Large-scale, multi-directional larval connectivity among coral reef fish populations in the Great Barrier Reef Marine Park
David H. Williamson, Hugo B. Harrison, Glenn R. Almany, Michael L. Berumen, Michael Bode, Mary C. Bonin, Severine Choukroun, Peter J. Doherty, Ashley J. Frisch, Pablo Saenz-Agudelo, Geoffrey P. Jones
Supporting information METHODS
Study species: Biology, ecology and fishery status of coral trout
This study focused on two species of coral reef grouper (Serranidae), the bar-cheek coral trout (Plectropomus maculatus) and the leopard coral trout (Plectropomus leopardus). Both P.
maculatus and P. leopardus are protogynous hermaphrodites (change sex from female to male) with females reaching maturity at approximately 30 cm in total length (TL) and 2 – 3 years of age (Ferreira 1993; Ferreira 1995). The mean size and age of sex change is 35 – 40 cm TL and 4 yr, but is highly variable and may be influenced by a number of factors including population density, size structure, and fishing intensity (Ferreira 1993). Like many other grouper species, P.
maculatus and P. leopardus can form large spawning aggregations at predictable locations and times in some regions, while small group spawning has also been documented in both species (Samoilys & Squire 1994; De Mitcheson et al. 2008). Larger males are polygynous and actively exclude subordinate males from spawning sites (Samoilys & Squire 1994). The peak spawning period for coral trout in the Great Barrier Reef (GBR) region is during the Austral summer (September – February), with most spawning events occurring within several days either side of the new moon lunar phase (Samoilys 1997). Aside from relatively short (generally less than 10 km) migrations to aggregation sites, adult coral trout occupy distinct home ranges in the order of 1 - 4 ha and rarely move among reefs separated by expanses of open sand or low-relief benthic habitat (Zeller 1997, 1998; Bunt & Kingsford 2014).
All coral trout (Plectropomus spp.) species are highly regarded for their eating qualities, they are targeted by commercial, recreational, and subsistence fishers throughout the Indo-Pacific region, and they have been locally depleted by overfishing throughout much of their ranges (Sadovy de Mitcheson et al. 2013). On the GBR, P. leopardus and P. maculatus are the most abundant coral trout species and they are primary targets of commercial and recreational fisheries (DAFF 2012).
The fishery catch of both species is limited by a range of management measures including a minimum legal size limit of 38 cm TL, limited entry licensing, a total allowable catch (TAC) for the commercial sector, and possession limits for recreational fishers (DAFF 2012). The annual commercial harvest of coral trout in Queensland waters is currently around 800 metric tones, the vast majority of which is sourced from coral reefs within the GBRMP and exported live to Asian markets (DAFF 2012). The recreational harvest of coral trout in Queensland waters for 2010 was estimated to be 104,572 fish ( 14,778 SE), which was approximately 25% of the commercial harvest in that year (Taylor et al. 2012).
1 2 34 5 6 7 89 1011 12 13 1415 16 1718 19 2021 22 2324 25 26 2728 29 3031 32 3334 35 36 3738 39 4041 42 43 44 45
Towed-GPS underwater visual census and estimation of coral trout densities
A towed-GPS UVC method was used to survey coral trout (Plectropomus spp.) populations on each of the focal reefs in the Keppel, Percy and Capricorn Bunker regions. Handheld GPS units were attached to small body boards and observer divers towed the units with spool reels. Survey tracks were stratified between four reef habitat types (reef slope, reef crest, reef flat, lagoon).
Each UVC track was 10 minutes in length and the GPS units were set to record waypoints at 1 minute intervals. Observers synchronized their watches or dive computer time to the GPS time prior to conducting surveys. The distance covered on each replicate track varied among reefs and among habitat strata, but typically ranged from 80 m to 160 m. The track survey width was standardized to 10 m (5 m either side of the observer) and a minimum of 1 minute of steady swimming between replicate tracks was used to ensure the independence of each track count.
Observers used both SCUBA (reef slope and lagoon habitats) and snorkel (reef flat and crest) during UVC surveys. All observers were trained and calibrated in underwater length estimation using plastic coral trout models.
A total of 518 replicate UVC track surveys were conducted on 17 reefs in the Keppel Islands (n = 198), two reefs in the Percy Islands (n = 19), and five reefs in the Capricorn Bunker region (n = 301). UVC surveys were focused on the reefs at which adult coral trout were sampled. At the Keppel Islands and Capricorn Bunker reefs, 89 and 142 replicate UVC tracks were conducted on no-take reserve reefs, and 99 and 159 tracks were conducted on non-reserve reefs, respectively.
In the Percy Islands, all 19 replicate UVC tracks were conducted on non-reserve reefs.
The total area surveyed on each UVC track was calculated using the GPS recorded track lengths and all raw UVC track counts were subsequently standardized to densities (ha-1). In addition to the generation of reef-specific density estimates for total population estimates, UVC track counts were also pooled for reserve and non-reserve reefs within each of the three focal regions (Keppel, Percy, Capricorn Bunker). Mean densities of adult coral trout (P. maculatus and P. leopardus pooled) were calculated for reserves and non-reserves in each region and two-factor analysis of variance (ANOVA) was used to test the significance of differences in densities among
management zones and regions.
Population size estimates for coral trout on the focal reefs
Density estimates of adult P. maculatus and P. leopardus were generated from habitat stratified, towed-GPS underwater visual census (UVC) surveys conducted on each reef where adult fish were sampled. Reef habitats on each of the focal reefs were mapped from high-resolution satellite imagery in ArcGIS (ESRI, Redlands, CA) and the total area within each reef habitat strata (slope.
crest, flat, lagoon) was calculated. Habitat-stratified coral trout density estimates were combined to provide an estimate of the total population size on each reef. Total population size (T) on each focal reef and standard error (TSE) were calculated as follows:
4647 4849 50 51 5253 54 5556 57 5859 60 61 6263 64 6566 67 68 6970 71 7273 74 7576 77 7879 80 81 8283 84 8586 87 88 89
(1). T =XrsNrs+XrcNrc+XrfNrf +XlNl
(2).
TSE =N´ Wrs2×Srs2 nrs æ èç
ö
ø÷+ Wrc2×Src2 nrc æ èç
ö
ø÷+ Wrf2×Srf2 nrf æ
èç ö
ø÷ + Wl2×Sl2 nl æ èç
ö ø÷
Where:
= mean density in each reef strata (reef slope – rs, reef crest – rc, reef flat – rf, lagoon – l) N = number of replicates that fit into the total habitat area
W = proportion of the total reef area within each reef strata S = standard deviation for each reef strata
n = number of replicates in each reef strata X
91 9293
94 9596 97 9899 100 101 102
Table S1: Summary of locations, sample sizes, and population estimates of adult Plectropomus maculatus and P. leopardus.
Plectropomus maculatus Plectropomus leopardus
Region Reef Zone No.
Sampled Pop. Est.
(± 1 se) Prop.
Sampled No.
Sampled Pop. Est.
(± 1 se) Prop.
Sampled
Keppel 452 - - 11
Humpy Is Fished (CP) 1 1071 (± 290) < 0.01 0 0 0
40 Acre Paddock Fished (HP) 2 - - 0 - -
Barren Is Fished (HP) 6 2142 (± 597) < 0.01 2 14 (± 7) 0.14
Corroboree Is Fished (HP) 3 391 (± 290) 0.01 0 0 0
Big Peninsula Fished (HP) 11 388 (± 84) 0.03 0 0 0
Passage Rocks Fished (HP) 15 - - 0 - -
Wreck Bay Fished (HP) 3 964 (± 319) < 0.01 0 0 0
Wyndham Cove Fished (HP) 6 303 (± 117) 0.02 0 0 0
Halfway Is - West Fished (HP) 20 669 (± 222) 0.03 0 0 0
Miall Is Fished (HP) 3 300 (± 61) 0.01 0 0 0
North Keppel Is - South Fished (HP) 2 390 (± 74) 0.01 0 0 0
Egg Rock Reserve (MNP) 123 580 (± 287) 0.21 7 17 (± 6) 0.41
Clam Bay Reserve (MNP) 107 2127 (± 254) 0.05 0 0 0
Halfway Is - East Reserve (MNP) 98 1138 (± 412) 0.09 1 9 (± 4) 0.11
Middle Is Reserve (MNP) 47 539 (± 85) 0.09 1 3 (± 2) 0.33
North Keppel Is. - East/West Reserve (MNP) 5 2290 (± 615) < 0.01 0 0 0
Percy 167 71
Middle Percy Is Fished (HP) 10 2160 (± 657) < 0.01 7 743 (±177) < 0.01
South Percy Is Fished (HP) 157 1962 (± 510) 0.08 64 392 (± 94) 0.16
Capricorn Bunker 261 - - 577 - -
Masthead Fished (CP) 0 594 (± 152) 0 5 2023 (± 314) < 0.01
Heron Fished (CP) / Reserve 0 - - 147 - -
Northwest Fished (CP) / Reserve 104 3022 (± 1076) 0.03 5 9119 (±1248) < 0.01
Erskine Reserve (MNP) 0 0 0 82 980 (± 187) 0.08
Polmaise Reserve (MNP) 157 4708 (± 1386) 0.03 108 5503 (± 1546) 0.02
Tryon Reserve (MNP) 0 0 0 210 3700 (± 563) 0.06
One Tree Reserve (SR) 0 - - 20 - -
103 104
REFERENCES
Bunt CM, Kingsford MJ (2014) Movement, habitat utilization and behaviour of coral trout Plectropomus leopardus during and after the reproductive period on the
southern Great Barrier Reef. Marine Ecology Progress Series, 496, 33-45.
DAFF (2012) Annual status report 2011 - Coral Reef Fin Fish Fishery. URL
https://www.daff.qld.gov.au/__data/assets/pdf_file/0017/66212/ASR_CRFFF20 11.pdf
De Mitcheson YS, Cornish A, Domeier M, Colin PL, Russell M, Lindeman KC (2008) A global baseline for spawning aggregations of reef fishes. Conservation Biology, 22, 1233-1244.
Ferreira BP (1993) Reproduction of the inshore coral trout Plectropomus maculatus (Perciformes: Serranidae) from the central Great Barrier Reef, Australia. Journal of Fish Biology, 42, 831-844.
Ferreira BP (1995) Reproduction of the common coral trout Plectropomus leopardus (Serranidae: Epinephelinae) from the central and northern Great Barrier Reef, Australia. Bulletin of Marine Science, 56, 653-669.
Frisch, AJ, Cameron DS, Pratchett MS, Williamson DH, Williams AJ, Reynolds AD, Hoey AS, Rizzari JR, Evans L, Kerrigan B, Muldoon G, Welch DJ, Hobbs J-PA (2016) Key aspects of the biology, fisheries and management of coral grouper. Reviews in Fish Biology and Fisheries, 26, 303-325.
Sadovy de Mitcheson Y, Craig MT, Bertoncini AA, Carpenter KE, Cheung WWL, Choat JH, Cornish AS, Fennessy ST, Ferreira BP, Heemstra PC, Liu M, Myers RF, Pollard DA, Rhodes KL, Rocha LA, Russell BC, Samoilys MA, Sanciangco J (2013) Fishing groupers towards extinction: a global assessment of threats and extinction risks in a billion dollar fishery. Fish and Fisheries, 14, 119-136.
Samoilys MA, Squire LC (1994) Preliminary observations on the spawning behavior of coral trout, Plectropomus leopardus (Pisces: Serranidae), on the Great Barrier Reef. Bulletin of Marine Science, 54, 332-342.
Samoilys MA (1997) Periodicity of spawning aggregations of coral trout Plectropomus leopardus (Pisces: Serranidae) on the northern Great Barrier Reef. Marine Ecology Progress Series, 160, 149-159.
Taylor S, Webley J, McInnes K (2012) 2010 Statewide Recreational Fishing Survey. p. 93.
Department of Agriculture, Fisheries and Forestry, Qld, Australia.
Zeller DC (1997) Home range and activity patterns of the coral trout Plectropomus leopardus (Serranidae). Marine Ecology Progress Series, 154, 65-77.
Zeller DC (1998) Spawning aggregations: patterns of movement of the coral trout Plectropomus leopardus (Serranidae) as determined by ultrasonic telemetry.
Marine Ecology Progress Series, 162, 253-263.
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