Degree Name

Master of Science (MS)

Semester of Degree Completion

1980

Thesis Director

Edward O. Moll

Abstract

The effect of heating on aquatic ecosystems by energy producing power plants has not been fully determined. A comparative study of the reproduction of Pseudemys scripta was conducted in heated and natural lakes in southwestern Illinois from 30 March to 10 July, 1979. Lakes used were the same as those used for comparative growth studies of P. scripta by another researcher. Lake Baldwin (heated) has had a reduction in vegetation since that researcher's work. Temperatures were taken of air, water surface, and one meter deep.

Turtles were caught by hand, trammel nets, and in carp-baited hoop nets. Captured turtles were weighed and measured. Turtles not dissected were marked and released. Some females eventually released were injected with a synthetic oxytocin to induce egg laying. Turtles to be dissected were kept in a cooler until dissection.

Oviducal eggs were weighed and egg width and length were measured. Ovaries were examined for corpora lutea which were used to determine previous clutches of the season, and size of the clutches. Follicles 10mm, or greater, in diameter were used to determine maturity, and number of potential clutches for the year.

Water temperatures were always warmer in Lake Baldwin. In March the temperature was more than twice that of control lakes (17.5 to 8°C). Throughout the summer temperatures remain 4-6 degrees warmer.

Lake Baldwin females matured around 185mm plastron length (age of three years), while control females matured at 180mm plastron length (age of four years). Males from both areas matured in one year, at 100-110mm plastron length.

Lake Baldwin females laid larger and more clutches per year than control females, but not significantly so. However, reproductive potential was significantly larger in Lake Baldwin. Clutches per year had a significantly positive correlation to plastron length, carapace length, carapace width, carapace height,and body weight in control but not Lake Baldwin females. Clutch size had a significant positive correlation to plastron length, carapace length, carapace width, and carapace height in both populations. Control female body weight had a significant positive correlation to clutch size, but Lake Baldwin female body did not.

Male reproductive cycles appeared unchanged by thermal effluent. The female reproductive cycle has changed presumably due to the warming of Lake Baldwin, and from the change in productivity of the lake. Warmer water has probably increased the metabolic rate. This enables clutches to develop faster, resulting in more clutches per year. Nesting season in Lake Baldwin appeared to be from 2 May to 4 July, while in control females it was from 23 May to 13 July.

Clutch size has also apparently increased in Lake Baldwin females causing egg shape to change. Eggs weighed the same in the two areas, but were wider from Lake Baldwin than from control lakes.

The disappearance of aquatic macrophytes in the past five years may be affecting the reproduction of Lake Baldwin turtles, since plants are the main food of adult P. scripta. Evidence of food shortages would be expected to appear in reproductive output if plants continue to be the main food in adult P. scripta diets. Evidence of food shortages were reductions in clutch size, number of clutches, reproductive potential; an enlargement of egg yolk size; and evidence of atretic follicles when comparing 1979 with 1975 data. Therefore, reproductive potential has been increased by heated effluent, but currently appears to be decreasing due to food shortages.

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