PICES 16th : BIO_P-4200 (1 Nov, 2007)

Feeding habits of mesopelagic fishes off the coast of western Kyushu, Japan Hiroshige Tanaka1, Seiji Ohshimo1, Chiyuki Sassa1 and Ichiro Aoki2 1Seikai National Research Institute, Fisheries Research Agency 2Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo

Diaphus chrysorhynchus Myctophum obtusirostre Ceratoscopelus warmingii

Myctophum asperum Diaphus garmani Background and Objective

• Mesopelagic fishes (e.g., Myctophidae) have large biomass in the East China Sea and its adjacent waters, where pelagic fish also co-exist. • In general, myctophids feed on zooplankton in the epipelagic zone at night- time in relation to their diel vertical migration (DVM). • Trophic niche of mesopelagic fish is to be revealed especially from the viewpoint of relationship with pelagic fish.

Pearlside 700 127Ο E132Ο E Lanternfish 35Ο N Jack mackerel 600 Round herring Anchovy 500

400 Kyushu

300 Biomass index Biomass 200 East China 100 Sea

0 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 200 m 30Ο N Year Biomass index by acoustic surveys. (Ohshimo 2004, Ohshimo unpubl.) Materials (Sampling) • Area: off the coast of western Kyushu • Seasons and year: summer months (Aug. and Sep.) of 2002, 2003, and winter month (Jan.) of 2007

• Time: Night time (after sunset) 127Ο E 132Ο E • Gear: Mid-water trawl 35Ο N • Layer: 30-120 m

Kyushu

East Pacific Ocean China Sea 200 m 30Ο N DVM observed by the acoustic survey

0 m

Day bottom

250 m

0 m

Night bottom

250 m Species of myctophids

Dominant species (summer and winter) Total catch of myctophids collected in the Diaphus chrysorhynchus (n = 235, 48-105 mm BL) western Kyushu waters from 2002 to 2006 (Sassa unpubl.)

Species Weight (g) Number

Diaphus garmani (n = 190, 20-65 mm BL) Diaphus chrysorhynchus 129332.3 23526 Diaphus garmani 101385.9 78971 Lampanyctus nobilis 5718.7 8938 Myctophum obtusirostre 4646.4 1774 Bnthosema pterotum 1094.0 644 Myctophum asperum 819.3 326 Other species (summer only) Ceratoscopelus warmingii 638.8 505 Diaphus aliciae 212.6 562 Diaphus perspicillatus 91.7 119 Myctophum obtusirostre Diaphus regani 68.9 118 (n = 56, 42-78 mm BL) Diaphus suborbitalis 54.3 87 Myctophum asperum Diaphus fulgens 45.4 118 Diaphus schmidti 41.6 142 (n = 40, 45-65 mm BL) Myctophum orientale 18.0 19 Ceratoscopelus warmingii Myctophum nitidulum 16.8 17 Diaphus kuroshio 7.6 24 (n = 20, 45-59 mm BL) Diaphus nielseni 4.8 6 Lampanictus spp. 3.8 3 Bnthosema fibulatum 2.3 1 Methods

• Stomach content analysis: – Observation: count, weigh, and measure of prey organisms – %N (number), %W (weight), %F (frequency) – IRI (Index of relative importance) = (%N + %W)×%F

• Stable isotope analysis (δ13C and δ15N) : – Dorsal muscle was used – All samples were defatted before the analysis to remove lipids – Mass spectrometer (Delta Plus Advantage) with an elemental analyzer (EA1100, Thermo Electron) 13 15 – δ C, δ N = [Rsample / Rstandard – 1]*1000 (R = 13C/12C or 15N/14N) Stomach content composition (D. chrysorhynchus)

Ostracoda Amphipoda Decapoda (larvae) %N Oncaeidae Euphausiacea Appendicularia

Summer Calanoida

Calanoida Oncaeaidae Winter Calanoida other copepods Ostracoda Amphipoda 0 20406080100Euphausiacea Decapoda Decapoda (larval stage) %W Crustacea Amphipoda Decapoda (larvae) Cephalopoda Sagittoidea Appendicularia Summer Calanoida Euphausiacea Pisces Thaliacea Pisces Cephalopoda Miscellaneous Winter Calanoida Euphausiacea

0 20406080100 Stomach content composition (D. garmani)

Euphausiacea %N Oncaeidae Amphipoda Decapoda (larvae)

Summer Calanoida Appendicularia

Calanoida Oncaeaidae Winter Calanoida Ostracoda Appendicularia other copepods Ostracoda Amphipoda 0 20406080100Euphausiacea Decapoda Decapoda (larval stage) %W Crustacea Ostracoda Amphipoda Decapoda (larvae) Appendicularia Sagittoidea Appendicularia Summer Calanoida Pisces Thaliacea Pisces Cephalopoda Miscellaneous Winter Calanoida Euphausiacea

0 20406080100 IRI of major prey items (summer vs. winter) Diaphus chrysorhynchus Copepoda-Calanoida

Copepoda-Poecilostomatoida

Ostracoda summer winter Euphausiacea

Decapoda (larvae)

Appendicularia

0 2000 4000 6000 8000 Diaphus garmani

Copepoda-Calanoida

Copepoda-Poecilostomatoida

Ostracoda

Euphausiacea

Decapoda (larvae)

Appendicularia

0 1000 2000 3000 4000 IRI Prey size

D. chrysorhynchus D. garmani 7 7 6 6 5 5 4 4 3 3 2 2 Prey width (mm) width Prey (mm) width Prey 1 1 0 0 40 50 60 70 80 90 100 110 20 30 40 50 60 70 Body length (mm) Body length (mm)

30 25

25 20 20 15 15 10 10 Prey (mm) length Prey (mm) length 5 5

0 0 40 50 60 70 80 90 100 110 20 30 40 50 60 70 Body length (mm) Body length (mm) Stomach content composition (other species)

Myctophum obtusirostre Amphipoda Decapoda (larvae)

%N Calanoida

%W Calanoida Euphausiacea Sagittoidea

0 20406080100 Myctophum asperum Calanoida Oncaeaidae other copepods Ostracoda %N Appendicularia Thaliacea Amphipoda Euphausiacea Decapoda %W Thaliacea Decapoda (larval stage) Amphipoda Crustacea Sagittoidea Appendicularia 0 20406080100Thaliacea Pisces Ceratoscopelus warmingii Cephalopoda Pisces Miscellaneous

%N Appendicularia

%W Calanoida Appendicularia Thaliacea

0 20406080100 IRI of major prey items Myctophum obtusirostre Copepoda-Calanoida Amphipoda Euphausiacea Decapoda Decapoda (larvae) Sagittoidea Appendicularia Thaliacea Myctophum asperum 0 2000 4000 6000 8000 10000 Copepoda-Calanoida Amphipoda Euphausiacea Decapoda Decapoda (larvae) Sagittoidea Appendicularia Thaliacea 0 1000 2000 3000 4000 5000 6000 Ceratoscopelus warmingii Copepoda-Calanoida Amphipoda Euphausiacea Decapoda Decapoda (larvae) Sagittoidea Appendicularia Thaliacea 0 2000 4000 6000 8000 10000 Relationship between pelagic and mesopelagic fish

Feeding habits of pelagic fish (80-140 mm body length) in the northwestern Kyushu in summer months from 2001 to 2003 (Tanaka 2006; Tanaka et al. 2006):

Decapoda (larvae) Amphipoda Calanoid Oncaea Engraulis japonicus Calanoida Oncaeidae other copepods Ostracoda Amphipoda Euphausiacea Etrumeus teres Calanoida Decapoda Decapoda (larval stage) Crustacea Saggitoidea Trachurus japonicus Calanoida Appendicularia Myosomata Pisces Cephalopoda 0 20406080100Miscellaneous %N

Copepods (Calanoida, Poecilostomatoida) are the major prey items in the pelagic fish diet. Cluster analysis

Myctophum asperum

Ceratoscopelus warmingii

Diaphus garmani

Engraulis japonicus

Myctophum obtusirostre

Diaphus chrysorhynchus

Etrumeus teres

Trachurus japonicus

0 10203040 Standardized squared Euclidean distance Stable isotope ratios

Pelagic fish Pelagic fish -16 12 Myctophids Myctophids

11 -17

10 -18 C (per mil) N (per mil) 13 15 δ δ 9 -19

8 Etrumeus teres Etrumeus teres Diaphus garmani Diaphus garmani Diaphus Engraulis japonicus Engraulis japonicus Trachurus japonicus Trachurus japonicus Trachurus Myctophum asperum Myctophum asperum Myctophum Myctophum obtusirostre Myctophum obtusirostre Myctophum Sardinops melanostictus Sardinops melanostictus Sardinops Diaphus chrysorhynchus Diaphus chrysorhynchus Diaphus Ceratoscopelus warmingii Ceratoscopelus warmingii Ceratoscopelus Summary Feeding habits of myctophids • D. chrysorhynchus: crustacean such as copepods, euphausids, and larval decapods • D. garmani: crustaceans and appendicularians. • Seasonal variation (summer vs. winter): euphausids, ostracods, and larval decapods • M. obtusirostre: crustaceans, sagittoids • M. asperum & C. warmingii: appendicularians, thaliaceans Relationship between pelagic and mesopelagic fish • Comparisons of stomach contents and stable isotope ratios (δ13C) suggest the difference in the trophic niche between pelagic fish and myctophids, so a potential for competition should be low in the qualitative sense for the most of the fishes, but.., • Overlap of trophic niche found to be relatively high between D. chrysorhynchus, Etrumeus teres and Trachurus japonicus (juveniles). Further study: Quantitative analysis (daily ration) for D. chrysorhynchus