Age determination manual of the Alaska Fisheries Science Center Age and Growth Program

The Age and Growth Program at the Alaska Fisheries Science Center is tasked with providing age data in order to improve the basic understanding of the ecology and fisheries dynamics of Alaskan fish species. The primary focus of the Age and Growth Program is to estimate ages from otoliths and other calcified structures for age-structured modeling of commercially exploited stocks; however, the program has recently expanded its interests to include numerous studies on topics ranging from age estimate validation to the growth and life history of non-target species. Because so many applications rely upon age data and particularly upon assurances as to their accuracy and precision, the Age and Growth Program has developed this practical guide to document the age determination of key groundfish species from Alaskan waters. The main objective of this manual is to describe techniques specific to the age determination of commercially and ecologically important species studied by the Age and Growth Program. The manual also provides general background information on otolith morphology, dissection, and preparation, as well as descriptions of methods used to measure precision and accuracy of age estimates. This manual is intended not only as a reference for age readers at the AFSC and other laboratories, but also to give insight into the quality of age estimates to scientists who routinely use such data.

Effect of contact time on the acute toxicity of mercury to scale carp

The behaviour of metals in aquatic ecosystems is dependent on various environmental factors. Experiments were conducted in five different contact times (0.5, 2, 12, 24 and 48h) between soil sediment and mercury on Cyprinus carpio var communis. It was observed that contact time with soil sediment had significant effect in reducing the toxicity of mercury. Higher the time of contact, greater the effect. Medium hard water (150 mg/L CaC0 sub(3) of total hardness) had the highest effect as compared to other water in reducing the toxicity of mercury when combined with underlying soil sediment. With the increase in contact time, complexation and adsorption of inorganic mercury ions with the dissolved and particulate phases of water and soil sediment were increased; thereby bioaccumulation of mercury ions by scale carp was more. Applicability of the result of this experiment in natural ecosystems was also suggested.