Vol. 344: 271–275, 2007 MARINE ECOLOGY PROGRESS SERIES Published August 23 doi: 10.3354/meps06941 Mar Ecol Prog Ser Deep-diving and diel changes in vertical habitat use by Caribbean reef sharks Carcharhinus perezi Demian D. Chapman1, 2,*, Ellen K. Pikitch3, Elizabeth A. Babcock2, Mahmood S. Shivji1 1Guy Harvey Research Institute/Nova Southeastern University Oceanographic Center, 8000 N. Ocean Drive, Dania Beach, Florida 33004, USA 2Pew Institute for Ocean Science, Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, Florida 33133, USA 3Pew Institute for Ocean Science, Rosenstiel School of Marine and Atmospheric Science, University of Miami, 126 E. 56th Street, New York, New York 10022, USA ABSTRACT: Longline sampling (83 sets) supplemented with 6 pop-off archival transmitting (PAT) tag deployments were used to characterize vertical habitat use by Caribbean reef sharks Carcharhinus perezi at Glover’s Reef atoll, Belize. Longline catch-per-unit-effort (CPUE) in 2 shallow reef habitats (lagoon <18 m depth, fore-reef <40 m depth) underwent significant nocturnal increases for sharks larger than 110 cm total length (TL), but not for smaller sharks. Nocturnal CPUE of small sharks appeared to increase in the lagoon and decrease on the fore-reef, suggestive of movements to avoid larger conspecifics. PAT tag deployments (7 to 20 d) indicate that large C. perezi generally increased the amount of time they spent in the upper 40 m of the water column during the night, and inhabited much greater depths and tolerated lower temperatures than previously described. The wide vertical (0 to 356 m) and temperature range (31 to 12.4°C) documented for this top-predator reveals ecologi- cal coupling of deep and shallow reef habitats and has implications for Marine Protected Area (MPA) design. KEY WORDS: Satellite tracking · Depth range · Coral reef ecology · Marine Protected Area · Carcharhinidae Resale or republication not permitted without written consent of the publisher INTRODUCTION more common inside the lagoon (<18 m depth) than larger sharks, which are mostly caught in relatively The Caribbean reef shark Carcharhinus perezi is the shallow fore-reef habitats (<40 m) adjacent to much most abundant large carcharhinid shark observed on deeper water (>400 m, Pikitch et al. 2005). Automated shallow coral reefs in the tropical western Atlantic acoustic tracking coupled with limited stomach con- (Compagno 1984, 2002, Opitz 1996), where it has pre- tents analysis revealed that large C. perezi routinely viously been recorded at depths up to 30 m (Com- visit and likely forage in these shallow reef habitats pagno 1984, 2002). Although ecosystem modelling (Chapman et al. 2005, Garla et al. 2006a1). However, suggests that overexploitation of large sharks like C. the proportion of time spent in shallow-reef habitats perezi could impact community structure on shallow and the depth range of large C. perezi remains Caribbean coral reefs (Bascompte et al. 2005), little is unknown. This information is important from the per- known about the habitat use and ecology of this spe- spective of elucidating the ecological role of the spe- cies. Shallow tropical reefs (<40 m depth) are impor- cies on coral reefs and developing placed-based tant habitat for this species during their early life- conservation measures (e.g. Marine Protected Areas history (Pikitch et al. 2005, Garla et al. 2006a,b), and ontogenetic changes in habitat use have been docu- mented at Glover’s Reef atoll, Belize (Pikitch et al. 1 See also Carcharhinus perezi under www.iucnredlist.org/ 2005). Small juveniles (<110 cm total length [TL]) are search/details.php/60217/summ *Email: [email protected] © Inter-Research 2007 · www.int-res.com 272 Mar Ecol Prog Ser 344: 271–275, 2007 [MPAs]) for this top predator, which is vulnerable to ted with PAT3 tags (Wildlife Computers) during May overexploitation (Compagno 1984, 2002, Garla et al. 2003 at Glover’s Reef. In June 2005, a large juvenile 2006a; see also footnote 1). female (183 cm TL) was fitted with a PAT4 tag on the The objectives of the present study were to charac- coast of nearby Turneffe atoll (Fig. 1). Tags were terize the depth range of Carcharhinus perezi and attached using a 100 kg-test, abrasion-resistant delineate diel and ontogenetic changes in the use of 2 monofilament bridle threaded through the base of the shallow-reef habitats at Glover’s Reef atoll (i.e. lagoon first dorsal fin, approximately 10 cm from its trailing <18 m, fore-reef <40 m). This was achieved using a edge, and secured with 2 stainless steel crimps. PAT combination of fishery-independent longline sampling tags archived ambient depth and temperature every 1 at this site and pop-off archival transmitting (PAT) tag- min of deployment and transmitted 3 h summaries in ging of large juvenile and adult sharks. pre-programmed bins. They also provided minimum and maximum depths and temperature recordings for each summary period. Tags were programmed to MATERIALS AND METHODS detach and transmit data summaries 90 to 180 d after deployment. All summarized data received were man- Detailed descriptions of Glover’s Reef atoll and the ually checked for appropriate co-variation between ongoing shark survey were reported by Pikitch et al. depth, light and temperature in order to ensure that (2005). Longline gear was deployed during sampling the tag was on the shark and functioning properly for expeditions conducted in May-June each year from the duration of the track. Detachment was recognized 2001 to 2006. Surface-set lines consisted of 40 to 70 by constant surface depth readings. For each tagged baited hooks (16/0 Mustad circle) spaced at 20 m shark, a chi-square test was used to determine intervals, hanging approximately 3.5 m below the whether there were significant differences in the pro- mainline. Set locations were categorized into 1 of 2 portion of time spent above a depth of 40 m (the shallow macrohabitat types. ‘Fore-reef’ lines were set approximate depth of the beginning of the reef slope) over the narrow fore-reef (<500 m wide) that fringes between day (06:00 to 17:59 h) and night (18:00 to Glover’s Reef, in 6 to 40 m of water. The fore-reef 05:59 h) hours. abruptly drops off in a wall formation at Glover’s Reef, quickly exceeding 400 m. ‘Lagoon’ lines were set inside the atoll, in 3 to 18 m of water over mixed sea- RESULTS grass, soft-bottom and patch-reef substrates. Each longline set was categorized as ‘day’ or ‘night’ based A total of 83 standard longline sets (50 day, 33 night; on the recorded set and haul times. Log-transformed 36 fore-reef, 47 lagoon) were completed, resulting in catch-per-unit effort (CPUE [no. sharks 100 hooks–1 the capture of 68 Carcharhinus perezi in the ‘small’ h–1]) was determined separately for 2 size categories; category (39 males, 29 females). Neither habitat nor juvenile sharks <110 cm total length (TL, measured time of day significantly influenced log-transformed on a straight line from the rostrum to the tip of the CPUE of small C. perezi (ANOVA, p = 0.55 and p = upper caudal lobe) were defined as ‘small’, while 0.79 respectively, Fig. 2a); however, the interaction of larger juvenile and adult Carcharhinus perezi >110 time and habitat approached significance (p = 0.065). cm TL were defined as ‘large’. These categories fol- CPUE of small sharks was higher in the lagoon during low those used by Pikitch et al. (2005) and Garla et al. the night, but higher on the fore-reef during the day (2006b) for elucidating ontogenetic habitat use pat- (Fig. 2a). The same 83 standard longline sets resulted terns in this species. Sharks were also assigned matu- in the capture of 59 C. perezi within the ‘large’ size cat- rity based on clasper size and calcification in males egory (26 males, 42% mature; 33 females, 21% (Pikitch et al. 2005) and the size at maturity (200 cm) mature). Unlike that of the small sharks, log-trans- given by Compagno (1984) for females. To test formed CPUE was significantly greater at night than in whether time of day, habitat, or the interaction the day, regardless of habitat, and was significantly between these 2 factors had significant effects on log- higher on the ocean reef than in the deep lagoon transformed CPUE of small and/or large C. perezi, (ANOVA, p < 0.0001 and p < 0.01 respectively, Fig. 2b). ANOVA tests were performed using SPSS version The interaction between time of day and habitat was 13.0 for Windows. Year effects were not examined non-significant (p = 0.064). because Pikitch et al. (2005) previously demonstrated PAT tags remained attached for 7 to 20 d before that this factor had no effect on log-transformed prematurely detaching and surfacing in the same CPUE from 2001 to 2005. general area in which the individual was released Five adult Carcharhinus perezi (3 males of 170, 192, (Fig. 1). Four of the 6 tags transmitted summarized 193 cm TL, and 2 females of 210, 230 cm TL) were fit- data records for the entire track (3 adult males, 1 Chapman et al.: Reef shark vertical habitat use 273 Fig. 1. Glover’s Reef atoll, Belize (ca. 16° 44–56’ N, 87° 42–53’ W): locations of standard longlines (white circles) and release locations for PAT-fitted Carcharhinus perezi (asterisks) at Glover’s Reef; shark ID codes are followed by track duration (d) and max. recorded depth (m). ‘Coast of Belize’ inset: release location and data for shark tagged at Turneffe atoll. Prefixes of shark ID codes are: G, Glover’s Reef; T, Turneffe; AM, adult male; AF, presumed adult female; JF, juvenile female 0.5 adult female; Fig.