Age, Growth, Feeding, and Behavior of Sacramento Squawfish (Ptychocheilus grandis) in Bear Creek, Colusa Co., California

Abstract

I studied the age, growth, feeding, and behavior of Sacramento squawfish, Ptychocheilus grandis, in a small stream to provide basic life history information on this species in a habitat where it is often abundant. Young-of-year squawfish in Bear Creek grew throughout the summer and early fall. Mean back-calculated lengths of squawfish ranged from 65 mm SL (standard length) at age I to 257 mm SL at age IV. Mean back-calculated lengths varied among year-classes only at age I, with lengths varying from 55 mm SL for the 1979 year-class to 84 mm SL for the 1977 year-class. Bear Creek contained a large number of small mature fish (ages III and IV), but fish older than age IV were rare. Young squawfish (-100 mm SL) consumed primarily insects and occasionally small fish. Fish became the dominant prey (>50% by weight) at a size of 100 to 150 mm SL. When squawfish were assigned to 50-mm size-classes, diet diversity calculated by size-class (proportions based on the summed contents of all individuals in the size group) was greatest for fish 51 to 100 mm SL. Individual diet diversities (proportions based on individual gut contents) did not vary among size-classes. Stomach fullness of squawfish 5100 mm SL declined from May through December 1980. Individual diet diversity of fish :100 mm SL did not vary over the same time period. Large squawfish (100 to 500 mm SL) were sedentary and exhibited little movement within or between pools, during observations of summer, daytime behavior. Large squawfish did not interact aggressively with each other or with similar-sized Sacramento sucker, Catostomus occidentalis. A flexible pattern of growth of young-ofyear, partitioning of food among life stages, and the sedentary, nonaggressive behavior of large squawfish all contribute to the success of the species in small streams. The Sacramento squawfish, Ptychocheilus grandis, is a large, predatory cyprinid, endemic to the middle and lower elevation streams of the Sacramento-San Joaquin, Pajaro-Salinas, and Russian river drainages of California (Moyle, 1976). Most research on Sacramento squawfish has been limited to studies of its interactions with salmon, Oncorhynchus sp., and rainbow trout, Oncorhynchus mykiss (see Brown and Moyle, 1982, for a review), or studies of its distribution and abundance within drainages of California (Moyle and Nichols, 1973; Dettman, 1976; Moyle and Daniels, 1982; Moyle et al., 1982; Smith, 1982; Taylor et al., 1982). The latter studies indicate that the Sacramento squawfish is one of the most abundant fishes in waters ranging from intermittent streams to large rivers. Taylor et al. (1982) and Moyle et al. (1982) have suggested that this success is the result of its specialization as the top predator in these streams, partitioning of food and space among different life stages, and its reproductive strategy of long life and moderate fecundity. However, the published life history information needed to evaluate these statements is limited to an early study by Taft and Murphy (1950) and the mentioned distributional studies. The objective of the present study was to examine squawfish life history in a small stream supporting large numbers of squawfish. Such data should increase our understanding of squawfish life history in small streams and provide comparative data for future studies. Life history traits examined include age, growth, feeding, and behavior. MATERIALS AND METHODS-Bear Creek originated at an elevation of 456 m, on the eastern slope of the coastal mountains in Colusa Co., California (Fig. 1). It flowed for about 30 km in a southerly direction to its confluence with Cache Creek, a tributary of the This content downloaded from 157.55.39.27 on Mon, 05 Sep 2016 06:02:12 UTC All use subject to http://about.jstor.org/terms 250 The Southwestern Naturalist vol. 35, no. 3