A PILOT STUDY OF INSHORE REEF FISH ASSEMBLAGES ON KANGAROO ISLAND

By

S.A. Shepherd1, M. Kinloch2 and H. Bartram2

1 South Australian Research and Development Institute (Aquatic Sciences), PO Box 120, Henley Beach, SA 5022. 2 Kangaroo Island Natural Resources Board, PO Box 520, Kingscote, SA 5223

Summary In this pilot study, we examined the feasibility of establishing a quantitative monitoring system for coastal reef fishes around the Kangaroo Island (KI) coastline. In this system, fish species abundances and size compositions are estimated visually along measured transect lines, or during standard timed swims, and recorded on waterproof data sheets attached to underwater slates. The pilot study was conducted at six sites, encompassing two reefs in each of three bays on KI: Emu Bay, D’Estrees Bay and Hanson Bay (see Figure 1). Across all sites, 16 species of fish were recorded at total densities ranging from 0.10 - 0.16 fish per square metre (m-2). Three species occurred in moderate to high abundance, (blue-throated wrasse, banded sweep and zebra fish) but the most suitable indicator species are likely to be blue-throated wrasse, western blue groper, magpie perch and moonlighter because of their position at the top of the food chain and their susceptibility to fishing pressure. The sex ratio of blue-throated wrasse is also a useful indicator of the intensity of recreational rock fishing. The abundance of juvenile and sub-adult blue groper, a protected species in parts of SA, was very high at Osmanli Reef, suggesting a recruitment hotspot within D’Estrees Bay.

Introduction A biodiversity monitoring program is currently being developed for the marine and coastal environments of Kangaroo Island, South Australia. This involves the selection of representative indicator species and index sites to assess trends in the condition of regional biodiversity assets and identify threats to ecosystem structure and function. The species composition and size structure of fish assemblages are useful indicators of the health of subtidal rocky reefs. Fish feed at different levels of the food web, from herbivores to top carnivores, and their abundance and size are affected by fishing, pollution and other human impacts. Repeated, quantitative surveys of reef fish fauna are therefore a valuable means of detecting impacts and monitoring changes in inshore, hard-bottomed marine ecosystems.

Methods We used the standard visual census technique (Barrett & Buxton 2002) to estimate the sizes and numbers of all fishes sighted within 2.5 metres (m) either side of a 100-m transect line, set at a given depth (see Shepherd & Brook 2003b for further details). Six reef systems situated on the north and south coasts of KI were selected for study and surveys were conducted over three consecutive days (25 – 27) in late November 2004. Reef locations are shown in Figure 1, and further details about each site are given in Table 1.

At each site, one diver deployed the transect line, then all three divers swam along the line about 1 m above the algal canopy and independently recorded the count and length, by species, of every fish seen within the 5-m wide swathe. Where large schools of fish were encountered, the number of fish in the school and their average length were estimated visually. The sex composition of blue-throated wrasse was also recorded by one author (SAS) and these data were used to calculate the sex ratio for mature fish, assuming that all fish > 15 cm long were sexually mature (see Shepherd & Brook 2003b). At some sites, after establishing that a diver could swim 100 m in 10 min., we

2 used timed 10-min swims instead of laying a transect line, thus providing considerable savings in time. Four to six replicate transects were surveyed per site, except at the first two sites in Emu Bay, where training sessions for the second and third authors were conducted, reducing survey time and hence the number of transects. Replicate fish counts from each diver were used to calculate mean species abundances, with standard deviations, at each site

Table 1. Locations of sites surveyed, with number of replicate samples (N), estimated rocky bottom relief (R), water depth (D) and exposure to swell (E). Relief and depth are recorded in metres. Exposure to swell is given in three categories: sheltered (s), moderately exposed (m), and fully exposed (e).

Location Site Lat. Long. N R D E Emu Bay 1. East Point 35º 34´ 18.25″ S; 137º 33´ 51.4″ E 2 2 3 s-m 2. Cape D’Estaing 35º 34´ 25.0″ S; 137º 30´ 00.0″ E 3 2 5 m D’Estrees Bay 3. Osmanli Reef 35º 58´ 47.1″ S; 137º 37´ 26.7″ E 4 1.5 3 e 4. Point Tinline 35º 59´ 7.0″ S; 137º 37´ 26.7″ E 4 2.5 3 e Hanson Bay 5. Outer bar 36º 1´ 4.9″ S; 136º 51´ 13.6″ E 6 3 5 e 6. Inner bay 36º 1´ 4.9″ S; 136º 51´ 13.6″ E 6 2 3 s

Figure 1. Locations of survey sites listed in Table 1.

Results In presenting our data, we follow the reef fish classification of Shepherd & Brook (2003b). In this system, five ecological groups of fish are recognised according to behaviour and life habit as follows (see Figure 2): Group 1 – pelagic and mid-water species; Group 2 – species that live in seagrass beds but wander into algal habitats; Group 3 – demersal, site-attached species that swim above and close to the algal canopy; Group 4 – demersal, site-attached species usually cryptic within the algal canopy; and Group 5 – cryptic or cave-dwelling species, active mainly at night.

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Figure 2. Ecological groups of fish on coastal reefs. See text for explanation of each group.

A total of 16 species of fish representing three of the ecological groups were recorded at the six sites. The missing groups were Group 2 and Group 5; this is not unusual as transects did not pass over sandy or seagrass habitats, nor were they conducted at night. The fish species encountered and their mean densities per site are given in Table 2. The suite of species present was that generally found on exposed coasts of central South Australia. Only four species (western blue groper, magpie perch, zebra fish and blue- throated wrasse) were recorded at all six sites; absences of particular species at some sites may reflect local habitat features (see below). For example, tommy ruff occurred in highest density at the fully exposed, ‘oceanic’ site on the southwest coast of KI .

Total fish densities were in the range 0.1 - 0.16 m-2, as expected for coastal reefs of high relief (see Shepherd & Brook 2003b). Highest mean densities were recorded for Group 3 species at sites of moderate to full exposure. Juvenile and sub-adult western blue groper, a protected species on the northern and eastern coasts of KI, were especially abundant at Site 3 (Osmanli Reef, D’Estrees Bay), with a size range of 10 - 50 cm, suggesting a local recruitment hotspot.

The lowest species diversity was recorded at Point Tinline and the highest at the two sites in Hanson Bay. Of special interest were sightings of the purple wrasse at Sites 5 and 6, as this species has not previously been recorded west of Robe, SA (Hutchins & Swainston 1999). At the six sites sampled, the sex ratio of blue-throated wrasse (female: male) ranged from 7:1 at Site 4 off Point Tinline, to 16:1 at Site 2, Cape D’Estaing (mean = 11.7:1 (s.d. 1.1)).

4 Table 2. List of fish species recorded at six sites around Kangaroo Island at 2 - 5 m depth, ordered according to ecological group (see Figure 2 and text for explanation). Mean densities for each site are given in numbers per 500 m-2. Figures in brackets are standard deviations. FT is feeding type, where BC = benthic carnivore; C = carnivore; H = herbivore; O = omnivore; P = planktivore. E Pt = East Point, CD’est = Cape D’Estaing, Oreef = Osmanli Reef, PtTin = Point Tinline, HBO = Hanson Bay outer, HBI = Hanson Bay inner.

Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 FT Name of species E Pt CD’est OReef PtTin HBO HBI Group 1: Pelagic and mid-water species Scorpis aequipinnis P - - - - 11.7 4.2 Sea sweep (3.5) (1.8) Scorpis georgianus P 24.0 11.0 11.5 11.8 - - Banded sweep (7.1) (5.0) (3.0) (2.5) Arripis georgiana P - - 2.0 - 5.5 1.8 Tommy ruff (1.2) (3.9) (3.7) Mean density 24.0 11.0 13.5 11.8 17.2 6.0

Group 3: Demersal species Achoerodus gouldii BC 1.0 1.7 8.0 2.5 2.5 3.8 Western blue groper (0) (0.7) (2.2) (0.6) (1.1) (1.0) Dactylophora nigricans H - - 0.5 - 0.8 1.5 Dusky morwong (0.4) (0.5) (0.5) Kyphosus sydneyanus H 1.5 5.0 - - 2.2 10.7 Silver drummer (0.4) (2.4) (0.8) (7.5) Cheilodactylus nigripes BC 1.5 3.0 2.0 0.8 0.8 0.5 Magpie perch (1.1) (1.3) (0.6) (0.4) (0.4) (0.2) Girella zebra H 6.5 12.7 7.3 32.0 27.0 9.7 Zebra fish (4.6) (8.9) (3.1) (5.6) (10.1) (2.5) Notolabrus tetricus BC 28.0 31.0 23.0 30.5 26.7 18.2 Blue-throated wrasse (7.8) (13.0) (1.3) (1.8) (6.5) (4.2) Pseudolabrus fucicola BC - - - - 1.8 0.7 Purple wrasse (1.6) (0.5) Meuschenia flavolineata O - 7.3 0.3 - - - Yellowstripe leatherjacket (1.7) (0.3) Meuschenia hippocrepis BC 1.5 5.3 - - - - Horseshoe leatherjacket (1.1) (2.2) Mean density 40.0 65.9 41.1 65.8 61.8 45.1

Group 4: Demersal cryptic species Aplodactylus westralis H - - 0.3 0.5 1.0 0.5 Western sea carp (0.3) (0.3) (0.3) (0.3) Odax cyanomelas H 2.5 4.0 - - 0.8 0.3 Herring cale (2.1) (1.7) (0.5) (0.2) Parma victoriae H - - 3.5 2.0 3.0 1.0 Victorian scalyfin (0.9) (0.6) (1.3) (0.5) Tilodon sexfasciatum BC 0.5 1.0 0.8 - - - Moonlighter (0.4) (0.8) Mean density 3.0 5.0 4.6 2.5 4.8 1.8

Total species density 67.0 81.9 59.2 80.1 83.4 52.9 Total no. of species 9 10 11 7 12 12

5 Discussion It is well established that habitat-related features are the main determinants of the composition and abundance of temperate fish assemblages (reviewed by Martha et al. 2004). Bottom topography (i.e. degree of rocky bottom relief), algal cover and substratum type are the main habitat features of importance for reef species (e.g. Shepherd & Brook 2003b). Hence, the abundance of the Victorian scalyfin and leatherjackets depends on the presence of suitable holes or caves. Furthermore, leatherjackets are poor swimmers and tend to avoid areas of strong surge, occurring predominantly at sites in Emu Bay, where exposure to swell is low to moderate. In contrast, sweep favour strong surge, especially where vertical faces are present, and hence occurred in lowest densities at Site 6. The presence or abundance of herring cale depends on the abundance of its preferred food, the laminarian alga, Ecklonia (see Shepherd & Brook 2003b). The abundance of juvenile and sub-adult blue groper at Site 3 is the highest so far recorded on KI (Shepherd & Brook 2002), other than in the artificial harbour at Penneshaw. This may reflect the abundance of creviced habitat for shelter, high survival of settlers, and/or the local hydrodynamics favouring high larval retention of settling groper.

Of the anthropogenic effects, rocky shore fishing is the most significant factor affecting the size composition of fish on nearshore reefs. For example, earlier studies by Shepherd & Brook (2003a) have shown that the mean size of blue-throated wrasse decreases with increasing rock fishing pressure as large individuals of this species voraciously take the hook. The mean size of blue groper was also shown to be correlated with that of blue-throated wrasse, suggesting that, despite being protected, this species was also taken by shore fishers. Other species taken by shore fishers include: magpie perch, moonlighter, leatherjackets and sweep. Hence, a substantial proportion of the species recorded in visual censuses is harvested by recreational fishers, and therefore, in principle, useful as indicators of the intensity of fishing pressure on reef fish assemblages. The sex ratio of the blue-throated wrasse has also been shown to indicate the intensity of shore fishing, such that ratios of females to males exceeding ~ 16:1 are indicative of moderate to intense fishing (Shepherd & Brook 2003a). The high ratio of 16:1 recorded in this study at Cape D’Estaing may therefore reflect the fact that this reef is subjected to greater fishing effort than the other five sites (Tony Geyer pers. comm.) as a result of its sheltered location on the north coast of KI as well as its proximity to the Emu Bay boat ramp, and concomitant accessibility to the recreational boat fishing sector.

Recommendations The authors suggest that a valuable component of any monitoring program for the marine biota of Kangaroo Island would be the coastal reef fish communities. Specifically, we propose that: 1. Pairs of impact and control sites be selected that are reasonably similar in terms of bottom substrate, topography and wave exposure. Ideally, these pairs of sites should be located several kilometres apart, along the more accessible parts of the island’s coast (i.e. along the north coast of KI east of Cape Borda, on parts of the east coast and in selected areas of the south coast such as D’Estrees Bay, Vivonne Bay and Hanson Bay).

6 2. Annual monitoring is normally adequate, although some sites could initially be monitored more frequently to detect any seasonal differences in fish abundances and size compositions relating either to population dynamics or changes in fishing pressure (e.g. as a result of fluctuating tourist numbers). 3. Monitoring should be quantitative, as in this pilot study, and should also estimate fish size compositions. Observer training may be useful to improve underwater estimates of length. 4. A smaller suite of indicator fish species could be selected for more intense monitoring; candidates for indicator species include blue-throated wrasse, western blue groper, magpie perch, and moonlighter. These species are (a) carnivores and therefore likely to reflect any disruption of the food web at lower trophic levels, and (b) are themselves susceptible to fishing, the first two from line fishing and the last two from spearfishing. 5. Monitoring surveys be normally conducted between around 1000 h and 1600 h to avoid variability due to the sheltering behaviour of fish in the early morning and late afternoon. Biodiversity assessment surveys, however, should be conducted at different times of the day, including after dark, in order to determine the full suite of species present at a site. Early evening and after dark dives are useful to detect crepuscular and nocturnal activity of fishes, normally cryptic by day. 6. Video transects may also be useful at some sites for cross-checking with visual estimates and to provide a permanent record of the fish assemblages and underwater habitats.

Acknowledgements We thank the Chairperson, Executive Officer and members of the Kangaroo Island Natural Resources Board for their support of this pilot study.

References Barrett, N.S. and C. Buxton ((2002) Examining underwater visual census techniques for the assessment of population structure and biodiversity in temperate coastal marine protected areas. TAFI Technical Report Series No. 11. 114 pp.

Hutchins, B. and R. Swainston (1999) Sea fishes of Southern Australia. 2nd Ed. Gary Allen, Sydney.

Martha, K., M. Jones, D.G. Fitzgerald and P.F. Sale (2004) Comparative ecology of marine fish communities. In PJB Hart and JD Reynolds (eds) Handbook of Fish Biology and Fisheries, Volume 1, pp 341-357. Blackwell, Oxford.

Shepherd, S.A. & J.B. Brook (2002) A preliminary survey of the western blue groper on Kangaroo I. Reef Watch Report, Conservation Council of South Australia. 10 pp.

Shepherd, S.A. & J.B. Brook (2003a) A survey of the western blue groper on southern Yorke Peninsula. Reef Watch Report, Conservation Council of South Australia. 12 pp.

Shepherd, S.A. & J.B. Brook (2003b) Encounter 2002 expedition to the Isles of St Francis, South Australia: reef fishes. Trans R. Soc. S. Aust. 127: 269-279.

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