Comparison of ages determined by using an Eberbach projector and a microscope to read scales from Atlantic menhaden (Brevoortia tyrannus) and Gulf menhaden (B. patronus)

Issue:

Author(s): 
Amy M. Schueller, Amanda Rezek, Raymond M. Mroch III, Eric Fitzpatrick, and Alicia Cheripka
Cover date: 
2021
doi: 
10.7755/FB.119.1.4
Pages: 
21-32
Supplementary material: 
Supplementary figures 1-6
10.7755/FB.119.1.4s1
Supplementary figures 7-14
10.7755/FB.119.1.4s2
Supplementary figure 15
10.7755/FB.119.1.4s3
Supplementary figures 16-17
10.7755/FB.119.1.4s4
Supplementary table 1
10.7755/FB.119.1.4s5
Supplementary figure 18
10.7755/FB.119.1.4s6
Supplementary table 2
10.7755/FB.119.1.4s7
Published online 5 April 2021
Abstract: 

Age determination is important for estimating productivity and status in fisheries stock assessments. Aging methods must balance advances in technology with continuity of data for long-term sampling programs. The long-term sampling program for Atlantic menhaden (Brevoortia tyrannus) and Gulf menhaden (B. patronus) has resulted in a database of ages that were determined by using an Eberbach projector, a now outdated technology. The objective of this study was to compare ages determined with an Eberbach projector to those determined with a more recent technology, the stereo microscope. Scales from Atlantic (total number of fish [N]=1317) and Gulf menhaden (N=1569) were aged by using both an Eberbach projector and a stereo microscope, and results were compared by using percent agreement, average percent error, Chang’s average coefficient of variation, bias tests, and simultaneous multinomial confidence intervals. The results from these measures for comparing age estimates were generally within standard, expected levels. Some bias was detected between estimates from the use of the 2 devices but was likely due to the use of poorly preserved scales or images of low quality on the Eberbach projector. Our results indicate that the use of a microscope will help maintain continuity in age estimates over time for long-term monitoring and for stock assessments.