A recent experimental study by Thomas et al. This is especially critical when researchers are working with threatened or endangered species.Ītlantic salmon have experienced marked declines across their range, particularly in southern North America, necessitating non-lethal methods of population assessment (Parrish et al., 1998). Scales require relatively little time and expense to age (Beakes et al., 2014) and, importantly, can be collected non-lethally. Although other hard structures, such as otoliths, may be more reliable especially in older age classes of fish (Robillard et al., 1996 Braaten et al., 1999), many state and provincial agencies in the United States and Canada prefer to use scales over these other hard structures for aging common game species (Maceina et al., 2007). Similar observations have been made for a range of species, juvenile steelhead Oncorhynchus mykiss (Beakes et al., 2014) and northern pike Esox lucius (Laine et al., 1991) among them.
Havey (1959) reported that scales represent a reliable method for aging Atlantic salmon Salmo salar.
His detailed observations on scale structure and ages were not the first of their kind (Dahl, 1907), and nor were they the last. He found that the relative spacing of annuli was so consistent for single scales that this spacing could be used to back-calculate growth that took place in previous years of the fish’s life. In 1910, Lea, who was studying herring at the time, showed that scale growth is proportional to body length (Lea, 1910). Keywords: Atlantic salmon, Gulf of Maine, scale circuli, scale growth The results of this study indicate that the pattern of circulus deposition and scale growth of Atlantic salmon vary greatly during the early marine phase, and this dynamic should be taken into account when assessing growth, especially over short time periods. Both rates decreased over the course of the study, presumably related to the fish reaching sexual maturity. Neither circulus deposition rate nor growth rate were constant through time and the same trend held when circulus deposition and growth were related to thermal experience. Fish were sampled 13 times over a period of 25 months. Scales were collected from Atlantic salmon raised in marine net pens off of the coast of Maine in order to characterize the formation of scale circuli and the growth of scales during the ocean phase, and to relate circulus deposition and scale growth rate to water temperature. However, because circuli formation is influenced by somatic growth, the rate at which circuli are formed and the factors influencing these rates must be taken into account for the given life stage of the study species. Scale circuli yield valuable information about the life history, age, and growth of a fish. Scale growth rates and scale circulus deposition rates of marine-stage Atlantic salmon Salmo salar raised under semi-natural conditions. Peterson, E., Sheehan, T.F., and Zydlewski, J.D. Geological Survey, Maine Cooperative Fish and Wildlife Research Unit,
Zydlewski 3,1ġDepartment of Wildlife, Fisheries, and Conservation Biology,ĢNational Marine Fisheries Service, Northeast Fisheries Science CenterģU.S.
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