LINKING BLUEGILL AND GIZZARD SHAD PREY ASSEMBLAGES TO GROWTH OF AGE-0LARGEMOUTH BASS IN RESERVOIRS

Either gizzard shad Dorosoma cepedianum or bluegills Lepomis macrochir us dominate prey assemblages in many small (<100 ha) Ohio reservoirs. Because gizzard shad spawn early in the spring and their offspring gro w rapidly, age-0 gizzard shad may be invulnerable to age-0 largemouth bass Micropterus salmoides, thereby compromising this piscivore's grow th and, potentially, recruitment. To test this hypothesis, we quantifi ed growth, abundance, and diets of age-0 largemouth bass in reservoirs dominated by age-0 bluegills (one reservoir) or age-0 gizzard shad (t wo reservoirs) during June through early October 1992-1994. In the blu egill-dominated reservoir, age-0 largemouth bass grew slowly (about 0. 04 g/d) during June through mid-August. Though age-0 bluegills became abundant after mid-August, contributing to rapid growth (about 0.2 g/d ) of age-0 largemouth bass, these age-0 largemouth bass only reached s mall to moderate sizes by fall (range of mean wet weights, 3-7 g). In the reservoirs dominated by gizzard shad, summer growth and fall sizes of largemouth bass varied among systems and years. During one summer in one shad-dominated reservoir, an early rise in temperature plus sma ll age-0 gizzard shad probably contributed to rapid growth (similar to 0.12 g/d) and large fall size (mean wet weight, 10.8 g) of age-0 larg emouth bass. More commonly, age-0 largemouth bass grew slowly or moder ately (similar to 0.06 g/d). However, fall sizes of largemouth bass al ways were equivalent to or exceeded those in the bluegill-dominated re servoir (range of mean wet weights, 3-11 g). Our results suggest that growth of age-0 largemouth bass should vary more in systems dominated by gizzard shad than in bluegill-dominated ones. Management efforts th at increase gizzard shad vulnerability during early summer may reduce this variability, thereby enhancing first-summer growth and, potential ly, recruitment success of largemouth bass.