Electronic Tagging

The yellowfin tuna is one of the most important commercially and recreationally caught fish species in the Gulf of Mexico and a majority of the landings in both categories occur in Louisiana. Given their highly-migratory behavior and worldwide distribution in tropical and subtropical waters, yellowfin tuna are managed at federal and international levels.

Yet despite their recreational popularity and commercial importance, relatively little is known about yellowfin tuna in the Gulf of Mexico. The Louisiana Department of Wildlife and Fisheries is conducting several studies to better understand the biology, ecology and movement of yellowfin tuna from the northern Gulf of Mexico. The tagging component of the larger yellowfin tuna initiative seeks to gather long-term electronic tagging information by using two tag types: pop-off tags (PSAT) and internal archival (IA) tags. PSATs have been used on yellowfin tuna in the Gulf of Mexico before, but previous studies had trouble keeping the tags attached to yellowfin, which can transit tens-of-thousands of vertical feet in the water column daily. Because yelllowfin tuna are so active vertically, LDWF biologists have developed a new attachment method that has greatly increased the length of time these tags stay on the fish. Also, IAs are being used to increase the length of the track. These tags have batteries that can last for over 5 years (as opposed to 1 year for the pop-up tags). While recapture is necessary to recover these tags, the rate of recapture of yellowfin tuna in the north-central Gulf of Mexico (8.62 percent per LDWF Cooperative Tagging Program) appears to be higher that the Gulf-wide rate (2.2 percent, NMFS Cooperative Tagging Center). The recapture rate for IA tags to date has been 11.1 percent, making this a very successful study!

Our goal is to have adequate scientific information available for incorporation into future management plans and international policy before there becomes a critical conservation need. Good management based on accurate scientific research will enable Louisiana-based user groups to continue to fish for and harvest this valuable resource for generations to come.

To date, LDWF has released over 150 electronically tagged yellowfin tuna. Our plan is to have tagged 250 yellowfin tuna with electronic tags by the end of 2015. Fishermen should be aware of our study and keep their eyes out for tagged fish for at least the next 5-10 years. If a tagged fish is captured, anglers should record the exact GPS coordinates, date and time of capture and an accurate length measurement. Carefully remove the tag from the fish. The light stalk of the internal tag can be seen protruding from the abdomen of the fish and should remain intact with the body of the tag inside the fish. A reward is offered once the tag is returned in good condition to LDWF. The reward line for tag returns is 855-728-8247 or [email protected].

Whale sharks are the largest fish in the sea, growing up to 20 tons and 45 plus feet long. Whale sharks are solitary animals, but they are known to occur in large numbers (anywhere from 10 individuals to over 100) at the same location when there is an abundant food source. These groups are called feeding aggregations. Natural bank habitats south of Louisiana are important feeding habitat for large aggregations of whale sharks in the northern Gulf of Mexico. The Louisiana Department of Wildlife and Fisheries has been monitoring these large feeding aggregations and deploying satellite tags in order to better understand shelf-edge habitat use by whale sharks in the region.

Satellite tagging helps us to better understand movement and the preferred habitat of these filter-feeding giants. Additionally, we collect small tissue samples to help with global population assessments. To date, 37 satellite tags have been attached to whale sharks in conjunction with this LDWF-supported program (24 PSAT & 13 SPOT), and 40 biological samples have been collected. An interesting behavior discovered with pop-off tags is that whale sharks travel at much deeper depths than previously reported. The first series of tags used in this study were actually crushed by the pressure at the depths that these sharks were traveling when crossing the Gulf of Mexico. Changes were made to the tag housing, and we now have several records of whale sharks at depths of over 2000 meters in the Gulf of Mexico!

Scalloped hammerhead sharks occur off the coast of Louisiana almost year-round. Tuna fishermen often report encounters of scalloped hammerhead sharks near shelf-edge banks, canyon habitats and deep-water rigs. They are capable of long migrations but also demonstrate fidelity to certain “hot spots” within their range. They feed on a variety of prey species including fish, squid and rays; deep diving behavior is believed to be associated with feeding. They are a slow-growing (10-15 years old at maturity) and long-lived species (20-30 year lifespan).

In the Gulf of Mexico, catch rates of large sharks have declined since the mid-1980s. A recent petition requested they be listed under the Endangered Species Act (ESA). Although the final ruling determined they are not at risk for local extinction, they do have a high risk to post-release mortality. In order to better understand their habitat use off the coast of Louisiana, and therefore assess risks as incidental by-catch to other fisheries, the Louisiana Department of Wildlife and Fisheries is using electronic tags to study these fish.

Tagging efforts are conducted using a combination of rod and reel fishing and bottom longline surveys. Upon capture, sharks are either handled alongside the vessel or in a modified cradle. Biological measurements are collected and gender is assessed. The tag is mounted to the dorsal fin by drilling two holes into the fin and mounting a special to clamp to the fin. When the animal surfaces, the tag transmits a signal through the Argos satellite system allowing for active-tracking with accuracy between 250 to 1,500 meters. Since 2012, 31 scalloped hammerhead sharks (25 males, 5 females, 1 unknown) have been released in the northern Gulf of Mexico fitted with SPOTs.

The Atlantic tarpon is a highly prized game fish throughout its international range, and Louisiana anglers are lucky to have a very good fishery right here at home. Adult tarpon typically show up in Louisiana waters in the summer and early fall. Historical fisheries existed across the Louisiana coast from Lake Calcasieu to Lake Pontchartrain and reports from LDWF’s own journal, the Louisiana Conservationist indicate that tarpon may have been one of the first target species for fish tagging studies conducted in Louisiana. While previous tagging work suggests that tarpon leave the Gulf in the winter, reports from local divers indicate that some tarpon may spend the winter at offshore platforms off the Louisiana coast. Also, tarpon larvae have been collected just offshore of the Mississippi River Delta, and local researchers have collected tarpon in spawning condition in the area.

Unfortunately, anecdotal information from tarpon anglers indicates that tarpon populations have declined over the past few decades. Because recreationally landed tarpon are typically released, and there is no commercial fishery (and therefore no record of landings), it is difficult to evaluate the extent of the possible decline. So, in response to the needs of fisheries managers to understand the connectivity of Louisiana’s tarpon fishery with other regional tarpon fisheries, LDWF biologists are currently attaching satellite tags to tarpon in Louisiana. The information from this tagging study will help biologists and managers better understand the movements and habitat use of tarpon from the Louisiana fishery and will be shared with the public to educate them about Louisiana’s tarpon resource.

Blacktip sharks are one of the most common coastal sharks in Louisiana and can be encountered from the deeper waters of the continental shelf edge all the way into the interior waterways of Louisiana’s salt marshes. Some recreational anglers target these sharks because they are big, common and fun to catch, while others curse them for stealing some or all of their catch. Blacktips are also one of the most important species for the commercial shark fishery in Louisiana.

LDWF biologists are currently using satellite tags to study both the movements and post-release survival of blacktip sharks along the Gulf coast. In cooperation with researchers from NOAA, USM-GCRL and TAMUG, LDWF biologists are generating information that will help manage this recreationally and commercially important fishery.

Tiger sharks occur worldwide in tropical and subtropical waters and can inhabit a wide range of marine ecosystems. They can be found in turbid areas with high fresh water influence, like estuaries and harbors, and are found in association with island chains and coral atoll lagoons. They are capable of traveling long distances and make seasonal migrations. Many documented populations are female-biased, indicating sexual segregation; however sex-specific environmental preferences are still unknown for the species. Tiger sharks have one of the most diverse diets of any shark species, including human garbage. They are one of the few shark species that has a propensity to attack humans.

In the Gulf of Mexico, catch rates of large sharks have declined since the mid-1980s. Although tiger sharks comprise a large component of the large coastal species caught in the shark fisheries of the U.S. East Coast and Gulf of Mexico, tiger sharks are considered of limited food value and are often discarded at sea. They are also a popular recreational fishing target, specifically in large shark rodeos. But to prevent wanton waste of these long-lived predators, the Florida Fish and Wildlife Conservation Commission recently placed a complete ban on killing tiger sharks in Florida state waters.

Very little is known about the habitat use and distribution of tiger sharks in the northern Gulf of Mexico. As part of the Electronic Tagging Program, the Louisiana Department of Wildlife and Fisheries is using electronic tags to study these fish. Our goal is to increase the body of knowledge on these poorly understood pelagic fishes in order to make sound management decisions based on scientific studies.

Tagging efforts are conducted using bottom longline research surveys throughout the northern Gulf of Mexico shelf waters. Upon capture, the shark is handled in a modified cradle. Biological measurements are collected and gender is assessed. The tag is mounted to the dorsal fin by drilling two holes into the fin and mounting a special clamp to the fin. When at the surface, the tag transmits a signal through the satellite system allowing for active-tracking with accuracy between 250 to 1,500 meters. Since 2012, 22 tiger sharks (14 males and 8 females) have been satellite tagged with SPOT tags and released in the northern Gulf of Mexico by LDWF’s collaborative tagging team.

Tagging a tarpon with a satellite tag using spear gun gear.