Vol.XLV. September, 1923. No. 



BIOLOGICAL BULLETIN 



THE GROWTH OF THE PAINTED TURTLE. 



A. S. PEARSE, 

 ZOOLOGICAL LABORATORY, UNIVERSITY OF WISCONSIN. 



As Agassiz (1857) pointed out, the growth of turtles is exceed- 

 ingly slow. After comparing turtles of different sizes, Agassiz 

 concluded that the eastern painted turtle (Chrysemys picta), 

 after the eggs from which it hatched w T ere laid, attained about 

 the following lengths after one year: 26.5 mm.; 2:42; 3:51; 4:54; 

 5:59; 6:66; 772.5; 8:74; 9:77; 10:80; 13:92; 24:121. He affirms 

 that this turtle does not lay eggs until it has attained an age of 

 ten to eleven years. Lucas (1922) states that there are authentic 

 records of tortoises that have lived to be one hundred and fifty 

 years old. Barney (1922) has given a very careful account of the 

 growth and breeding of the diamond-back terrapin when reared 

 under cultural conditions in pens. He found that when domestic 

 terrapins are fed during the winter, egg production occurs as 

 early as the fourth year of age, but usually begins in the fifth or 

 sixth year. Terrapins may reach a length of 130 mm. to 150 mm. 

 in four years when fed in winter, and in six to seven years when 

 allowed to hibernate. The maximum growth in length recorded 

 for one year was 81 mm., and for two years 104 mm. 



Since 1919 the writer has had opportunity to study the growth 

 of the western painted turtle. 1 At various times, 406 turtles 

 were marked with aluminum tags and immediately released in 

 University Bay, Lake Mendota. These were measured when 

 they were released and were caught at intervals and measured 

 again. In this way the rate of growth was determined. The 

 portion of the bay behind the bar, where the turtles were studied, 

 is nowhere more than 1.5 meters in depth, has a soft, muddy 



1 Ruthven's (1912) Chrysemys belli Gray and C. cinera (Bonnaterre) appear to 

 intergrade in this locality, but a majority of the individuals resemble the former. 



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