First valid record of Gymnothorax vicinus (Pisces: Muraenidae) for macaronesian ecoregion (Canary Islands): a process of tropicalization?

              Rev. Acad. Canar. Cienc., Vol. XXVI, 121-128 {diciembre de 2014)
FIRST VALID RECORD OF Gymnothorax vicinus
(PISCES: MURAENIDAE) FOR MACARONESIAN ECOREGION
(CANARY ISLANDS): A PROCESS OF TROPICALIZATION?
*Brito, A., Dorta, C. & Falcon, J. M.
Biodiversidad, Ecologia Marina y Conservacion (BIOECOMAC)
Departamento de Biologia Animal (Ciencias Marinas), Universidad de La Laguna
Avenida Astrofisico Francisco Sanchez s/n, 38206 La Laguna, Tenerife, Islas Canarias.
* Author for correspondence (e-mail: abrito@ull.es)
RESUMEN
Se registra por primera vez en Canarias la presencia de la morena Gymnothorax vici-nus
(Castelnau, 1855), demostrando que los registros previos existentes para Canarias, Ma-deira
y Azores se debieron a errores de identificacion. La deteccion de esta especie tropical
en 2008 en la isla de El Hierro la de aguas mas calidas de la ecoregion macaronesica— ini-cialmente
nos condujo a pensar en un proceso de colonizacion reciente relacionado con el ca-lentamiento
global (tropicalizacion). Sin embargo, la informacion obtenida de los Pescadores
habla de una especie nativa en su limite norte de distribution, con poblaciones muy reduci-das.
Estos ban capturado muy esporadicamente algun ejemplar desde hace muchos anos. Su
reciente deteccion e incremento de la frecuencia de captura, en areas donde los peces litora-les
estan bien estudiados, obedece probablemente a que las condiciones ambientales actuales
le son favorables y han permitido incrementar la poblacion. Este proceso ya se habia obser-vado
en Canarias con otras especies termofilas. El analisis de los datos relativos a su poste-rior
captura en Tenerife lleva a la misma conclusion.
Palabras clave: Atlantico Oriental subtropical, cambio climatico, calentamiento global
ABSTRACT
We herein present the occurrence of the moray eel Gymnothorax vicinus (Castelnau,
1855) in the Canary Islands, highlighting that these truly are the first valid records for Mac-aronesia,
since previous existing records for the Azores, Madeira and Canary Islands were
caused by misidentification. The appearance of this tropical species in 2008 in the island of
El Hierro —the one with the wanner waters in the entire Macaronesian ecoregion initially
leads to thinking of a connection with global warming (tropicalization). Nevertheless, infor-mation
obtained from local fishermen speaks of a indigenous thermophilic species in its north
limit of distribution, with a very small populations. Fishermen have captured specimens only
intermittently for many years now. Its recent detection in an area where littoral fish are widely
studied has probably been caused by the increasingly favourable environmental conditions,
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which has triggered an increase in its population. This process had already been observed in
the Canarias amongst other thennophilic fish species. Results of the analysis of data regard-ing
their subsequent catch in Tenerife leads to the same conclusion.
Key words: Eastern Subtropical Atlantic, climatic change, global warming.
1. INTRODUCTION
Gymnothorax vicinus (Castelnau, 1855) is a moray eel known to inhabit littoral rocky
bottoms (down to 40 m of depth) in both tropical Atlantic shores (BOHLKE et al., 1989;
BOHLKE & SMITH, 2002). In Eastern Atlantic, it has only been recorded with certainty in
Cape Verde Islands (BLACHE, 1967; BOHLKE et al., 1989; BRITO et al., 1999; WIRTZ
et al., 2013), where its occurrence is rather frequent (A. BRITO & J. M. FALCON, non-pub-lished
data), Fernando Poo (BLACHE, 1967; BOHLKE et al., op. cit.), Ghana (BOHLKE
et al., op. cit
)
and Sao Tome and Principe (see AFONSO et al., 1999; WIRTZ et al., 2007),
although the latter authors base their research on old records and have not found the species
during their recent research expeditions. Despite the existence of very old works pointing
out the presence of G. vicinus in the Macaronesian archipelagos —Azores, Madeira and the
Canaries— (JORDAN & GUNN, 1898; BLACHE, 1967; BOHLKE, 1981; BAUCHOT,
1986; BOHLKE et al., 1989; SMITH & BOHLKE, 1990; BOHLKE & SMITH, 2002;
WIRTZ et al., 2008; FROESE & PAULY, 2010), its actual occurrence in those islands has
been questioned (BRITO, 1991; SANTOS et al., 1997; BRITO et al., 2002). Through the
analysis of the references given, it becomes evident that only two of them are based on the
study of fishes that were caught for certain in the waters of those islands: JORDAN &
GUNN ( 1 898) —with doubts of the correct affiliation of the specimens— and WIRTZ et al.
(2008).
Recently, we have had the opportunity to study six specimens and photographs of
G. vicinus caught within years 2008 and 2014 in the island of El Hierro (Canary Islands) and
unloaded in the only official point of first sale of fish in the island, located in the port of La
Restinga. We also had the possibility to examine pictures taken of a different specimen caught
in 2014 in Tenerife. The appearance of this moray in the westernmost island of the Canaries
also the one where waters reach warmer temperatures— led us to starting a discussion on
whether it is a recent colonization process linked to the warming of the waters in the Ca-naries
(tropicalization), or if it may be a consequence of the population growth of a indige-nous
thermophilic fish species, with very small populations inhabiting the northernmost
distribution limit, and their spread over the islands’ thermal gradient from the ones with
warmer waters (occidentalization), just like what has already happened with other tropical
species BRITO et al. (2005).
2. MATERIALS AND METHODS
Two specimens caught in the island of El Hierro September 2009 and May 2010 were
examined. Besides, pictures of other four specimens were taken in September 2008, Septem-ber
2009 and July 2014. All of them came from different localities in the island of El Hierro
and were caught by local fishermen in depths ranging from 10 to 20 m. Pictures of a speci-men
caught in Punta del Hidalgo (Tenerife) about 5m deep on October 2013. The first two
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specimens, which were studied in detail, are now in the ichthyological collection of Departa-mento
de Biologia Animal (Ciencias Marinas) de la Universidad de La Laguna. Morphome-tric
and meristic parameters were taken according to BOHLKE ( 1 989), and specifications for
Muranidae family in Bohlke et al. {op. cit.) were followed. In addition to the study of the
specimens, we had talks with local moray-fishermen so as to gather all the information they
had on this species.
3. RESULTS
The studied specimens (figure 1) show morphometric and meristic characteristics as
described in table 1. Characteristics match up with those described by BLACHE (1967) and
BOHLKE et cil. {op. cit.). The biggest specimen reached a total length of 152 cm, exceeding
the 122 cm that were recorded up till now as the maximum size for this species (BOHLKE &
SMITH, 2002). G. vicinns belongs to the group of Atlantic moray of the Gymnothorax genus
that show a sharp elongated snout, jaws elongate, eye above midjaw, smooth uniserial teeth
in jaws and vomer, with some long canine teeth anteriorly. The species can be easily identi-fied
by the general colour of its body as well as by the presence of a dark mark in the comer
of the mouth (BOHLKE et al., 1989).
Coloration of the specimens studied by us corresponds almost entirely with the de-scription
by BLACHE {op. cit.), that is, olive grey or dark brown —slightly lighter in ventral
area— and the absence of marks (figure 1). This coloration is dominant in the tropical East-ern
Atlantic, as we have been able to observe in Cape Verde Islands too. The dark mark in the
corner of the mouth always stands out, although it can look more or less intense depending
on the colour of the surroundings. The only remarkable variation is the one found in the biggest
specimen: the white rim of its anal and dorsal fins is considerably thinner than the standard;
it can be seen only in its caudal most part.
The biggest specimen, caught in May 2010, is a male individual that shows gonads in
initial growth stage after the rest phase. Whereas the second specimen caught in September
2009, is a female individual with ripe gonads close to the spawning. Ovocytes sizes went from
0,7 to 1,1 mm.
4. DISCUSSION
JORDAN & GUNN ( 1 898) doubtfully identify three specimens of moray from the Ca-nary
Islands as G.vicinus. Doubts arise due to coloration being different than the one attrib-uted
to G.vicinus. In fact, the white-mottled pattern described by these authors seems more
likely to correspond with Gymnothorax polygonius (Poey, 1876), which is a frequent species
in deep littoral waters of the archipelago (BRITO et a/., 2002) and also in fish markets all
over the Canary Islands. However, BLACHE {op. cit.), in his excellent work on moray eels
in the Western African coastline, accepted this reference and also pointed out the high prob-ability
of the species occurring in Madeira based on a not very clear reference by KAUP
(1856), who identifies it as Thyrsoidea cancellata (non Rich., 1844). The other authors men-tioned
in the introduction have based their conclusions on the reference by BLACHE {op.
cit.) in some cases even misplacing geographical location— and on the recent catalogue of
littoral fishes in Madeira by WIRTZ et al. (2008).
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Catalogues of fishes in the Azores (SANTOS et al., 1997) and the Canaries (BRITO
et al., 2002) do not comprise G. victims , since the above mentioned authors find the existing
references of G. victims to be caused by confusions with G. polygonius. Only in the recent cat-alogue
of Madeira (WIRTZ et al., op. cit.) is this species included on the basis of an specimen
deposited in the Museu Municipal do Funchal (reference: MMF 36398) that was caught at a
depth of 150 m —this is an unusual depth for G. victims—. The specimen was re-examined
in 2009, at our request, by one of the authors of the catalogue, who confirmed it to actually
be a specimen of G. polygonius (M. J. BISCOITO, com. in lift.).
The appearance of G. victims precisely in El Hierro —the island with the most trop-ical-
like environmental conditions and ichthyofauna in the Canaries and the entire Mac-aronesia
ecoregion (FALCON et al., 1996)—, makes it possible to suspect of a recent
colonization process related to the rising temperatures of Canarian waters (tropicalization),
as it has happened in other cases of tropical fish with high swimming capability or special-ized
planktotrophic larvae (BRITO et al., 2005). One argument supporting such hypothesis
is that of the wide and comprehensive study of littoral fish that has been carried on over time
in this marine community (BORTONE et al., 1991; FALCON et al., op. cite, CLAUDET et
al., 2010), largely because of the creation of a marine reserve in the island in 1996. More-over,
G. victims turns out to be one of the less cryptic and more aggressive of moray (BOH-LKE
& SMITH, op. cit.), as we have had the chance to confirm in Cape Verde Islands (Brito
& Falcon, obs. pers.), where these moray often follow divers that approach the crevices they
hide in.
Nonetheless, the most experienced moray eel fishermen from El Hierro have known
this species for over 30 years now, and even have a common name for it, “Morena congrio”,
that refers to the apparent morphologic similarities G. vicinus has with the Conger eel. Con-ger
conger. They also describe G. vicinus as the most combative of moray eels. Data gathered
from fishermen indicates that it is a very rare species that is caught only sporadically with
long periods of time when not one specimen can be seen or caught. In fact, despite the nu-merous
studies of ichthyofauna and fish conducted in the island along the past three decades,
it had never before been recorded. The specimens we have studied are the only ones recorded
in the captured unloaded fish within 2008-2014. All of this speaks of a native species in its
limit of geographical distribution, with really small populations that are now probably grow-ing
larger due to the favourable environmental conditions that prevail. Development of gonads
in the specimen we studied, as in relation with the dates of capture, leads us to believe that they
breed in El Hierro and that the spawning takes place from the end of the summer to the beg-ging
of the autumn —period of time when the temperatures are the highest of the year in these
waters— BLACHE {op. cit.) found mature specimens of both sexes in June in Cape Verde
Islands, while in the Western tropical Atlantic they are recorded within June and December
(BOHLKE et al., op. cit.).
Regarding Punta del Hidalgo (Tenerife), fishermen also point out that they have very
rarely caught a specimen only in two specific areas, and that they have become increasingly
normal to find over the past few years. This way, the process in both cases seems similar, that
is to say, the case of a growth in population of long established species related to the warm-ing
of the waters —the sea temperature in these having raised over a degree since the early
90s—. Nevertheless, in the case of Tenerife, a process of initial expansion (occidentalization)
from the spawning stock in El Hierro cannot be ruled out, since a similar colonization pattern
has been noticed in other littoral fish (BRITO et al., 2005).
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5. ACKNOWLEDGEMENTS
We would like to thank M. J. Biscoito, ichthyologist colleague from Madeira, for his
prompt reply at our request ot re-examining the specimen deposited in the Museu Municipal
do Funchal. We also thank fishermen of La Restinga (El Hierro) and Punta del Hidalgo (Tener-ife),
especially Carmelo Dorta, Severo Mora and Adrian. We extend our gratitude for his co-operation
to Agustin Espinosa (Fishery Services, Cabildo de Tenerife), Juan “Piloto” (Fishery
Inspection), Juan “Moreno” and the companies Pesca Restinga and Pescados Ramon. Thanks
to M. M. Brito Campos, in charge of the translation into English.
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Figure 1 .- Gymnothorax vicinus : Preserved specimens, 152 cm total length male (A); the first specimen
identified (non-preserved), right after its capture in September 2008 (B).
127
Table 1 .- Morphometric and ineristic data of the specimens of Gymnothorax vicinus studied.
Morphometric parameters
Size (mm) Meristic
parameters
Number
1 (male) 2 (female) 1 2
Total length 1520 1100 Branchial pores 3/3 2/3
Preanal length 640 477 Infraorbital pores 4/5 4/4
Trunk length 450 325
Depth at anus 101 85
Depth at gill opening 141 85
Predorsal length 137 108
Head length 198 146
Jaw length 83 66
Snout length 38 29
Eye diameter 16 13
Mass (Kg)
Total mass 7.0 2.8
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