Spatial distribution of zooplankton in the Kolsaiskie mountain lakes (Kungey Ala Tau, south-east Kazakhstan) and its connection with environment factors

The values of Clark W-statistics, ∆-Shannon-Weaver, and an average individual mass of specimen were used to characterize the spatial distribution of zooplankton in the Kolsay lakes. With a relatively constant species composition, the interannual dynamics of the size and quantity variables of zooplankton testified to an increase in the eutrophication processes of three of the four Kolsay lakes. Interannual changes in the structure of the zooplankton community were mostly determined by the introduction of allochthonous species of fish, reduction of the water level, and enhancement of biogenic load due to recreational use of the lakes. The effect of very low concentrations of heavy metals on the dimensional variables of zooplankton can be connected with the oligotrophic status of Kolsaiskie lakes.

Maturation and Fecundity of Pacific Herring (Clupea harengus pallasi): An Experimental Study with Comparisons to Natural Populations

Approximately 3 mo before spawning, Pacific herring (Clupea harengus pallasi) were captured and transferred to experimental netpens varying in fish density, cover, and feeding regimes. Fecundity decreased as the fish ripened. Concurrently, ovary weight and egg weight increased and somatic weight decreased. Length-specific fecundities of fed and unfed fish were similar, but the unfed fish had higher weight-specific fecundities, corresponding to a greater loss of somatic tissue during impoundment. Feeding accelerated the rate of maturity, and fed fish spawned earlier with heavier eggs than unfed fish. Relative fecundity (eggs per gram) was highest among the unfed fish. Reduction in preovulatory egg number probably was a consequence of follicular atresia (observed but not quantified here). Age-, length-, and weight-specific fecundity of impounded herring varied within the range observed for naturally maturing populations (1974 and 1980). Fecundity in impounded fish varied no more than observed in nature: there was a greater difference in age-, length-, and weight-specific fecundity between years than there was between experimental treatments. We suggest that reduction in the number of maturing oocytes occurs naturally and reflects a mechanism that allows herring to adjust their egg size and egg number according to energetic resources and environmental conditions.