Prey consumption and condition of endangered age-0 pallid sturgeon Scaphirhynchus albus and co-located congeners: An assessment of surrogacy.

The capture of wild age-0 pallid sturgeon Scaphirhynchus albus was rare historically. However, an unprecedented high number of captures during 2021, coupled with a more typical year in 2020, provided a unique opportunity to address diet-related knowledge gaps during early life and evaluate surrogacy relationships with abundant congener individuals. We assessed diet and body condition of 55 age-0 pallid sturgeon and 139 co-located non-pallid Scaphirhynchus individuals of similar size. Both pallid and non-pallid individuals primarily consumed Chironomidae (Diptera), with Lopescladius and Paracladopelma being the most frequently consumed prey genera for both groups. Age-0 pallid sturgeon also yielded similar body condition as co-located non-pallid individuals during both years. Given the unprecedented number of captures, this work is a valuable case study for assessing surrogacy relationships involving an endangered fish in the wild and provides increased confidence in previous studies with more limited captures suggesting a valid surrogate relationship between an abundant congener (shovelnose sturgeon Scaphirhynchus platorynchus) and rarer age-0 pallid sturgeon <40-mm long. These results, coupled with prior research, provide evidence refuting the hypotheses that inadequate prey resources or less efficient prey assimilation are the limiting factor for pallid sturgeon recruitment to age 1.