In situ Tagging of Nassau Grouper Epinephelus striatus Using Closed-Circuit Rebreathers at a Spawning Aggregation in Puerto Rico

January/February 2015 Volume 49 Number 1 115 that significantly reduce the survival rate of the fish and ultimately compromise the outcome of the tagging study (Bridger & Booth, 2003; Lindholm et al., 2005). Barotrauma—pressurerelated stress caused by the overexpansion and possible rupture of the swim bladder—is the most detrimental effect to fishes retrieved from relatively deeper depths (Parrish & Moffitt, 1992; Starr et al., 2000; Bartholomew& Bohnsack, 2005; Rummer & Bennet, 2006; Campbell et al., 2009; Sumpton et al., 2010). A study conducted by Wilson and Burns (1996) found that survival rates for both red grouper (Epinephelus morio) and scamp grouper (Mycteroperca phenax) decreased to <33% with fish captured at depths greater than 44 m. Other lethal and sublethal stressors associated with surface tagging include thermal shock, physical trauma, predation, physiological imbalance, and prolonged exposure to sunlight and air (Lindholm et al., 2005; Campbell et al., 2009). A solution to these risks include methodologies utilizing true in situ tagging where the capture, tagging, and release are completed entirely at the depth in which the fish occurs naturally (Lindholm et al., 2005; Feeley et al., 2012). In situ tagging is an unconventional procedure compared to traditional fish tagging. Starr et al. (2000) first conducted in situ tagging procedures on deep-water rockfish. However, this method involved reeling the fish to a manageable depth for normal diving operations, subjecting the fish to barotrauma and other physiological stressors. Lindholm et al. (2005) conducted in situ tagging via saturation diving missions at the Aquarius Undersea Laboratory. This method, although highly successful, is impractical for scientific diving conducted at remote locations, as it requires an underwater living facility. Similarly, both of these studies completed tagging at a depth of 20 m. However, to date there has yet to be a practical method developed for true in situ tagging for fish that occur at deeper depths. Over the past several decades, the use of closed-circuit rebreather (CCR) technology has become increasingly available to the scientific diving community (Pyle, 2000; Lindfield et al., 2014). Closed-circuit rebreathers offer several advantages over traditional open circuit (OC) diving, including higher gas efficiency, lower operational costs, shortened decompression obligations, and near silent operations (Pyle, 1999; Bozanic, 2002; Parrish & Pyle, 2002; Butler, 2004; Tetlow& Jenkins, 2005; Shreeves & Richardson, 2006; Sieber & Pyle, 2010; Lindfield et al., 2014). Closed-circuit rebreather technology differs from OC technology in that the divers exhaled breath is no longer expelled into the surrounding environment but rather is recirculated, chemically scrubbed of carbon dioxide, replenished with oxygen, and returned to the diver (Pyle, 2000; Bozanic, 2002; Shreeves & Richardson, 2006). Rebreathers deliver a dynamic breathing mixture by maintaining a preset, optimal oxygen partial pressure at all depths, thus significantly reducing the diver’s decompression obligation, while increasing bottom time duration and depth capabilities (Pyle, 1999; Shreeves & Richardson, 2006, Sieber & Pyle, 2010). Additionally, bubble and noise-free operation enhances the diver’s ability to both approach fish and observe behavior unaffected by diver presence (Lobel, 2001; Cole et al., 2007, Lindfield et al., 2014). The use of CCR technology has recently opened environments at mesophotic depths (30–150+ m, Hinderstein et al., 2010) to more extensive and rigorous study (e.g., Pyle, 2000; Sherman et al., 2010; Garcia-Sais, 2010; Bejarano et al., 2014), and with this comes the need to investigate ecological processes, with the issue of connectivity and the application of acoustic tagging being at the forefront. The purpose of this study was to develop and implement the methodologies for conducting true in situ acoustic transmitter implantation using CCR technology. Motivation for this study was to gather information on the movements of the Nassau grouper (Epinephelus striatus) relative to its habitat and reproduction. This species is known to form large spawning aggregations, yet has been overfished throughout its range (Aguilar-Perera, 2006; Sadovy de Mitcheson et al., 2008; Schärer et al., 2012). It is currently considered threatened by the International Union for the Conservancy of Nature (IUCN), so quantification of movement patterns, especially relative to reproduction, would have high conservation value (Cornish & Eklund, 2003). Materials and Methods Site Description All diving operat ions of this study were conducted at Bajo de Sico (BDS), a seamount located in the Mona Passage, 27 km off Puerto Rico’s western coast (Figure 1). Reef bathymetry is characterized by a ridge of highly rugose rock promontories ranging in depths from 25 to 45 m, which rises from a mostly flat, gradually sloping shelf that extends to 100 m. Below this depth, the shelf ends in a vertical wall that reaches depths of 200–300 m to the southeast and over 1,000 m to the north. The dominant oceanographic features and its location within the Mona Passage 116 Marine Technology Society Journal make this area subject to periods of strong, persistent northerly currents. The area harbors highly diverse and taxonomically complex fish assemblages and is a known Nassau grouper spawning aggregation site (Garcia-Sias et al., 2007). All dives conducted for the purpose of tagging were completed during the days following the full moons of the winter months, to coincide with the grouper spawning aggregation period (Colin, 1992; Whaylen et al., 2006; Schärer et al., 2012). Fish Capture In situ fish collection was conducted using Antillean arrowhead fish traps (dimensions: 1.2 m × 1.2 m × 50 cm). The traps were composed of a 3/8-inch rebar frame covered with 2.54 cm mesh PVC-coated chicken wire. Each trap contained two-side doors for fish removal and a thin vertical slot (approx. 2.3 × 50 cm), opposite the entry chute, through which a panel could be inserted to guide fish toward one of the doors (Figure 2). Trap design and divider implementation were developed based on earlier procedures utilized by the Florida Fish and Wildlife Conservation Commission (A. Acosta and P. Barbera, personal communication). The panel was constructed of 2.54-cmmesh PVC-coated chicken wire enclosed in a frame made of 1.27-cm PVC, which added structural support as well as prevented snagging of the wire mesh while the divider was slid into the trap. A total of four traps were deployed at 40to 50-m depths along the base of two sand-bottom channels. These locations were chosen prior to deployment based on their minimal live benthic cover and position relative to the dominant current regime. Trap locations were in close proximity to the spawning aggregation site, which potentially increased catch per unit effort and allowed for the traps to be observed by open circuit divers working in the area. The distance between trapping locations was such that all four traps could be serviced on a single CCR dive. Divers utilized the Inspiration (Ambient Pressure Diving®, Cornwall, United Kingdom) electronically controlled CCR (eCCR) units, FIGURE 1 Bajo de Sico Bank (18°14′N, 67°26′W), Puerto Rico. (A) Study location 27 km off the west coast of Puerto Rico. (B) Depth contours depicting bathymetric features between 30 and 80m. (C) Blue line indicated the 200-m depth contour. (Color version of figures are available online at: http://www. ingentaconnect.com/content/mts/mtsj/2015/00000049/00000001.)