Effects of rostrum injuries on body condition and dam passage of Paddlefish

Objective The Paddlefish Polyodon spathula rostrum aids in finding zooplankton prey, increases feeding efficiency, and provides lift and stability during swimming. This structure can sometimes be damaged or even completely missing, with little known about the effects of rostrum injury or loss on growth, survival, and swimming capability. Our objectives were to (1) determine the proportion of Paddlefish with a damaged rostrum in the Alabama River and assess how this proportion varied based on location along the river, fish length, and sex; (2) quantify the relationship between Paddlefish rostrum damage and body condition or gonad development; and (3) investigate the correlation between Paddlefish rostrum injury and dam passage rate at Claiborne Lock and Dam. Methods We collected Paddlefish (n = 409) from throughout the Alabama River and quantified rostrum injuries for each. Gonad weights (from 309 fish) and rostrum weights (from 93 fish) were quantified, and a subset of 100 fish was implanted with combined acoustic and radio transmitters and tracked via both stationary acoustic and radio receivers. Results The highest percentage of Paddlefish with rostrum damage occurred in the lower two sections of the Alabama River (lower Alabama River and Claiborne Lake), whereas lower percentages were observed in the upper two sections (William “Bill” Dannelly Reservoir and Jones Bluff Reservoir). Female Paddlefish had significantly better rostrum condition scores than males, and rostrum condition did not vary as a function of fish length. Males with rostrum damage had significantly lower body condition than males without damage, whereas there was no significant effect in females. Upstream passage rates past Claiborne Lock and Dam did not differ between individuals with rostrum damage and those without rostrum damage, and a calculated rostrum damage score did not differ significantly between fish that passed the dam and those that did not pass. Conclusions Although the occurrence of damaged rostra varied among dam sites and the body condition of males varied slightly (albeit significantly), the body condition of females and passage by fish with damaged versus undamaged rostra did not differ. As such, the overall effects of rostrum damage did not appear to be detrimental given the parameters that we measured for damaged individuals.