Don W. Hayne

Effects of the Removal of the Fish Population on the Fish-Food Organisms of a Lake

Almost all of the macroscopic aquatic organisms can serve as food for fishes under certain conditions and the many quantitative and qualitative studies of the standing crops of fish-food animals have been of value in estimating the capacity of a body of water to produce fish. While investigations of the production of fish-food animals are numerous, the majority of these studies are based upon summer season collections only. A very few of the workers have made estimates of production of invertebrates (Lundbeck 1926; Miller 1941). Ricker (1946) presented an analysis and review of the literature with a discussion of certain problems of the dynamics of production and also delineated the fundamental concepts of productivity which have an ecological application. Clarke (1946) has outlined concepts of productivity in a marine area. Certain of the interrelationships of a fish population and the invertebrate fauna in one of Michigans lakes have been considered by Ball (1948). The present report is concerned with a study, in this same lake, first, of the composition of the invertebrate fish-food population for a period of three years and, second, of the responses of these organisms to the removal of the fish population.

Apparent Home Range of Microtus in Relation to Distance between Traps

Estimation of size of home range has become a usual procedure in life history studies of small mammals and, in the total, a tremendous amount of effort has been devoted to such studies. By comparison, the effect of varying techniques of measurement has been little investigated. The present paper reports an experimental study of the effect upon apparent home ranges produced by varying one aspect of the technique-the distance between traps. All home range determinations reported here relate to the meadow vole (Microtus pennsylvanicus pennsylvanicus Ord) in southern Michigan. A reasonably accurate understanding of home range is important not only in life histories, but also in the problems of censusing and of control of small animals. With regard to censusing, for example, it has been pointed out by Dice (1941) that the animals in contact with a particular set of traps not only comprise those whose home ranges are contained within the area under traps, but also may include those animals which inhabit the neighboring areas and which have within their home ranges one or more of the traps. Any estimate of population density which ignores this fact may be subject to very large errors, especially where small plots are trapped. Blair (1941 b) and Stickel (1946) have used differing methods for correcting the actual area under traps according to values of home ranges judged from the trapping records. It is clear that the usefulness of such techniques depends at least in part upon the reliability of the home range measurements.

Effects of heptachlor-contaminated earthworms on woodcocks

The effects on woodcocks (Philohela minor) of eating heptachlor-contaminated earthworms were studied experimentally in a series of feeding trials in Louisiana in the winter of 1960-61. Six of 12 woodcocks fed worms which had been contaminated at an average of 2.86 ppm of heptachlor epoxide died within 35 days; 4 more had died by the fifty-third day, when the other 2 were killed for analysis. Worms from areas in Louisiana treated with 2 pounds of heptachlor per acre often contain more than 3 ppm of heptachlor epoxide. Eleven of 12 woodcocks fed worms contaminated at an average of 0.65 ppm survived the full 60 days of the experiment; one died on the forty-fifth day, apparently from other causes. All 11 untreated birds survived. Survivors were kept on one-quarter rations of untreated worms for 11 days. Two woodcocks, untreated previously, died during this starvation period. Five previously treated died; two were observed in spasms at death, and these contained 5.9 and 7.2 ppm heptachlor epoxide in their tissues, suggesting that the previous contaminated diet may have influenced mortality, even though the difference between two of nine dying and five of nine dying is not statistically significant. Surviving starved birds given an unrestricted supply of treated or untreated worms for 5 days survived and gained weight. Residues accumulated in their tissues in this time approached levels in birds that died of heptachlor poisoning. Residues in tissues of birds with different histories suggested residue loss at a rate of approximately 2.8 percent per day. Toxicant absorption was estimated to be in the approximate range of 16-20 percent. Residues in birds fed worms containing 0.65 ppm heptachlor epoxide were in the same general magnitude as those in field-caught birds, suggesting a similar average contamination of food supply. Weights and weight changes did not differ significantly between untreated birds and those receiving the lower level of toxicant. Among birds on one-quarter rations, the percentage of weight that could be lost without danger seemed to be near 20 percent. Woodcocks ate 18-208 grams of worms per day (average, 121 grams), representing 11-143 percent (average, 77 percent) of their body weights; birds ate contaminated and uncontaminated food in essentially equivalent amounts. Symptoms of heptachlor poisoning differed considerably between birds. The program initiated in 1958 for control of the imported fire ant (Solernopsis saevissima) created active concern for the woodcock population of North America, for most American woodcocks winter in the Gulf States, where 27 million acres were scheduled for treatment with heptachlor or dieldrin at the dangerous rate of 2 pounds