64
G. Duhamel
Islands (Ratmanoff colony: 49°23'S - 70 0 30'E). The period of sampling
(first half of March 1995) corresponded to the intense summer feeding
period of chicks.
While the birds (n = 9) were being fitted with their instrumentation, the
25 m long scientific vessel "La Curieuse" was positioned in front of the
breeding king penguin colony. At the first reception of a satellite signal,
the vessel followed the given positions to cross the foraging range of some
(n = 4) of the selected birds. The adopted fishing strategy was to conduct
simultaneous standardized trawls in the geographic area, limiting the
deeper hauls to the known maximum diving depth (300 m) of the king
penguin [6]. Four depth horizons were sampled (50, 150, 250, 300 m) day
and night to take into account the diel vertical migration of pelagic fish [7].
Hauls were undertaken during the day (09 00 - 16 00 h LMT) and at night
(20 00 - 00 30 h LMT) (LMT = GMT + 4 h). The fishing gear was the
IYGPT (International Young Gadoid Pelagic Trawl; width: 12 m, height: 7
m) with a 10 mm mesh size in the codend. Each trawl, towed at the
selected depth, was fished for 30 minutes at 3 knots. Fishing depth was
estimated with wire-out tables (R. Williams personnal communication) and
regularly tested with a bathykimograph (TSURUMI 0-300 m). Two
periods have been studied (1-5 and 10-13 March 1995) which totaled 65
(37 + 28 respectively) midwater trawls including 51 successful
standardized hauls. Sorting of the catch was conducted on board and three
categories retained: fish, squid and macro zooplankton. The present study
includes only the fish. Fish were either deep frozen or fixed in a 10% sea
water buffered formalin. Identification, counting and weighing were
conducted in the laboratory, because the sea conditions did not allow the
work on board. The fish identification key used was the recent revision by
Gon and Heemstra [8] and, when the specimens were in poor condition, of
the available otolith keys [9-10]. The analysis was conducted on the
14 232 fish specimens (total weight: 37 483 g) from the standardized 51
hauls. The standard length (SL) (nearest mm below) has been used in the
measurements because numerous damaged caudal fins precludes the use of
the total length, especially in myctophid specimens. A caliper connected to
a computer with approriate software (DataQ) allowed the data to be
entered directly into the spreadsheet (Lotus 123), which was used to
establish the length frequency distributions (LFD). Where sexual
dimorphism was visible from external characters (e.g. photophores), the
sex was also recorded. To compare the catch data an index of abundance
was used. The number of specimens of each species per standard fishing
hour of the IYGPT was calculated.
Results
Thirty three fish species (Table 1) were identified in the foraging range of
G. Duhamel
Islands (Ratmanoff colony: 49°23'S - 70 0 30'E). The period of sampling
(first half of March 1995) corresponded to the intense summer feeding
period of chicks.
While the birds (n = 9) were being fitted with their instrumentation, the
25 m long scientific vessel "La Curieuse" was positioned in front of the
breeding king penguin colony. At the first reception of a satellite signal,
the vessel followed the given positions to cross the foraging range of some
(n = 4) of the selected birds. The adopted fishing strategy was to conduct
simultaneous standardized trawls in the geographic area, limiting the
deeper hauls to the known maximum diving depth (300 m) of the king
penguin [6]. Four depth horizons were sampled (50, 150, 250, 300 m) day
and night to take into account the diel vertical migration of pelagic fish [7].
Hauls were undertaken during the day (09 00 - 16 00 h LMT) and at night
(20 00 - 00 30 h LMT) (LMT = GMT + 4 h). The fishing gear was the
IYGPT (International Young Gadoid Pelagic Trawl; width: 12 m, height: 7
m) with a 10 mm mesh size in the codend. Each trawl, towed at the
selected depth, was fished for 30 minutes at 3 knots. Fishing depth was
estimated with wire-out tables (R. Williams personnal communication) and
regularly tested with a bathykimograph (TSURUMI 0-300 m). Two
periods have been studied (1-5 and 10-13 March 1995) which totaled 65
(37 + 28 respectively) midwater trawls including 51 successful
standardized hauls. Sorting of the catch was conducted on board and three
categories retained: fish, squid and macro zooplankton. The present study
includes only the fish. Fish were either deep frozen or fixed in a 10% sea
water buffered formalin. Identification, counting and weighing were
conducted in the laboratory, because the sea conditions did not allow the
work on board. The fish identification key used was the recent revision by
Gon and Heemstra [8] and, when the specimens were in poor condition, of
the available otolith keys [9-10]. The analysis was conducted on the
14 232 fish specimens (total weight: 37 483 g) from the standardized 51
hauls. The standard length (SL) (nearest mm below) has been used in the
measurements because numerous damaged caudal fins precludes the use of
the total length, especially in myctophid specimens. A caliper connected to
a computer with approriate software (DataQ) allowed the data to be
entered directly into the spreadsheet (Lotus 123), which was used to
establish the length frequency distributions (LFD). Where sexual
dimorphism was visible from external characters (e.g. photophores), the
sex was also recorded. To compare the catch data an index of abundance
was used. The number of specimens of each species per standard fishing
hour of the IYGPT was calculated.
Results
Thirty three fish species (Table 1) were identified in the foraging range of