. The Canadian field-naturalist. 128 The Canadian Field-Naturalist Vol. 96 {Spirodela sp. and Lemna sp.) and waterweeds {Ege- ria densa). The most common aquatic insects are hemipterans (Pelocoris sp., Belostoma sp. and Rana- tra sp.) and dragonfly nymphs. Other turtles in the bayou include the Red-eared Slider, Pseudemys scripta elegans, the Missouri Slider, Pseudemys flori- danahoyi, the Spiny Softshell, Trionyx spiniferus, the Musk Turtle, Sternotherus odoratus, and the Snap- ping Turtle. Methods Turtles were captured by hand or dip net, and in baited funnel traps. Sex was determined by dis
. The Canadian field-naturalist. 128 The Canadian Field-Naturalist Vol. 96 {Spirodela sp. and Lemna sp.) and waterweeds {Ege- ria densa). The most common aquatic insects are hemipterans (Pelocoris sp., Belostoma sp. and Rana- tra sp.) and dragonfly nymphs. Other turtles in the bayou include the Red-eared Slider, Pseudemys scripta elegans, the Missouri Slider, Pseudemys flori- danahoyi, the Spiny Softshell, Trionyx spiniferus, the Musk Turtle, Sternotherus odoratus, and the Snap- ping Turtle. Methods Turtles were captured by hand or dip net, and in baited funnel traps. Sex was determined by dissection, or by the presence of elongated foreclaws and pre-anal tail regions in mature males (Cagle 1954; Gibbons 1968; Moll 1973). Enlarged ovarian follicles (> 10 mm) were used as the criterion for sexual maturity in females (Cagle 1954; Gibbons 1968; Moll 1973). Plas- tral measurements, made with vernier calipers, included total plastron length (L), abdominal scute length (C), and lengths of discernible annuli on the abdominal scute {C^). These measurements were used to calculate plastron lengths at the time of annulus formation (Cagle 1954; Ernst 1971), according to the formula L,/L =C,/C. Calculated plastron lengths were used to construct Walford plots of growth (Walford 1946). These plots provide a graphical description of the relationship between length in one season and that in the previous season. The relationship is linear when length approaches an asymptotic value smoothly, following the Bertalanffy growth model (Poole 1974). This model approximated female growth closely and linear regression lines were fitted by least squares to the female data. The linear model was considered inap- propriate for males, since their growth slowed more abruptly near maturity, causing non-linear trends in residuals (Durbin-Watson test, ). Results In Manitoba, 39 seasonal growth increments were calculated from 22 captured turtles (12 males, 10 females), and food was recovered fr
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