Quantifying the Largest Aggregation of Giant Trevally Caranx Ignobilis (Carangidae) on Record: Implications for Management
African Journal of Marine Science
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Quantifying the largest aggregation of giant trevally Caranx ignobilis (Carangidae) on record: implications for management
R Daly, CAK Daly, RH Bennett, PD Cowley, MAM Pereira & JD Filmalter
To cite this article: R Daly, CAK Daly, RH Bennett, PD Cowley, MAM Pereira & JD Filmalter (2018) Quantifying the largest aggregation of giant trevally Caranxignobilis (Carangidae) on record: implications for management, African Journal of Marine Science, 40:3, 315-321, DOI: 10.2989/1814232X.2018.1496950 To link to this article: https://doi.org/10.2989/1814232X.2018.1496950
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Quantifying the largest aggregation of giant trevally Caranx ignobilis (Carangidae) on record: implications for management
R Daly1,2*, CAK Daly2, RH Bennett3, PD Cowley3 , MAM Pereira4 and JD Filmalter3
1 Port Elizabeth Museum at Bayworld, Humewood, Port Elizabeth, South Africa 2 Save Our Seas Foundation (SOSF) D’Arros Research Centre, Geneva, Switzerland 3 South African Institute for Aquatic Biodiversity (SAIAB), Grahamstown, South Africa 4 Centro Terra Viva, Maputo, Mozambique * Corresponding author, e-mail: [email protected]
The giant trevally Caranx ignobilis (Forsskål) is an important apex predatory fish typically associated with coral reef communities. It is prized in recreational and commercial fisheries, yet little is known about its aggregation dynamics and susceptibility to fishing pressure. This study reports on a previously undocumented aggregation of mature giant trevally observed over a period of eight years (2010–2017) at Ponta do Ouro Partial Marine Reserve in southern Mozambique. The aggregation is one of the few recorded for this carangid in the western Indian Ocean and represents the first subtropical aggregation of giant trevally. The aggregation is also the largest recorded for this species, with up to 2 413 individuals representing an estimated biomass of approximately 30 tonnes. The size and predictability of this annual aggregation make it vulnerable to overexploitation and point towards the need for an appropriate conservation management strategy.
Keywords: Carangidae, fish aggregation, fisheries management, marine protected area, Mozambique, predatory teleosts, site fidelity, video observations
Online supplementary information: A dive log of all observations at the study site (Table S1) and an image revealing colour dimorphism and pairing between giant trevally (Figure S1) are available at https://doi.org/10.2989/1814232X.2018.1496950
Introduction
The giant trevally Caranx ignobilis (Forsskål 1775) is a Mass aggregations are common among coral-reef- large predatory fish, reaching up to 170 cm total length associated fishes and may be represented by hundreds and 87 kg (Meyer et al. 2007; Murakami et al. 2007). or many thousands of conspecifics concentrating within a As such, it is one of the largest top predatory teleosts small area. Fish aggregate primarily to enhance feeding, associated with coral reefs throughout its tropical to safety or reproduction (Pitcher et al. 1982; Pitcher 1986; warm-temperate Indo-Pacific distribution and it plays a key Domeier and Colin 1997; Claydon 2004). During aggrega- predatory role in these ecosystems (Sudekum et al. 1991; tion (especially for spawning) fish might be susceptible to, Maggs 2013; Froese and Pauly 2018). The giant trevally is and might not recover from, overexploitation by fisheries prized by recreational anglers for its strong fighting abilities (Rowe and Hutchings 2003; Sadovy de Mitcheson et al. and by artisanal and commercial fishers for its large 2008). The economic, biological and ecological value size, resulting in considerable demand for this species of fish aggregations, coupled with their vulnerability to throughout its distribution (Sudekum et al. 1991; Gaffney fishing, necessitate appropriate management of known 2000; Meyer et al. 2000; Maggs 2013; FAO 2014). To aggregation sites (Sadovy de Mitcheson 2016). Thus, date, the giant trevally has received substantial research understanding the dynamics of such aggregations is attention in the Pacific Ocean, yet despite its ecological essential for improving current conservation management importance and fishery value, little information exists for practices (Domeier and Colin 1997; Sadovy de Mitcheson this species in the western Indian Ocean (Sudekum et al. and Domeier 2005). 1991; Wetherbee et al. 2004; Meyer et al. 2007; Maggs The aim of this study was to investigate the persis- 2013; Lédée et al. 2015). Furthermore, little is known tence, size and biomass of a giant trevally aggregation about the aggregation dynamics of this carangid or its in the Ponta do Ouro Partial Marine Reserve (PPMR), vulnerability to fishing during aggregation events (Claydon southern Mozambique (Figure 1), in order to improve our 2004; Maggs 2013). understanding of the aggregation dynamics of the species.
African Journal of Marine Science is co-published by NISC (Pty) Ltd and Informa UK Limited [trading as Taylor & Francis Group] Published online 28 Sep 2018 316 Daly, Daly, Bennett, Cowley, Pereira and Filmalter
ZAMBIA
AFRICA ZIMBABWE 25° S MOZAMBIQUE Mozambique MADAGASCAR Mozambique Channel
See enlarged area
SOUTH INDIAN OCEAN AFRICA
SOUTH AFRICA 0 30 60 km Komati
Inhaca Island Matola Maputo
Maputo 26° S Bay
Mlaula INDIAN OCEAN
Maputo
SWAZILAND
PPMR Boundary MOZAMBIQUE
SOUTH AFRICA 27° S
32° E 33° E
Figure 1: Location of the Ponta do Ouro Partial Marine Reserve (PPMR), situated between Maputo Bay, Mozambique, and the South African border, where the giant trevally aggregation was observed African Journal of Marine Science 2018, 40(3): 315–321 317
Materials and methods was observed (Cappo et al. 2006). The second estimate (a ‘running count’) was based on a derived method where Study site video footage was scrutinised for short segments in which This study took place in southern Mozambique, within the giant trevally shoal moved in one direction relative to the Ponta do Ouro Partial Marine Reserve (PPMR). The the camera’s field of view, analogous to a diver-operated PPMR is located within a biogeographical transition area video transect (Langlois et al. 2010). The third estimate (a referred to as the Delagoa Bioregion (Turpie et al. 2000) ‘volume count’), also derived, was based on the geometry of and encompasses 98.5 km of coastline extending from the the shoal (roughly spherical) and was used to include in the South African border in the south to the Maputo River in the abundance estimate those individuals that may have been north (DNAC 2009). Primary reef formations are charac- obscured by others closer to the lens. For the ‘volume count,’ terised by submerged late Pleistocene beach rock that is the number of fish recorded side-by-side along a single axis colonised by a thin veneer of Indo-Pacific corals (Ramsay (z axis) of the shoal, in a single video frame, was used to and Mason 1990; Ramsay 1994) and are associated with represent the diameter of the shoal. Visual assessment of a diverse Indo-Pacific fish community (Floros et al. 2012). video footage indicated that fish length (x axis) was approxi- Recreational fishing within the PPMR is restricted to multiple- mately three-times greater than dorsoventral height (y axis) use zones and is subject to partial restrictions (only pelagic or lateral width (z axis). Therefore, the ‘volume’ of fish (as a fish may be targeted, including giant trevally) and bag limits proxy for abundance) was estimated using the equation for (10 fish per person per day). No industrial or semi-industrial volume of an ellipsoid (i.e. unequal radii), where anterior– fishing is allowed, and commercial fishing is restricted to posterior (x axis) radius was assumed to be one-third of multiple-use zones for registered small-scale fisheries from the horizontal and vertical radii (i.e. the x axis could hold local communities (DNAC 2009). However, the relatively one-third the number of fish as the y and z axes), as follows: high recreational and commercial value of the giant trevally 4 r makes the species vulnerable and potentially subject to Abundance (volume) = x rr Daly Eq1 illegal and unregulated fishing pressure in the region. 33yz (1)
Data collection and abundance estimates where rx, ry and rz represent axial (anterior–posterior) radius, Observational dives were conducted at the study site using vertical radius and horizontal (side-by-side) radius, respec- SCUBA and snorkel gear, from January 2010 to December tively. Maximum abundance estimates for each video 2017. In total, 140 diving days were logged over this period, recording are presented. primarily during austral spring and summer (November to Additionally, in December 2017, stereo video footage of May). Dives were conducted between sunrise and sunset the aggregation was recorded (four separate video record- (due to vessel restrictions as well as diving and boating ings) with a calibrated stereo video system (using SeaGIS safety) and when the wind speed was less than 15 knots CAL software and calibration cube). The stereo video and water visibility exceeded 20 m. An aggregation was footage was then analysed using SeaGIS EventMeasure considered to be present when there was a considerable software to measure the fork lengths of 345 individual fish. increase (at least ten-fold) in the typical observed density of Fork lengths were then converted to individual weights (van giant trevally in the area (Domeier 2012). der Elst and Adkin 1991) and the biomass of the aggrega- The frequency of occurrence of the giant trevally tion was estimated by multiplying the mean weight of aggregation in relation to the phase of the moon was individual fish by the abundance estimates. assessed for observations made between 2011 and 2016, using the statistical software package Oriana 4 (Kovach Results Computing Services). Rao’s spacing test (Batschelet 1981) was used to test for uniformity in the temporal data: that is, Over the eight-year observational period (2010–2017) the testing the null-hypothesis that aggregations were distrib- aggregation of giant trevally was observed 40 times at the uted evenly over all lunar phases. The level of statistical same site, every year between November and December significance was determined from a table of simulated and in February in one year (2014). Absence of the aggrega- critical points (Russell and Levitin 1996) with α set at 0.05. tion was noted on all other observational dives (n = 100) When the aggregation was sighted, the date, time and throughout the study period (Supplementary Table S1). location were recorded. When possible, video footage of Observations of the giant trevally aggregation appeared the aggregation was recorded using a Canon EOS 5D Mark to be more frequent between the first and third quarters of II with a 17–40 mm rectilinear lens contained in a Subal the lunar cycle (Figure 2). However, the results from Rao’s underwater housing. In general, the giant trevally aggrega- spacing test did not support the hypothesis that the data tion was cautious of divers and it did not come close enough were unevenly distributed or biased relative to a particular for video footage to be recorded in 2012 and 2016. Thus, lunar phase (p > 0.05). the abundance of giant trevally in the aggregation was The three different metrics used to estimate the estimated from video recordings collected in 2011 (n = 1 abundance of giant trevally provided estimates ranging recording), 2013 (n = 3), 2014 (n = 3), 2015 (n = 1) and 2017 from 261 to 2 413 individuals (Table 1). MaxN gave the (n = 4). Abundance was estimated using three metrics. First, lowest estimates, with a mean of 428 fish (SD 157) and the standard ‘MaxN’ (maximum number) approach (Priede maximum of 835 fish (Figure 3). The running counts were et al. 1994; Ellis and DeMartini 1995) was used to identify variable but were consistently higher than the MaxN counts, the frame in which the greatest number of individual fish with a mean of 750 fish (SD 268) and a maximum of 1 329 318 Daly, Daly, Bennett, Cowley, Pereira and Filmalter
The aggregation represented a spatially and temporally Lunar phase predictable aggregation of conspecific mature-size fish, New moon and was present most frequently between the first and third quarters of the lunar cycle, during November and December of each year, with evidence that it may persist through to February. The seasonal timing and longevity (2 to 3 months) of the aggregation during the austral summer months are consistent with previously reported giant trevally spawning aggregations in other regions (Sudekum et al. 1991; da Silva et al. 2014). Additionally, there was some evidence 3rd 1st quarter quarter to suggest that fish in the aggregation were spawning (two male giant trevally captured from the aggregation in December 2016 freely released sperm when handled, and colour dimorphism and pairing was observed in the aggrega- tion [Supplementary Figure S1]). This suggests that the purpose of the aggregation was for spawning, but additional direct evidence of spawning is required.
Full moon Aggregation size Giant trevally are known to form dense aggregations during the spawning season (Claydon 2004; Meyer et al. Figure 2: Frequency distribution of the giant trevally aggregation 2007; Dale et al. 2011). However, the aggregation of adult sightings at the study site relative to the lunar phase giant trevally recorded here is considerably larger than any previously reported aggregation of this species, with examples from elsewhere being >100 fish in the Philippines Table 1: Abundance estimates of the giant trevally aggregation (von Westernhagen 1974) and >1 000 fish in northern using three different methods (MaxN, running count, and volume Mozambique (da Silva et al. 2014). Despite the reported count). Multiple counts within some years were based on separate video recordings taken on separate days. NA indicates that a aggregation being the largest on record, taking into consid- suitable video segment was not available. eration the various constraints of each abundance metric presented here (cf. Squire 1978; Denny and Babcock 2004; Cappo et al. 2006; Schobernd et al. 2014), our estimates Running Volume Year Month MaxN are likely underestimates of its true abundance, and the count count aggregation may in reality comprise more individuals than 2011 December 451 1 329 1 018 2013c November 449 955 715 the counts presented. It is also possible that the aggrega- 2013a December 349 612 589 tion exhibits a gradual turnover of individuals throughout the 2013b December 358 676 715 protracted aggregation period, in which case the absolute 2014a December 304 NA 715 number of giant trevally taking part in the aggregation may 2014b December 401 455 1 396 be higher still. Nonetheless, with up to 2 413 individuals at 2014c December 445 638 715 one point in time, this aggregation is likely of major ecological 2015 December 835 497 2 413 significance, both to the species and to the ichthyofaunal 2017 December 261 841 2 405 community at the aggregation site. Mean (SD) 428 (157) 750 (268) 1 187 (692) Biomass The mean length (85.5 cm FL [SD 10.5]) of the giant trevally fish. Volume counts gave the highest and probably the was found to be consistent with the mean length of 24 fish most-realistic estimates, with a mean of 1 187 fish (SD 692) captured from the aggregation (78.4 cm FL [SD 12.4]). This and a maximum of 2 413 fish. suggests that the stereo video system and software could Stereo video recordings were used to measure the fork be used to accurately measure the size of fish within the lengths (FL) of 345 individual fish within the aggrega- aggregation and provide a relatively accurate estimate of tion. Fork lengths ranged from 62.8 to 131.2 cm with a giant trevally biomass within the aggregation. Additionally, mean of 85.5 cm (SD 10.5). Of the 345 fish measured, the all 345 fish measured in the aggregation in December 2017 majority (77%) were between 80 and 100 cm FL (Figure 4). were larger than the size at 50% maturity (Maggs 2013), Weights of the fish, estimated from FL, ranged from 4.87 suggesting that all individuals in the aggregation were to 43.97 kg, with a mean individual fish weight of 12.77 kg reproductively mature, providing further evidence to suggest (SD 5.19). The total biomass of the aggregation was that the purpose of the aggregation is for spawning. estimated to range between 3 882 and 30 814 kg. Ecological significance Discussion The seasonal presence of up to 2 413 mature giant trevally with a maximum estimated biomass of 30 814 kg, as This study reports on the first record of a subtropical described in this study, represents a significant increase in aggregation of giant trevally in the Southern Hemisphere. the biomass of top predatory fish within a spatially restricted African Journal of Marine Science 2018, 40(3): 315–321 319
Figure 3: A screen shot from video footage of the giant trevally aggregation at Ponta do Ouro Partial Marine Reserve, southern Mozambique, in December 2015; the MaxN estimation from this video sequence was 835 fish
giant trevally, is associated with the giant trevally aggrega- tion (Daly et al. 2013, 2014). The seasonal influx of so 120 n = 345 fish many large predatory fish must certainly be of importance 100 to the local marine community in the PPMR, and further studies are required to elucidate the broader ecological role 80 that the aggregation plays.
60 Management implications and summary The spatially and temporally predictable aggregation of FREQUENCY 40 this economically important fishery species makes the giant trevally highly susceptible to exploitation by recrea- 20 tional, artisanal and commercial sectors, and thus deserves prioritised management intervention (Meyer et al. 2007; 60 70 80 90 100 110 120 130 140 150 Grüss et al. 2013). Targeting fish during aggregations FORK LENGTH (cm) is common, and several families, for example groupers (Epinephelidae), face severe threats as a result (Robinson Figure 4: Frequency histogram of fork lengths of the giant trevally et al. 2014; Sadovy de Mitcheson 2016). Well-enforced in the aggregation in December 2017, as measured from stereo no-take zones within marine protected areas that incorpo- video footage rate aggregation sites, and seasonal fishery closures during periods of aggregation, may both be effective conservation tools (Meyer et al. 2007; Robinson et al. coral reef habitat. Such an influx of a top predator may 2008; Grüss et al. 2013). Additionally, because fish may play an important role in structuring the local community also be subject to high fishing mortality on migration routes dynamics through predation (Dulvy et al. 2004; Bascompte to and from aggregation sites, the extent of the species’ et al. 2005). Additionally, the giant trevally aggregation functional migration area should also be considered may facilitate various unique trophic interactions during the (Claydon 2004; Nemeth 2012; Sadovy de Mitcheson 2016). aggregation period (Claydon 2004; Heyman et al. 2005; As the aggregation described in this study occurs within Domeier 2012). 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Manuscript received March 2018 / revised May 2018 / accepted May 2018 Supplementary Information
Quantifying the largest aggregation of giant trevally Caranx ignobilis (Carangidae) on record: implications for management R Daly, CAK Daly, RH Bennett, PD Cowley, MAM Pereira and JD Filmalter African Journal of Marine Science 2018, 40(3): 315–321. https://doi.org/10.2989/1814232X.2018.1496950
Table S1: Dive log of all observations at the study site (Ponta do Ouro Partial Marine Reserve, southern Mozambique) showing the date, observation start and end times (to the nearest 15 minutes), effort, presence or absence of the giant trevally Caranx ignobilis aggregation, and the lunar phase at Maputo, Mozambique. In total, 140 observations were made between 2010 and 2017, with the aggregation observed 40 times
Giant trevally Observation Observation Effort observation Lunar phase Observation no. Date start time end time (hours:minutes) (Yes/No) (% illumination) 1 23/01/2010 09:45 13:30 03:45 N 52.20 2 25/01/2010 09:00 10:45 01:45 N 73.50 3 31/01/2010 08:30 10:30 02:00 N 99.20 4 03/02/2010 10:00 11:15 01:15 N 80.20 5 04/02/2010 10:00 11:30 01:30 N 70.10 6 05/02/2010 08:15 09:15 01:00 N 59.30 7 08/02/2010 08:30 12:00 03:30 N 28.30 8 09/02/2010 13:00 13:30 00:30 N 19.70 9 10/02/2010 10:30 11:00 00:30 N 12.50 10 11/02/2010 09:30 10:00 00:30 N 6.70 11 13/02/2010 08:00 12:00 04:00 N 0.50 12 15/02/2010 07:30 11:00 03:30 N 1.70 13 03/03/2010 09:30 11:00 01:30 N 92.30 14 08/04/2010 08:30 09:15 00:45 N 33.10 15 09/04/2010 08:00 11:30 03:30 N 24.40 16 11/04/2010 09:00 11:00 02:00 N 10.00 17 13/04/2010 08:00 10:00 02:00 N 1.50 18 16/04/2010 07:50 10:30 02:40 N 4.20 19 17/04/2010 08:00 11:00 03:00 N 9.60 20 19/04/2010 10:00 11:00 01:00 N 26.60 21 25/04/2010 07:45 08:45 01:00 N 90.40 22 27/04/2010 09:30 10:30 01:00 N 99.30 23 06/05/2010 07:45 10:00 02:15 N 50.20
1 24 07/05/2010 09:30 11:00 01:30 N 40.50 25 10/05/2010 14:00 15:30 01:30 N 14.70 26 16/05/2010 07:30 08:15 00:45 N 7.20 27 17/05/2010 07:45 09:00 01:15 N 14.50 28 11/11/2010 12:00 16:45 04:45 N 30.30 29 01/12/2010 07:00 12:30 05:30 N 24.10 30 02/12/2010 07:30 10:00 02:30 N 14.70 31 11/01/2011 07:30 08:20 00:50 N 42.10 32 13/01/2011 13:00 13:40 00:40 N 61.70 33 16/01/2011 07:30 08:15 00:45 N 88.30 34 18/01/2011 12:00 15:30 03:30 N 98.60 35 22/01/2011 07:30 00:00 16:30 N 93.70 36 12/11/2011 15:00 18:00 03:00 N 98.90 37 14/11/2011 15:00 17:30 02:30 Y 91.00 38 16/11/2011 12:00 16:00 04:00 N 75.90 39 18/11/2011 13:00 17:00 04:00 Y 55.50 40 05/12/2011 09:00 14:00 05:00 Y 79.80 41 07/12/2011 09:00 11:00 02:00 Y 92.80 42 20/01/2012 09:00 14:00 05:00 N 11.00 43 21/01/2012 08:00 14:00 06:00 N 4.80 44 23/01/2012 09:00 14:30 05:30 N 0.10 45 30/01/2012 09:30 10:30 01:00 N 45.10 46 02/02/2012 08:30 12:00 03:30 N 73.60 47 04/02/2012 08:30 09:15 00:45 N 89.20 48 05/02/2012 08:00 11:00 03:00 N 94.90 49 07/02/2012 09:00 12:15 03:15 N 99.80 50 08/02/2012 11:00 15:30 04:30 N 98.60 51 12/03/2012 12:00 15:00 03:00 N 82.10 52 13/03/2012 09:00 13:00 04:00 N 71.80 53 19/03/2012 08:00 14:00 06:00 N 10.70 54 25/03/2012 07:30 09:00 01:30 N 7.60 55 27/03/2012 15:30 16:30 01:00 N 20.70 56 05/04/2012 07:00 07:45 00:45 N 98.50 57 11/04/2012 09:00 09:30 00:30 N 75.50 58 11/09/2012 08:45 10:00 01:15 N 25.20 59 12/09/2012 08:30 09:10 00:40 N 16.70 60 17/09/2012 08:30 08:45 00:15 N 2.60 61 20/09/2012 09:00 09:30 00:30 N 25.30 62 24/09/2012 08:30 09:00 00:30 N 70.70 63 01/11/2012 07:00 08:30 01:30 N 96.00 64 07/11/2012 08:00 11:00 03:00 N 48.70 65 09/11/2012 07:00 11:00 04:00 Y 27.80 66 17/11/2012 09:00 12:00 03:00 N 18.50 67 18/11/2012 07:00 09:00 02:00 N 28.60 68 19/11/2012 08:00 12:00 04:00 N 39.60 69 22/11/2012 14:00 17:00 03:00 Y 71.20
2 70 23/11/2012 10:00 13:00 03:00 Y 80.00 71 28/11/2012 13:00 15:30 02:30 Y 99.90 72 20/01/2013 07:30 08:15 00:45 N 66.20 73 24/01/2013 07:00 11:00 04:00 N 94.70 74 26/01/2013 14:00 15:45 01:45 N 99.70 75 28/01/2013 11:00 14:30 03:30 N 99.30 76 09/11/2013 09:30 10:30 01:00 Y 43.20 77 10/11/2013 10:00 11:00 01:00 Y 54.90 78 16/11/2013 13:00 17:30 04:30 N 99.40 79 19/11/2013 13:00 15:00 02:00 Y 98.30 80 22/11/2013 14:00 14:30 00:30 N 82.90 81 27/11/2013 07:00 11:00 04:00 Y 36.60 82 01/12/2013 08:30 12:00 03:30 Y 3.90 83 12/12/2013 09:00 17:30 08:30 Y 80.70 84 13/12/2013 12:00 15:00 03:00 Y 88.20 85 16/01/2014 06:00 09:30 03:30 N 100.00 86 17/01/2014 06:00 07:30 01:30 N 99.30 87 18/01/2014 08:00 11:30 03:30 N 97.10 88 19/01/2014 06:00 06:30 00:30 N 93.00 89 20/01/2014 06:00 09:00 03:00 N 87.20 90 28/01/2014 06:30 09:30 03:00 N 10.10 91 03/02/2014 13:00 15:00 02:00 N 18.10 92 04/02/2014 15:00 18:00 03:00 N 27.70 93 05/02/2014 06:30 11:00 04:30 N 38.00 94 10/02/2014 14:30 17:30 03:00 Y 84.80 95 11/02/2014 14:30 18:00 03:30 Y 91.00 96 12/02/2014 14:30 18:00 03:30 Y 95.70 97 13/02/2014 14:30 16:30 02:00 Y 98.70 98 17/02/2014 06:00 09:00 03:00 N 96.30 99 18/02/2014 06:00 09:00 03:00 N 91.60 100 19/02/2014 06:00 09:00 03:00 N 85.10 101 20/02/2014 11:00 14:00 03:00 N 76.90 102 07/11/2014 14:00 16:00 02:00 Y 100.00 103 08/11/2014 07:00 13:00 06:00 Y 98.70 104 11/11/2014 10:00 15:00 05:00 Y 82.00 105 19/11/2014 13:00 15:30 02:30 Y 11.00 106 01/12/2014 13:30 16:30 03:00 N 75.20 107 08/05/2015 13:00 17:00 04:00 N 84.30 108 09/05/2015 07:00 14:00 07:00 N 75.30 109 10/05/2015 13:00 17:00 04:00 N 64.80 110 11/05/2015 07:00 12:00 05:00 N 53.40 111 12/05/2015 08:00 16:00 08:00 N 41.60 112 13/05/2015 09:00 15:00 06:00 N 30.10 113 15/05/2015 11:00 13:00 02:00 N 10.90 114 17/05/2015 09:15 12:30 03:15 N 0.90 115 24/11/2015 11:00 16:15 05:15 Y 98.20
3 116 25/11/2015 09:00 14:00 05:00 N 99.80 117 28/11/2015 11:00 15:15 04:15 N 94.40 118 29/11/2015 13:00 16:00 03:00 Y 88.10 119 02/12/2015 14:15 16:45 02:30 Y 61.60 120 03/12/2015 12:00 17:15 05:15 N 51.70 121 05/12/2015 07:15 14:00 06:45 Y 32.60 122 06/12/2015 13:45 17:00 03:15 Y 23.90 123 07/12/2015 07:00 12:30 05:30 N 16.20 124 09/12/2015 08:00 16:15 08:15 Y 4.60 125 09/12/2016 13:00 17:00 04:00 Y 75.40 126 10/12/2016 12:15 16:30 04:15 Y 85.00 127 12/12/2016 11:00 16:15 05:15 Y 97.80 128 13/12/2016 09:00 15:15 06:15 Y 99.80 129 14/12/2016 13:45 16:45 03:00 Y 100.00 130 15/12/2016 07:45 12:00 04:15 Y 98.50 131 16/12/2016 08:00 15:30 07:30 Y 94.30 132 17/12/2016 08:15 16:00 07:45 Y 87.60 133 06/12/2017 12:00 17:00 05:00 Y 91.80 134 08/12/2017 11:30 17:15 05:45 Y 73.90 135 11/12/2017 06:45 13:30 06:45 N 41.10 136 12/12/2017 09:00 11:45 02:45 N 30.90 137 13/12/2017 07:00 11:15 04:15 N 21.90 138 15/12/2017 11:30 16:15 04:45 Y 8.00 139 16/12/2017 09:00 15:30 06:30 N 3.50 140 17/12/2017 07:00 14:30 07:30 N 0.90
4 Figure S1: A close-up image showing colour dimorphism and pairing exhibited between giant trevally Caranx ignobilis within the aggregation at Ponta do Ouro Partial Marine Reserve. Colour dimorphism and pairing was observed on multiple occasions and is a characteristic of previously observed giant trevally spawning aggregations (von Westernhagen 1974; Sudekum et al. 1991), suggesting it may be indicative of spawning-related behaviour
References
Sudekum AE, Parrish JD, Radtke RL, Ralston S. 1991. Life history and ecology of large jacks in undisturbed, shallow, oceanic communities. Fishery Bulletin 89: 493–513. von Westernhagen H. 1974. Observations on the natural spawning of Alectis indicus (Rüppell) and Caranx ignobilis (Forsk.) (Carangidae). Journal of Fish Biology 6: 513–516.