Journal of Fish Biology (2015) 87, 179–186 doi:10.1111/jfb.12703, available online at wileyonlinelibrary.com

First record of a spawning aggregation for the tropical eastern Pacific endemic grouper Mycteroperca olfax in the Galapagos Marine Reserve P. Salinas-de-León*, E. Rastoin and D. Acuña-Marrero Department of Marine Sciences, Charles Darwin Research Station, Av Charles Darwin s/n, Puerto Ayora, Santa Cruz Island, Galapagos Islands, Ecuador

(Received 24 November 2014, Accepted 19 March 2015) This study provides direct and indirect evidence of temporally and spatially consistent spawning aggregations for the grouper Mycteroperca olfax. Recently reported declines in population numbers, probably related to the direct targeting of aggregations by artisanal fishermen, highlight the urgent need for species-specific management actions in the Galapagos Marine Reserve, such as minimum and maximum landing sizes, and the importance of protecting key aggregation sites with the declaration of no-take areas and the establishment of total fishing bans during the reproductive season. © 2015 The Fisheries Society of the British Isles

Key words: Epinephelidae; Galapagos Islands; marine protected areas; reproduction.

Groupers (Epinephelidae) are common members of tropical reef fish communities and are represented by six genera and 11 species in the Galapagos Islands, located in the tropical eastern Pacific (TEP) (Craig & Hastings, 2007; McCosker & Rosenblatt, 2010). Industrial, recreational and artisanal fisheries worldwide heavily target this group of species, with an estimated global landing of 275 000 t in 2009 (Sadovy de Mitcheson et al., 2013). Groupers are especially vulnerable to fishing as they are characterized by slow growth, late sexual maturity, high territoriality and a predominantly protogynous (sex change from female to male) reproductive strategy at late stages in their life cycle (Coleman et al., 1996, 2000; Erisman et al., 2009a). Many species of groupers are also known to aggregate to spawn at specific locations, seasons and moon phases throughout tropical and sub-tropical marine ecosystems (Colin, 2012). In recent years, fish spawning aggregations have received increasing attention, not only for their ecological significance and importance for fisheries, but also because many aggregations have declined or even disappeared due to overfishing (Colin, 1996; Sala et al., 2001; Sadovy & Domeier, 2005; Aguilar-Perera, 2006; Russell et al., 2012). *Author to whom correspondence should be addressed. Tel.: +593997478133; email: pelayo.salinas@ fcdarwin.org.ec

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The sailfin grouper Mycteroperca olfax (Jenyns 1840) is a large grouper (c. 110 cm maximum total length, LT ), distributed among rocky and coral reefs to a depth of c. 100 m, where it is one of the top reef predators (Rodriguez, 1984; Okey, 2004). Its distribution is restricted to the Galapagos, Cocos and Malpelo archipelagos in the TEP, although the Galapagos are considered to harbour the most important populations (Froese & Pauly, 2007). Given their limited geographic range, intrinsic vulnerability due to life-history traits, and fishery-dependant evidence of population declines, the bacalao (as it is locally known in the Galapagos) has been included as vulnerable in the IUCN list of endangered species since 2008. Mycteroperca olfax size at first maturity for females is estimated at c. 50 cm, equivalent to c. 4 years of age (Rodriguez, 1984; Coello, 1989). Skewed sex ratios and restriction of males to larger size classes suggest that M. olfax is a protogynous hermaphrodite, with sex change from female to male in some individuals from c. 80 cm (Coello, 1989). This species has an annual reproductive cycle, with an estimated reproductive peak between October and January (Rodriguez, 1984; Coello & Grimm, 1993). Despite its socio-economic importance to the local artisanal fishery (Reck, 1983) and the documented declines in its abundance and size in the past 70 years due to overfishing (Burbano et al., 2014; Schiller et al., on-line), the reproductive patterns for M. olfax remain poorly understood. To date, there is no information available on the occurrence of spawning aggregations for this species within the TEP, despite aggregation events that have already been recorded for a number of other members of the Epinephelidae in the same region (Sala et al., 2003; Aburto-Oropeza & Hull, 2008; Erisman et al., 2009b). The Galapagos Marine Reserve (GMR) is located c. 1000 km from the west coast of South America (Fig. 1). The GMR harbours a wide range of marine ecosystems, given the congruence of four major oceanic currents, and its oceanographic conditions are dominated by a warm and cold season (Palacios, 2004). This study was conducted around Wolf and Darwin, two isolated oceanic islands situated in the far north bioregion in the archipelago (Edgar et al., 2004), and located 296 km north of the central island of Santa Cruz, where the Charles Darwin Research Station is based (Fig. 1). During November 2013, a field trip of 10 days duration was conducted to investigate spawning aggregation behaviour for M. olfax. Surveys were mainly focused around Wolf Island, based on an opportunistic observation during October 2012, where a group of 25–30 large M. olfax with distended abdomens were seen (D. Acuña-Marrero, pers. obs.). Therefore, the 2013 trip was timed to match a similar moon phase to that of the October 2012 observations (2 days after first quarter). A total of four study sites were monitored around Wolf and Darwin Islands during 12 to 16 November (Fig. 1). All surveys were conducted in the 15–25 m depth range. These sites were re-visited during 5 to 7 August 2014 to have a reference point out of the estimated peak reproductive season for this species in a similar lunar phase (2 days after first quarter). The monitoring approach of the Society of the Conservation of Reef Fish Aggregations manual (Colin et al., 2003) was followed and adapted to local conditions. Standard 25 m × 5 m belt transects were used to conduct underwater visual census (UVC). All observers that conducted UVC were experienced and trained divers in order to minimize any observer bias. Abundance data were converted to biomass (kg) using a length and mass formula (Rodriguez, 1984). An additional census was conducted in November 2013 using stereo-video, where a diver filmed all the fish within the aggregation to obtain very accurate length-frequency measurements of individuals (Harvey

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Fig. 1. (a) Location of the Mycteroperca olfax spawning aggregation in the Galapagos Marine Reserve, located 1000 km to the west of mainland Ecuador. Map shows the four survey locations around Darwin and Wolf Island (including 10 m isobaths). These islands are c. 296 km north-west of the Island of Santa Cruz, where the Charles Darwin Research Station (CDRS) is located. (b) Sketch of the depth, bathymetry and locations of the M. olfax aggregation site (direction of the observation is north–south). The specific location of the aggregation was deliberately not specified on the map to avoid additional fishing pressure.

& Shortis, 1995). Finally, eight individuals ranging from 50 to 78 cm LT were obtained from an artisanal fishing vessel that was fishing around Wolf Island on 18 November. Samples were processed following standard histological procedures (McMillan, 2007) and classified following standardized criteria (Brown-Peterson et al., 2011). A total of 42 transects were conducted across the four study sites in November 2013. An additional 10 transects were conducted in August 2014 at the identified aggregation site. Density (Kruskal–Wallis, H = 21⋅98, d.f. = 3, P < 0⋅05), median size (Kruskal–Wallis, H = 16⋅57, d.f. = 3, P < 0⋅05) and biomass (Kruskal–Wallis, H = 21⋅61, d.f. = 3, P < 0⋅05) were significantly higher at the aggregation site compared with the other sites (Fig. 2). It is important to note, however, that higher densities of the aggregating grouper were observed in deeper waters (>35 m) and >5 m away from the reef where surveys were conducted; therefore, the core of the aggregation was not recorded in the transects. The 79 fish measurements at the aggregation site analysing 15 min of stereo-video footage had a mean ± s.e. LT of 71⋅00 ± 1⋅32 cm. This mean length is over 50% higher than the 46⋅71 ± 4⋅86 cm LT recorded in a recent archipelago-wide survey using stereo-video that included 88 sites across the entire GMR (P. Salinas-de-León, unpubl. data). Histological analysis confirmed the presence of five females in the actively spawning sub-phase of the spawning capable status (Brown-Peterson

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LT (cm) Fig. 2. (a) Mean + s.e. density ( ) and biomass ( ) of Mycteroperca olfax at four survey sites around Darwin and Wolf Islands, Galapagos Marine Reserve. (b) Total length (LT ) frequency distribution [n = 79 fish measurements at the aggregation site using the Event Measure software (SeaGIS, Australia) for stereo-video analysis]. , predicted LT at first maturity for females;

, predicted LT at sex change from female to male.

et al., 2011), revealed by the presence of post-ovulatory follicles (POF), oocytes undergoing germinal vesicle breakdown (GVB) and germinal vesicle migration (GVM). Surveys conducted in August during the cold season at the aggregation site revealed a mean ± s.e. density of 1⋅68 ± 0⋅28 individuals 100 m−2 and biomass of 2⋅11 ± 0⋅66 kg 100 m−2 , the latter significantly lower compared with the spawning season (Kruskal–Wallis, H = 4⋅00, d.f. = 3, P < 0⋅05). On this occasion, no large individuals were observed in deeper waters or away from the reef where transects occurred. Although it was not possible to witness the spawning event, both direct and indirect evidence (Domeier & Colin, 1997; Domeier, 2012) presented here support the first recorded spawning aggregation for M. olfax. Histological analysis revealed the

© 2015 The Fisheries Society of the British Isles, Journal of Fish Biology 2015, 87, 179–186

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(a)

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Fig. 3. Mycteroperca olfax aggregating at the reported site, Galapagos Marine Reserve, November 2013. (a) Three large M. olfax displaying distended abdomens swimming in parallel at 35 m depth. (b) A large individual displaying a distended abdomen, darker colouration around the head and an upright dorsal fin. (c) Screen capture of a stereo-video measurement of four large (70–80 cm total length) individuals. (a, b) Video extracts from a camera mounted on a tripod and deployed at 35 m depth. (c) From the 15 min of stereo-video footage analysed for the length-frequency distribution analysis.

presence of POFs in the majority of the eight gonads analysed, direct evidence of spawning behaviour. During the surveys, photographic and video evidence of individuals with greatly distended abdomens was collected, indirect evidence of spawning behaviour (Fig. 3). A seven-fold increase in biomass at the aggregation site compared with the non-reproductive season was also reported; the length-frequency information revealed that a great proportion of individuals recorded during the aggregation event were mature and possible mating colouration and behaviour were recorded; all of the which are also indirect evidence of a spawning aggregation. The present observations of a relatively low number of aggregating individuals (40–60) of M. olfax are similar to those reported for other members of the genus, e.g. sawtail grouper Mycteroperca prionura Rosenblatt & Zahuranec 1967 (14–100), slightly higher than those reported for Gulf grouper Mycteroperca jordani (Jenkins & Evermann 1889) (20–30), but considerably lower than those reported for leopard grouper Mycteroperca rosacea (Streets 1877), scamp Mycteroperca phenax Jordan & Swain 1884 and gag Mycteroperca microlepis (Goode & Bean 1879), which tend to form larger aggregations of hundreds to thousands of individuals (Gilmore & Jones, 1992; Coleman et al., 1996; Sala et al., 2003; Erisman et al., 2007). Anecdotal information gathered from artisanal fishermen and long-term Galapagos residents suggests that M. olfax do not conduct major reproductive migrations or massive concentrations of individuals throughout the year. Based on this and the present observations, it is

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hypothesized that M. olfax may display site-specific, transient aggregations of limited size, rather than resident aggregations. The aggregation site at Wolf Island was visited again opportunistically in January 2014 and although no quantitative data were recorded, several individuals displaying distended abdomens were observed during a single dive (P. Salinas-de-León, pers. obs.). This suggests that spawning aggregations may occur at the northern islands of Darwin and Wolf during a great part of the reported peak reproductive period for this species between October and January (Rodriguez, 1984; Coello & Grimm, 1993). This hypothesis is supported by the extended spawning season between late April and early June reported for M. rosacea in the Gulf of California (Erisman et al., 2007). Due to logistical limitations, it was not possible to conduct surveys throughout the lunar cycle. In this study, the visit to the aggregation site was timed to match a similar lunar phase (2 days after first quarter) to that of the opportunistic observation in October 2012, given that many grouper species are known to synchronize spawning events (Sadovy de Mitcheson & Colin, 2012). Similar to 2012, spawning evidence was recorded around this lunar phase, which may suggest some moon synchrony as revealed for other members of the genus, such as Mycteroperca venenosa (Schärer et al., 2012). This needs to be adequately evaluated by conducting future surveys and gonad collections at different moon phases throughout the predicted peak reproductive season. The predicted duration and site specificity of spawning aggregations for M. olfax make them highly vulnerable to fishing pressure. Despite industrial fishing having been banned since 1998, an artisanal fishery of c. 1200 registered fishermen is allowed in the GMR. Fishermen have targeted M. olfax since the 1930s and recent evidence suggests severe declines in their populations over the past 70 years (Burbano et al., 2014; Schiller et al., on-line). The reproductive season for M. olfax (October to January) coincides with the peak of the fishing season during the months prior to Easter (April), where this species is the main ingredient in the preparation of the traditional Ecuadorian dish fanesca, which is served at Easter. Galapagos artisanal fishermen are targeting areas where M. olfax aggregate to reproduce, and research in other parts of the world has shown how artisanal fisheries can quickly deplete spawning aggregations (Hamilton et al., 2012; Sadovy de Mitcheson & Erisman, 2012). To date, there are no regulations in place for this fishery (e.g. no size restrictions or fishing closures) and over 80% of the coastal zones of the GMR are open to fishing, including the aggregation site reported in this study. It is thus urgent to establish a management plan for M. olfax that includes actions such as the implementation of maximum and minimum landing sizes, a fishery closure during reproductive months and the designation of key nursery and aggregation areas, such as the one reported in this study, as no-take zones. Future research should focus on gaining a better understanding of M. olfax reproductive biology through further histological work and the identification and characterization of additional aggregation sites throughout the archipelago. Funding was provided by grants from the Disney Worldwide, Mohammed Bin Zayed, Lindblad-National Geographic and Fundación Ataman conservation funds. We thank rangers of the Galapagos National Park Directorate and the crew of the M.V. Oberlús for logistical support. We thank I. Haro-Bilbao and C. Chong for assistance with laboratory analysis. This is contribution number 2114 from the Charles Darwin Research Station.

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© 2015 The Fisheries Society of the British Isles, Journal of Fish Biology 2015, 87, 179–186

First record of a spawning aggregation for the tropical eastern Pacific endemic grouper Mycteroperca olfax in the Galapagos Marine Reserve.

This study provides direct and indirect evidence of temporally and spatially consistent spawning aggregations for the grouper Mycteroperca olfax. Rece...
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