REPORT OF ACTIVITIES 2009 TURTLE ECOLOGY RESEARCH REPORT Crescent Lake National Wildlife Refuge 3 to 26 June 2009 A report submitted to Refuge Manager Mark Koepsel 17 July 2009 John B Iverson Dept. of Biology Earlham College PURPOSE: To continue studies of the natural history and population biology of the turtles on the Crescent Lake National Wildlife Refuge, and the spiny softshell turtle near Blue Creek on the Peterson Ranch north of Oshkosh. METHODS: We did not erect our drift fences at Gimlet Lake this summer. Instead, we deployed fyke net arrays in Island Lake to sample snapping turtles (after nesting season), and we visually monitored nesting areas for painted turtles at Gimlet Lake and snapping turtles at Gimlet and Island Lakes. CLIMATE BACKGROUND: Spring (April-June) was only slightly below normal in temperatures, but was the wettest spring in 40 years (13.09 total; 2005 was the next wettest with 12.87 ; normal, 7.72 ). June was particularly wet, with 6.78 (the wettest June in 40 years). The rainy, cloudy, cool weather delayed turtle nesting this year. RESULTS: NESTING: Snapping turtles The snapping turtle nesting season was later than normal this year because of the cold spring (Table 1). At Gimlet Lake, we recorded 23 nesting snappers (14 of them previously marked). Since 1981 we have now marked a total of 56 Gimlet Lake female snappers as they nested. We have rigorously monitored nesting at Island and Gimlet Lakes over the past several years (Table 2). The very obvious jump in nesting activity at Island Lake (but not Gimlet) in 2007 is evident, and is probably related to the draw-down and renovation of Island Lake in the fall of 2006. However, it is not clear why that would double nesting activity in 2007, but then return to normal the very next year. One hypothesis is that the draw-down concentrated fish for snappers
to eat, and the increased food availability to snappers in the fall of 2006 resulted in improved nutritional status in females, and hence a greater proportion of the females nested the following summer. The return to normal in 2008 would thus reflect a return to normal nutritional levels and normal nesting frequency rates (i.e., more females were skipping reproduction in a given year). Table 1. Variation in nesting season and reproductive output of Nebraska snapping turtles at the CLNWR. Year Nesting season (n) Mean date Clutch size range (n) Clutch size mean ----------------------------------------------------------------------------------------------------- 1990 11-28 June (7) 18 June 37-73 (6) 54.8 1993 12-28 June (36) 20 June 29-71 (23) 48.3 1994 1-13 June (32) 6 June 31-72 (28) 45.4 1998 6-23 June (14) 11 June ------ --- 1999 4-22 June (29) 8 June 9-82 (27) 51.5 2000 29 May-12 June (21) 7 June 37-76 (19) 55.9 2004 29 May-15 June (15) 6 June 35-71 (12) 56.7 2005 7-21 June (36) 14 June 12-76 (33) 49.6 2006 1-11 June (29) 4 June 26-66 (24) 43.2 2007 28 May-14 June (91) 7 June 22-71 (32) 43.7 2008 15-25 June (54) 20 June 20-79 (44) 44.4 2009 11-24 June (65) 18 June 5-71 (39) 45.9 The number of nesting snappers at Gimlet Lake appears to be increasing (Table 2). This suggests 1) an increase in nesting frequency by individual females 10-15 years ago, 2) an increase in nest success at that time, and/or 3) an increase in females produced in eggs due to warmer incubation temperatures in the mid to late 1990s. As usual, this year coyotes and raccoons destroyed nearly every nest we identified (and many we didn t!). Table 2. Numbers of nests observed at three nesting areas over the past few years. Asterisks indicate locations not rigorously monitored. The Gimlet Lake site is along the Dike Road. Year Gimlet Island West Dock Island South Dock --------------------------------------------------------------------------- 2005 16 0* 2* 2006 9 7 11 2007 15 20 28 2008 21 4 11 2009 28 10 9 We also processed 10 female snappers at the South and West Docks at Island Lake during their nesting activities. Three of them were recaptures, including one (#101) originally marked after nesting at Gimlet Lake in 2005 and recaptured at Gimlet after nesting in 2007. On 17 June this year she was captured after she nested at the West Dock of Island Lake! Whether this represents
a long-distance dispersal event, or an accidental (mistaken) relocation of this turtle last year is uncertain. Last June we held snappers (for later release) caught in fyke nets at Island Lake in a large cattle tank near the Shop. It is possible that one of the seasonals saw #101 on a nesting foray, assumed it was an escapee from the tank, and mistakenly put it in the tank (from which it was later accidentally released in Island Lake). Once again this year we deployed six fyke nets in a nearly continuous line parallel to the shore and in about 2 of water off the West Dock of Island Lake (20-24 June). Fyke net traps were baited with pieces of carp provided by the NE Game and Parks Commission. Traps were checked and rebaited each morning between 6 and 8AM, and again between 3 and 4PM. We captured only 18 (11 males; 7 females; including five recaptures, compared to 27 in the same setting last year. The lower capture rate may be due to the much higher water levels this year. We noted that the metal tags were loose on several turtles, and that tags were missing (but screw openings still obvious) on others. This problem will compromise population estimates in the future. POPULATION ESTIMATES As I reported last year, estimating the number of snappers in a lake as large and complex as Island Lake is a difficult challenge. However, between my trapping efforts and nest site monitoring, and mark-recapture efforts of Refuge personnel during Avian Influenza surveys, our confidence in population estimates is increasing. For example, between 18 June and 29 October 2008, 145 snappers were tagged in Island Lake (103 by Marlin French, and 43 by me), and 87 were removed from the lake. During airboat surveys (presumably a random method of resampling) in 2009 (13 April to 1 July), 35 snappers were captured, including 10 originally marked in 2008. Using a simple Lincoln Index, this suggests that about 508 subadult and adult snappers [(145x35)/10] were in Island Lake in 2008 (in addition to the 87 removed). If ALL captures in 2009 are included (from my fyke nets and from nesting surveys), the total 2009 captures were 63 individual snappers, of which 17 were recaptures from 2008. This would suggest that 537 [(145x63)/17] subadults and adults were alive in 2008 (plus the 87 removed). These estimates of about 600 snappers are at the low end of the preliminary estimates generated last year (see 2008 report). However, during the fall of 2009, when water levels are lower and the water more clear, Marlin French intends to do a final intensive sampling effort for 2009. With those data in hand, we will do some more sophisticated population modeling in order to estimate population size and its variance more confidently. March 2009 Painted turtles Thirty-seven painted turtle nests that had been located around Gimlet Lake in June 2008 (and covered with wire mesh to discourage predators) were excavated to determine hatching and
winter survival rates through March 2009. In March, 14 of these (38.7%) were empty (presumably depredated by hognose snakes) and four others had only partial clutches of 1 to 6 eggs left after partial depredation by hognose snakes. With an average clutch size of about 12 eggs, 37 nests had the potential to produce 444 hatchlings! However, only 246 total eggs (from 23 nests) were accounted for in the excavated nests, and 143 of those had hatched (58.1%; compared to 84.5% in the previous year and 47.5% the year before that), and 110 of those were still alive in nests in March (44.7%; compared to 57.7% and18.2% over the last two years). Thus, 143 hatchlings began the winter alive, but only 110 survived the winter (76.9%; 68.3% and 39.7% over the previous two winters). This suggests that even in our protected nests only about 25% (110/444) of eggs laid produced hatchlings that survived the past winter. Of course, these hatchlings would still have had to dig out of the nest and migrate safely to the water. We saved them that peril by releasing them at the edge of the water just southwest of Marlin s house. The first year of the life of a painted turtle is not an easy one! The coldest nests with surviving hatchlings in March had fallen to temperatures of -11.9 to - 12.9C over the winter, but minimum nest temperature during the winter averaged -9.1C in 34 nests (data loggers died in two nests and a mole apparently carried another away). The two warmest nests (minima of only -5.6C and -4.7C) were on the exposed slope just southeast of the shop (with maximum exposure to the winter sun and protection from northwest winds). June 2009 Reflecting the cold, rainy start to June, the first nesting female painted turtle for the month was located on 6 June and the second on 12 June. Nevertheless, over the next two weeks we captured 44 females (13 previously unmarked) during their nesting forays. Higher than usual activity after 4PM in the shop area resulted in more disturbance of females, which returned to water without nesting. Hence, fewer nests (32) were located than expected given female activity. Close monitoring of covered nests each day allowed us to relocate four hognose snakes before they destroyed the nests, although two covered nests were still breached by snakes. For comparison, last year we lost part or all of 18 nests to hognose snakes (of 37 total). We mapped all 32 nests for over-winter monitoring, and a miniature temperature logger was buried next to each nest to record nest temperatures through incubation and through the coming winter. As in the past, these nests will be excavated next March (2010) to determine hatchling and overwintering success. Yellow mud turtles and Ornate box turtles Because of our time commitment to painted and snapping turtles, we did almost no work with either of these species this summer. However, we did pick up and freeze carcasses from box turtles found dead on the road. These were sent to Dr. John Placyk of the University of Texas at Tyler.
Spiny softshell turtles We trapped for softshell turtles for ten days (5-16 June) in the Blue Creek drainage near the Myron and Kay Peterson ranch (Campstool Cattle Company, NNE of Oshkosh), but captured only three adult females and two juveniles (all recaptures from previous years) in Rattlesnake Pond in our six 50 fyke net settings. Though the population in this pond is small, we are slowly accumulating important information on growth and reproduction.