Determination of water quality in lakes by biological indices

Some problems of evaluation of water quality by biological indices which can be applied in the practice of ecological monitoring on water bodies are considered in this report. Taking into account, that ecological monitoring is the most urgent for large lakes, situated in civilised (urbanised) and (or) agrarian landscapes the corresponding problems will be considered mainly in conformity with large deep lakes of temperate latitudes. The aim is a general evaluation of some of the methods from the point of view of their possible application for monitoring on large water bodies.

Prospects of fisheries development in India by 2000 AD

The fishery resources of India are extensive. The demand for fish for domestic consumption will be at least 10 million by 2000 AD. With proper planning and management, fish production from inland, brackishwater and marine sources can be increased to 5 million tonnes, 1 million tonne and 4 million tonnes respectively. But the increase in the last 37 years is approximately equals 2.1 million tonnes over the base level of 1950. If the present trend is continued, the expected fish production will be approximately equals 6 million tonnes by 2000 AD, and hence, only approximately equals 60% of the domestic demand can be met.

A method to improve size estimates of walleye pollock (Theragra chalcogramma) Atka mackerel (Pleurogrammus monopterygius) consumed by pinnipeds: digestion correction factors applied to bones and otoliths recovered in scats

The lengths of otoliths and other skeletal structures recovered from the scats of pinnipeds, such as Steller sea lions (Eumetopias jubatus), correlate with body size and can be used to estimate the length of prey consumed. Unfortunately, otoliths are often found in too few scats or are too digested to usefully estimate prey size. Alternative diagnostic bones are frequently recovered, but few bone-size to prey-size correlations exist and bones are also reduced in size by various degrees owing to digestion. To prevent underestimates in prey sizes consumed techniques are required to account for the degree of digestion of alternative bones prior to estimating prey size. We developed a method (using defined criteria and photo-reference material) to assign the degree of digestion for key cranial structures of two prey species: walleye pollock (Theragra chalcogramma) and Atka mackerel (Pleurogrammus monopterygius). The method grades each structure into one of three condition categories; good, fair or poor. We also conducted feeding trials with captive Steller sea lions, feeding both fish species to determine the extent of erosion of each structure and to derive condition-specific digestion correction factors to reconstruct the original sizes of the structures consumed. In general, larger structures were relatively more digested than smaller ones. Mean size reduction varied between different types of structures (3.3−26.3%), but was not influenced by the size of the prey consumed. Results from the observations and experiments were combined to be able to reconstruct the size of prey consumed by sea lions and other pinnipeds. The proposed method has four steps: 1) measure the recovered structures and grade the extent of digestion by using defined criteria and photo-reference collection; 2) exclude structures graded in poor condition; 3) multiply measurements of structures in good and fair condition by their appropriate digestion correction factors to derive their original size; and 4) calculate the size of prey from allometric regressions relating corrected structure measurements to body lengths. This technique can be readily applied to piscivore dietary studies that use hard remains of fish.