Life history characteristics of 54 Ontario lake trout (Salvelinus namaycush) populations vary with differences in lake area (range 25-450 000 ha) and total dissolved solids (TDS) (range 15-180 mg·L-1). Populations from large lakes exhibit greater maximum sizes, greater ages and sizes at first maturity, lower natural mortality rates, and lower sustainable yields. Populations from high-TDS lakes exhibit higher growth rates in early life, lower ages at first maturity, larger sizes at first maturity, and higher natural mortality rates. Angler catchability increases significantly at low population densities. With these relationships included in an age-structured population model, we found that the fishing mortality rate at maximum equilibrium yield ranges from 0.12·year-1 for a 100-ha, low-TDS lake to 0.37·year-1 for a 10 000-ha, high-TDS lake; the fishing effort level at maximum equilibrium yield ranges from 6.6 angler-h·ha-1· year-1 for a 100-ha, low-TDS lake to 4.0 angler-h·ha-1·year-1 for a 10 000-ha, high-TDS lake. Populations from small, low-TDS lakes are more sensitive to overexploitation than populations from large, high-TDS lakes. Easily measured, environmental correlates of life history characters may be common among fish species and are useful in developing exploitation guidelines for populations that are not well studied.

We present data on age, growth, mortality, population size, and fisheries for 12 populations of wild lentic brook trout Salvelinus fontinalis in Algonquin Park, Ontario, and incorporate the data in a simulation model. The populations showed a remarkable homogeneity of parameters; nearly all had very rapid growth, early maturity, high mortality, and small adult stocks. Growth and population density, however, were negatively associated with the complexity of fish communities. Modeling suggested that neither minimum nor maximum size limits will materially improve quality of fishing. A 360‐mm minimum size limit, for example, produced only marginal improvements in simulated catch per unit effort and mean length of harvested fish but sharp reductions in harvest per unit effort and yield. The model predicted the maximum annual sustainable yield of these fisheries to be 0.78 kg/ha, a value close to that predicted by the morphoedaphic index (total dissolved solids divided by mean depth). Our results have important management implications but are vulnerable to certain input parameters, such as those for stock–recruitment relationships, that need further refinement.

One. M 1 C 2 W7 Kower, 8. M., and 1. B. Sprague. 1989. Zinc avoidance by fathead minnows (Pimephases prome%as): cornputerized tracking and greater ecological relevance. Can. I. Fish. Aquat. Sci. 46: 494-502.Male fathead minnows (Pb'mephaBes promelas) avoided 0.284 rngeL-' sf zinc when given a choice of clean and dosed sides of a featureless openfield tank, as frequently used in avoidancelpreference experiments. More than six times as much zinc (1.83 rngaL-') was required to cause avoidance when males were allowed to establish a territory under a shelter on the side of the experimental chamber which was later dosed. Activity increased during zinc dosing when a shelter was present but did not change in ns-shelter tests. Control period activity was positively related to strength of avoidance response. By incorporating relevant motivational facton, behavisur observed in avoidance experiments should be more predictive to nature. A new computerized tracking system automatically recorded movements of the fish, calculated various measures sf Iscomotsr response and filed results in preparation for statistical analysis. Bes males du t6te-de-boule (Pimephaies promelas) evitent le zinc en concentration de 0,284 ~7lg.L-I quand ils 494 Can. 9. Fish. Aqeesat. Sci., . 1977. Field-lahasaaoq determined avoidances of the spotfin shiner and the bluntnose minnow to chlorinated &schxges. Water Resow. Bdl. 13: 1047-~~M m e w , B. G. E., m E. 1980. Max h m preference and avo spnse data: In B. E Uaver-p. S. dings of the sixth m u i d ts ber 6 7 , 1979, Winnipeg, Manitoba. Can. Tech. Rep. Fish. Aqua. Sci. 975. Dmca~, D. G . , rn 9. B. Smcim. 1981. AccBim~on-indued changes in toxicity of arsenic md cyanide to rainbow %rout, Salmo gaiadneri Richardson. J. Fish Bisl. 18: 579-589. D m m , C. We 1964 New tabk for mdtipk comp~mns with a con%rol.

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