Otolith characteristics and age estimation of an exceptionally old dogtooth grouper (Epinephelus caninus) captured off Majorca Island (western Mediterranean)

2005·1.6 MB·English

by  Morales-Nin, B

Otolith characteristics and age estimation of an
exceptionally old dogtooth grouper (Epinephelus caninus)
captured off Majorca Island (western Mediterranean)
by
Beatriz MORALES-NIN (1), Damià BAUZA (2) & Antoni M. GRAU (3)
RÉSUMÉ. - Caractéristiques des otolithes et estimation de l’âge mum age, both fundamental parameters for population dynamics in
d’un mérou gris (Epinephelus caninus) exceptionnellement vieux, a scarcely known species.
capturé au large de Majorque (Méditerranée occidentale).
En août 2003, un très gros Epinephelus caninus a été pêché à la
ligne à Majorque (Méditerranée). Il mesurait 164 cm TL et pesait
57 kg. Les otolithes ont permis d’estimer l’âge à 55 ans. En Médi- MATERIAL AND METHODS
terranée occidentale, quelques captures de gros individus de cette
espèce ont déjà été mentionnées, mais c’est la première fois qu’une The specimen was captured using hand line (volantí) over the
estimation d’âge est effectuée. shelf break off El Toro (39º24’36’’N-2º24’59’’W) at about 130 m
depth on 8th August 2003. The fish was measured and weighed on
port and the otoliths extracted. The fish was not preserved. Once in
Key words. - Serranidae - Epinephelus caninus - MED - Majorca
the laboratory sagittae were cleaned, weighed with a precision of
Island - Age - Sagitta otolith.
0.001 g and measured with callipers. The whole otolith was
observed immersed in water inside a dark container with reflected
Groupers (Pisces: Serranidae) are emblematic Mediterranean light and processed following standard methods (Panfili and
fish very sough after by recreational and small-scale fisheries. Due Morales-Nin, 2002). Briefly, transverse sections were obtained
to high market values and subjection to sport and spear diving fish- using a low speed saw with a diamond blade. To ensure cutting
eries, the populations of many species are under constant pressure. through the nucleus for the transverse section, the nucleus position
For this reason groupers are the most endangered fish species in was marked on the surface, thus helping to place the blade. The 0.5
many parts of the world, like the dusky grouper (Epinephelus mar- mm thick-section was observed either with reflected or transmitted
ginatus Lowe, 1834) in the Mediterranean (Zabala et al., 1997). light using rosemary oil as a clarifying medium. The otoliths were
Due to their high price, groupers are subjected to intensive research examined and photographed using a Leica microscope with camera
on aquaculture introduction (Glamuzina et al., 2000). The biology and image analysis software.
and population dynamics of E. marginatus have been studied in
recent years and protection measures have been applied for the con-
servation of the species (Bouain, 1986; Bouchereau et al., 1999; La
Mesa and Vacchi, 1999; Marino et al., 2001; Bodilis et al., 2003). RESULTS AND DISCUSSION
However, information on other grouper species in the Mediterra-
nean Sea is very scarce. The Epinephelus caninus specimen measured 164 cm total
Dogtooth grouper Epinephelus caninus (Valenciennes, 1843) is length and weighed 57 kg. The sex was not determined. The aver-
a subtropical species widely distributed in the Eastern Atlantic, age weight of both sagitta otoliths was 1.4899 g (s.d. = 0.0347) with
from Portugal to Angola, rare in the Canary Islands and not com- a maximum antero-posterior axis of 4.3 mm, with a minor dimor-
mon in the Mediterranean. Its maximum reported length is 157 cm phism between left and right otolith in their marginal ornamenta-
with a weight of at least 35 kg (Heemstra and Randall, 1993). The tion and hence in weight. Some irregular crystallization was
only available published information on the species is a report on observed on the dorsal side, probably of a CaCO3 polymorph other
essays to introduce it in aquaculture (Glamuzina et al., 2000) and a than aragonite, which is the major constituent of otoliths (Gauldie,
genetic study (Rodriguez Daga et al., 1993). 1996). The sulcus acusticus was well developed, with an anterior
The maximum weight reported for E. caninus should be updat- ostium. Otolith grows mainly in the antero-posterior axis and at the
ed because there is some unpublished information of specimens in inner side, resulting in a change of otolith growth direction after the
the Western Mediterranean. For instance, a specimen of 52 kg was first years of life. A second change was observed latter with a pref-
captured off Palos Cape in 2002 (Real Club Naútico Torrevieja, erential growth in the dorsal area, probably due to the constraint of
pers. com.). An unpublished capture of a fish of 54 kg is known the ventral growth of the otolith due to the cranial cavity where it is
from Majorca since 1979 (Grau, unpubl. data). In the exceptional placed.
capture reported in this note the fish weighed 57 kg. This is the first Whole otoliths examination revealed a relatively small nucle-
study of the otoliths and age estimate for this species. Age estimate us area (Fig. 1) and regular incremental growth, with alternatively
provided herein is relevant to assess absolute growth rate and maxi- translucent and opaque rings. The spacing and growth pattern of
(1) CSIC-UIB-IMEDEA, Miquel Marqués 21, 07190 Esporles, Illes Balears, SPAIN. [[email protected]]
(2) Federació Balear de Pesca i Càsting, Joan Miró, 325, Palma, Illes Balears, SPAIN.
(3) Direcció General Pesca, CAIB, Foners 10, Palma de Mallorca, Illes Balears, SPAIN.
Cybium 2005, 29(1): 100-102.
Otolith characteristics and age estimation of Epinephelus caninus M orales-NiN et al.
observed at age 4 and age 8, which might be related to first matu-
rity and sex reversal, respectively (Fig. 2, arrows). Due to the
nature of the available data, it was not possible to validate this age
estimate. Therefore, although the estimated age was precise, the
accuracy could not be determined.
E. caninus might reach 55 years old, a similar longevity than
in E. marginatus (Heemstra and Randall, 1993). In a scale-based
study on the age of E. marginatus in the Mediterranean Sea, the
maximum determined age was 19 years, an age superior to 50
years for a captive fish (Bouchereau et al., 1999). Thus, the excep-
tional longevity of the examined dogtooth grouper falls within the
range of maximum ages for other groupers.
In conclusion, the data provided in this note do not allow
determining the growth rate of the species, but they provide valu-
able information on a top predator that should be better known to
ensure adequate protection measures. Indeed, top predators are
relevant for the health of the ecosystem (Myers and Worm, 2003)
and their rapid decline at worldwide scales is a serious problem.
Figure 1. - Micrograph showing the central area of an Epinephelus
caninus sagitta. [Région centrale de la sagitta d’un Epinephelus
caninus.]
Figure 2. - Thin transverse section of a right sagitta
of Epinephelus caninus showing the growth pat-
terns and the changes in growth (arrows). [Section
transversale de l’otolithe droit de Epinephelus
caninus montrant le mode et les variations de
croissance (flèches).]
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