PICES 16 th : BIO_P-4200 (1 Nov, 2007) Feeding habits of mesopelagic fishes off the coast of western Kyushu, Japan Hiroshige Tanaka 1, Seiji Ohshimo 1, Chiyuki Sassa 1 and Ichiro Aoki 2 1 Seikai National Research Institute, Fisheries Research Agency 2 Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo Myctophum obtusirostre Diaphus chrysorhynchus 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 nighttime 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. 700 600 500 Pearlside Lanternfish Jack mackerel Round herring Anchovy 127 Ο E 132 Ο E 35 Ο N Biomass index 400 300 200 100 East China Sea Kyushu 0 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 Year Biomass index by acoustic surveys. (Ohshimo 2004, Ohshimo unpubl.) 200 m 30 Ο N
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) Gear: Mid-water trawl Layer: 30-120 m 127 Ο E 132 Ο E 35 Ο N Kyushu East China Sea Pacific Ocean 200 m 30 Ο 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) Diaphus chrysorhynchus (n = 235, 48-105 mm BL) Total catch of myctophids collected in the western Kyushu waters from 2002 to 2006 (Sassa unpubl.) Species Weight (g) Number Diaphus garmani (n = 190, 20-65 mm BL) Other species (summer only) Myctophum obtusirostre (n = 56, 42-78 mm BL) Myctophum asperum (n = 40, 45-65 mm BL) Ceratoscopelus warmingii (n = 20, 45-59 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 Ceratoscopelus warmingii 638.8 505 Diaphus aliciae 212.6 562 Diaphus perspicillatus 91.7 119 Diaphus regani 68.9 118 Diaphus suborbitalis 54.3 87 Diaphus fulgens 45.4 118 Diaphus schmidti 41.6 142 Myctophum orientale 18.0 19 Myctophum nitidulum 16.8 17 Diaphus kuroshio 7.6 24 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 (δ 13 C and δ 15 N) : 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) δ 13 C, δ 15 N = [R sample / R standard 1]*1000 (R = 13 C/ 12 C or 15 N/ 14 N)
Stomach content composition (D. chrysorhynchus) %N Ostracoda Decapoda (larvae) Oncaeidae Summer Winter 0 20 40 60 80 100 %W Decapoda (larvae) Cephalopoda Summer Pisces Winter Oncaeaidae other copepods Ostracoda Decapoda Decapoda (larval stage) Crustacea Sagittoidea Pisces Cephalopoda Miscellaneous 0 20 40 60 80 100
Stomach content composition (D. garmani) %N Oncaeidae Decapoda (larvae) Summer Winter Ostracoda 0 20 40 60 80 100 %W Ostracoda Decapoda (larvae) Summer Pisces Winter Oncaeaidae other copepods Ostracoda Decapoda Decapoda (larval stage) Crustacea Sagittoidea Pisces Cephalopoda Miscellaneous 0 20 40 60 80 100
IRI of major prey items (summer vs. winter) Diaphus chrysorhynchus Copepoda- Copepoda-Poecilostomatoida Ostracoda summer winter Decapoda (larvae) Diaphus garmani 0 2000 4000 6000 8000 Copepoda- Copepoda-Poecilostomatoida Ostracoda Decapoda (larvae) 0 1000 2000 3000 4000 IRI
Prey size Prey width (mm) 7 6 5 4 3 2 1 D. chrysorhynchus D. garmani 0 40 50 60 70 80 90 100 110 Body length (mm) Prey width (mm) 7 6 5 4 3 2 1 0 20 30 40 50 60 70 Body length (mm) 30 25 Prey length (mm) 25 20 15 10 5 Prey length (mm) 20 15 10 5 0 40 50 60 70 80 90 100 110 0 20 30 40 50 60 70 Body length (mm) Body length (mm)
Stomach content composition (other species) Myctophum obtusirostre Decapoda (larvae) %N %W Sagittoidea 0 20 40 60 80 100 Myctophum asperum %N %W 0 20 40 60 80 100 Ceratoscopelus warmingii Pisces Oncaeaidae other copepods Ostracoda Decapoda Decapoda (larval stage) Crustacea Sagittoidea Pisces Cephalopoda Miscellaneous %N %W 0 20 40 60 80 100
IRI of major prey items Myctophum obtusirostre Copepoda- Decapoda Decapoda (larvae) Sagittoidea Myctophum asperum Copepoda- Decapoda Decapoda (larvae) Sagittoidea Ceratoscopelus warmingii Copepoda- Decapoda Decapoda (larvae) Sagittoidea 0 2000 4000 6000 8000 10000 0 1000 2000 3000 4000 5000 6000 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): Engraulis japonicus Etrumeus teres Trachurus japonicus Oncaeidae 0 20 40 60 80 100 %N Decapoda (larvae) Calanoid Oncaea other copepods Ostracoda Decapoda Decapoda (larval stage) Crustacea Saggitoidea Myosomata Pisces Cephalopoda Miscellaneous Copepods (, 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 10 20 30 40 Standardized squared Euclidean distance
Stable isotope ratios Pelagic fish Myctophids Pelagic fish Myctophids Engraulis japonicus Etrumeus teres Sardinops melanostictus Trachurus japonicus Diaphus chrysorhynchus Diaphus garmani Myctophum obtusirostre Myctophum asperum Ceratoscopelus warmingii -16-17 -18 δ 13 C (per mil) Engraulis japonicus Etrumeus teres Sardinops melanostictus Trachurus japonicus Diaphus chrysorhynchus Diaphus garmani Myctophum obtusirostre Myctophum asperum Ceratoscopelus warmingii -19 12 11 10 9 8 δ 15 N (per mil)
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 (δ 13 C) 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