ASPECTS OF SACRAMENTO PIKEMINNOW BIOLOGY IN NEARSHORE HABITATS OF THE SACRAMENTO–SAN JOAQUIN DELTA, CALIFORNIA

Abstract

We documented distribution, relative abundance, diet composition, and body condition of Sacramento pikeminnow Ptychocheilus grandis during 2001 and 2003 at 5 sites in the Sacramento-San Joaquin Delta, California. Sacramento pikeminnow densities in nearshore habitats were higher in 2003 than 2001. In both years, spatial distribu- tion of beach seine densities was similar. There were no significant differences in density among sampling sites except for the southernmost site where the catch was near zero. Based on rotary screw-trap data from a 6th site, we found rela- tive abundance of Sacramento pikeminnow entering the Delta via an artificial floodplain was positively correlated with flow. Most individuals collected using all 3 gear types were age 1 or older, and appeared to grow quickly based on data from previous studies. Sacramento pikeminnow had diverse diets composed of freshwater and estuarine invertebrate and fish taxa. Incidence of piscivory was only 2% of the diet of individuals <150 mm, but increased to 50% for fish over 150 mm. No salmonids were observed in foregut contents during the study. In both years body condition declined abruptly in July. Our results suggest Sacramento pikeminnow are more common in the turbid, tidal freshwater habitats of the Delta than was previously recognized. Stream flows may play an important role in moving juvenile Sacramento pikeminnow into the Delta from upstream areas. Similar to northern pikeminnow P. oregonensis, but in seeming con- trast to endangered Colorado pikeminnow P. lucius, the present study showed that Sacramento pikeminnow can be suc- cessful in altered habitats.