Ontogenetic and habitat-related changes in diet of late larval and juvenile suckers (Catostomidae) in Upper Klamath Lake, Oregon

摘要

We describe ontogenetic patterns in the diets of shortnose and Lost River suckers (15.8-92.8 mm standard length) front Upper Klamath Lake in summer 1999. Both species made a transition from surface and planktonic prey to benthic prey at about 20-30 mm standard length, corresponding to the approximate size of the juvenile morphological transition. Surface prey was dominated by adult chironomids and undigestable pollen, while benthic prey was dominated by larval chironomids, chydorids, and ostracods. In the 15-20-mm size class, pollen made tip > 75% of food particles in 68% of specimens, and only 2 specimens in this size class lacked any pollen grains. A better understanding of the prey selection process in larval stickers is needed to determine the importance of this potential source of starvation. The planktonic prey eaten during the surface-to-benthic feeding transition were widely distributed in the lake, suggesting that larvae use emergent vegetation primarily as a refuge front predators. On a numerical basis, crustaceans and larval chironomids contributed most to the diets of larger juveniles. In specimens > 40 mm, shortnose suckers ate more Tanytarsini and Lost River stickers ate more chironomid pupae and chydorids. In specimens > 40 turn there was a strong habitat-related difference in diet: specimens collected in offshore samples ate more chironomid larvae and pupae, harpacticoid copepods, and chydorids, whereas onshore specimens ate more cyclopoid copepods and invertebrate eggs. The transition from onshore to offshore habitat appears to occur over a broad size range of about 40-90 mm.