70
G. Duhamel
in the 50 m night samples. The mean length in the L. squamifrons daylight
samples increases markedly with depth (22.1 mm at 50 m, 23.6 mm at 300
m). Finally large differences in the LFD are observed day/night and at each
depth for K. anderssoni.
Discussion
Some limitations due to the methods used can affect the above results and
must be first considered. The most important is the selectivity of the 10
mm mesh size probably affecting the catches of the small sized specimens.
Nevertheless the LFD showed that undersampling could only occur for
specimens less than 20 mm. Another bias could be introduced by the use
of a nonclosing net inducing catches of specimens from the untargeted
depths. Such hypothesis does not seem to occur because the quick retrieval
of the net automatically closes the mouth when hauling.
Two categories of fish are recognized from the trawl samples in the
foraging range of the king penguin off the Kerguelen Islands. The first
comprises the early life stages of demersal species occurring on the nearby
Plateau and the surrounding banks. L. squamifrons, D. eleginoides, M.
carinatus, C. gunnari, Z. spinifer postlarvae and M marmoratus, N rossii
and P. magellanica fingerlings belong to this group. The presence of earlylife stages of demersal species is a special situation due to the proximity of
a shelf. It does not seem to apply to other areas of the Antarctic Polar
Front. The observed density of two species (L. squamifrons and M.
marmoratus), over deep-sea bottom (> 2000 m, > 100 miles off the
shelves) supports the colonization process of the isolated seamounts in the
Southern Ocean, via the dispersion of young stages. The second group
comprises the major part of the mesopelagic species, mainly undersamp1ed
before and often recorded from single records [11-14]. The present cruise
provides the first data on dominance and densities for each species in the
upper mesopelagic layers. Some species such as K. macrura and B.
elongata have never been recorded in the area and, in the case of the first
species, in the Southern Ocean. The majority of these species are
Myctophidae (15 species) which allows consideration of the distribution
pattern types sensu Rulley [15]. All species (86.9% in number and 84.5%
in weight of the total collected fish specimens) belong to the cool water
group [15] which is divided into the temperate (south) and the polar
subgroups. Six species (P. andriashevi, P. gemmatum, E. carlsbergi, E.
subaspera, G. bolini and G. fraseri) have been recognized as
holosubAntarctic subpattern and three species (P. choriodon, M ventralis
and G. piabilis) as semi subAntarctic subpattern in the first subgroup.
These subpatterns include respectively 28.5% and 0.7% of the
G. Duhamel
in the 50 m night samples. The mean length in the L. squamifrons daylight
samples increases markedly with depth (22.1 mm at 50 m, 23.6 mm at 300
m). Finally large differences in the LFD are observed day/night and at each
depth for K. anderssoni.
Discussion
Some limitations due to the methods used can affect the above results and
must be first considered. The most important is the selectivity of the 10
mm mesh size probably affecting the catches of the small sized specimens.
Nevertheless the LFD showed that undersampling could only occur for
specimens less than 20 mm. Another bias could be introduced by the use
of a nonclosing net inducing catches of specimens from the untargeted
depths. Such hypothesis does not seem to occur because the quick retrieval
of the net automatically closes the mouth when hauling.
Two categories of fish are recognized from the trawl samples in the
foraging range of the king penguin off the Kerguelen Islands. The first
comprises the early life stages of demersal species occurring on the nearby
Plateau and the surrounding banks. L. squamifrons, D. eleginoides, M.
carinatus, C. gunnari, Z. spinifer postlarvae and M marmoratus, N rossii
and P. magellanica fingerlings belong to this group. The presence of earlylife stages of demersal species is a special situation due to the proximity of
a shelf. It does not seem to apply to other areas of the Antarctic Polar
Front. The observed density of two species (L. squamifrons and M.
marmoratus), over deep-sea bottom (> 2000 m, > 100 miles off the
shelves) supports the colonization process of the isolated seamounts in the
Southern Ocean, via the dispersion of young stages. The second group
comprises the major part of the mesopelagic species, mainly undersamp1ed
before and often recorded from single records [11-14]. The present cruise
provides the first data on dominance and densities for each species in the
upper mesopelagic layers. Some species such as K. macrura and B.
elongata have never been recorded in the area and, in the case of the first
species, in the Southern Ocean. The majority of these species are
Myctophidae (15 species) which allows consideration of the distribution
pattern types sensu Rulley [15]. All species (86.9% in number and 84.5%
in weight of the total collected fish specimens) belong to the cool water
group [15] which is divided into the temperate (south) and the polar
subgroups. Six species (P. andriashevi, P. gemmatum, E. carlsbergi, E.
subaspera, G. bolini and G. fraseri) have been recognized as
holosubAntarctic subpattern and three species (P. choriodon, M ventralis
and G. piabilis) as semi subAntarctic subpattern in the first subgroup.
These subpatterns include respectively 28.5% and 0.7% of the