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The Kefalonian Marine Turtle Project

Current Research

This page outlines the basics of our current research and findings on the loggerhead turtles of Kefalonia.


General Population Information

Scientific objectives for 1998 and beyond

Beach procedure

A close look at encounters

Links between Sea Turtle By-catch and tagging around Kefalonia

Tracks and Tracking

Tourism Study

Nesting site fidelity in Loggerhead Sea Turtles - Kefalonia

References


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Field research into the loggerhead turtle (Caretta caretta) population of Kefalonia has been carried out since 1984. This work has centred primarily around population dynamics and morphometrics of this species and has resulted in some related publications. The most notable contributions have arisen from the work of Hays (1992), Hays & Speakman (1991; 1992; 1993) and Hays et al (1991). One of the aims of the KMTP is to increase the availability of data and findings (in the form of publications) for use in local and international studies. This aim is being met by the improvement and realisation of scientific thought and procedure.

INTRODUCTION: THE POPULATION OF SEA TURTLES
ASSOCIATED WITH KEFALONIA

The use of the southern beaches of Kefalonia for nesting by long been Caretta caretta has documented (MTRP, 1993, nesting unpubl.). However, limitations in the monitoring of the environment has ultimately led to an underestimate in the number of nesting females. Monitoring of all beaches on the south of the island was introduced in 1997.

Most research, however, is carried out on the 2.7km Mounda beach, south-east Kefalonia. To date a total of 139 female Caretta caretta have been witnessed to nest on Mounda beach. The number of nests each season, and respective females can be seen in Figures 1 (a) and (b) below.

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Figure 1. The number of Caretta caretta (a) nesting females, (b) nests, (c) adult emergences, and (d) % of successful nesting emergences monitored on Mounda beach, Kefalonia, between 1984 and 1997.

From these graphs it is evident that the numbers of females visiting Mounda beach has varied greatly over the years of monitoring. Such fluctuations are widespread, and have been found in Florida (Owen et al, 1992; Bagley et al. 1995; Ehrhart et al, 1996), Surinam (Schultz, 1995), Australia (Limpus, 1995), Malaysia (Limpus, 1995b) and the pacific islands (Balazs, 1995). This may be attributable to the long inter-nesting period of loggerhead turtles estimated at two to three years. This infers that the high numbers consist of the same individuals returning, and those present in the 'low' years are either exhibiting a longer cycle or are out of synchrony with the rest of the population. Furthermore, there is cause for concern that long term population declines or increases may be masked by such population oscillations (Pritchard, 1995 b)


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SCIENTIFIC OBJECTIVES FOR 1998 AND BEYOND

Observing the movements of sea turtles
Population morphometrics
Nesting behaviour
Reproductive investment
Study of parasitic and commensal organisms
The nest environment
Reasons for egg failure and development mortality
Hatchling emergence
Behaviour of hatchlings in response to light
Foraging surveys

 

1. Observing the localised movements of sea turtles
In 1998 an investigation was devised to look at localised movements of sea turtles around Kefalonia during the inter-nesting period. As such, extensive validation trials were carried out on 3 radio transmitters (Advanced Telemetry Systems, USA) to test their applicability to sea turtle research. These trials proved highly successful and served as the forerunner for the deployment of the transmitters on 3 nesting females on Mounda beach. The data received is currently under analysis, and will be combined with data from the proposed redeployment in summer 1999.

2. Populations morphometrics
It has been well documented that size/age relationships between different geographically separated populations varies significantly (e.g. Dodd, 1988). Until now, measurements of carapace dimensions taken on Kefalonia have only been used in determining the relationship between size and fecundity (Hays and Speakman, 1991). Previous carapace measuring techniques are possibly too insensitive to measure carapace growth increments. Consequently, the system of measurement was improved in the 1997 season, by increasing the number and type of measurements taken, thereby reducing variability, which will allow for the determination of growth curves for comparison with other populations within the Mediterranean and further afield.

graphic of carapace measurement.

Figure 2. Carapace measurements. CCL = curved carapace length; SCL = straight carapace length. (Graphics courtesy of R. H. C. Poland, EuroTurtle)

measuring a green turtle in the caribbean.

Figure 3. Taking curved carapace length measurements - a former KMTP volunteer (Sarah Flood) measuring a green turtle nesting on Buck island, Caribbean. (Photo: L. Bateman, 1996)

3. Nesting behaviour
One of the most hotly debated questions in turtle biology is 'what determines the placement of a nest within an apparently homogeneous beach?'. There are many physical parameters that may influence nest placement and we have chosen to focus on sand temperature, water content, grain size and beach morphology. The results of this investigation are currently under analysis and should be ready in the near future.

4. Reproductive Investment
During a given nesting event, numerous variables are measured; for example clutch size, clutch volume, the duration of nesting stages and the number of nesting attempts. It is important to have data on such factors in order to determine how they relate to morphology and foraging ecology.

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5. Study of the parasitic and commensal organisms associated with Caretta caretta
Studies carried out on commensal organisms may offer some clues as to the geographical distribution of their hosts. The KMTP has collected qualitative and quantitative data of epiphytic organisms associated with nesting females since June 1995. Checks for fractures and lacerations are also carried out to identify any anthropogenic or predatory injuries incurred in the marine environment.

barnacle.

Figure 4. Giant barnacle found on loggerhead turtle. (Photo: R. H. C. Poland, EuroTurtle)

6. The Nest Environment
It is important to understand the environmental conditions to which any given clutch is subjected during its developmental stages. This can play an important role in the studies of egg viability, development mortality and population reproductive dynamics. During 1998 in-nest data loggers (Tinytalk II) were deployed in a number of nests on Mounda beach. The data retreived now forms the basis of predictive work on sex ratios within nests and studies on the atypical hatching/emergence patterns charactersitc of Kefalonia.

On Kefalonia, the success of a given nest is determined by post-hatching nest excavations. Data obtained by this technique have been combined with spatial and temporal descriptions of nest environments for the past three years.

7. Reasons for egg failure and development mortality
The early stages of embryonic development represent a crucial period in the life history of sea turtles. An array of biotic and abiotic factors contribute to high levels of egg failure and development mortality (Richardson & Richardson, 1981; Stancyk, 1981). Studies of nests have shown that many eggs fail to hatch (e.g. Fowler, 1979); 12% of egg failures in nests laid on Mounda beach in 1995 were due to infertility (Houghton, 1995).

Our investigation aims to ascertain the relationship between reproductive success within sea turtle nests and the numerous physical, chemical and biological factors which affect it.

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Figure 5 Examining the contents of an extinct nest (J. Houghton)

8. Hatchling emergence
Intermittent emergence from nests of up to four days has been reported amongst several populations, e.g. in Zakynthos (Hudson pers. comm.,1996) and in Florida (Witherington et al., 1990). However, on Kefalonia the period of emergence can last up to 20+ days. Recent studies using "in-nest" data loggers have related this to temperature ranges within nests and its subsequent effect upon incubation periods i.e. the greater the temperature range between the top and bottom of an egg chamber, the greater the period of hatching.

9. Behaviour of hatchlings in response to light
The orientation behaviour exhibited by hatchlings finding the sea has been well studied. The KMTP is currently studying the mis- and dis-orientation of hatchlings emerging from their nests on Mounda beach against variations in their natural environment. Results will be related to the impact of artificial light and conservation practices.

10. Foraging surveys
One of the most interesting features of Kefalonia is the foraging behaviour of male turtles in the harbour of the island's capital, Argostoli. Evidence suggests that males are coming into the harbour to feed on the extensive beds of bivalve molluscs that grow along the harbour causeway, and on the discarded fish entrails thrown into the harbour by local fishermen. As accounts of foraging and diving behaviour of male loggerheads are limited, this site offers a great opportunity for us to take a closer look at this area of sea turtle research.


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BEACH PROCEDURE

The basic patrol routine on Mounda beach
Patrol routines on other southern and western shores
Beach and nest marking

A detailed description of the scientific codes and procedures performed since 1997 can be found in Suggett et al (1997), and only a brief outline will be given here. These procedures are essentially a combination of those that have evolved with use on Kefalonia, in addition to an adaptation of procedures employed by other research projects.

The basic patrol routine on Mounda Beach (nesting season)
The centre of Mounda beach is used as the starting point; turtle emergences are rare in this area due to the rocky outcrop just offshore, and it splits the beach into halves of similar distance (the western end, 'Kaminia' and the eastern end, 'Potamakia'). The beach is monitored between 21.00hrs and 07:00hrs during the adult season. A total of approximately 1400 hours (138 nights) monitoring time is put in by the project volunteers throughout a season.

Volunteers are divided into 3 groups (depending on numbers). One group remains in the centre to meet any late visitors to the beach and to continue the patrols should a turtle be found by another group. The other volunteers patrol to the ends of the beach, walking quickly, quietly, and without torches at the waters edge, checking both seaward and for tracks. Volunteers wait for 20 minutes on arrival at the end of the beach, and then patrol back to the middle. The beach is patrolled fully every 25 minutes. The final run takes place around dawn, when any nests were thoroughly marked. This method strikes a balance between over-patrolling which may deter any potential nesting females from coming ashore, and under-patrolling whereby data may be missed.

turtle tracks

Figure 6. Distinctive turtle tracks. (Photo: R. H. C. Poland, EuroTurtle)

Patrol routines on other southern and western shores
The entire southern and western shores were surveyed during 1997. Throughout that season (June to the end of August), the coast was surveyed for nesting activity. Each beach was visited once a week via land or sea (depending on beach accessibility), with any activity categorised according to successful nesting or non-nesting emergence (unsuccessful nesting attempt(s); false crawl/U-turn). These beaches will continue to be monitored, but more regularly.

map of kefalonia's nesting beaches

Figure 7. Map outlining coastal areas of Kefalonia, where surveying showed turtle activity. Numbers indicate total number of emergences (number of nesting emergences). Taken from Houghton et al (1997).

Beach and Nest marking
At the start of each season, the beach is measured from Mounda point to the rocks at the far end of Kaminia along the curved path of the vegetation line. The vegetation line represents the only realistically stable landmark on the beach. At 50m intervals a straight measurement is taken to the high water mark and then to the waters edge. The positions of prominent natural and man-made features are plotted on a map. At 15m intervals starting from Mounda point, beach markers (labelled strips of plastic yellow tape) are positioned on shrubs at the vegetation line. From these points a triangulation can be taken to each turtle nest, and distances recorded.

In the past this method has proved to be reliable when relocating turtle nest, however a more rigorous method of beach marking is being devised at present.


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If readers of this page wish to contact the KMTP, they can do so via

[email protected]

or

[email protected]

phone/fax (+44) 1983 740321, or by post (see below).

The Kefalonian Marine Turtle Project
c/o 'Heronfield',
Main Road,
Shorwell,
Near Newport,
Isle of Wight.
PO30 3JL
UK
T. B. Stringell [email protected]
Last modified: 25 th January 1999

The Kefalonian Marine Turtle Project is a Limited Company with Charitable Status
(registered in England and Wales, No 1062312).

Copyright 1998, KMTP. All Rights Reserved. Permission is granted by the KMTP for classroom supervisors/teachers and students to make reprographic copies of worksheets for non-commercial use. This permission does not extend to copying for promotional purposes, creating new collective works, or resale.