Reproduction and Nesting of the Endangered Ringed Map Turtle, Graptemys Oculifera, in Mississippi

Chelonian Conservation and Biology, 2006, 5(2): 195–209 Ó 2006 Chelonian Research Foundation Reproduction and Nesting of the Endangered Ringed Map Turtle, Graptemys oculifera, in Mississippi ROBERT L. JONES1 1Mississippi Department of Wildlife, Fisheries, and Parks, Museum of Natural Science, 2148 Riverside Drive, Jackson, Mississippi 39202 USA [[email protected]] ABSTRACT. – Reproduction and nesting in the ringed map turtle (Graptemys oculifera) were investigated in the Pearl River of west-central Mississippi in 1995 and 1996. Nesting occurred from mid-May until mid-July but peaked in mid-June. Minimum carapace length of females at sexual maturity was 130 mm, but mean size at maturity was between 130 and 140 mm. Mean and modal CSs were 3.7 and 3. Larger females were gravid earlier than smaller ones and both egg and CS declined as the nesting season progressed. CS was positively correlated with both female carapace length and body mass. Mean egg length, width, and mass were 38.8 mm, 22.7 mm, and 11.8 g, respectively. Hatchlings averaged 35.5 mm carapace length and 8.9 g in mass. Annual clutch frequency may range from 0.96 to 1.42, and a minimum of ca. 60% of females reproduced on an annual basis. Predators destroyed an average of 86% of nests each year. Major vertebrate nest predators were armadillos, raccoons, and fish crows. Invertebrate egg predators destroyed an additional 24% of eggs known to be fertile. KEY WORDS. – Reptilia; Testudines; Emydidae; Graptemys oculifera; turtle; female body size; CS; clutch frequency; egg size; nesting; nest predation; Mississippi; United States Many turtles of conservation interest are inhabitants of ling size, nesting season, the incubation period, nesting rivers, but as Jackson and Walker (1997) pointed out, we success, and nest predation in the species. know less about the ecology of riverine turtles than of almost any other chelonian group. Graptemys, with 12 METHODS described species, is a genus of small to medium-sized turtles that inhabit rivers and streams of Gulf of Mexico The study was conducted on the Pearl River near drainages in central and eastern North America (Ernst et al. Ratliff Ferry, Madison County, Mississippi (Fig. 1), an 1994). One of these, the ringed map turtle (Graptemys area previously identified as having a high density of G. oculifera), is restricted to the Pearl River watershed of oculifera (Jones and Hartfield 1995). The river at the study Mississippi and Louisiana, where it occurs primarily in the site ranged from 40 m in width in side channels to main channels of the Pearl River and its largest tributary, approximately 200 m in bendways. Water depths ranged the Bogue Chitto River. Although G. oculifera has been from , 2to. 9 m. The 30-year (1962–1992) average discharge of the Pearl River at Jackson (ca. 45 km listed as a threatened species by the US Fish and Wildlife downstream) was 4627 cubic feet per second (Plunkett et Service since 1986 and is listed as endangered by the al. 1993). Highest flows occurred in March and April, and IUCN Red List (IUCN 2004), little information is lowest in September. The highest mean monthly temper- available on its nesting biology and reproduction. atures recorded over a 54-year period (1939–1993) at Females mature at a relatively small size (115–120 Jackson International Airport, ca. 38 km southwest, mm plastron length) and at a relatively late age (10 years) occurred in July and the greatest precipitation occurred (Jones and Hartfield 1995). Cagle (1953) described a in March (Ruffner and Blair 1981; Wood 1996). nesting attempt and provided data from a gravid female Females were captured in open-topped traps, con- indicating that she would have produced 2 clutches in a structed of either 1-inch nylon mesh in a metal frame, 1- season. Anderson (1958) briefly described the locations of inch poultry netting, or 5 3 10–cm wire mesh, which were nests on a sandbar in the Pearl River and provided attached to limbs and logs used as basking sites by the information on the movements of hatchlings at emergence. turtles. Trapping began on 1 May in 1995 and 30 April in Kofron (1991) examined a series of museum specimens 1996 and continued until no gravid females were present and concluded that ovulation and nesting occurred from in weekly samples and/or nesting was no longer observed May through July, that hatching occurred in August, and in the study area. Approximately 15 traps were used each that CS (CS) was 2–3 eggs. Given the paucity of data on day for 4 days during each week of sampling. reproduction in G. oculifera and its conservation status, Captured turtles were permanently marked by drilling the objectives of this study were to acquire information on holes in the marginals using Cagle’s (1939) numbering female body size, CS, clutch frequency, egg size, hatch- system. Straight-line carapace length (CL) and maximum 196 CHELONIAN CONSERVATION AND BIOLOGY, Volume 5, Number 2 – 2006 Figure 1. Map of the study area on the Pearl River, Mississippi. The numbered areas are the 11 sandbars monitored for Graptemys oculifera nesting activity. The inset shows the location of the study area in west-central Mississippi. plastron length (PL) were measured to the nearest nests found in the absence of females were from ca. 2 to 12 millimeter with aluminum timber calipers. Midline hours old. Nests were excavated and for each egg the plastron length (MPL) was measured to the nearest 0.1 following was recorded: egg length (EL) and egg width mm with dial calipers. Body mass (BM) was measured to (EW), both measured to the nearest 0.1 mm, and egg mass the nearest gram using a portable electronic balance. (EM), measured to the nearest 0.1 g. Eggs were then Females were palpated and gravid individuals were reburied in the nest cavity. Nest sites were plotted on a transported to a veterinarian for radiography (Gibbons and scale map of the sandbar and keyed to numbered Greene 1979), which was used to determine CS and clutch aluminum tags attached to nearby trees. Both distance frequency. Gravid females found while attempting to nest and compass bearing from the tags were recorded to were measured and marked but were not X-rayed. facilitate relocation of the nests. Eleven sandbars were monitored for nesting activity Physical characteristics of G. oculifera nest sites were by G. oculifera (Fig. 1). Available nesting habitat, measured for intact nests and when females were measured using a hipchain, was considered to be the area discovered while nesting. These included straight-line between the river and the treeline at the top of the bar. distances of the nest site from the river and to the closest Both the percentage of vegetative cover and open sand on vegetation, whether the latter was herbaceous or woody, each bar were estimated by point counts. Most sandbars in the study area were used for camping by recreational the number of both herbaceous and woody stems within a boaters for at least part of the nesting season. This 0.5-m circle centered on the nest site, the percent shade at occurred sporadically during the week and was greatest on 1 m above the nest site as determined with a concave weekends and major holidays. Human presence on the 11 densiometer, soil particle diameter determined using a soil monitored sandbars was recorded daily during the week grain sizing folder (Forestry Suppliers No. 77332), and throughout the 1996 nesting season. substrate type (sand or sand/soil mixture). Nest cavity I surveyed sandbars several times each day for intact depth and diameter were measured when no alteration of nests, which were located either by direct observation of these dimensions had been made while excavating the nest nesting females or by following tracks to nest sites. Given cavity. Substrate temperature at the nest site and air the frequency with which sandbars were surveyed, most temperature 1 m above the substrate in both open and JONES — Reproduction and Nesting of Graptemys oculifera in Mississippi 197 shaded conditions were measured when females were plastic trays filled with moistened vermiculite. Trays were encountered while nesting. placed in circulated-air incubators (Hovabator Model Temperatures were monitored for 10 nests in each 1583) at 28.58–29.58C and misted weekly to reduce year of the study with a HOBO-XT7 data logger (Onsett evaporative water loss. CL, PL, and BM were measured Computer Corporation) attached to a 1.8-m cable with a for all hatchlings upon emergence from the nest cavity or thermistor probe. The data logger was sealed in a plastic after yolk absorption in lab-incubated turtles. Hatchlings container and buried ca. 1 m from the nest cavity with the were then released near the sandbar from which the eggs probe inserted at the approximate midpoint of the clutch. originally came. Data loggers were programmed to record nest tempera- Statistical tests were performed using Statistica tures at the same time each day at 48-minute intervals (30 (Statsoft, Inc. 1999). Variables were transformed to their measurements/day) throughout the incubation period. natural logarithms where appropriate to meet the assump- Nests were caged in plastic mesh, which prevented tions of parametric tests. Comparison-wise error rates were predation and permitted an investigation of the incubation set at alpha ¼ 0.05. Sequential Bonferroni adjustments for period. The mesh was folded into an open box and buried multiple comparisons were calculated as in Rice (1989) open-side down over the clutch ca. 3 cm below the soil with an experiment-wise error rate set at alpha ¼ 0.10 surface.

Load more