What’s on the Other End of Your Line May Surprise You

Chumming for tuna on the East Lump? Watch out! You might hook into a giant shark – or a shark tracking device.

Anglers out of Cocodrie were sure they hooked into a giant tuna this weekend out at the “East Lump,” but weren’t able to turn it or get a visual before they pulled the hook. When they brought up the line, they were surprised to find a mysterious item covered in algae attached to their hook.  The intermittent red blinking light indicated it must be something of importance.

SPOT tag deployed on a scalloped hammerhead off the coast of Louisiana for 399 days. Tag was foul hooked by an angler at the same location as the original release. Biofouling, algae and barnacle growth can often reduce or terminate tag function. (Photo courtesy of Stephen Babcock.)

Important indeed, the mysterious object turned out to be one of our electronic shark tags. This particular tag was deployed on an 8-foot male scalloped hammerhead at the “East Lump” back in January 2015. Accumulated biofouling on the tag interrupted the signal, and the shark’s last reported location was received in July.  Although the tags and mounting pads are coated with an antifouling paint, swimming speeds are often not fast enough to completely inhibit growth.

The LDWF Electronic Tagging Program utilizies tags like these to study multiple species of sharks in the northern Gulf of Mexico. Smart Position Only tags work best on fish that spend time at the surface. When at the surface, these tags transmit signals that can be detected by the satellite-based Argos tracking system. Most live-tracking applications are based on SPOTs, which can generate multiple positions per day for a given fish. The tags can either be fin-mounted or towed behind a tagged fish. Since 2012, 37 scalloped hammerheads have been fitted with SPOT tags and released in the northern Gulf of Mexico.

Catch rates of sharks in the Gulf of Mexico have declined since the mid-1980s. Globally, some populations of scalloped hammerhead sharks are listed as “near threatened” or “endangered” and protected under the Endangered Species Act. Although not listed as threatened or endangered off of Louisiana’s coast, they do have a high risk to post-release mortality in commercial fisheries. The Department uses these tags to better understand their habitat use off our coast and assess risks such as incidental by-catch to other fisheries.