Food Habits of Lesser Scaup (Aythya affinis) Occupying Baitfish Aquaculture Facilities in Arkansas

-Lesser scaup Aythya afinis, mediumsized black and white diving ducks, were collected at Arkansas baitfish farms during November-December 1999 (N = 33), January-February 2000 (N = 39), and March-April 2000 (N = 22) to determine seasonal differences in their diet and their relative impact to baitfish production. The mass of gastrointestinal contents was used to determine the proportion of each diet item relative to all items recovered during stomach analyses. Chironomids were the primary food item recovered. Ten of 94 (10.6%) scaup contained identifiable fish biomass. Fish bones and otoliths were found in an additional 14 scaup (14.9%). All fish remains were identified (via otoliths) as those commonly produced at Arkansas baitfish farms (Cyprinidae). Other diet items (ranked by proportional mass) were vegetative seeds, snails, insects, crayfish, and other aquatic worms (class Oligochaeta). Scaup diets were similar among collection periods, between males and females, and between juvenile and mature ducks. We estimated the economic impact of lesser scaup to baitfish production based upon estimated duration of ducks at farms, the proportion of ducks containing fish, and scaup energetic requirements. Provided estimates of scaup abundance and the cost of bird harassment at a particular farm, economic thresholds (i.e., fish replacement cost as a function of scaup predation) will facilitate cost-effective decisions regarding bird damage management at Arkansas baitfish aquaculture facilities. Arkansas has the largest baitfish aquaculture industry in the United States, encompassing 11,250 ha o f production in 1998 (Collins and Stone 1999). Although baitfish aquaculture exists throughout Arkansas, the production o f golden shiners ' Present address: United States Department of Interior, Bureau of Indian Affairs, Pacific Regional Office-Branch of Forestry, 2800 Cottage Way, Sacramento, California 95825 USA. Corresponding author's present address: United States Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services, National Wildlife Research Center, 4101 LaPorte Avenue, Fort Collins, Colorado 80521 USA. Notemigonus crysoleucas, goldfish Carassius auratus, and fathead minnows Pimephales promelas is located primarily in central Arkansas, east o f Little Rock (Lonoke and Prairie counties). Most Arkansas baitfish acreage occurs along the Mississippi flyway where these facilities are occupied by many species o f waterbirds. Although much research has substantiated the existing or potential impacts to North American aquaculture from herons, egrets, pelicans, and cormorants (Stickley et al. 1992; Glahn and Brugger 1995; Stickley et al. 1995; Wywialowski 1999; King and Werner 2001; Werner et al. 2001 ; Glahn and Dorr 2002; Glahn et al. 2002), there is a paucity o f information regarding the impacts o f diving ducks (e.g., bluebill or lesser scaup Aythya af$nis) on baitfish production. Philipp and Hoy (1997) reported that 45 o f 223 scaup (20%) collected at Arkansas baitfish facilities (in March 1995, and from December 1995 to March 1996) contained baitfish. These authors estimated that the replacement cost o f golden shiners and goldfish consumed per scaup foraging bout was $0.04 and $0.12, respectively, based upon scaup abundance and consumption rate, and baitfish market values. Afton et al. (1991) suggested that fish comprised 3.5% o f lesser scaup diets. C. Custer (United States Geological Survey, personal communication) has also observed scaup feeding on fish in the tailwaters o f hydroelectric dams when all other water was iced over. Most studies have not observed piscivory among lesser scaup (Cronan 1957; Harmon 1962; Rogers and Korschgen 1966; Bartonek and Hickey 1969; Dirschl 1969; Bartonek and Murdy 0 Copyright by thc World Aquaculture Society 2(K)4 SCAUP AND ARKANSAS BAITFISH