Many species of sharks return to the same place each year, but how do they find their way back? Bryan will explore the possibility that they use the earth’s geomagnetic field as a massive global compass.
I grew up in Tucson, Arizona, part of the Sonoran Desert. People often ask how a kid from the desert could become so interested in the ocean and quite frankly, it wouldn’t have been possible without my parents. I remember taking many trips to California to visit beaches and aquariums, visits that crafted my appreciation for marine life. The animals we saw were all mesmerisingly beautiful, but I was far more intrigued by the mystery that surrounded them. Specifically, I remember watching a pufferfish swimming by itself in a fish tank and I could have sworn it was watching me...
In the Edisto River, S. tiburo exhibits philopatric migrations, which demonstrates the ability to navigate to the estuary from nearby locations. Individuals will be displaced offshore with a geomagnetic tagging package, and the recovered data will be analysed to determine if S. tiburo uses magnetic-based navigation to facilitate philopatric migrations.
A recent US stock assessment suggested that bonnethead sharks could be currently overfished/vulnerable to overfishing. The conservation of vulnerable, marine species is predicated upon the ability to accurately locate individuals, but researchers cannot accurately determine a migratory animal’s precise location unless the individuals breach the surface for a prolonged period, during which data transmission occurs. Other geolocational tools that do not require surfacing, such as light-based geolocators, can be inaccurate up to 180km. We must assess the role of magnetic-based navigation in the spatial ecology of coastal sharks to determine if predictable migratory routes are being utilized. In doing so, the technology to geolocate a migratory animal with magnetic variables will be developed and could also allow researchers to delineate migration paths and identify habitat use patterns, such as areas for parturition, mating or aggregation. These proposed benefits will affect all marine animals, especially those that are endangered.
Ecosystem health is subject to the abundance and distribution of species that occupy a region. Studies have shown that the spatial and temporal ecology of communities to be affected by variables including mate presence, prey availability, and temperature. Fluctuations of these variables drive behavioral adaptations, such as migration. In some cases, animals return to their original habitat, a philopatric behavior, and thus, exhibit site fidelity. Site fidelity demonstrates the ability for an animal to migrate between two locations successfully, however, the navigational mechanism is variable. The loggerhead sea turtle and some salmonids facilitate philopatric behavior through the use of geomagnetic cues. Recently, sharks were shown to be capable of detecting geomagnetic signals, which supports the theory that sharks use these signals to facilitate philopatric movements. However, no study has monitored geomagnetic variables in-situ and thus, there has not been an adequate analysis of the role that geomagnetic cues have in the spatial ecology of elasmobranchs. The bonnethead has been shown to migrate between South Carolina and Florida, returning to the Edisto River annually. This site fidelity makes the bonnethead a good model for our study. We will displace bonnetheads offshore with a magnetic geologger and allow the animal to ‘home’ back to our study site. Upon recovery of the tag, we will assess the reliance on geomagnetic cues during orientation and navigation. The findings from this project will fill a serious scientific void, while developing a novel technique for increasing the accuracy and feasibility of geolocation for marine animals.
Managing sawshark populations requires good information on where they move and what their relative abundance. Jane and Paddy are using a variety of methods to improve our understanding of the conservation status and management of sawsharks threatened by fishing in south-eastern Australia.