40th CIESM Congress, Marseille,
28 October - November 1st, 2013
DIET OF THE SHORTFIN MAKO
ISURUS OXYRINCHUS AND THE
BLUE SHARK PRIONACE GLAUCA
IN THE NORTHEASTERN ATLANTIC
OCEAN
Abstract. The diet of mostly juveniles of Isurus oxyrinchus and Prionace glauca is
strongly dominated by teleosts (mainly Scomberesox saurus) and cephalopods
(mainly Histioteuthis sp.), respectively (Fig. 3).
3. Results and discussion
2. Material and methods
The study area was located between the Azores
Archipelago and the Iberian Peninsula (15o-35oW and
30o-45oN) (Fig.2). 82 shortfin makos and 54 blue sharks
were studied between March and October 2012. Most
individuals (respectively 95% and 82%) were juveniles,
according to the size at sexual maturity [1, 2]. The
identification (to the species or a higher taxon level) of
the prey was carried out through the analysis of the
vertebrae (teleosts and cetaceans) and the beak
characteristics (cephalopods) [3, 4]. Frequency of
occurrence (%O) is the percentage of non-empty
stomachs containing a type of prey. Percent number
(%N) is the percentage of individuals of a given prey
versus the overall number of prey within non-empty
stomachs.
Sebastián Biton Porsmoguer (speaker)
Daniela Banaru
Philippe Béarez
Ivan Dekeyser
Manuel Merchán Fornelino
Raúl Míguez-Lozano
Charles-François Boudouresque
Aix-Marseille University - Mediterranean Institute of
Oceanography (MIO), Luminy Campus, 13288 Marseille
France. [email protected]
1. The problem
The shortfin mako Isurus oxyrinchus and the blue shark
Prionace glauca (Fig1) are the elasmobranch species most
affected by the sea surface longliners. These pelagic species
have a slow growth rate and low fecundity [1] and are located
in the highest level of the marine food web.
The number of stomachs containing prey was 51 (out of 82) and 23 (out
of 54) for I. oxyrinchus and P. glauca, respectively. The diet of I.
oxyrinchus is essentially (85%) based on teleosts (Table 1). More than
90% of individuals of Teleost prey belonged to one species, Scomberesox
saurus. In addition, remains of a loggerhead turtle Caretta caretta and
several cetaceans were present. Literature data are in agreement with
our results, but report a conspicuously higher diversity of teleost prey
[e.g. 5]. As far as P. glauca is concerned, cephalopods represent the main
prey (~87%), mostly consisting of Histioteuthis sp. Teleosts (mainly
Scomber scombrus) and cetaceans were also consumed. Our results
confirm some literature data [6], but strongly contrast with other data
which report a mainly teleost diet [e.g. 7].
Table 1. Prey found
in stomachs of the
analysed species. For
the meaning of %
O and %N, see text.
Fig. 2. Distribution of the sampling areas (northeastern Atlantic): zone A
(southwestern of the Azores Archipelago), zone B (northeastern of the Azores)
and zone C (between the Azores and the Iberian Peninsula).
References
Fig. 1. Shortfin mako (Isurus oxyrinchus) and Blue shark
(Prionace glauca). Photos X.
1 - Moreno J.A., 2004. Guía de los tiburones de aguas ibéricas, Atlántico nororiental y Mediterráneo.
Omega publ., Barcelona.
2 - Hazin F.H.V. and Lessa R.P. 2005. Synopsis of biological information available on blue shark,
Prionace glauca, from the southwestern Atlantic
ocean. Col. Vol. Sci. Pap. ICCAT. 58(3): 1179-1187.
3 - Clarke M.R., 1986. A handbook for the identification of cephalopod beaks. Clarendon Press, Oxford.
4 - Grassé P.P. (ed.), 1958. Traité de zoologie, anatomie, systématique, biologie. Volume XIII. Agnathes
et poissons. Anatomie, éthologie,
systématique. Masson publ., Paris.
5 - Maia A., Queiroz N., Correira J. and Cabral H., 2006. Food habits of the shortfin mako, Isurus
oxyrinchus, off the southwest coast of Portugal.
Environ. Biol. Fishes 77: 157-167.
6 - Mendonça A. 2009. Diet of the blue shark, Prionace glauca, in the Northeast Atlantic. Doctoral
Thesis, Departamento de biologia, Facultade de Ciências da Universidade do Porto.
7 - Clarke M.R., Clarke D.C., Martins H.R. and Da Silva H.M., 1996. The diet of the blue shark (Prionace
glauca L.) in Azorean waters. Arquipélago, 14A: 41-56.
Fig. 3. Main prey of Isurus oxyrinchus and Prionace glauca,
Scomberesox saurus and Histioteuthis sp, respectively. Photos X.