Zusammenfassung: The authors simulated length-frequency distributions for 3-, 7-, and 13-age-class exploited populations (Peprilus triacanthus, Gadus morhua, Paralichthys dentatus, Pomatomus saltatrix ) to compare the performance of Shepherd's length composition analysis (SRLCA) and MULTIFAN in resolving the distributions to age frequencies. The length distributions were characterized by von Bertalanffy growth, variable recruitment, variable mortality, partial selectivity of fishing gear for the youngest age-groups, and a length-dependent trend in the standard deviation in length at age. Comparative performance of SRLCA and MULTIFAN was assessed quantitatively by using the Kolmogorov-Smirnov cumulative distribution test to compare calculated proportions at age with the simulated values. Shepherd's analysis provided a good return for the amount of computational resources invested, with limited subjective user input. In contrast, MULTIFAN offered a much more complex but powerful estimation technique, and performed consistently better than SRLCA in matching the simulated proportions at age.

Zusammenfassung: The feeding habits of C.taenia were studied by means of monthly samples taken over a 2-year period, October 1972-October 1974, from two sites, one on the River Great Ouse at Newport Pagnell and the other at some neighbouring gravel pits. Dietary components, seasonal variation in these components, and seasonal and diurnal variation in feeding intensity were examined. The ecological niche of the food items and their size range are discussed, since both these factors appeared important in governing the microhabitat of the fish. The feeding activity followed a seasonal cycle with little or no feeding in the winter and a high level of feeding activity in mid-summer. The diet showed a predominance of small food items, such as chydorids, copepods and rhizopods. These items varied in occurrence during the feeding period which appeared to be related to their own abundance, pointing to non-selective feeding by the fish. The small size and benthic habits of the food items, many of which are closely associated with surface layers of mud and weed, indicated a preference by C.taenia (L.) for feeding in this type of habitat and on this type of food, in contrast to the stone loach, Noemacheilus barbatulus (L.), which is believed to inhabit stony areas and take larger food items.

Zusammenfassung: The authors determined the statistical properties of the index of biotic integrity (IBI) from electrofishing samples collected from Ohio streams. Although IBI is widely used to evaluate the condition of water resources by biologists and resource managers, expanding its role as a regulatory tool depends on statistical validation of its precision and power. We addressed these issues by constructing an additive variance model for IBI and testing the assumptions of that model directly with a bootstrap resampling algorithm and simulations using field data. Statistical properties of IBI supported the use of standard analysis techniques such as ANOVA for hypothesis testing. We determined with power analysis that IBI can distinguish between five and six nonoverlapping categories of biotic integrity based on a model that includes the effects of measurement error, variability of fish assemblages through time, and statistical interaction of location and time.