Productivity of a herbivorous pupfish population (Cyprinodon nevadensis) in a warm desert stream

Abstract

Production and food intake by an herbivorous pupfish population (Cyprinodon nevadensis amargosae) living in the outflow of a thermal artesian well (Tecopa Bore) near Death Valley, California is described. Water issues from the ground at 47.5° C and cools 8.12° C before leaving the study area 300 m from the source. High stream temperatures restricted the pupfish population to some 41 % of the study area, with a resulting mean density of 89 individuals m−2 (range = 13 to 196m−2). Biomass estimates ranged from 7 kcal m−2 to 42 kcal m−2. The mean annual standing crop of pupfishes (24 kcal m−2) turned over about five times annually. Growth rates were highest in juveniles (♂= 9.5% day−1) and slowest in large adults (♀= 08% day−1). Monthly production ranged from 22 kcal m−2 in September to 3 kcal m−2 in July and August. Pupfish in Tecopa Bore fed on algae and detritus, ingesting 1941 kcal m−2 yr−1 or 17.5% of the annual net primary production. 119 kcal m−2 yr−1 was deposited in growth. This latter value is approximately ten times greater than values previously reported for large carnivorous fishes but is comparable lo values reported for herbivorous fishes under pond culture.