Sea Turtles and the Environmental Management of Industrial Activities in North West W.A. - Hatchling orientation

Brief description

The effects of three of the most common light types identified in Chapter 5 of the thesis were individually tested under controlled conditions to see if light in a field situation would cause misorientation of hatchlings from 1998 to 2005. The intensity at which each light type might reduce the ability for hatchlings to find the ocean was also tested.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: - Animal collection and treatment - The timing for the light experiments was determined by assessing nesting activity over each of the three summers 2000, 2001 and 2002. Where possible, trips to the islands were then scheduled 6-8 weeks after the peak of the nesting effort for each species each summer. Hatchlings were found by a combination of searching the beaches for emerging or partially emerged nests and monitoring terrestrial predator behaviour. - Arena experiments - Hatchling orientation in the presence of both controlled light source (described in section 6.3.2 of thesis) and uncontrolled (described in section 6.3.3 of thesis) were tested using a circular pitfall arena design. Arenas were used to test the effects of uncontrolled light on misorientation of hawksbill and flatback hatchlings on Varanus Island in 1998 and of controlled light on misorientation of flatback and green turtle hatchlings on Barrow Island in 2004 and 2005. Arenas were positioned between the high tide line and the dune vegetation line. They ranged from 4-8 metres in diameter depending on the amount of beach available between the vegetation and high tide line. A circular trench approximately 30cm deep and 30cm wide was dug around the circumference of the arenas. During the 2005 trials walls of the trench were lined with fine mesh material that stabilised the walls. The trench was subdivided into 12 segments of approximately 30 degrees each. The segments were divided by rigid boards. Segments 1 and 12 were positioned most seaward. The segments (1-12) proceeded in numerical order clockwise around the arena. Prominent rocks or debris were removed from within the arena. Turtle hatchlings were collected and held in the dark in a darkened container until testing. The hatchlings, in groups of 30, were released at the center of each arena by upending them from a cloth bag attached to a line that was run to the outside edge of the arena. The hatchlings were given 3 minutes to reach the trench at the edge of the arena. Hatchlings were then collected and the number in each segment, as well as those remaining in the center, was scored for the 30 degree intervals. See section 6.3.1, 6.3.2 and 6.3.3 of thesis for further information. - Fan mapping - Three hundred and eighty four nests were mapped on Lowendal, Montebello and Barrow Islands between 1998 and 2003. The fan mapping methods developed for this study are similar to those described by Salmon and Witherington (1995). The basic criteria measured for each nest are shown in Figure 6.4 of the thesis and include; fan spread (angle between the fan arms, A - B) and offset (angle between the fan angle midpoint and the most direct line to the ocean, C - X). A compass bearing was taken from the nest down the otside arms of the fan encompassing the tracks (A and B). Occasionally fans were characterised by stray tracks, where hatchlings had travelled in a direction different to the bulk of the nest. The bearings of these strays (n =< 5 tracks) were recorded separately and were not included in the fan angle or offset measurements. A bearing was also taken on the most direct line to the ocean from the nest (X) in addition to angles of visible light sources within 3km of the nesting beach. This data was then used to calculate the offset angle between the ocean bearing (X) and the midpoint of the fan spread (C). All nearby onshore and offshore light sources were recorded and coded for each nest record. Nests and fan orientation were noted on maps of each beach and where possible the nests were dug to confirm hatchling species. Each nest was coded for moon phase. Logistical and resource constraints prevented documentation of nest emergence times more accurately than to the night of emergence. Nests were therefore coded for the moon phase at 2300 hours on the night the nest emerged. It is not possible to determine if the nests emerged before or after moonrise. Moon phase predictions were made using QuickPhase Pro version 2 (http://www.bluemarmont.com/)

Notes

Credit
ChevronTexaco

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Apache Energy

Credit
Natural Hertiage Trust Grant #9924

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BHP Billiton

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Santos

Credit
Woodside

Purpose
To document and quantify the impact of oil and gas facilities on sea turtle hatchlings and to develop hatchling emergence fan mapping methods that could be simply incorporated into company environmental monitoring programs.