9592 - Laserfiche WebLink

Home Browse Search

Bonytail Chub Foods and Feeding Habits, Cibola High Levee Pond, lower Colorado River, Arizona and California, 2003.2004 Paul C. Marsh and Jason D. Schooley School of Life Sciences Arizona State University Tempe, Arizona 85287-4501 Introduction This report presents one aspect of ongoing studies of native bonytail Gila elegans and razorback sucker Xyrauchen texanus in the Cibola High Levee Pond (HLP). The Cibola HLP is a small (ca. 5 acre) remnant of the lower Colorado River channel located between the river and inland (high) levees on the U.S. Fish and Wildlife Service's Cibola National Wildlife Refuge in La Paz County, Arizona and Imperial County, California. The pond was reclaimed to eliminate non-native fishes and first stocked with native species in 1993, and since then the site has served roles in both management and research (see LaBarbara and Minckley 1999, Marsh 2000, Mueller et al. 2003). The purposes of this investigation were to (1) document foods utilized by bonytail, (2) examine food utilization as a function of fish size, and (3) investigate temporal aspect of feeding habitats and food utilization by bonytail inhabiting the Cibola HLP. These goals were to be accomplished by acquiring non-lethal stomach samples from evening and nighttime collections of bonytail representing relatively larger and relatively smaller fish across two years. Methods Sample Collection. A combined sample of 72 bonytail was acquired from trammel net collections made on 7 May 2003 and 4-5 May 2004. Nets were placed to sample two different feeding times, evening (samples collected from 1800 to 2400 hrs) and night (samples collected from 0100 to 0545 hrs). A distinct size class was sampled each year -- nominal TL for 2003 was >375 mm (n=28) and for 2004 was <375 mm (n=44). Fish were held in a floating live car for a brief time after capture, then measured (total length [TL), nearest mm) and weighted (nearest 2 gm). Stomach and intestinal (GI) contents were removed by flushing GI material through the vent by using a special apparatus inserted into the esophagus (Wasowicz and Valdez 1994) that was an effective method to avoid fish sacrifice. The apparatus consisted of a one-way, rubber squeeze bulb and tygon tubing of varying sizes (6.5, 8.0, 9.5, and 11.0 mm outside diameter), with tubing size matched appropriately to fish gape size. GI tracts were flushed with clear water from the sample site through a sieve, and into a sample container. Fish with empty tracts were noted. . Samples were fixed in 10% formalin and later rinsed in fresh water and transferred to 70% ethanol for examination in the laboratory. Gut Content Examination. Gastrointestinal samples were individually washed through a 500 micron-mesh sieve and solids wet-weighed to the nearest 0.001 g. The contents of each sample was visually examined with the aid of a binocular dissecting scope, and the percent of the total quantity was estimated for each of the following six categories: amorphic organic matter (AOM), inorganic matter, plant, fish, invertebrate, or other. When possible, individual prey items were identified to family-level. Samples were then placed in 70% ethanol for storage. Results Bonytail examined from 2003 (n=28) ranged in total length from 376 to 510 mm with a mean of 447, and ranged in weight from 305 to 1136 g with a mean of 565, while fish from 2004 (n=44) were smaller; 271 to 509 mm long with mean of 325 and weight 129 to 710 g with a mean of 222 g (see Fig. 1). Weight-length relationships represented a continuum from smaller to larger fish, and there was more variation among larger individuals (Figs. 1 and 2). 1