Oxytetracycline (OTC) injections were used in a mark-recapture study undertaken to validate the otolith method of age determination for yellowtail rockfish Sebastesfiavidus. Otoliths from recaptured fish were broken across the focus and burned to enhance the contrast of features in the internal structure. The number of opaque and translucent zones laid down in the otolith after the deposition of the fluorescent OTC mark at the time of tagging agreed with the number of years (up to four) that the fish had been at liberty. These results validate the annual pattern of banding in otoliths of fish of ages 8-34 years. A larger sample of fish aged by this technique indicated an instantaneous natural mortality rate (M) of 0.07, a value only 28% of the estimate presently used for stock assessment and management of yellowtail rockfish. Rockfishes (genus $ebastes) dominate landings by the domestic trawl fleet on the Pacific coast of North America. Alaska-California landings exceeded 55,000 tonnes and had a value of over $27 million (U.S.) in 1985. As a group, rockfishes occupy a wide variety of habitats, from inshore waters to depths over 1,000 m. Most of the species exploited in the trawl fishery are relatively long lived and slow growing by the standards of other commercial species, such as clupeids and gadids. Current management approaches for rockfishes are strongly influenced by estimated rates of natural mortality (M), which are calculated from the age structure of unexploited or lightly exploited stocks.Therefore, it is important to have accurate ages for the calculation of these rates. The purpose of this study was to test an improved age-validation
S U M M A R Y This paper describes a new method that can be used to estimate the geomagnetic K-index values automatically with a computer. The underlying philosophy of the method together with a short description of the mathematics involved are discussed. It is shown how existing ideas in the relatively new field of data-adaptive filtering can be modified and extended to develop a powerful Linear-phase Robust Non-linear Smoothing method (LRNS method). The properties of this method are ideally suited for the computer K-index estimation problem.The method was applied to Hermanus digital geomagnetic data which extend to nearly one decade. Even with this large amount of data a 99 per cent agreement with handscaled values was still obtained when differences of fl in the K-values were neglected. A 70-80 per cent total agreement was determined with the majority of the differences occurring during quiet days. This is the result of the very small dynamic range of small K-indices (0 and 1) at Hermanus resulting in the handscaler frequently giving a value of 0 where the computer can detect this small variation and gives a value of 1.What is more important, is that the performance of the method stays virtually the same irrespective of the day or month of the year, or the year or years used in the comparisons. This proves the method's adaptiveness to any changes in the SR pattern irrespective of day-to-day , seasonal or solar activity variations. This is achieved without any changes in the original input parameters. Because of its adaptiveness it is believed that the method will also adapt to data from different geographical locations thus giving us a possible global method.
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