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Habitat Preferences and Site Fidelity of the Ornate Wobbegong Shark (Orectolobus Ornatus) on Rocky Reefs of New South Wales1

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Habitat Preferences and Site Fidelity of the Ornate Wobbegong Shark (Orectolobus Ornatus) on Rocky Reefs of New South Wales1 Habitat Preferences and Site Fidelity of the Ornate Wobbegong Shark (Orectolobus ornatus) on Rocky Reefs of New South Wales1 Robert Carraro2 and William Gladstone2,3 Abstract: Habitat and microhabitat preferences and site fidelity of Orectolobus ornatus were assessed between September 2002 and August 2003 to assess poten- tial suitability of marine reserves for its conservation. Of six rocky reef habitats available in the study area (sponge gardens, artificial structures, barren boulders, sand, sea grass, macroalgae), O. ornatus exhibited a significant preference for sponge gardens, artificial structures, and barren boulders habitats. Habitat pref- erences of males and females, and individuals <1 m and >1 m, did not differ. Orectolobus ornatus selected daytime resting positions with a high topographic complexity and crevice volume and did not select on the basis of prey avail- ability. Habitat and microhabitat preferences may be related to the need for predator avoidance. Regular monitoring of 40 individually identified O. ornatus revealed that none was a permanent resident of the study area. Seven individuals exhibited short-term temporary fidelity to the study area; they were resighted frequently for part of an intensive 100-day survey. Remaining individuals were temporary visitors; they were resighted at most once after initial identification or returning after extended absences. Monthly population surveys confirmed the turnover of O. ornatus in the study area. The lack of long-term site fidelity sug- gests that small marine reserves will be ineffective as a conservation strategy for O. ornatus. A primary requirement for conserving ma- processes such as competition, predation, rine species is an understanding of the pro- and recruitment ( Jones and Syms 1998). The cesses underlying patterns in distribution and importance of habitat has received increas- abundance (Bell et al. 1991). One such factor ing attention from conservation biologists that has received considerable attention is because anthropogenic degradation of habi- habitat variation. The patchy distribution of tat is a primary cause of global declines in habitats influences distribution and abun- biodiversity and as spatial approaches to con- dance at many spatial scales (Syms 1995). servation and management (such as marine Habitat structure or quality of habitats may protected areas) are increasingly utilized limit populations through the availability of (Ray and McCormick-Ray 2004). Under- critical resources and may modify ecological standing the importance of habitat for species requires the separation of habitat usage and 1 This research was funded by grants from the Uni- preference, where habitat usage includes the versity of Newcastle and is a contribution from the habitats in which individuals occur and habi- Centre for Sustainable Use of Coasts and Catchments. tat preference is a species’ use of a habitat in Manuscript accepted 2 June 2005. relation to its relative availability (Manly et al. 2 Centre for Sustainable Use of Coasts and Catch- 1993). ments, School of Applied Sciences, University of New- castle (Ourimbah Campus), P.O. Box 127, Ourimbah, Although elasmobranch nursery habitats New South Wales 2258, Australia. have been well studied, there are few studies 3 Corresponding author (e-mail: william.gladstone@ of usage and preference for other life stages newcastle.edu.au). and habitats, despite the critical importance of habitat in determining distribution and Pacific Science (2006), vol. 60, no. 2:207–223 abundance and the application of this in- : 2006 by University of Hawai‘i Press formation for conservation planning (Simp- All rights reserved fendorfer and Heupel 2004). The available 207 208 PACIFIC SCIENCE . April 2006 quantitative studies of habitat preference between 1990 and 2000 raised concerns about demonstrate fine-scale discrimination among the status of wobbegong populations (NSW available habitats. Juvenile lemon sharks Fisheries 2002a). Other sources of anthropo- (Negaprion brevirostris) prefer habitats less genic mortality include recreational fishing than 50 cm depth, with water temperature and protective beach meshing programs (Po- greater than 29 C, and consisting of a mix- gonoski et al. 2002). Due to recent declines ture of rock and sand (Morrisey and Gruber in populations, O. ornatus has been classified 1993a). Tiger sharks (Galeocerdo cuvier)in as vulnerable in New South Wales and near- Shark Bay, Western Australia, prefer shallow threatened throughout its range (Cavanagh sea-grass beds, where their prey is more et al. 2003). Marine reserves have been advo- abundant (Heithaus et al. 2002). With the ex- cated as a strategy to conserve wobbegong ception of general habitat descriptions little sharks (Otway and Parker 2000, NSW Fish- data have been obtained for the habitat usage eries 2002b). However, the ecological under- of wobbegong sharks. There is, therefore, standing about wobbegongs necessary for considerable scope for studies of habitat evaluating the potential usefulness of marine preference in this and other shark species of reserves is lacking (Pogonoski et al. 2002). conservation significance whose habitat is af- This lack of information is a critical gap given fected by human activities. the conservation and management concerns The related concept of site fidelity ex- for this species. The aims of this study were presses the temporal attachment of an indi- to determine (1) habitat preferences and (2) vidual to a space in its habitat. The degree site fidelity of O. ornatus and to use this infor- of site fidelity varies in relation to the avail- mation to assess the potential usefulness of ability and defensibility of critical resources marine reserves as a conservation and man- and ranges between strict territoriality, shared agement strategy. home ranges, and nomadism, although terri- toriality has not been demonstrated in sharks (Heithaus 2004). Site fidelity is known to oc- materials and methods cur at some stage in the life cycle of a number Study Species of sharks (McKibben and Nelson 1986, Hol- land et al. 1993, Morrissey and Gruber 1993b, Orectolobus ornatus is a nocturnal benthic Goldman and Anderson 1999, Rechisky and predator that occurs in all Australian states Wetherbee 2003). The existence of site fidel- and Papua New Guinea to a depth of at least ity will determine the likely success of spa- 100 m. During daylight hours it rests in pro- tially based management strategies such as tected parts of reefs. Orectolobus ornatus is marine protected areas (Kramer and Chap- ovoviviparous and pups are born at @20 cm man 1999). Further understanding of the ex- length, with adults growing to a maximum istence of site fidelity in sharks is important length of @300 cm. Sexual maturity is be- in assessing the potential usefulness of marine lieved to occur at 175 cm length (Last and protected areas for conservation and manage- Stevens 1994). ment. Two species of wobbegong sharks (family Study Area Orectolobidae) occur in southeastern Austra- lia: Orectolobus ornatus (De Vis, 1883) and O. This study occurred between September maculatus (Bonnaterre, 1788). Both species 2002 and August 2003 in the Fly Point– are demersal, inhabit temperate rocky reefs, Halifax Park Aquatic Reserve (hereafter and are likely to have an important functional ‘‘the reserve’’) in Port Stephens, New South significance because of their role as top pred- Wales, Australia, at 32 42 0 50 00 S, 152 90 ators (Last and Stevens 1994). Wobbegongs 20 00 E (Figure 1). Habitats within the reserve are caught by commercial fishers in New were typical of those present in adjacent South Wales as a target group and as by- nearshore areas (Underwood et al. 1991) and catch. Declines in annual catches of >60% included fringe (dominated by foliose macro- Figure 1. Location of study areas (a) within Port Stephens and (b) within the Fly Point–Halifax Park Aquatic Reserve. The boundary of the reserve is shown within the waters of Port Stephens and the land is shaded gray. 210 PACIFIC SCIENCE . April 2006 algae in depths of 1–8 m), barren boulders Habitat preferences were determined from (with high coverage of crustose coralline al- resource selection ratios (Manly et al. 1993) gae and high abundance of the sea urchin using the formula w^i ¼ oi/pI , where oi is Centrostephanus rodgersii in depths of 2–12 the proportion of habitats used that are in m), sponge gardens (high coverage of en- category i, pI is the proportional availability crusting and foliose sponges and limited cov- of habitat i, and w^i is the preference score erage of algae in depths of 10–20 m), sand, for habitat category i. The standard error sea grass (Posidonia australis, Halophila ovalis, (SE)pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi of w^i was calculated by SEðw^iÞ¼ and Zostera capricorni), and artificial structures w^i f1/ui À 1/uþ þ 1/mi À 1/mþg, where ui is (small sunken boats, refuse, and artificial reefs the number of sharks in habitat i, uþ is the constructed of metal frames in depths of 6– total number of observations of sharks, mi 12 m). Observations reported here were un- is the frequency of occurrence of habitat i, dertaken at three sites in the reserve: Fly and mþ is the total occurrence of all habitats. Point, Little Beach, and Halifax Park. Fixed w^i 95% confidence intervals were calculated G transects of 500-m length by 5-m width that from w^i Za/ðIÞSEðw^iÞ, where Za/ðIÞ is the covered all habitats and the depth range of 100a/ðIÞ percentage point of the standard each site were established at the beginning normal distribution and I is the number of of the study. The boundaries of the transects habitat groups. A Bonferroni correction was were noted in relation to prominent substra- applied by dividing the a significance level tum features. (0.05) by the number of habitat groups to allow for multiple comparisons between all Habitat Availability and Preferences habitat categories. Confidence intervals were used to determine the significance of prefer- The relative availability of each habitat in the ence scores.
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