The Pelagic Fish Community of the Polar Frontal Zone off the Kerguelen Islands
71
specimens. The polar subgroup consisted of five Broadly Antarctic Pattern
species (K. anderssoni, P. bolini, P. tenisoni, G. braueri and G. nicholsi)
and of only E. antarctica in the Antarctic Pattern (respectively 44.8% and
26% of the specimens). Hydrographic data collected recently off the
Kerguelen shelf [16], in the exact area on the foraging study, have pointed
out the presence of the Antarctic Polar Front running northward off the
eastern slope with the typical 2 °C isotherm at 200 m depth. The
biogeographic affinities and the dominance of the polar subgroup in terms
of number of specimens are in accordance with the conclusion on the
presence of the water masses off the islands [17]. In terms of species
dominance the results form a continuity with Bekker's study [18]
conducted in the area between the subAntarctic and the subtropical fronts,
north of the Kerguelen Plateau.
The day distribution showed a low diversity, abundance and biomass in
the whole water column sampled, with patchy distributions observed in the
main species. L. squamifrons early life stages, M marmoratus pelagic
juveniles, K. anderssoni, P. bolini and P. andriashevi occupied
successively deeper layers. It appears that, within the myctophids, only K.
anderssoni occurs in the intermediate upper layers (150 - 250 m) of the
water column in the day. Other species, partly noted in the day's sampled
deepest range, invaded all depths at night with maximum abundance and
biomass in the upper surface layer. Some species (E. antarctica, G.
braueri, G. fraseri, P. bolini and P. tenisoni) formed the bulk of the deeper
living migratory species. Others (K. anderssoni, E. carlsbergi, B. tenuis)
did not reach the surface. In the case of E. carlsbergi this situation is
probably related to the natural migration of the species from the epipelagic
layer in summer to deeper zone (350 - 500 m) in winter [19] The high
proportional biomass of G. bolini at night, which is due to the iarge
individual size of the sampled specimens of this world-largest myctophid
species, was surprising. It contrasted with the numerous but individually
light « 1 g) species such as K. anderssoni, P. bolini or P. tenisoni and the
small mass of L. squamifrons postlarvae.
Modal values in the pooled size structure of the species in the day
corresponded with species dominance at each depth. The 50 m peak
corresponded to 20 mm SL L. squamifrons, probably undersampled due to
the mesh size. The 40 mm SL peak at 150 m was a mixture of two species
(unimodal M. marmoratus LFD and second mode in the K. anderssoni
LFD). The two modal values at 250 m comprised the smallest size group
(10 mm) of K. anderssoni, a group previously recorded in the
ichthyoplankton surveys conducted in the same area [20], and the 40 mm
peak of M marmoratus. Finally the 300 m peak (50 mm) concerned a
mixture of three species P. andriashevi, P. bolini and the largest specimens
71
specimens. The polar subgroup consisted of five Broadly Antarctic Pattern
species (K. anderssoni, P. bolini, P. tenisoni, G. braueri and G. nicholsi)
and of only E. antarctica in the Antarctic Pattern (respectively 44.8% and
26% of the specimens). Hydrographic data collected recently off the
Kerguelen shelf [16], in the exact area on the foraging study, have pointed
out the presence of the Antarctic Polar Front running northward off the
eastern slope with the typical 2 °C isotherm at 200 m depth. The
biogeographic affinities and the dominance of the polar subgroup in terms
of number of specimens are in accordance with the conclusion on the
presence of the water masses off the islands [17]. In terms of species
dominance the results form a continuity with Bekker's study [18]
conducted in the area between the subAntarctic and the subtropical fronts,
north of the Kerguelen Plateau.
The day distribution showed a low diversity, abundance and biomass in
the whole water column sampled, with patchy distributions observed in the
main species. L. squamifrons early life stages, M marmoratus pelagic
juveniles, K. anderssoni, P. bolini and P. andriashevi occupied
successively deeper layers. It appears that, within the myctophids, only K.
anderssoni occurs in the intermediate upper layers (150 - 250 m) of the
water column in the day. Other species, partly noted in the day's sampled
deepest range, invaded all depths at night with maximum abundance and
biomass in the upper surface layer. Some species (E. antarctica, G.
braueri, G. fraseri, P. bolini and P. tenisoni) formed the bulk of the deeper
living migratory species. Others (K. anderssoni, E. carlsbergi, B. tenuis)
did not reach the surface. In the case of E. carlsbergi this situation is
probably related to the natural migration of the species from the epipelagic
layer in summer to deeper zone (350 - 500 m) in winter [19] The high
proportional biomass of G. bolini at night, which is due to the iarge
individual size of the sampled specimens of this world-largest myctophid
species, was surprising. It contrasted with the numerous but individually
light « 1 g) species such as K. anderssoni, P. bolini or P. tenisoni and the
small mass of L. squamifrons postlarvae.
Modal values in the pooled size structure of the species in the day
corresponded with species dominance at each depth. The 50 m peak
corresponded to 20 mm SL L. squamifrons, probably undersampled due to
the mesh size. The 40 mm SL peak at 150 m was a mixture of two species
(unimodal M. marmoratus LFD and second mode in the K. anderssoni
LFD). The two modal values at 250 m comprised the smallest size group
(10 mm) of K. anderssoni, a group previously recorded in the
ichthyoplankton surveys conducted in the same area [20], and the 40 mm
peak of M marmoratus. Finally the 300 m peak (50 mm) concerned a
mixture of three species P. andriashevi, P. bolini and the largest specimens