M.L. Miller | Search USGS

USGS2016

Early life history of three pelagic-spawning minnows Macrhybopsis spp. in the lower Missouri River

Life-history characteristics of age-0 sturgeon chub Macrhybopsis gelida , shoal chub Macrhybopsis hyostoma and sicklefin chub Macrhybopsis meeki were compared using several methods. All Macrhybopsis species consumed mostly midge pupae, but M. meeki had the most general diet (Levins' index, B = 0·22) compared with M. hyostoma ( B = 0·02) and M. gelida ( B = 0·09). Morisita's diet overlap index among species pairs ranged from 0·62 to 0·97 and was highest between M. hyostoma and M. gelida . Daily ages estimated from lapilli otoliths for each species ranged from 15 to 43 days for M. gelida , 19 to 44 for M. hyostoma and from 16 to 64 days for M. meeki . Mean growth rates ranged from 0·79 mm day −1 for M. meeki to 1·39 mm day −1 for M. gelida . Mortality estimates indicated high daily survivorship rates for M. meeki (0·985), but could not be estimated for the other two species. Hatch date histograms were congruent with the belief that M. hyostoma and M. gelida spawn periodically from June to September. Macrhybopsis meeki , however, appeared to respond to a specific spawning cue as hatch dates were unimodal with a peak in July. These results fill a gap in current knowledge of these imperilled species that can be used to guide management decisions.

Missouri↗

USGS2016

Age-0 Shovelnose Sturgeon prey consumption in the Lower Missouri River

A lack of nutritious food during the first year of life is a hypothesized factor that may limit survival of endangered pallid sturgeon Scaphirhynchus albus in the lower Missouri River (LMOR). Unfortunately, information for age-0 pallid sturgeon diets remains limited, but diet analyses for age-0 Scaphirhynchus spp. (sturgeon hereafter) have occurred. Little information, however, exists on age-0 sturgeon diets in the LMOR; thus, our primary objective was to document age-0 sturgeon diets in this system. We examined guts contents from 30 individuals, which were genetically identified as shovelnose sturgeon Scaphirhynchus platorynchus , and three stomachs were empty. The remaining age-0 shovelnose sturgeon consumed chironomid larvae almost exclusively (>98% of prey items consumed). Our results were similar to studies conducted in other systems, and it appears unlikely that a lack of nutritious food was a major factor affecting the individuals captured during this study. This effort provides important information to help guide ongoing adaptive management efforts in the LMOR.

Missouri↗