Effects of Rostrum Injuries on Body Condition, Dam Passage, and Hydrodynamics of Paddlefish (Polyodon spathula) in the Alabama River

Abstract

The rostrum of Paddlefish (Polyodon spathula) aids in finding zooplankton prey as well as provides lift and stability during swimming, but this structure can sometimes be damaged or even completely missing. Injury or loss of the rostrum may have non-lethal impacts on body condition and swimming ability, although little data exist concerning such effects. Here I quantify the extent and prevalence of Paddlefish rostrum damage across the Alabama River, as well as potential sublethal effects of such damage. Data collected across the Alabama River during 2017-2023 by both Auburn University and Alabama Division of Wildlife and Freshwater Fisheries personnel were combined to determine (1) the proportion of fish with damaged rostra across the four river sections separated by three lock-and dam structures, and how rostrum condition varied by length and sex, (2) the impact of damage on body condition and gonad development, (3) whether severity of rostrum damage was related to passage/non-passage over the crested spillway at Claiborne Lock and Dam, and (4) impacts of various types of rostrum damage on hydrodynamics around the rostrum. I found that the highest percentage of Paddlefish with rostrum damage was in the lower two sections of the Alabama River (lower Alabama River and Claiborne Lake), with lower values in the upper two sections (William “Bill” Dannelly Reservoir and Jones Bluff Reservoir). Female paddlefish had significantly better rostrum condition scores than males. Rostrum condition did not vary as a function of length. Males with rostrum damage had significantly lower body condition than those fish without damage, however there was no difference in females. Passage rate past Claiborne Lock and Dam did not differ between individuals with versus those without rostrum damage, and a calculated rostrum damage score did not differ significantly between fish that passed versus those that did not pass. Differences in flow disruption around rostrum models showed an overall effect of rostrum damage type. However, there were no differences between rostrum damage types at low water velocity, and some differences were observed at higher water velocity. This project calls for additional investigation into how water forces interact with different types of rostrum damage to fully characterize the effects on hydrodynamics.