Crayfishes (Order Decapoda) are common inhabitants of agricultural headwater streams in the Midwestern United States. The frequency and severity of injuries within crayfish communities are an indicator of levels of crayfish aggression, which is influenced by physical habitat conditions, stress, and crayfish density. However, previous studies have not evaluated the relative determinants of the frequency and severity of crayfish injuries within agricultural headwater streams in the Midwestern United States. Identifying the most influential factor on the frequency and severity of crayfish injuries will assist with determining if these sublethal response variables can serve as an indicator of physical habitat quality or water quality in agricultural headwater streams. We hypothesized that the frequency and severity of crayfish injuries within agricultural headwater streams would be more strongly influenced by physical habitat and water quality than crayfish density. We sampled crayfishes, documented the frequency and type of injuries, and measured instream habitat and water chemistry in 2014 and 2015 within 12 agricultural headwater streams in northeastern Indiana, southern Michigan, and central Ohio. A linear mixed effect model analysis was conducted to evaluate if crayfish injury response variables were more influenced by physical habitat quality, water quality, or crayfish density.
Results/Conclusions
We documented five crayfish species from 1641 adult captures from all sites. The most commonly captured species were Faxonius immunis, Faxonius rusticus, and Faxonius propinquus. The standardized coefficients from the linear mixed effect model analyses indicated that mean number of injuries per individual, the proportion of injured individuals, the mean number of claw injuries, and the proportion of individuals with multiple injuries were more strongly influenced by crayfish density than physical habitat quality or water quality. The linear mixed effect model analysis also indicated that the four crayfish injury variables were positively correlated with crayfish density (P < 0.001) and physical habitat quality (P < 0.05). Our results indicated that the frequency and severity of crayfish injuries within agricultural headwater streams in the Midwest are more influenced by crayfish density than physical habitat quality or water quality.