PICES XV
W9-2781
Oral
Comparison of three sampling gears during the first Micronekton Intercalibration
Experiment (MIE-1): Size composition of selected taxonomic groups and total
macroplankton and micronekton
Evgeny A. Pakhomov1,2, M.P. Seki3, A.V. Suntsov4, R.D. Brodeur5 and K.R. Owen6
1
2
3
4
5
6
Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, BC, Canada. E-mail: epakhomov@eos.ubc.ca
Department of Zoology, University of Fort Hare, Alice, South Africa
Pacific Islands Fisheries Science Center, NOAA Fisheries, Honolulu, HI, U.S.A.
Harbor Branch Oceanographic Institution, FL, U.S.A.
Northwest Fisheries Science Center, NOAA Fisheries, Newport, OR, U.S.A.
University of East Anglia, Norwich, NR4 7TJ, United Kingdom
Results from the first Micronekton Intercalibration Experiment (MIE-1) conducted during October 6-12, 2004
on the leeward side of Oahu Island, Hawaii are presented. Three sampling gears, including a 140 m 2 pelagic
Cobb trawl (CT), a 4 m2 Hokkaido University rectangular frame trawl (HT) and a 2-m Isaacs-Kidd Midwater
Trawl (IKMT) were deployed in a random sequence either in the upper 150m during the darkness or at 550m
during the daytime from the NOAA research vessel Oscar Elton Sette. Deployment of the three types of gear
resulted in a collection of more than 100 species of macroplankton and micronekton. Midwater fish, family
Myctophidae in particular, predominated among identified species. Based on our preliminary taxonomic
treatment, basic community indices to estimate diversity, e.g. evenness and species richness, were very similar
for the HT and IKMT gears. This was particularly evident for the number of species and for daytime diversity
and evenness indices. Both day and night deployment of the CT clearly procured more species per trawl, which
was also reflected in higher diversity and evenness indices. Overall, it was evident that, although the taxonomic
composition of catches was similar, the individual gears sampled different size groups of macroplankton and
micronekton. In the sampled size range, the most intercomparable data were obtained within the 30 to 50 mm
size spectrum. A closer scrutiny of gear types and mesh sizes prior to similar experiments as well as an adoption
of the “standard” sampling gear is recommended.
PICES XV
W9-3125
Oral
Diversity and abundance of Hawaiian ichthyoplankton: Comparison of three types of
midwater nets
Andrey V. Suntsov1, Michael P. Seki2, Evgeny A. Pakhomov3 and Richard D. Brodeur4
1
2
3
4
Laboratory of Geography, Institute of Aquatic Resources of the Arctic, Petrozavodsk, Karelia, 185030, Russia
E-mail: asuntsov@mail.ru
Pacific Island Fisheries Science Center, Honolulu, HI, 96822, U.S.A.
Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, V6T 1Z4, Canada
Northwest Fisheries Science Center, National Oceanic and Atmospheric Administration, 2032 Southeast OSU Drive, Newport, OR,
97365, U. S. A.
During a recent Micronekton Intercalibration Experiment (PICES initiative, October 2004), an intensive
sampling of oceanic micronekton was carried out off the leeward side of Oahu, Hawaii using three types of
sampling gear – a 140 m2 pelagic Cobb Trawl, a 4 m2 Hokkaido University Rectangular Frame Trawl and a
standard 2 m Isaaks-Kidd Midwater Trawl. Fish larvae, opportunistically collected in these tropical oligotrophic
waters, showed high diversity, with a total of 61 families and 115-120 species recorded during the entire
sampling period. Family Myctophidae was the most diverse, represented by 18 species, followed by
Muraenidae (6-8 species) and Paralepididae, Gonostomatidae, Serranidae - (4 species). The majority of fish
families (84%) were represented by 1-2 species. Larvae of deep-sea pelagic fishes dominated (26 families)
followed by coastal families (21), epipelagic (9) and demersal groups (5). In terms of occurrence, lanternfish
larvae were most frequently collected (present in 73% of samples), followed by larval bothids (67%), gempylids
(60%) and engraulids (52%). The most common and abundant fish larvae (forming over 3% of total abundance)
were Encrasicholina punctifer (Engraulidae), Ceratoscopelus warmingi (Myctophidae), Gempylus serpens
(Gempylidae), Engyprosopon sp. (Bothidae) and Cubiceps pauciradiatus (Nomeidae). Samples collected with
the Hokkaido University Rectangular Frame Trawl showed the highest ichthyoplankton diversity and abundance
as indicatedby the number of families, species and total individuals collected. This trend was universal for both
day and night sampling. Cobb Trawl samples showed the lowest diversity and abundance, and Isaaks-Kidd
Trawl samples were intermediate.
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PICES XV
W9-3193
Oral
Inter-calibration of micronekton sampling gear during the 2005 MIE-2 cruise
Orio Yamamura1, Hiroya Sugizaki2, Shin-suke Abe3, Kazuhiro Sadayasu3, Ryu-ichi Matsukura3, Kazushi
Miyashita3, Akihiro Hino4 and Tadashi Tokai4
1
2
3
4
Hokkaido National Fisheries Research Institute, FRA, Kushiro, 085-0802, Japan. E-mail: orioy@fra.affrc.go.jp
Tohoku National Fisheries Research Institute, FRA, Shiogama, 985-0011, Japan
Hokkaido University, Hakodate, 041-8611, Japan
Tokyo University of Marine Science and Technology, Minato-ku, 108-8477, Japan
Catchability of sampling gears for micronekton was compared during the MIE-2 cruise aboard the Hokko-Maru
(904t) in the coastal area off southeastern Hokkaido Island during Sep 23-Oct 3, 2005. The gears compared
were: MOCNESS-10 (MOC), MOHT (Oozeki et al, 2004), Hokkaido Univ. Frame Trawl (HUFT: Itaya et al.
2001) and a stern midwater trawling net (MT) equipped with a Multi-Sampler (an opening-closing multiple
codend system). Every net was towed at 4 stations at the outer shelf (bottom depth: 380-480m) during daytime
and nighttime, with an exception of MT, which was towed at 2 stations only during daytime. Every net was
towed obliquely from a depth of 300 m to the sea surface (MOHT & HUFT), or specimens from the 300-0 m
layer were used (MOC and MT). In total, the myctophid Diaphus theta was the dominant micronekton caught
(> 80% in number, > 70% in wet wt). The catch efficiency of different gears was determined using catch
number and weight of D. theta per volume of water filtered. D. theta was divided into two distinct size classes
(20-30 mm and 40-84 mm) and the catch efficiency (Ec) for each size class was compared. Overall, MOHT
showed the highest Ec for large-sized fish (approximate ratio of Ec ; MOC: HUFT: MOHT: MT = 1: 1: 10: 1.5),
and the HUFT showed equally high Ec for small-sized fish (≤ 30 mm; 1:10: 10: 0). This result perhaps reflects
the high towing speed (3-5 kt) and stable towing angle (8°) of MOHT, which was attained by the newly
designed depressor. Based on the present results, we strongly recommend employing MOHT for the
quantitative sampling of micronekton.
PICES XV
W9-2821
Oral
Acoustic identification and density estimate of a lanternfish, Diaphus theta, off
Hokkaido, Japan
Hiroki Yasuma1, Kazushi Miyashita 1 and Orio Yamamura2
1
2
Field Science Center for the Northern Biosphere, Hokkaido University, 3-1-1, Minato, Hakodate, Hokkaido, 041-8611, Japan
E-mail: ANB52615@nifty.com
Hokkaido National Fisheries Research Institute, Kushiro, 085-0802, Japan
Diaphus theta is the most abundant mesopelagic fish in the northwestern Pacific. Field acoustic data and
biological samples were obtained both day and night off of eastern Hokkaido, Japan in September 2006 to
estimate fish density and to estimate diel changes in vertical distribution. The difference in acoustical target
strength (TS) between 38 kHz and 120 kHz was applied to identify D. theta using field echo data. Theoretical
estimation using swimbladder acoustic scattering models showed that the TS difference (ΔTS = TS120kHzTS38kHz) of larger fishes (> 60 mm) was between –4 and 1 dB whereas for smaller fishes (< 60 mm) it was less
than –4 dB. These values differed from those of other major component species of the deep-scattering layer,
such as krill and pollock, suggesting that the echo from D. theta is acoustically unique. Diel vertical
distributions of D. theta were estimated after acoustic identification. Relatively dense schools were observed at
around 400 m during daytime, although the schools were scattered widely above 100-m during nighttime.
These results correlated well with biological sampling data obtained by MOCNESS or IKMT nets. In the
surface layer (< 100 m), estimated fish densities were about ten-fold higher at nighttime than in daytime.
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