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Shorter Version of the Tagging Video from Isla Mar Research Expeditions on Vimeo. Nassau grouper (Epinephelus striatus) have long been an icon of the Caribbean and were considered the most commercially important grouper species in the region. Unfortunately, due to decades of direct fishing on spawning aggregations, their numbers have drastically declined, and the species is currently in the final stages of being listed under the Endangered Species Act. Puerto Rico is no exception to this trend, as all Nassau grouper aggregations were thought to have completely collapsed in previous decades. In early 2012 a group of researchers from the University of Puerto Rico, Mayagüez (UPRM) and the Caribbean Coral Reef Institute discovered a small aggregation of Nassau grouper at a remote location west of Mayagüez. This discovery provided a unique opportunity for monitoring this reproductive phenomenon. Characterizing this spawning aggregation required not only quantifying the number of individuals participating, but also the seasonality of spawning and the movement and distribution of individuals, especially in relation to spawning sites and available habitat types. This required in situ studies at the mesophotic depths (> 50 m) where this aggregation was located. Led by PhD candidate Evan Tuohy (UPRM), a non-traditional approach was developed to be able to utilize acoustic telemetry to track fish movements across seascapes. Acoustic telemetry surgically implants acoustic transmitters inside the fish’s abdomen. In most studies the surgical procedures are conducted at the surface on boats or in the laboratory. However, removing the fish from mesophotic depths adds potentially fatal stress that could kill fish and significantly reduce the number of individuals available both for the study and for spawning. The solution was surgical tagging conducted entirely in situ using closed-circuit rebreathers (CCR). In situ tagging – where the capture, tagging, and release are completed entirely at the depth in which the fish occurs naturally – had never been done with CCR at mesophotic depths. The greatest limiting factor at this depth is reduced time at the seafloor, however CCR technology provides an optimal breathing mixture to the diver at all times with a minimum of amount of equipment carried, thus reducing diver effort. This combined benefit allows for increased time spent at depth within the mesophotic realm. Nassau grouper were captured in baited fish traps. Once fish were in the traps, CCR divers would conduct tagging by guiding the grouper out of the trap and into a mesh catch bag. After the fish was restrained upside-down to induce a calm state, a 3 cm incision was made below the pelvic fins, an acoustic tag inserted into the body cavity and the incision sealed with surgical staples. This method proved highly efficient with average handling time of 10 minutes; therefore multiple fish could be tagged during a single dive. After surgery, each fish was released, and no signs of distress were observed as they swam away to the reef. A 100% survival rate was documented, which has never been reported in other tagging studies. To date researchers have tagged 30 grouper with this methodology and the information gathered from these tags will yield critical information on the spatial and temporal dynamics of the spawning aggregation. This will provide a significant contribution to long-term monitoring of this species, with hopes of recovering the populations of Nassau grouper within the US Caribbean.
For additional information on in situ tagging using CCR please see reference below or contact Evan Tuohy at evan.tuohy@upr.edu
Tuohy, E, Nemeth, M, Bejeranno, I, Sharer, M and Appeldoorn, RS. 2015. In situ tagging of Nassau grouper (Epinephelus striatus) using closed-circuit rebreathers at a spawning aggregation in Puerto Rico. Marine Technology Society Journal. 49(1): 115-123.
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