With the dramatic declines in shark populations caused by shark-finning and other forms of commercial fishing, the need for protection of shark species worldwide has reached a critical point.  To this point, the Guy Harvey Ocean Foundation is aggressively supporting several fisheries management studies that are gathering crucial data that can be used to design and implement protective measures.

One of these studies is an ongoing project to track tiger shark migratory patterns in the western Atlantic.  For the past two summers, representatives from the GHOF and the Guy Harvey Research Institute have helped tag and track almost twenty tiger sharks off the coast of Bermuda.  The expeditions have produced previously unknown data about the tiger sharks in that region, information which may very well lead to new fisheries management practices in the western Atlantic and Caribbean.

Guy Harvey Ocean Foundation Expedition: Bermuda - Part I

In August of 2009, the staff of the Guy Harvey Ocean Foundation and the Guy Harvey Research Institute collaborated with the Bermuda Shark Project on an expedition to tag and track adult tiger sharks a few miles southwest of Bermuda.  We concentrated our efforts in a location known as Challenger Bank, which is a known as a hot spot for tiger shark activity.  The area certainly lived up to its reputation – by the end of the week, we had caught, tagged and safely released seven adult tiger sharks with PSAT and SPOT electronic tags.

The tagging project was being led by two Bermudians, Dr. Neil Burnie and Choy Aming, with the representatives of the GHOF and GHRI providing assistance in the form of tag provision and deployment, as well as follow-up analysis of the sharks’ migration patterns through the western region of the north Atlantic.  Dr. Mahmood Shivji, Director of the GHRI, and Dr. Brad Wetherbee of the University of Rhode Island – both of whom have extensive experience working with tiger sharks in the Bahamas and the USVI – were on hand to calibrate the tags and assist with deployment.  And, my children Jessica and Alex – both of whom are world-class fishermen with several IGFA records between them – rounded out the team as our expert tiger shark wranglers.

We used Neil’s 34’ Prowler, Bones, as the expedition’s work boat while Captain James Robinson’s Wound Up served as the catch boat.  The sharks were caught on 20/0 circle hooks with no barb and130# gear, then tail roped and restrained by a harness that kept them snug to the boat while Neil drilled small holes in the shark’s dorsal fin to attach the SPOT tags.  On average, the process was usually completed in about 15 minutes, during which time the shark’s head remained submerged in the water so it could ventilate normally.

Once the tag had been securely fastened, the tail rope and harness were released and the sharks would swim away at a rapid clip.  I was in the water to film the hook removal and rope/harness release, while my professional camera team of Rick Westphal and Dee Gele filmed all the action for a tiger shark documentary I am producing.

The results of last year’s expedition were successful beyond our expectations. Using the tags, we were able to track the sharks’ migration as they moved away from Bermuda when seawater temperatures dropped in October, during which time they migrated south towards the Bahamas, Turk and Caicos Islands, and the Virgin Islands.  The tracks showed the sharks were not wandering aimlessly but were actually headed in a more-or-less straight line, as if they knew where they were going.  Based on their amazingly direct movements, it’s highly likely the individual animals have taken this migratory path before.

For the rest of the winter months, the tiger sharks behaved like reef sharks, tracking the edges of deep island drop-offs.  Presumably, they were feeding opportunistically along the way.  As they searched for food at or near the surface, their dorsal fins would be exposed above the water line, which would allow the Argos satellites to pick up the signal from the tags and pinpoint the shark’s location (NOTE: The SPOT tag technology is more suited for attachment on air-breathing mammals and reptiles that constantly interact with the surface. Only a few ocean-going sharks exhibit the necessary type of behavior needed to use the SPOT tag for tracking. For example, my friend Dr. Michael Domeier uses the same equipment in his ongoing research of white shark populations in the Pacific).

As the seawater temperatures started to rise in April and May, the tiger sharks began a northward migration, with some aiming directly for Bermuda.  As they approached the island, they began to veer off on an easterly track that led them well north of Bermuda and into the north Atlantic, where some have stayed for most of the summer (Katrin, the only female tagged last year, is currently on a latitude adjacent to New York!).

This pattern of migration away from the island and in to open water raises some big questions: “What are they doing out in the middle of the Atlantic Ocean?”, “Are they feeding, and if so, on what – turtles, dead sea birds, squid?”, “Or, are they perhaps breeding?” These are serious questions that need to be answered in order for our research to have any practical or meaningful conclusions. So, we decided to once again mount an expedition to Bermuda to see exactly what is going on with these perplexing tiger sharks.

See our next week’s blog for Part II

For a complete list of our other featured blog posts and to see the full line of Guy Harvey Sportswear, please visit: www.guyharveysportswear.com

Related posts:

1. Grabbing Tigers By the Tail — A Return to Bermuda —Part II
2. OF SHIPS AND TIGERS
3. Tiger Beach Tagging
4. The Misunderstood Tiger Shark Shows Remarkable Migratory Behavior
5. Tagging Tiger Sharks in Bimini

Tags: Catch & Release, Guy Harvey, Guy Harvey Ocean Foundation, Guy Harvey Research Institute, Shark

This entry was posted on Friday, August 13th, 2010 at 3:49 pm and is filed under Fishing, Our Oceans. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.