INTRODUCTION
The fish family Antennariidae comprises 13 genera and 49 valid species (Fricke & Eschmeyer, Reference Fricke and Eschmeyer2014) and it is mainly distributed in tropical areas at depths from 0 to 300 m, although, some species can reside in higher latitudes (Arnold & Pietsch, Reference Arnold and Pietsch2012). These fish are found in benthic habitats, feeding on fishes and invertebrates, and their most distinctive morphological traits are the presence of a modified first dorsal fin spine (the illicium), which has been modified and elongated to use as a lure, and also a tube-like opening under the pectoral fin that is used for locomotion by jet propulsion (Schneider & Lavenberg, Reference Schneider, Lavenberg, Fischer, Krupp, Schneider, Sommer, Carpenter and Niem1995).
Crucially, the roughbar frogfish was previously known as Antennarius avalonis, but after a recent study of the phylogeny of this group, molecular analysis recovered two major groups, modifying the genera of this species to the genus Fowrelichthys (Arnold & Pietsch, Reference Arnold and Pietsch2012). Thus, the antennariids have two subfamilies (Antennariinae and Hystiophyrinnae), of which only representatives of the former can be found in waters of the eastern Pacific. There, five species are present, three of the genus Antennatus; Antennatus coccineus (Lesson, 1831), Antennatus sanguineus (Gill, 1863) and Antennatus strigatus (Gill, 1863), one of Antennarius; Antennarius commerson (Latreille, 1804) and one of Fowlerichthys; F. avalonis (Jordan & Starks, 1907). Those of the Antennatus genera occur in the region from north and central Mexico to Central America or Peru, while Antennarius commerson is an Indo-Pacific taxon found from Costa Rica to Colombia, as well as in the oceanic islands Revillagigedos (Mexico), Cocos (Costa Rica) and Malpelo (Colombia) (Robertson & Allen, Reference Robertson and Allen2008).
The roughbar frogfish Fowlerichthys avalonis is the most widely distributed species in its family along the eastern Pacific, being found from southern California (USA: 34°N) to Chile (15°S), but it is present only in three oceanic islands: Galápagos (Ecuador), Cocos (Costa Rica) and Guadalupe (Mexico) (Miller & Lea, Reference Miller and Lea1972; Pietsch & Grobecker, Reference Pietsch and Grobecker1987; Robertson & Allen, Reference Robertson and Allen2008; Sielfeld, Reference Sielfeld2010; Walther et al., Reference Walther Mendoza, Ayala Bocos, Hoyos Padilla and Reyes Bonilla2013). This fish usually resides in the hides of rocky substrates or at the deep edges of reefs over muddy or sandy bottoms, at depths from 10 to 300 m (although, mostly in waters less than 100 m deep), and it can grow up to 36 cm in total length (Thomson et al., Reference Thomson, Findley and Kerstitch1979; Robertson & Allen, Reference Robertson and Allen2008). It preys on fish and crustaceans (trophic level 4.01 ± 0.66; Fitch & Lavenberg, Reference Fitch and Lavenberg1975; Froese & Pauly, Reference Froese and Pauly2014), is dioecious and reproduces by external fertilization; its larvae and egg masses can be found in the water column between the months of August to October in California (Watson, Reference Watson and Moser1996).
The absence of F. avalonis on the other islands and archipelagos is noticeable, and could be caused by the difficulty in access to deep areas where this fish used to reside. In this case, we took advantage of the increasing use of human-occupied submersibles for deep-sea research. These vehicles allow one or two scientists per dive to make direct underwater observations and real-time recordings. In the submersible, every observation, whether geological, chemical or biological, is precisely recorded on the seafloor, relative to its well-characterized geologic setting or ecological habitat. The objective of this paper is to document the first finding of this frogfish species at Socorro Island, the biggest of the four islands of the Revillagigedo Archipelago.
MATERIAL AND METHODS
Socorro Island belongs to the Revillagigedo Archipelago, a biosphere reserve located about 450 km south-west of the tip of the Baja California Peninsula, Mexico. Socorro is the largest of the four islands; it is 16 km long, 11.5 km wide and approximately 132 km2. The island rises abruptly from the sea to 1050 m (3440 feet) in elevation at its summit. Isla Socorro is a shield volcano. The island is part of the northern Mathematicians Ridge, a mid-ocean ridge that became largely inactive 3.5 million years ago when activity moved it to the East Pacific Rise. All four islands, along with the many seamounts on the ridge, are post-abandonment alkaline volcanoes (Bohrson & Reid, Reference Bohrson and Reid1997).
The study was performed from 6 to 30 March 2014, during a survey of the bottom fauna of the island. Dives were conducted inside the submersible DeepSee (Triumph model, able to reach 457 m in depth), carrying a pilot and two passengers. Two of the authors (M. Hoyos-Padilla and D. Garcia-Benito) performed 35 surveys at five different areas: Socorro Island (Bahía Braithwaite, Cabo Pearce and Punta Tosca), San Benedicto Island (El Cañon) and Roca Partida, each survey covering two to four observation hours. Information on depth and temperature was taken, and also a number of images and videos of the most conspicuous fish species were taken with HD video cameras and digital still cameras.
The identification of the observed specimen of the roughbar frogfish was made on the basis of photographs that evidenced the diagnostic characteristics of the Fowlerichthys avalonis (suggested by Rachel J. Arnold). Finally, we consulted a number of expert ichthyologists from Mexico and the United States in order to confirm our taxonomic determination.
Once the name of the species was confirmed, we then verified its geographic range using specialized literature and revised data on the collected specimens from 25 museums worldwide, available on the Global Biodiversity Information Facility webpage (http://data.gbif.org), the Ocean Biogeographic Information System (http://www.iobis.org/), the National Science Foundation (http://www.vertnet.org) and the International Centre for Living Aquatic Resources Management (http://www.fishbase.org). This was in order to confirm that there was no existing record of this fish from the Revillagigedo Archipelago.
RESULTS
A single individual of Fowlerichthys avalonis was found at a depth of 66 m (water temperature: 15.4°C) off the coast of Socorro Island at the coordinates 18°46′19″N 110°53′43″W, during a survey on 22 March 2014. The fish was not collected, but nevertheless, positive identification was based on its diagnostic globular body, which was partially compressed, and a black spot bordered by a ring of orange in the basal part of the dorsal fin. The specimen was brown in colour, approximately 30 cm long and had a visible lure (Figure 1). The basis of the report is a single high-definition video. We identified the individual in the picture using the main feature of this fish; a black spot bordered by a ring of orange colour in the basal part of the dorsal fin (Robertson & Allen, Reference Robertson and Allen2008). In the same locality, another frogfish was observed and probably corresponded to the same species (Figure 2), but the position of the organism in the photograph did not allow discerning its diagnostic traits useful for taxonomic determination. The individual was found motionless and half of its body was inside the crevice of a massive volcanic rock of approximately 20 m wide by 10 m high. The rock was covered with small sponges, bryozoans and polychaetes. In the same rock and in the vicinity of the frogfish, several adult Spotback scorpionfish (Pontinus vaughani) were recorded, representing the dominant fish species in rocks below 80 m.
Fowlerichthys avalonis (Jordan and Starks, 1907) specimen observed at Socorro Island (66 m deep). Scale bar = 10 cm. Photo by Diana Garcia Benito.
Individual of unidentified frogfish species, seen at Cabo Pierce, Socorro Island, Revillagigedo Archipelago. Photo by Diana Garcia Benito.
According to the information found in the literature and in museum records (Jordan & McGregor, Reference Jordan and McGregor1899; Schneider & Lavenberg, Reference Schneider, Lavenberg, Fischer, Krupp, Schneider, Sommer, Carpenter and Niem1995; Castro Aguirre & Balart, Reference Castro Aguirre, Balart and Lozano-Vilano2002; Robertson & Allen, Reference Robertson and Allen2008; Chávez-Comparán et al., Reference Chávez-Comparán, Patiño-Barragán, Calderón-Riveroll, Lezama-Cervantes, Lara-Chávez, Ibarra-Casillas and Bautista-Laureano2010; see methods section for the museum database), the range distribution of F. avalonis is from Santa Catalina Island, California to Iquique, Chile. There are no previous reports from the Revillagigedo Islands. The finding of F. avalonis at Socorro Island increases the number of known species for this archipelago family to four.
DISCUSSION
Whilst the distribution of Fowlerichthys avalonis in oceanic islands (Cocos, Galapagos and Guadalupe) has been recorded, it is possible that the fish had not been seen in the Revillagigedo Archipelago, due to the lack of appropriate technology to reach depths greater than 100 m, and to the scarce time and effort devoted to explore the islands from this archipelago. Although considerably more expensive than instrument deployments from research vessels, observations from submersibles have been key to the discovery of unique geological, geochemical and biological phenomena, and to furthering our understanding of many important seafloor processes. Also, submersible surveys are especially important when working in logistically remote locations where staging expenses prohibit the timely return to a site (Bachmayer et al., Reference Bachmayer, Humphris, Fornari, Dover, Howland, Bowen, Elder, Crook, Gleason, Sellers and Lerner1998).
Recent surveys of the fish and invertebrate faunas from Socorro Island (Fourriere, Reference Fourriere2012) indicate that the island is home to 435 species. The presence of F. avalonis improves these figures by one species and genus, and confirms that almost all eastern Pacific species of Antennariidae are present at the Revillagigedo Archipelago, except Antennatus coccineus (Pietsch & Grobecker, Reference Pietsch and Grobecker1987; Robertson & Allen, Reference Robertson and Allen2008).
On the other hand, in recent years the use of effective sampling methods, including photographic surveys and direct observations using deep-sea submersibles, have revealed highly diverse benthic communities in the deep sea. In addition, these tools allow researchers to learn more about the wildlife in deeper waters that cannot be normally reached by scuba (40 m).
In conclusion, the results of this paper extend the accepted distribution range of the roughbar frogfish Fowlerichthys avalonis to the oceanic Socorro Island in the Revillagigedo Archipelago. This new information will be useful in biogeographic research, which in accompaniment with ecological and connectivity studies, will lead to a better understanding of the distributional patterns of the different species.
ACKNOWLEDGEMENTS
The submersible expedition was funded by Televisa, Aeroméxico and Grupo Nacional Provincial (Documentary: Por el Planeta). We are grateful to the administrator of the Revillagigedo Archipelago Biosphere Reserve (María Jossué Navarro-Sánchez) for giving us the correspondent authorization to conduct this expedition, and to Rachel J. Arnold for her valuable opinion concerning the photo identification. Our thanks to Hector Reyes Bonilla for his support and advice in the preparation of this paper and, finally, to the anonymous reviewers for their valuable comments and observations.
