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Abstract
Length measurements of fishes are commonly used by fishery scientists because of their ease of collection and the profound insight into fish populations that they provide. Specifically, obtaining accurate fish lengths is imperative for obtaining accurate population demographics. Thus, reproducibility and consistency of measuring an individual fish over time can greatly influence population level metrics and ultimately management decisions. To investigate this, we recorded fork lengths of 526 shovelnose sturgeon Scaphirhynchus platorynchus captured, measured, and marked in the field and recaptured within six years. Secondarily, we evaluated 37 shovelnose sturgeon measured in a controlled laboratory setting. We found that in both our field and laboratory evaluation that experienced biologists (between 5 and 20 years experience as fishery biologists) inaccurately measured (greater than 15 mm reduction in length) shovelnose sturgeon in approximately 5% of all cases. Of the approximately 5% erroneous measurements, substantial negative growth (greater than 100 mm reduction in length) occurred in some situations. This suggests that errors in recorded fish lengths exist and because of this, we believe multiple steps should be taken to minimize measurement error. Individual fishery biologists performing measurements should strive to ensure every fish is measured properly (i.e., fish laid completely flat on measuring board) and is recorded accurately. To this end, fishery biologists must accept that measurement error occurs and perform periodic quality assurance/quality control measures to account for these inaccuracies.