BRUVS at the Cape Eleuthera Institute
Project Leaders: Andy Danylchuk & Edd Brooks
Read the project blog here.Background
Understanding the population ecology, life history, and movements of sharks is fundamentally important when attempting to protect these important apex predators. Currently, the standard population assessment for sharks involves the use of baited long-lines. Although this method can provide an accurate estimate of shark diversity and abundance, it does have significant drawbacks in that it is invasive and sometimes destructive. This potential destructiveness seems contradictory to shark conservation goals, and as such it is critical that other techniques for assessing shark diversity and abundance be tested.
One potential alternative is the use of baited remote underwater video surveys (BRUVS). BRUVS were initially developed by the Australian Institute of Marine Science, and have recently been used to quantify the diversity, relative abundance, and stock structure of sharks in Australia. This technique involves lowering a baited digital video camera to the seabed and recording the sharks that come into the field of view when attracted by the bait plume. The positive benefits of BRUVS are that it is relatively inexpensive, easy and quick to deploy, and sharks are not physically handled or stressed in any way.
One potential alternative is the use of baited remote underwater video surveys (BRUVS). BRUVS were initially developed by the Australian Institute of Marine Science, and have recently been used to quantify the diversity, relative abundance, and stock structure of sharks in Australia. This technique involves lowering a baited digital video camera to the seabed and recording the sharks that come into the field of view when attracted by the bait plume. The positive benefits of BRUVS are that it is relatively inexpensive, easy and quick to deploy, and sharks are not physically handled or stressed in any way.
In the field
The Bahamian Archipelago is a region of the western Atlantic that maintains a rich assemblage of sharks because of its relatively pristine waters and high diversity of marine environments. These characteristics, along with its close proximity to the United State, have made the Bahamian Archipelago a popular tourist destination especially for water-based activates such as SCUBA diving. Although tourism can have positive economic benefits to countries such as The Bahamas, rapid increases in tourism-related development can also lead to significant environmental degradation, some of which could affect sharks.
Given that the pressure on shark populations is likely to increase in The Bahamas, it is critical to conduct a comprehensive assessment of the status of sharks in this region. One of the goals of the Shark Research and Conservation Program at the Cape Eleuthera Institute is to test whether BRUVS can provide similar diversity and abundance data to that which is collected via traditional long-line surveys. Our study is being conducted in the waters off Eleuthera, The Bahamas, and is encompassing a wide range of marine habitats from deep coral reefs to shallow banks. To understand more about the movements of sharks in this region, all sharks caught via long-line are receiving external tags so that we can monitor recaptures not only on the long-lines but when externally tagged sharks are ‘caught’ on the BRUVS. Caribbean reef sharks, tiger sharks, and bull sharks caught on long-lines will also be surgically implanted with ultrasonic tags and their fine-scale movements monitored with a stationary receiver array spanning over 40 km2.
Given that the pressure on shark populations is likely to increase in The Bahamas, it is critical to conduct a comprehensive assessment of the status of sharks in this region. One of the goals of the Shark Research and Conservation Program at the Cape Eleuthera Institute is to test whether BRUVS can provide similar diversity and abundance data to that which is collected via traditional long-line surveys. Our study is being conducted in the waters off Eleuthera, The Bahamas, and is encompassing a wide range of marine habitats from deep coral reefs to shallow banks. To understand more about the movements of sharks in this region, all sharks caught via long-line are receiving external tags so that we can monitor recaptures not only on the long-lines but when externally tagged sharks are ‘caught’ on the BRUVS. Caribbean reef sharks, tiger sharks, and bull sharks caught on long-lines will also be surgically implanted with ultrasonic tags and their fine-scale movements monitored with a stationary receiver array spanning over 40 km2.
Aims & objectives
Our study is the first in the tropical waters of the western Atlantic to test the effectiveness of BRUVS as a less traumatic method for assessing the diversity, abundance, population structure of sharks. If successful, BRUVS could become an effective tool for assessing shark populations throughout the Bahamian Archipelago. This work will not only test the effectiveness of BRUVS, but it will provide the only quantitative data on the diversity and abundance of sharks near Eleuthera. The secondary outcome of our research will be to examine the habitat use and site fidelity of sharks in The Bahamas across a wide range of marine environments. By combining passive tagging and acoustic telemetry, we will be able to determine the extent to which the distribution of sharks overlaps with human activities and potential disturbances. Collectively, all the data we will be collecting on sharks in the waters near Eleuthera will ultimately assist in the management the local marine environment, including the development of a proposed marine reserve.
Project Update: 2008
We have nearly completed our first of four quarterly sampling periods utilizing both BRUVS and long-line surveys, as well as conducted additional long-line surveys for the deployment of acoustic transmitters. To date, we have ‘captured’ 35 sharks on the BRUVS, including Caribbean reef sharks, nurse sharks, tiger sharks, and lemon sharks. During long-line sets we have captured and externally tagged 36 sharks, from six species including Atlantic and Caribbean sharpnose sharks.
We have already recaptured three tagged Caribbean reef sharks with a maximum of 12 weeks at liberty. All recaptures have been within 2.5 km from their original tagging location suggesting strong site fidelity at least during summer months. Of the long-line caught sharks, we have surgically implanted ten Caribbean reef sharks and one tiger shark with acoustic transmitters. Preliminary data from the remote receivers is showing that the range of movement for these sharks is quite large however they are spending a considerable amount of time in the habitat encompassed by our array.
We have already recaptured three tagged Caribbean reef sharks with a maximum of 12 weeks at liberty. All recaptures have been within 2.5 km from their original tagging location suggesting strong site fidelity at least during summer months. Of the long-line caught sharks, we have surgically implanted ten Caribbean reef sharks and one tiger shark with acoustic transmitters. Preliminary data from the remote receivers is showing that the range of movement for these sharks is quite large however they are spending a considerable amount of time in the habitat encompassed by our array.