American Dipper Page

Dr. Donnelly is a professor at Oglethorpe University and recently became a member of the board of the Atlanta Audubon Society. Dr. Donnelly opened his lecture by discussing western trout management. Currently, trout are in need of management for a variety of reasons; habitat loss due to damns, invasives, disease, and pollution. Invasives include Brook Trout (Salvelinus fontinalis) and Rainbow Trout (Oncorhynchus mykiss). While these species are native to Georgia, in Bozeman, MT where this study took place they are considered an invasive. Whirling disease is another challenge faced by native trout and can lead to deformed skeletons.

There are a few different ways to fix some of these issues. Through regulations state and local governments have created stream buffers which improve the quality of the streams. Felt-soled waders have also been banned in several states as part of conservation efforts. The felt bottom allows for more traction on the river bottom but also serves as a carrier for invasive species such as rock snot (Didymosphenia geminata) and zebra mussels (Dreissena polymorpha). In addition to these regulations, there have also been restoration efforts. Most of these involve using piscicides to remove invasive fish and then introduce the fish that you want to populate the area. This method of restoration has been increasingly popular because it is cheap and you don’t have to access the whole stream to treat it. Electroshocking and removing non-native fish has also been done but missing just one gravid female ruins the effort.

Piscicides are toxic because they prevent oxidative phosphorylation which causes electron transfer during cellular respiration, or in other words, fish are unable to turn food into usable energy. This raises the question, how do piscicides impact non-native species? Most macroinvertebrates have minimum impacts on them but three orders, in particular, are heavily impacts; mayflies (Ephemeroptera), stoneflies (Plecoptera) and caddisflies (Trichoptera). You may recall that these are the orders that are used to measure EPT, and they also are the preferred food sources of American Dipper. We don’t know yet what impact this can have on other trophic levels, as it has yet to be studied. Tadpoles are also impacted by piscicides but adult frogs, toads, and salamanders do not seem to be impacted. Piscicides are applied at low flow, usually in the fall so the smallest amount possible can be used. The treatment lasts 5 to 7 days.

Dr. Donnelly studied Cherry Creek in which restoration of Westslope Cutthroat Trout (Oncorhynchus clarki lewisi) was going to occur. The Westslope Cutthroat Trout is one of 2 native cutthroat subspecies, and both subspecies are the state fish. Due to hybridization with other trout and habitat lose it can only be found in 5 percent of the area it once was, therefore leading to habitat restorations like this one. The habitat was ideal, containing a barrier at the base to prevent non-native from migrating back upstream. Non-natives found in the area included Rainbow Trout, Brook Trout, and Yellowstone Cutthroat Trout (Oncorhynchus clarkii bouvieri).

Dr. Donnelly did a BACI study of the system meaning he looked at American Dippers before, during, and after the application of piscicides. He has been able to study them for 8 days for 13 breeding seasons. He predicted that they would have lower body condition because the application took place during the breeding season, one of the most energetically stressful times for dippers. Body condition leads to higher fitness. The study did not include any data related to the baby birds because the nests are hard to access, which prevents predators from accessing them. Adults where trapped and marked. Wing chord and weight were used to estimate body condition, this allows to control for the different sizes of birds. Birds were given a unique color combination of bands, as well as a numbered band.

The results of the study indicated that birds during treatment have lower body mass than predicted. Dippers do not migrate, so surviving a tough Montana winter requires good body condition. Dippers have connected and large habitat so they won’t be that impacted by piscicides but there could be larger impacts on more vulnerable species. Dr. Donnelly said it is important that people follow the manual related to piscicides and we need to think about the whole community. He emphasized that he is not saying don’t use piscicides and that they shouldnt be used with American Dipper; we should just be careful.

Here is a link to the study


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