Comparison of Two Otolith Processing Methods for Estimating Age of Three Catfish Species

When performing studies that require fish age estimation, biologists must achieve a high level of accuracy and precision, as age, growth, and survival data are often used in models that inform management decisions. Otolith processing techniques vary, and no studies have assessed which methodology is more precise and cost effective. Our goal was to assess the precision, effort, and resources needed to perform the ground otolith and cut otolith methods in estimating ages of Blue Catfish Ictalurus furcatus, Channel Catfish I. punctatus, and Flathead Catfish Pylodictis olivaris. Readers exhibited high initial agreement rates for both aging methods with Blue Catfish (93.3–97.8%) and Flathead Catfish (88.9–96.3%). However, readers were more confident in their age estimates with the cut otolith method, and age–bias plots revealed significant bias between the techniques. The ground otolith method yielded lower age estimates compared to the cut otolith method by roughly 1 year for Flathead Catfish from age 6 through age 10 and yielded lower age estimates by about 1 year for Blue Catfish at ages 4 and 5. Conversely, for Channel Catfish, reader agreement and confidence were lower with the cut otolith method compared to the ground otolith method (66.7% and 95.7%), but no significant bias was detected between the processing techniques. The ground otolith method required lower startup costs and less effort than the cut otolith method for Blue Catfish and Channel Catfish, whereas the cut otolith method required less effort for Flathead Catfish. The cut otolith method required higher startup costs and was more expensive to perform than the ground otolith method. This study presents advantages and disadvantages of both methods, and we recommend that fishery professionals weigh the costs and benefits of each method when developing a program for applying a method to their study systems.