Hillsboro Beach Pressure Equalizing Modules Experimental Project

Sea Turtle Monitoring Report

January 2010

Curtis M. Burney, PhD

Nova Southeastern University Oceanographic Center

Survey Personnel: Mieka Kalinoski, Teal Kawana, Nina Thompson, Patricia Waikel, Jessie Watters, Megan Wilson and Laura Wright; Nova Southeastern University.

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Table of Contents: List of Figures 2 List of Tables 2

Executive Summary 3 Introduction 3 Materials and Methods 4 Results 5 Discussion 11 References 12 Appendix 14 List of Figures Figure 1:Layout of temperature/humidity recorders 6 Figure 2: Numbers of loggerhead and green nests deposited per zone in the PEM and control areas areas. 8 Figure 3: Nesting success of loggerhead and green turtles in the PEM and control areas. 9 Figure 4: Emergence success of loggerhead nests in the PEM and control areas. 10 Figure 5: Comparison of sand temperatures at 12 inch depths in the north (PEM2) and south (PEM44) control area

with PEM32 in the project area. 11 List of Tables: Table 1: The individual numbers and placement of temperature/humidity sensors at the locations in

Figure 1. 7

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Executive Summary Sea turtle nest counts, nesting success and emergence success as well as sand temperatures were determined as part of the second year of monitoring of the Pressure Equalizing Modules (PEM) experimental project in Hillsboro Beach Florida, were a series 6 ft x 2.5 in. hollow perforated plastic tubes were installed vertically in the beach in order to lower the water table of the beach and allow more surface drainage, reducing the back swash from waves and allowing more sand to remain on the beach. The conclusions of the turtle monitoring were as follows.

• There was no evidence of a reduction of nesting in the PEM area. Loggerhead and green turtle nesting in the PEM area was similar to the south control area and higher than the north control area.

• There was no evidence of a consistent reduction in loggerhead

and green nesting success (nests / total crawls). Loggerhead nesting success was both higher and lower in some project areas than in the control areas.

• There was no evidence of a consistent reduction in loggerhead

or green hatchling emergence success in the PEM area. One-way ANOVA of 110 evaluated loggerhead nests showed no significant differences in PEM and control zones. The mean emergence success of the 4 evaluated green nests in the project area was 71 percent. No green nests were evaluated in the control zones.

• Only one temperature/humidity sensor was recovered from the

project area (R12) and it malfunctioned on 28 April, however the mean daily temperatures at this location during March and April were very similar to readings from the north and south control areas.

Introduction On February 25, 2008 a series of Pressure Equalizing Modules (PEMs) were installed in Hillsboro Beach by EcoShore Inc. in zones R9 through R12. These consisted of 6 ft x 2.5 in. hollow perforated plastic tubes placed vertically with the tops about 1-3 ft. beneath the surface.

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The purpose was to lower the water table of the beach by allowing water to drain to deeper beach levels, thereby reducing the back swash by allowing more water to drain into the sand. This should allow more of the sand carried onto the beach by the up swash to remain there, and thereby increase beach accretion. Materials and Methods

The beach was patrolled each morning from March 1 through September 30 as part of the Broward County Sea Turtle Conservation Project (BCSTCP) and during October by contract with EcoShore, Inc. Sea turtle nests and false crawls were found, identified to species and located by GPS and by Department of Environmental Protection (DEP) survey markers (R-zone). After hatching, a total of 110 loggerhead nests from the PEM project area and adjacent control areas were excavated for post emergence examination. The number of hatchlings that emerged on their own from each nest was determined as well as the numbers of live and dead hatchlings found in the nest, pipped eggs and unhatched eggs. Emergence success for each nest was defined as the number of naturally emerged hatchlings divided by the total number of eggs. Nesting, nesting success (nests/total crawls) and hatchling emergence success were plotted and analyzed for the PEM project area defined by Department of Environmental Protection survey monuments R9 – R12 in Hillsboro Beach, as well as for zones R5 - 6 and R13 -14 which served as controls. Temperature and humidity recorders (Lascar EL-USB-2 data loggers) were also placed in the beach on 25 February 2009, to see if the project caused changes in sand temperature that

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could potentially affect hatchling sex ratios (Mrosovsky and Yntema, 1980). The sensors recorded data every hour. Figure 1 shows the layout of the temperature/humidity recorders. They were placed on 8 transects at landward and seaward locations. Three recorders were placed at each location at depths of 6”, 12” and 24”. Table 1 gives the locations and numbers assigned to each recorder from 1-48. Attempts to recover the sensors were made during November, 2009, but only 8 could be found and only one was from the project area. Only one recovered sensor (PEM2 from the north control area) recorded until recovery. The recorder from the project area (PEM32) malfunctioned on 28 April. After downloading, average daily temperatures were calculated and plotted (Appendix). Results Figure 2 shows the numbers of loggerhead and green nests per zone in the PEM project area and the two adjacent control areas. Nesting is historically low in the north control zone so the south control area is more representative. Loggerhead nest counts increased from the north control area through the PEM area to the south control zones. Nest numbers from the center and southern sections of the PEM area were very similar to the south control area. Green turtle nesting was minimal in the project and control areas. Figure 3 gives nesting success results for the PEM and control zones. Loggerhead nesting success generally increased from north to south through the PEM area to values similar to the Hillsboro Beach average of 47.6 percent (Burney and Wright, 2010). The nesting success of green turtles was highly variable in the PEM area. Zones R 7 and R11 had zero values, which resulted from one false crawl

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and no nests in those areas. However, R9 received 3 nests with no false crawls and R12 had 9 nests with 1 false crawl. Figure 3 illustrates hatchling emergence rates for each evaluated loggerhead nest in the PEM and control areas. The zone averages are shown in red. A one-way ANOVA showed no significant differences throughout the project and control areas (P = 0.98). There were only 4 evaluated green nests in the PEM area and none in the control areas. Their average emergence rate in the PEM zones was 71 percent. Only two leatherback nests were evaluated in R 7 and R 11, which had emergences of 91 and 70 percent, respectively.

R 6

R 9

R 10

R 11

R 12

R 14

R 13

R 5

PEM

North Control

PEM

A – 6“

B – 12“

C – 24“

Layout of Temperature and Humidity Study

TH15 ABC TH16 ABC

TH13 ABC TH14 ABC

TH11 ABC

TH9 ABC

TH 7 ABC

TH5 ABC

TH 3ABC

TH 1 ABC

TH12 ABC

TH10 ABC

TH 8 ABC

TH 6 ABC

TH4 ABC

TH 2 ABC

T/H Loggers were installed on Feb 28, 2008

South Control

N

Feb 29,2008

Figure 1: The layout of the temperature/humidity recorders at landward and seaward locations along 8 transects in the North Control (R5-6), PEM Project Area (R9-12) and South Control Area (R13-14)

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454443TH 15 – R14

484746TH 16 – R14

424140TH 14 – R13

363534TH 12 – R12

393837TH 13 – R13

333231TH 11 – R12

302928TH 10 – R11

272625TH 9 – R11

242322TH 8 – R10

212019TH 7 – R10

181716TH 6 – R9

151413TH 5 – R9

121110TH 4 – R6

987TH 3 – R6

654TH 2 – R5

321TH 1 – R5

C – 24”B – 12”A – 6”Location and #

NC

ontro

lS

Con

trol

PEM

Layout of Temperature and Humidity Study

Table 1: The individual numbers (1-48) and placement of the temperature/humidity recorders at the locations in Figure 1.

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Figure 2: Numbers of loggerhead and green turtle nests deposited per zone in the PEM and North and South Control Areas.

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Figure 3: Nesting success of loggerhead and green turtles in the PEM and North and South Control Areas.

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Figure 4: Emergence success of each evaluated loggerhead and green turtle nest in the PEM and control areas with averages in each zone.

Figure 5 compares mean daily sand temperatures from sensor PEM32 in the R12 in the south end of the PEM area with sensors PEM44 in the south control area (R14) and PEM 2 in north control zone (R5). All of these sensors were initially buried at a depth of 12 inches in the sand. Sensor PEM2 provided continuous data from 1 March to 31 October. Sensors PEM32 and PEM 44 malfunctioned on April 28 (Julian 118) and 15 July (Julian 196), respectively. The relative humidity recorded by all recovered sensors rapidly increased and reached 100% between 9 March and 18 March. After that, all sensors recorded 100% relative humidity until sensor recovery or malfunction.

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Figure 5: Comparison of sand temperatures (C) at original depths of 12 inches at the mid beach stations at R12 in the PEM area (PEM32) with data from R5 in the north control area (PEM2) and from R14 in the south control area (PEM44).

Discussion Figure 2 shows that loggerhead nesting increased through the PEM project area from the historically low values in the north control area to the higher values in the south control zones. Nesting in the south half of the PEM area was not different than the south control area. The low number of green turtle nests make comparisons difficult, but the 9 nests deposited in R12 in the PEM area was the highest number of green turtle nests deposited in any zone in Broward County (Burney and Wright, 2010). Loggerhead nesting success (Fig. 3) also increased from north to south through the PEM area, with values in the southern PEM area that

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were similar to the overall average for Hillsboro Beach. Green turtle nesting success was highly variable in the PEM area, but some percentages from the PEM area were higher and lower than control values and there does not appear to be any systematic pattern that suggests that the PEMs were adversely affecting nesting success. The analysis of loggerhead hatchling emergence success (Fig. 4) found no significant differences between any of the PEM and control zones, suggesting that the PEMs did not adversely affect hatchling emergence. Overall, our results do not indicate that the PEM tubes had any negative impacts on sea turtles. Since only one temperature sensor was recovered from the PEM project area, conclusions are tentative, but during the early part of the turtle season, average daily temperatures recorded by PEM32 closely tracked the temperatures from PEM2 in the north control and PEM44 in the south control. Since there very small differences in mean daily sand temperatures between the control and project zones during March and April, this suggests that the PEM tubes were having no significant effect on sand temperatures, because they had already been in place for over one year, and any major effects should have already become apparent. References Burney, C.M. and Laura J. Wright. 2010. Sea turtle conservation

program Broward County, Florida. Technical Report EPD 10-01. Broward County Natural Resource Planning and Management Division, Fort Lauderdale, Florida, 50 pp.

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Burney, C.M. and Laura J. Wright. 2009. Sea turtle conservation program Broward County, Florida. Technical Report EPD 09-01. Broward County Environmental Protection and Growth Management Department, Fort Lauderdale, Florida, 52 pp.

Mrosovsky N., C. Baptistotte and M.H. Godfrey. 1999. Validation of incubation duration as an index of sex ratio of hatchling sea turtles. Can. J. Zool./Rev. Can. Zool. 77: 831-835.

Mrosovsky N. and C.L. Yntema. 1980. Temperature dependence of sexual differentiation in sea turtles: implications for conservation practices. Biol. Conserv. 18: 271-280.

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Appendix: Mean daily temperature data from all recovered temperature/humidity recorders.

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