Comparison of 4 aging structures in the American shad (Alosa sapidissima)

Multiple structures can be used for the age determination of fishes.Choosing the structure that provides the most precise ages is important for the provision of consistent data for the management of commercially and recreationally important species, such as the American shad (Alosa sapidissima).In this study, we compared the precision of age estimates obtained from sagittal otoliths, vertebrae, scales, and opercula as structures for the age determination of American shad.Two readers examined structures removed from 462 American shad, which were collected from the Merrimack River in Lawrence, Massachusetts, during May and June of 2008-2010.The precision of age estimates were evaluated by comparisons of ages from different readers and structures.Age estimates determined from otoliths were the most precise (76.2% agreement, 2.99% coefficient of variation).Ages derived from scales were overestimated in young (≤5 years) fish and underestimated in older (≥7 years) fish, compared with ages determined from otoliths.Age estimates determined from vertebrae agreed with those obtained from otoliths better than ages from any other structure tested, but they were less precise and vertebrae required more processing than otoliths.Opercula were difficult to read, resulting in underestimation of the ages of fish that were age 5 and older.The results of this study indicate that the sagittal otolith is the most appropriate structure for determining the age of American shad.