Project Title: Using steroid hormone analysis, ultrasonography and telemetry as non-invasive tools for examining reproduction in tiger sharks
Overview
Determining the reproductive strategies and mating behaviors of animals is crucial for management and conservation. For example, identifying gestating, mating or pupping grounds could be use to implement reserves or reduce exploitation in these areas critical to the survival of threatened species. The goal of this project is to determine the mating, gestation and pupping grounds of tiger sharks in the western Atlantic.
Historically, the reproductive biology of sharks has been studied by sacrificing the animals; however, in this study, we will be performing ultrasounds on tiger sharks as well as taking blood samples for hormone analysis to determine reproductive status of these large predators. Coupling these techniques (ultrasonography imaging and blood hormone analysis) will allow us to examine the reproductive state (e.g. pregnancy), cycle and length of gestation of sharks during our ongoing research. After their “pregnancy check-ups,” the sharks will also be tagged with satellite transmitters to track their movements and evaluate behavioral patterns that may reveal locations where mating, gestation, or giving birth is occurring. The ultimate goal is to use these data to establish effective marine protection in these areas critical to the reproduction of these large sharks.
Methodology
1. The fieldwork for this project will occur within a region of the Bahamas named Tiger Beach. This region is a known aggregation area for larger female tiger sharks. Fieldwork will utilize the Shear Water, a recreational dive boat owned and operated by Jim Abernethy Scuba Adventures.
2. A handline will be utilized to catch the tiger sharks. The gangion will be baited with either a barracuda steak or a jack head, and composed of a 16/0 non-offset circle hook affixed to four strands of 900 lb monofiliment and connected to a small bouy to keep the bait near the surface of the water. The gangion will be crimped to 100 ft of single strand 900 lb monofiliment and 100 ft of polyester boat line, and then further attached to a larger poly buoy and three sequential strands of thick bungee cord that are connected to the boat.
3. After capture, each shark will be restrained on the dive platform, partially submerged in the water with an oxygen enriched water pump in the shark’s mouth to provide continued water flow and oxygenation of the gills.
4. All sharks will be measured, and fin samples, muscle biopsies and blood will be collected.
5. Ultrasonography will also be preformed, with an Interson 5 MHz SeeMore USB general-purpose abdominal probe, to detect the presence or absence of pups.
6. Ultrasound image of Squalus acanthias uterus containing three embryos (P1, P2, P3). Image courtesy Dr. Sulikowski
7. Finally, each female tiger shark will be fitted with a spot satellite tag and released.
Citizen Science™
The major outreach component of this project is through the participation of conservation enthusiasts. Six people were able to share in the research experience by helping to catch the sharks, collect fin and muscle samples, measure the sharks, and learn about some of the ultrasound and blood analysis techniques. Moreover, the conservation enthusiasts were given the opportunity to dive with these charismatic megafauna, one of which was a female tiger shark tagged during the trip, in an effort to further ecological understanding, and promote the dissemination of conservation awareness.
Hammerschlag N, Sulikowski J. 2011. Killing for Conservation: The Need for Alternatives to Lethal Sampling of Apex Predatory Sharks. Endangered Species Research 14: 135–140
Investigators
Project Lead:
• Dr. N Hammerschlag
• Dr. J Sulikowski
Co-Investigators & Collaborators:
• A Gallagher
• B Prohaska