Reef Relief and Volume Are Predictors of Atlantic Goliath Grouper Presence and Abundance in the Eastern Gulf of Mexico

Bull Mar Sci. 91(4):399–418. 2015 research paper http://dx.doi.org/10.5343/bms.2015.1001 Reef relief and volume are predictors of Atlantic goliath grouper presence and abundance in the eastern Gulf of Mexico 1 Florida Fish and Wildlife AB Collins 1, 2 * Conservation Commission, Fish LR Barbieri 1 and Wildlife Research Institute, 3 100 8th Avenue SE, Saint RS McBride Petersburg, Florida 33701. ED McCoy 4 2 Current address: Florida Sea PJ Motta 4 Grant Agent, University of Florida IFAS Extension, Manatee County Government, 1303 17th Street West, Palmetto, Florida ABSTRACT.—Atlantic goliath grouper, Epinephelus 34221. itajara (Lichtenstein, 1822), presence, abundance, and size 3 National Marine Fisheries distribution were assessed during monthly underwater visual Service, Northeast Fisheries surveys at natural and artificial reefs in the central eastern Science Center, 166 Water Gulf of Mexico (7–50 m depth). Atlantic goliath grouper were Street, Woods Hole, more likely to be present, and to occur in greater abundance, Massachusetts 02543. at artificial reefs. Abundance was positively related to vertical 4 University of South Florida, relief and structural volume, and the largest numbers of Department of Integrative individuals were observed at high volume artificial reefs (e.g., Biology, 4202 East Fowler shipwrecks). This was likely due to greater refuge availability Avenue, Tampa, Florida 33620. provided by artificial reefs within the study region, where * Corresponding author email: structurally comparable natural habitats are rare. Atlantic <[email protected]>, telephone: goliath grouper measured via underwater video ranged in (941) 722-4524, fax: (941) 721- size from 36 to 214 cm total length (TL; median = 121 cm). No 6608. relationship was observed between TL and site depth or reef type. Tagged individuals were documented to move distances ranging 10–203 km, but the majority of tag return data indicated high site fidelity. The strong site fidelity of goliath grouper combined with their continuous and predictable association with artificial reefs allows for relatively efficient Date Submitted: 8 January, 2015. monitoring of individuals within a given region; however, Date Accepted: 31 August, 2015. these traits also increase vulnerability to exploitation and Available Online: 2 October, 2015. underline the need for cautious management. The spatial distribution of marine fish populations is rarely uniform. Whether or not a species is present within a given area is influenced by an extensive suite of factors, including habitat suitability, individual movement, and the presence of con- specifics (Sinclair 1988, MacCall 1990). Numerous studies have demonstrated the influence of habitat features upon fish presence and abundance, especially for reef fishes (e.g., Sale and Douglas 1984, Jones 1991, Hixon and Beets 1993, Sale et al. 1994, Nagelkerken et al. 2000, Wilson et al. 2010, Heyman and Wright 2011), and assess- ments of populations and stock status are better informed when measures of habitat association and suitability are well defined (Jones and Syms 1998). In the case of exploited or protected species, identification of the parameters that influence habitat Bulletin of Marine Science 399 © 2015 Rosenstiel School of Marine & Atmospheric Science of the University of Miami 400 Bulletin of Marine Science. Vol 91, No 4. 2015 selection is critical to ensure management of important areas and to efficiently target monitoring efforts during attempts to assess recovery or disturbance (MacCall 1990, Jones and Syms 1998). Atlantic goliath grouper [Epinephelus itajara (Lichtenstein, 1822); hereafter “goliath grouper”] may attain 2.5 m in total length (TL), weigh up to 400 kg, and live at least 37 yrs (Bullock et al. 1992, Craig et al. 2011). The species historically oc- curred throughout subtropical and tropical waters of the Atlantic Ocean and Gulf of Mexico (Bullock et al. 1992, Craig et al. 2011), but a significant population decline was observed through the latter part of the 20th century after intense fishing pressure (Sadovy and Eklund 1999). Goliath grouper were protected from harvest in US waters in 1990 (GMFMC 1990, SAFMC 1990) and in 1994 the species was listed as criti- cally endangered on the IUCN World Conservation Union’s Red List of Threatened Species (Pusack and Graham 2009). The species remains protected in US waters at this time and is also protected in other parts of the Atlantic Ocean and Caribbean region (Craig et al. 2011), but fisheries persist in some areas and the status of goliath grouper throughout the geographic range of the species remains uncertain. Within US waters, goliath grouper have responded well to protection and are show- ing signs of recovery (Cass-Calay and Schmidt 2009, Koenig et al. 2011). However, their life history characteristics make them especially susceptible to overfishing (e.g., long lived, late maturation, aggregate to spawn; Bullock et al. 1992, Musick 1999, Sadovy and Eklund 1999, Musick et al. 2000). Juvenile goliath grouper settle in shallow, nearshore estuaries, commonly near mangroves (Eklund and Schull 2001, Koenig et al. 2007, Lara et al. 2009), and display an ontogenetic shift to offshore marine habitats with growth (Smith 1976, Koenig et al. 2007). Adults are reef associated, and typically occur at depths <50 m (Bullock et al. 1992, Heemstra and Randall 1993, Colin 1994, Gerhardinger et al. 2006, Koenig et al. 2011). Individuals are sedentary and display high site fidelity through most of the year, except during reproductive periods (August–September), when they may travel hundreds of kilometers to reach spawning aggregations (Sadovy and Eklund 1999, Koenig et al. 2011, Koenig and Coleman 2013, Collins 2014). This predictable and continuous association with reef habitats which are relatively close to shore, further increases goliath grouper vulnerability to exploitation (Huntsman et al. 1999, Koenig et al. 2011). Future success of the goliath grouper population depends upon responsible management as well as the availability of suitable habitat and resources throughout on- togeny. The southeastern Gulf of Mexico has historically been a center of abundance for goliath grouper (Bullock and Smith 1991), and this region is also the area where recovery has been most evident (Koenig et al. 2011). Using visual survey data at reef habitats from volunteer and scientific divers collected from 1994 through 2008, Koenig et al. (2011) performed a comprehensive assessment of goliath grouper recovery in waters off the state of Florida. They documented the greatest numbers of goliath grouper at high relief artificial and rocky reefs, and greatest densities were observed off the southwest coast of Florida (between Charlotte Harbor and the Florida Keys). We aimed to build on this work by providing a detailed quantitative assessment of relative abundance and size distribution of goliath grouper as associated with specific habitat features off the central west coast of Florida. The study area is just north of the species’ historical center of abundance, and provides data for a region where relatively few quantitative surveys have been performed. Collins et al.: Predictors of goliath grouper presence and abundance 401 Based on what is known regarding the life history of this species and their pref- erence for high-relief habitat that provides shelter (Bullock et al. 1992, Sadovy and Eklund 1999, Koenig et al. 2011), we predicted that goliath grouper relative abundance would exhibit a positive relationship with habitat relief and volume. Further, we expected that there would be a positive relationship between fish size and depth, since they settle in estuaries and are expected to move offshore as they approach maturity. In the absence of landings data and the associated life history information (e.g., length and age composition), quantification of size structure can provide a proxy for age distribution. Therefore, the present study aimed to: (1) describe the presence and abundance of goliath grouper as related to specific habitat features (artificial vs natural, depth, relief, volume) within a region where high relief natural reefs are rare; and (2) provide detailed information regarding size distribution of the species within the study area. This information should advance the ability to monitor population changes through time, and assist with predictions of population dynam- ics for a species currently in a period of stock recovery. Methods Selection and Evaluation of Survey Sites.—Visual surveys and underwater video were used to quantify the abundance and size distribution of goliath grouper within the study area between October 2007 and May 2010. Surveys (n = 379) were conducted during daylight hours in all months of the year, and survey sites (n = 80) were distributed across a range of depths to 50 m to include both artificial and natural reefs (Fig. 1). Artificial reefs n( = 36 sites, 268 surveys) included mostly shipwrecks, but also incorporated other anthropogenic structures (concrete pilings or concrete rubble fields). Natural reefs n( = 44 sites, 111 surveys) included lime- stone ledges, pinnacles, and offshore freshwater spring openings, which comprise the typical hard-bottom habitat within the study area (Smith 1976, Simmons et al. 2014). Sites were selected to ensure that the full spectrum of available reef types within the region were included, and effort was made to survey a diverse distribution of habitat types with varying levels of structural complexity

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