Is the first annulus on the otolith of the Atka mackerel , Pleurogrammus monopterygius , missing ? Seasonality of translucent-zone formation Methods

A monthly series ofAtka mackerel otoliths was selected from a collection maintained by the Age and Growth Unit at the Alaska Fisheries Science Center (AFSC). Young fish otoliths (observed with 2 to 3 translucent zones) were chosen to minimize affects ofage-related factors on the marginal increment formation. A lack of fall and winter collections limited our samples to 19 or 20 otoliths per month. Otoliths meeting our criteria of less than four translucent zones were available from all months except November and December. The sample was assigned to an age reader to determine the marginal increment stage of each otolith. Otoliths were prepared by snapping each one along the dorsal-ventral plane and by passing the broken surface over a flame. The burnt surface was examined with a dissecting microscope and illuminated by reflected light. Marginal increment determination was made along the ventral proximal edge of the broken surface at 50x magnification. The stages ofmarginal increment development were defined as follows: stage 1 = a translucent zone is forming along the otolith growth margin; stage 2 = area of opaque growth between the otolith growth