Return to Conservation Biology Research on Reptiles
Pappas, M.J., J. Congdon, and A. Pappas. 2001. Weaver Bottoms 2001 turtle survey; management and conservation concerns. Report submitted to the Nongame Wildlife Program, Minnesota Department of Natural Resources. 28 pp.
Summary:
- The current survey suggests that the populations of six of the eight species of turtles inhabiting Weaver Bottoms are being impacted negatively. Populations with large adults missing and highly biased sex ratios suggest harvest damage (Chelydra, and both Trionyx). Depressed populations and fragmented population structure are symptomatic of habitat destruction (Trionyx muticus, Emydoidea, Graptemys ouachitensis, and Graptemys geographica). Chronic reduction in the survival of adults through over harvesting or habitat loss, requires increased recruitment and survivorship of juveniles to maintain population stability. The probability that juvenile survivorship could increase enough to compensate for adult mortality is very low considering the degradation of habitat in the Weaver Bottoms.
- The five areas sampled in Weaver Bottoms were well vegetated and were picked to represent the best turtle habitats available. Due to the limited number of traps, open areas were not sampled.
- (Location information removed to protect rare turtle populations) There was no evidence of recruitment of hatchling or young juveniles into the population in Weaver Bottoms.
- Eight species of turtles were capture in Weaver Bottoms: two softshell turtles (Trionyx muticus and Trionyx spiniferus); three map turtles (Graptemys ouachitensis, Graptemys geographica, Graptemys pseudogeographica); two emydid turtles (Emydoidea blandingii and Chrysemys picta belli); and the common snapping turtle (Chelydra serpentina).
- Four of the species appeared to be well represented (Chelydra serpentina, Trionyx spiniferus, Graptemys pseudogeographica, and Chrysemys picta belli); two species were less well represented (Emydoidea blandingii, Graptemys geographic); and two species were rare(Graptemys ouachitensis, Trionyx muticus).
- Three species are directly harvested for meat (Chelydra serpentina, Trionyx muticus, and Trionyx spiniferus), and all three species are also at risk of being captured and drowned by set lines used for commercial fishing. Chelydra and Trionyx spiniferus appear reduced in numbers because of harvesting pressures.
- All Spiny Softshell females over 210 mm that were captured in Weaver Bottoms were females. Females may not reproduce until they are 255 and 285 mm in carapace length (Webb, 1962). Breckingridge (1955) indicated that it takes 15 to 20 years for a spiny softshell female to reach 300 mm. This data would suggest that almost all sizes of reproductive females are presently allowed to be harvested, and that the recovery time for a harvested female is considerable. The small proportion of reproductive-sized females (17% of the turtles captured) seems low and may be the result of harvesting pressure.
- Snapping turtles represented 7.4% of the turtle captures in the Weaver Bottoms; whereas Paisley (Wisconsin DNR Report, 1997-99) found in similar habitat at Pool #8 of the Mississippi River that snapping turtles made up 42% of the turtles caught. Adult sex ratios are strongly male biased (15 females per 100 males) in Weaver Bottoms (adult sex ratios in an unharvested population in Michigan is 1:1). Both the small percentage of snapping turtles present in the Weaver Bottoms, and their highly biased male sex ratio, suggest harvest damage. It appears to take snapping turtles between 10 to 12 years to reach harvestable size.
- Adult sex ratio of Chrysemys picta belli at Weaver Bottoms was male biased (5:1). One other population in Michigan has a male biased sex ratio (2.3:1) that does not result from trapping bias (Congdon, pers. comm). Some females appear to mature in Weaver Bottoms in 6 to 9 years at a carapace length of 145 to 160 mm. In Minnesota, painted turtles less than five inches in carapace length (130 mm) can be harvested with no limits. Based on the size restriction, 32% of the turtles sample could be harvested.
- Less than 3% of the aquatic habitat of Weaver Bottoms was surveyed. More baseline data needs to be collected through a longer and more intensive trapping regiment in order to accumulate enough information to draw up a multi-species management plan for the turtles of Weaver Bottoms.
Full document (2537 KB)
Please note that location information has been removed from this document to protect rare turtle populations.