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Winter 2003/2004
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Using GIS Along the East Coast of Australia

Volunteer Divers Map Habitats of Endangered Grey Nurse Sharks

By Chris Roelfsema and Carley Bansemer, Unidive

  grey nurse shark
Grey nurse shark photographed in a habitat along the coastline of South East Queensland, Australia (photo: C. Roelfsema 2003).

The population of grey nurse sharks along the east coast of Australia has been listed as critically endangered under the Commonwealth's Environment Protection and Biodiversity Conservation Act 1999. This means there is a high chance this population could become extinct if urgent remedial actions are not taken.

Grey nurse sharks are docile despite their fierce appearance and feed mainly on fish. They are not known to attack humans. In the past the species had an undeserved reputation as a man-eater, and thousands were killed by spear and line fishers until the 1970s, causing a dramatic decline in their numbers. Although they are now fully protected in Australian water, they are still critically endangered and the level of protection needs to be increased. The Queensland government requires more research be undertaken on grey nurse sharks and their critical habitats to protect them from key threats to survival.

Research such as this is time-consuming and expensive and, as such, the Queensland government has relied greatly on the diving community (recreational and professional) for data. As a result of the data collected by divers and the Queensland Parks and Wildlife Service, six sites have been identified as key aggregation sites for grey nurse sharks in southeast Queensland. Furthermore, the Queensland government is now considering management options for the protection of the grey nurse sharks from key threats at these sites.

There had been no detailed maps made of these key aggregation sites although maps would improve understanding of these habitats and their importance to the grey nurse shark.

The researchers received help in mapping and surveying the habitats from a team of volunteers of Unidive (the University of Queensland's underwater club). Unidive received funding from the World Wildlife Fund and the Threatened Species Network to undertake this project, which was coordinated by the authors. In kind support (e.g., training, knowledge, hardware and software, and photo and video equipment) was received from the Center for Marine Studies and the Biophysical Remote Sensing Group (School of Geography, Planning and Architecture) both at the University of Queensland and the Queensland Parks and Wildlife Service.

During 2003, volunteers conducted more than 600 dives at the different sites to collect the information needed to create maps and characterize the habitats. They focused their surveys on mapping the habitat and identifying and counting fish, both invertebrate and substrate species.

click to see enlargement
A habitat map of the grey nurse shark made from bathymetry and feature mapping surveys conducted by volunteer divers.
 

The mapping had two primary components: water depth and feature mapping. For both components, Esri's ArcView 3.x was used to analyze the data and produce maps. Esri products are some of the major educational GIS tools used by the School of Geography, Planning and Architecture at the University of Queensland and were used for this project.

For water depth mapping, the dive boat was equipped with an echo sounder that was directly linked to a handheld Garmin GPSMAP 76 positioning device. The boat traversed over the habitat, and the GPS stored the position and depth every five to 10 meters. This information was then downloaded and the location and depth imported into ArcView using existing Garmin software and an ArcView extension (Avgarmin). The Avgarmin extension transfers Garmin GPS data file format into ArcView shapefiles, which results in quick and easy interpretation of the GPS data.

Since the depth measurements would not pick up all characteristic features (e.g., gullies, walls, caverns, caves, ridges), feature mapping was needed. Feature mapping was conducted by placing a Garmin GPSMAP device (either a model 76 or 72 depending on individual dive requirements) in a dry bag. The bag was connected, via a float with a dive flag, to a line that a scuba diver held. The diver swam underwater over and around the characteristic features followed by the GPS at the surface. A second diver made notes on waterproof paper about the feature types and size while recording the time. Using an underwater range finder, the diver measured and recorded feature sizes (e.g., cave height, gully width). The data from the GPS was then downloaded and imported into ArcView.

Since the diver's watch was synchronized with the GPS time, the notes could be linked to the position stored in the GPS. Point (e.g., cave), line (e.g., wall), and polygon (e.g., outline of a big rock) features were then digitized matching the time (using the identify tool in ArcView) of a location with the corresponding time of the notes. For each point, line, or polygon created, the administrative information (notes on the waterproof paper) was transferred into the table of the shapefile. For each feature, depth was recorded as well. This data, together with the bathymetry data, was then presented in the view. Contour lines were then manually digitized using the view by plotting the depth of point features and the graduated symbols of the depth measurement.

Cross sections of habitats were determined by using the ArcView distance measurement tool to measure the distance from a fixed point to a characteristic depth spot such as contour line or top of rock. Distance and depth were then plotted in a graph to symbolize the profile, which will help divers interpret depth contours better.

To determine the surface area covered by rock or sand, the surface area of the polygons was calculated using ArcView extension Xtools. This extension has several options and can also be used to combine or merge features. The ArcView Layout tool helped create maps overlaid with a grid. This grid will help divers pinpoint grid cell coordinates on the map that resemble the position where grey nurse sharks have been sighted.

The second focus of the survey was to gather information about the diversity of the plants and animals. Divers were assigned jobs to specifically search for fish, invertebrate, or substrate species. When they saw an unfamiliar species, they noted the characteristics and then used reference ID books after the dive to identify them properly. The abundance of fish species was determined by having divers swim for five minutes in a set direction and counting the fish families in an imaginary tunnel with a radius of two and one-half meters. Using quadrates of half-meter squares, they counted substrate and invertebrate groups. This information about diversity was integrated into the labeling of the different features in the map as well.

In December 2003, the project was completed and the understanding of habitat selection by grey nurse sharks will have been enhanced. More data about the biological and physical characteristics of the sites is becoming known, and the project produced georeferenced maps with underwater features of the key aggregation sites.

Protection of critical grey nurse shark habitats has been recommended by national and state governments. The data collected through this project and the monitoring program will enable assessment of the effectiveness of any management measure implemented (and thus justify its implementation) to protect grey nurse sharks and improve the ecological health of these sites.

This project shows that through training in the use of GPS operations and ArcView 3.x, volunteers can successfully create georeferenced maps that can be used to better understand grey nurse sharks in their habitats.

For more information, visit http://unidive.org/grey_nurse_project.

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