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Development of GIS-based models for indigenous management of marine turtle nesting beaches

Baker, Bryan Anthony (2000). Development of GIS-based models for indigenous management of marine turtle nesting beaches. Honours Thesis, Northern Territory University.

Document type: Thesis
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Author Baker, Bryan Anthony
Title Development of GIS-based models for indigenous management of marine turtle nesting beaches
School, Department or Centre School of Biological, Environmental and Chemical Sciences
Institution Northern Territory University
Publication Date 2000
Thesis Type Honours
Supervisor Pearson, Diane
Kennett, Rod
Subjects ENVIRONMENTAL SCIENCES
Abstract The principal aims of this study were to develop a GIS for the collection and modelling of beach characteristics which influence selection of nest sites by marine turtles on the north east Arnhem Land coast. Additionally, the association between the proximity of human settlements and probability of a site being used for nesting was examined.

The study involved the use of aerial photography, other data collected by remote sensing, and existing GIS coverages to characterise mainland nesting beaches between Cape Wilberforce and Cape Shield in north east Arnhem Land. Beaches on numerous small rocky islands were difficult to characterise with available data and were not mapped. Nesting data from aerial and ground surveys collected between 1993 and 1999 by the Parks and Wildlife Commission of the NT was used to map the presence of nesting throughout the study area.

A total of 224 beaches was identified with a total length of 355 km, representing 55% of the coastline in the study area. Nesting activity occurred on 61 beaches which covered a total length of 150 km. Data limitations required the use of a binomial response variable, defined as the presence or absence of nesting activity by a mix of species recorded at least once over the seven years of survey.

Logistic regression analysis was used to derive a model relating the probability of a beach being used by nesting marine turtles to the physical characteristics that could be derived from small scale remotely sensed and GIS data. A parsimonious model was produced with beach exposure and length of beaches, accounting for approximately 30% of the variation in nesting activity.

Increased exposure of beaches to open sea was significantly associated with nesting activity. This is interpreted as evidence that nesting females choose exposed beaches that offer access to open sea currents which may increase survivorship of hatchlings by minimising energy expenditure to reach feeding areas.

An examination of the proximity of settlements to nesting beaches using Euclidean distance showed a significant negative association with the presence of nesting when entered alone into a model. However, when entered into a model with exposure of beaches it did not add significantly to the explained variance. This is interpreted as a product of intercorrelation between exposure of beaches and proximity of settlements. Settlements are typically found on sheltered bays, where choices made to site outstations are based on values unrelated to turtle nesting activity.

The methods used to develop models to determine suitable nesting beaches have scope for adaptation to guide further surveys of nest distribution and abundance. The GIS produced in this study will provide indigenous land managers in north east Arnhem Land with a planning tool for management of nesting beaches in the region.


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