A Bioenergetics Approach to Modeling PCB Bioaccumulation in Lake Ontario Salmonids

The objective of this paper is to compare the trend of polychlorinated biphenyls (PCBs) bioaccumulation in three species of Lake Ontario salmonids with similar diet patterns and habitat. The concept of bioenergetics, which relates the growth and energy expenditure of a fish directly to its food consumption, is integrated into the study of pollutant accumulation. The resulting bioaccumulation model is a comprehensive approach that combines the physiological information of the fish, such as diet, metabolism, respiration, habitat, age and species, with the environmental conditions in the lake. The three species of salmonids studied are Lake Trout (Salvelinus namaycush), Brown Trout (Salmo trutta), and Chinook Salmon (Oncorhynchus tshawytscha). The model, which relies on a lakewide water quality and fish sampling database from the Ontario Ministry of Environment and Energy, is applied to study the pattern of total body burden of PCBs over the life span of the fish. Results from the model compare favorably to the data, and the observations clearly demonstrate the relative effects of food and water contamination on the time-dependent accumulation of PCBs in the bodies of fish. It is observed that different species sharing the same habitat and exposed to similar water contaminant concentrations are exhibiting marked difference in the body accumulation of PCBs. This difference is successfully reproduced with the model through judicious representation of their diet preferences and generically-governed metabolisms.     

Restoration of spawning grounds for trout and grayling in the river High-Rhine

In January 1990 10 m³ of washed gravel (grain size 16–50 mm) were introduced in an impounded section of the River High-Rhine to test its potential as a spawning ground for salmonids. The process of infiltration of fine sediments into the gravel and subsequent clogging was monitored for three years. Levels of clogging of the gravel matrix were estimated and ranged from slight to moderately-heavy. The degree of clogging was lower in winter than in summer. Since no bedload transport was observed during the study period, flood events could wash out sediments from the top layer of the gravel bed only. An equilibrium diffusion technique using porewater samplers was employed to measure oxygen concentrations within the interstitial space during the spawning period ofThymallus thymallus (April),Salmo trutta fario andOncorhynchus mykiss (December till February). Oxygen concentration decreased with increasing depth and during the course of the study period. Oxygen concentrations measured as a reference in the interstitial of the confluence of the river Glatt were considerably lower than those of the new gravel bed. A wide range of O₂ concentrations was found in winter 1991/92 and in spring 1992. This could be explained by the heterogeneous microstructure of the substrate. Successful embryonic and larval development of grayling in the gravel bed was observed in spring 1991 and 1992. However, no eggs or larvae of brown trout or rainbow trout were found. Habitat restoration projects for salmonids in impoundments of the High-Rhine are critically discussed.     

Geomorphic Assessment of the Effects of Flow Diversion on Anadromous Fish Spawning Habitat: Newhalem Creek,Washington*

A simple model for estimating streamflow competence is used to assess the impact of water diversion on the retention of spawning gravels in Newhalem Creek, a small watershed in the Cascade Mountains. Surveyed stream cross sections and discharge estimates are employed to characterize the routine tractive force conditions of the streambed. A conservative estimation procedure results in tractive force values of 120–390 Nm^?2for one-year, five-year, and 10-year recurrence interval events. Theoretical and empirical estimates of critical tractive force for particle sizes suggest a routine competence of 100–450 mm diameter for these flows. Substantial accumulations of bed material in the range of 1–100 mm diameter is desirable for anadromous fish spawning redds. As a result, Newhalem Creek is naturally poor habitat for spawning. Steep channel gradients and a “flashy” hydrograph conspire to routinely flush the main channel of spawning-size substrate. In this instance, the modest water diversion is immaterial to the maintenance of spawning habitat.     

Seasonal and spatial variation in lipid and triacylglycerol levels in juvenile chinook salmon (Oncorhynchus tshawytscha) from the Bridge River, British Columbia

Triacylglycerols (TAGs) are the primary form of energy storage in fish, but little work has been done on the dynamics of TAG storage and use in relation to environmental conditions. We sampled age-0 chinook salmon (Oncorhynchus tshawytscha) in two reaches of a regulated river in British Columbia, Canada that had different discharge regimes. During the summer, fish from the reach with high freshet flows grew more slowly and had lower TAG levels than those from the reach with lower and more stable flows. In addition, smaller individuals had lower TAG levels than larger ones. We suggest that in the reach with higher flows fish were unable to obtain sufficient surplus energy for somatic growth and lipid storage. In the fall, when flows were lower, TAG storage increased and the proportion of total lipids that were TAGs were similar for both small and large fish. The allocation of energy to TAG stores was likely a strategy to ensure individuals had sufficient energy for overwintering. Our results suggest that individual-based variation in TAG levels may be sensitive to environmental factors and can be used as a measure of fish condition and performance, but more work is needed to fully understand lipid dynamics in seasonally and spatially variable rearing environments.