Digitized scale and otolith microstructures as correlates of juvenile pink salmon size

The purpose of this study was to determine whether scale or otolith microstructures were more strongly related to fish growth. Scales and otoliths were sampled from 231 juvenile pink salmon (Oncorhynchus gorbuscha) collected from the marine waters of Southeast Alaska during two periods in 1993 and 1994. A computerized image analysis system was used to measure several periodic and non-periodic scale and otolith microstructures from each specimen. The measurements from each fish were compared with each other and with fish length using nonparametric correlation analysis and parametric regressions. As expected, growth of most scale and otolith microstructures was significantly positively correlated with fish growth. Scales and otoliths also portrayed recent marine growth (growth near the time of capture) more reliably than earlier marine growth (growth more distant from the time of capture). An unexpected result was that the number and width of periodic scale microstructures (circuli) were more strongly related to fish length than were the number and width of periodic otolith microstructures (increments). These results indicate that, at least for pink salmon, there is a trade off between the finer temporal resolution available from otolith increments (near daily) and the stronger correlation with fish length available from scale circulus measurements.