Radiata2008(3)e

Herbert Meier & Ingo

Herbert Meier & Ingo Schaefer Clutch sizes range from 8 to 30 eggs. These are hard-shelled and ball-shaped, resembling table tennis balls, with diameters of 35-39 mm and weights of 35-40 g (comp. Meier & Schaefer 2003a, b). In the wild, oviposition and hatching of baby matamatas are closely correlated to water levels, which in turn are a function of the rainy seasons. The eggs are laid after the rainy season has ended and water levels begin to recede (September/October). The first hatchlings emerge around the onset of the next rainy season (April/May). Oviposition usually takes place at night, or at least late at dusk, at a spot very close to the water. There seem to be no particular requirements for the nesting spot either with regard to the substrate or the degree of insolation. The matamatas in the care of Schaefer (1986) laid all their eggs in the late evening hours of the months of October/November. They were always buried some 15-20 cm deep and subsequently covered. The turtles kept by Meier buried their clutches up to 25 cm deep, but did so at dawn, in one instance even during the early morning hours. A second clutch often follows about eight weeks later. The number of eggs in that second clutch is usually distinctly lower (8-12) than in the first one. A female of the senior author’s buried a clutch of altogether twelve eggs in the terrestrial section intended for this purpose in 2001. This event was preceded by two eggs that were dropped in the water. These showed an oval shape that was entirely atypical for Chelus fimbriata, and they later turned out to be infertile. Actual oviposition must have taken place in June of 2001, but remained undetected until January of 2002. It was only during a search for eggs from an Emydura subglobosa subglobosa that the clutch was accidentally discovered. The terrestrial part is heated only in an indirect manner by the surrounding water of the tank, which causes the substrate temperature to drop constantly to about 24 °C during winter. Substrate moisture levels vary substantially as well. All twelve eggs had meanwhile perished and smelled very intensely. They were opened nonetheless, revealing that the yolk was still clearly separated and had a fresh yellow colouration in some of them. Most, however, only contained stinking sludge. Five eggs had been fertile, and two had started developing, evidence of which was present in the shape of embryos of 1-2 cm in length that were at an advanced stage of decomposition (comp. Meier & Schaefer 2003a, b). Another oval egg was found in the water in June of 2002. It also turned out to be infertile. Palpation of the adult females identified one that was obviously containing several follicles. A total of nine eggs were then buried in the moss-filled terrestrial section during the night from 19. to 20.07.2002. The moss had been kept slightly moist over the preceding weeks. On 23.07., it was noted that the substrate of the terrestrial section had again been overturned, and a search yielded another twelve eggs. Further eggs A third female – sexually mature but still very young (about eight years of age) - that had joined the group in November of 2002, dropped five eggs into the water over a period of two weeks in mid-January 2003. The eggs were small, almost round, with diameters of 28-29 and 31-33 mm, respectively, and weights of 16 g. They were heavily overcalcified, which provided them with a surface as coarse as sandpaper (Meier & Schaefer 2003a, b). In late January, Meier noted that the moss of the terrestrial section had been dug over during the previous night. He smoothed the surface and marked it. Digging in the terrestrial section continued every night until 08.02., even though no eggs could be felt in any of the matamata or river turtle females so it remained uncertain which specimen was responsible for the nightly digging. In the afternoon of 09.02., the matamata female that had been added last 30 RADIATA 17 (3), 2008

The Matamata, Chelus fimbriata was seen trying to climb on land. However, she was disturbed and fled back into the water. On 10.02., the moss was found to have been disturbed once more. This time, however, checking revealed ten normally shelled eggs at a depth of about 15 cm. These corresponded in both dimensions and weights to those found in the water earlier. They were transferred to a styrofoam incubator, but subsequently turned out to be infertile. The brief acclimatization period and the young age of the female might have been reasons for this. A routine palpation on 29.03.2003 revealed that both of the two older females contained follicles. Like in previous years, (three) oval eggs were then found in the water on 05.05.2003. Their shells were so thin and fragile that they weighed only 28 g each although they measured up to 51 × 31 mm. The abortion of oval eggs in the water a few days to a week before oviposition had also been observed by Schaefer (1986). In the early morning hours of 05.05.2003, one of the females was seen excavating a nest pit. She started laying her eggs around 08.30 h and was finished within just a few minutes, but the subsequent closing of the pit then took more than an hour. Two of these eggs already showed a distinct white germination spot each, and within four days, these spots were visible in altogether five eggs. They were joined by a sixth egg another two days later. Around the end of May of 2003, the second older female began with the excavation of “test nests” and continued for two weeks. She aborted one oval infertile egg each in the water on 01.06. and 06.06., respectively. Oviposition then eventually followed during the night of 12.06.2003. First indications of fertility showed after six days. The first female laid another sixteen eggs in the early morning hours of 18.06. of which at least nine later proved fertile. Yet another and totally unexpected clutch was produced on 02.08., but since the terrestrial section had not been prepared, the eggs were dropped in the water. Twelve more eggs were then buried on land on 18.08.2003. Incubation Incubation periods are commonly given as 180-200 days (comp. Meier & Schaefer 2003a, b). Schaefer (1986) had a baby hatching after 194 days, Hausmann (1964) recorded 200-207 days, but in the case of McCord (in litt.) hatching occurred only after about 300 days. In nature, incubation periods are probably much shorter than 180 days (see above). The major differences in incubation periods and the almost always very low numbers of hatchlings suggest that incubation conditions have so far been suboptimal. Because the eggs are often buried only superficially in the wild, temperatures and temperature fluctuations would seem to be of lesser importance for the incubation success, as long as the minimum temperatures required for the development of the eggs are present. A more influential factor could be the degree of substrate moisture, though. McCord (in litt.) incubates Chelus fimbriata eggs in moist, slightly acidic moss. An incubation temperature of 29 ± 1 °C is viewed as ideal. Substrate temperature measurements taken in the south of Venezuela in February ranged from 28 to 31 °C at a depth of 12 cm. Even in a fully shaded spot on a rainy day, a value of 27,4 °C was recorded. The lowest values were measured at the time of predawn, and the highest during the afternoon and evening hours. Differences in temperature between measurements taken in the afternoon and evening were only noted in conjunction with rain. Schaefer (1986) incubated his matamata eggs in an incubator according to Budde (1980), at temperatures of 28-30 °C and 100 % relative humidity. The substrate specified in his publication of 1986 was subsequently exchanged for moist moss (Meier & Schaefer 2003a, b). One possibility for improving hatching ratios, aside from enhancing the quality of the food RADIATA 17 (3), 2008 31