Abundance and movement of the Texas diamondback terrapin in the Deer Island complex, Galveston, Texas

A total of 151 diamondback terrapins were captured on North and South Deer Islands between March 2008 and February 2009, including 12 recaptures. Nearly 60% of terrapin captures occurred within the channels that span the length of South Deer Island. The average terrapin catch per hour of effort was 1.2. The average recapture period was 92 days with travel distances ranging from 44 to 414 meters and averaging 169 meters. Greater population readings were found throughout April and May, while populations dramatically dropped from September 2008 through February 2009. Biological data collected on terrapins indicated a male to female sex ratio of 1.1 to 1. An average of 6 growth rings were counted on male terrapins and an average of 8 growth rings were counted on female terrapins. Females were significantly larger than males in all measurements. The average carapace lengths for male and female terrapins were 131.7 cm (SD=7.6) and 186 cm (SD=27.3) respectively. Mean plastron lengths for male and female terrapins were 111.1 (SD=6.4) and 164.2 (SD=21.4), respectively. The average male weight (.38 kg, SD=.07) was significantly smaller than the mean female weight (1.2 kg, SD=.36). Six terrapins were fitted with radio transmitters. One female on South Deer Island was tracked 30.9 meters away from her original capture location, 7 days later. Spartina alterniflora and Salicornia depressa were the two dominant vegetation types recorded near collected terrapins. No nesting behavior or nesting sites were discovered during this study.