OTN collaborator tracking critical reef fish in the Gulf of Mexico

Dr. Sue Lowerre-Barbieri, an OTN international project lead, and fisheries ecologist splits her time between the University of Florida and the FWC Fish and Wildlife Research Institute. Additionally, Lowerre-Barbieri heads the Integrated Tracking of Aquatic Animals in the Gulf of Mexico (iTAG) network — a community of researchers working to advance marine animal tracking capabilities in the Gulf. Her research focuses on assessing spatial ecology and reproductive resilience of exploited marine fishes. Acoustic telemetry is a key tool in many of Lowerre-Barbieri’s studies.

Through the loan of OTN receivers, federal and state support, and important collaborations with the FWRI Keys lab and FWC law enforcement group, her team has been able to deploy extensive acoustic arrays in two important Florida reef systems: the Florida Keys and in Madison Swanson—a deep-water marine reserve in the North East Gulf of Mexico. These deployments provide the infrastructure needed to study movement ecology of important reef fish, allow for monitoring of relatively deep water habitats and build collaborations with other telemetry scientists.

The Florida Keys National Marine Sanctuary (FKNMS), borders the Florida Straits, dividing the Atlantic Ocean to the east from the Gulf of Mexico to the Northwest. At its narrowest point, the Florida Straits is only 90 miles from Cuba. 69 receivers have been deployed (37 from the OTN and 32 from FWRI) in the Florida Keys to develop five “gates” to assess the potential migratory pathway along the reef edge, as well as key ecological hot spots, including eight wrecks, and four “humps” or sea mounts (Fig. 1).

Figure 1. Locations of receiver arrays in the Florida Keys.

In contrast, Madison Swanson is at the shelf edge off the panhandle in the Gulf of Mexico.  It includes some of the highest relief habitat on the West Florida Shelf (up to eight meters, Fig. 2), including a limestone ledge and rocky outcroppings. It is 115 nm2 and was created in 2000 to protect gag grouper spawning sites.

Lowerre-Barbieri’s lab is conducting multiple studies at this site including assessing gag grouper reproductive dynamics, red snapper release mortality, and greater amberjack numbers and residency using capture-based sampling, video, and telemetry. They have developed an array of 35 OTN receivers along the reef edge to monitor fish movements and detected a range of species, including great white sharks, which were tagged off of Cape Cod, Massachusetts by Dr. Greg Skomal of the Atlantic White Shark Conservancy. These detections have changed the understanding of top predators at this reserve.

Figure 2. Location of the Madison Swanson marine reserve, its bottom habitat, and common fish species detected on underwater camera surveys.

One of the species the lab is currently studying is greater amberjack (Seriola dumerili), which occurs in both Madison Swanson and the seamounts off the Florida Keys. Greater amberjack is the largest of the Carangids, growing to over a meter long and often weighing more than 100 lbs. It is highly targeted both by commercial and recreational fishermen throughout the Gulf of Mexico, but especially in Florida. Although habitat associations are well-known, with juveniles found in May and June in offshore waters associated with Sargassum mats and adults found congregated around structures (e.g., oil rigs, reefs, and wrecks), little is known about individual movements or spawning site selection.

Figure 3. Greater amberjack capture, tag implantation, and depredation off the Florida Keys

The seamounts off the Florida Keys are the best known greater amberjack spawning sites and have been hypothesized to disproportionately contribute to the SE stock’s productivity and possibly the Gulf stock’s as well. However, the movement ecology of greater amberjack at this site is unknown. Some fish appear to be residents year-round, while others may travel long distances to this site to spawn. Potential discard mortality and depredation on this spawning site are also unknown. Lastly, fishermen in the area have raised concerns that they no longer see the large schools of greater amberjack over natural habitat that they used to, potentially due to the increased numbers of artificial reefs in the area.  It is unknown how these changes in spawning site selection might affect productivity. Understanding this is the long-term goal of this research.

Figure 4. Sharing the tag recapture hotline number with fishermen

To address these knowledge gaps and better understand why the Gulf of Mexico stock has failed to rebuild according to rebuilding timelines established in the Fishery Management Plan, Lowerre-Barbieri’s lab has started an acoustic tagging study on the sea mounts, a popular offshore fishing area in the Florida Keys. In April 2017, 15 greater amberjack were captured and implanted with acoustic tags (Fig. 3). All fish were spawning capable, based on ovarian biopsies and strip-spawned milt. Shark depredation was observed on captured but not released fish (Fig. 3). Fishermen are working closely with the lab, reporting recaptured fish and sharing their observations, with four fish already recaptured and reported to the tagging hotline.

Video analysis and capture rates in Madison Swanson indicate fairly large numbers of greater amberjack, with some fish occurring during all sampling months (December through May), but an apparent increase during spring spawning months. In the upcoming sampling season, Lowerre-Barbieri’s lab will assess if active spawners occur at this site as well as begin preliminary tagging.  This cross-site comparison in two very different habitats with extremely different fishing pressure will provide key information about spawning site selection, site fidelity, and potential mixing between the stocks. This research will build the needed foundation to better understand these complex processes and how they affect stock resilience and would not have been possible without the loan of OTN receivers.

Figure 5. Greater amberjack in Madison Swanson

For more information on Dr. Sue Lowerre-Barbieri’s research, visit iTAG’s website or follow their Facebook, Twitter, and Instagram pages where updates are posted regularly.