Validation of methods for aging goosefish (Lophius americanus) based on length-mode progression of a strong cohort

Abstract

Northeast Fisheries Science Center National Marine Fisheries Service, NOAA 166 Water Street Woods Hole, Massachusetts 02543 Abstract—An unusually strong year class of goosefish (Lophius americanus) was first observed in the spring of 2015, and the length mode for this particular cohort remained evident for several years. We collected monthly samples from within this length mode over a period of 3 years and considered them fish with known ages for validating ages estimated by using illicia and vertebrae. Recent research had found vertebral ages for goosefish to be inaccurate, and a method in which illicia are used for Lophius species in Europe seemed promising. However, ring counts from illicia matched the known age only 50% of the time and were not replicable (9% agreement). Ring counts from vertebrae never matched the known age but were replicable in 68% of samples. Marginal increment analysis of illicia from fish that matched the known age provided evidence that one annulus is formed on the illicium in spring or summer of each year for fish aged from 1 to 2 years. Because of the low accuracy of age estimates made with both illicia and vertebrae, as well as the high bias of aging with vertebrae, we concluded that the methods based on these structures did not provide useful age estimates of goosefish. The observed growth rate, based on the progression of the length mode during our study, was much faster than the growth rates based on vertebral ages.