Kuroshio Current

Tsushima Strait

Main spawning ground

FIS-P-14041

Early life history of Japanese horse mackerel Trachurus japonicusin the north Satsunan area, southern Japan

Kei Nakaya1, Gen Kume1, Toru Kobari1, Tsutomu Takeda1, Hiroumi Kuroda1, Mutsuo Ichinomiya2, Tomohiro Komorita2, Junya Hirai3, Maki Aita-Noguchi4 and Fujio Hyodo5

1 Aquatic Sciences, Faculty of Fisheries, Kagoshima University, 4-50-20 Shimoarata, 2 Faculty of Environmental and Symbiotic Sciences, Prefectural University of Kumamoto, 3 Atmosphere and Ocean Research Institute, The University of Tokyo, 4 Research and Development Center for Global Change, Japan Agency for Marine-Earth Science and Technology,

5 Research Core for Interdisciplinary Sciences, Okayama University,

IntroductionSurveyPeriod: January-May in 2015-2019

Study area: Inner part KB1-6; Outer part SK1-9Sample collection: • ORI net was obliquely towed from the bottom

to the surface at approximately 2 knots for 30 min.

• Water temperature and salinity was recorded by CTD.

• Zooplankton samples were collected by towing a twin-type NORPAC vertically from 200 m or near bottom to sea surface at each station.

Analysis• Spatiotemporal occurrence• Growth and dietary analyses

2015 nen

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1.0

0 2 4 6 8 10 12 14 16 18 20 222016 nen

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0 2 4 6 8 10 12 14 16 18 20 222017 nen

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0.4

0.6

0.8

1.0

0 2 4 6 8 10 12 14 16 18 20 22

2018 nen

0.0

0.2

0.4

0.6

0.8

1.0

0 2 4 6 8 10 12 14 16 18 20 222019 nen

0.0

0.2

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0.8

1.0

0 2 4 6 8 10 12 14 16 18 20 22

0 4 8 12 16 20

0 4 8 12 16 20

Body length (mm)

2015n=100Mean=4.18

2016n=1233Mean=3.55

2017n=35Mean=6.14

2018n=36Mean=6.31

2019n=142Mean=6.10

Body length (mm)

Rela

tive

freq

uenc

y

Fig. 2 Sampling stations in the north Satsunan area.

Materials and methods

Result and discussion

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

マアジ

カタクチイワシ

ホウボウ科

カサゴ属

ヨコエソ

アラハダカ

Ratio

of M

OTU

s rea

d nu

mbe

r (%

)

アカルチア科

カラヌス科

メトリディア科

カンダシア科

アエティデウス科

クラウソカラヌス科

ユウカラヌス科

スコレシスリックス科

パラカラヌス科

カロカラヌス科

ユーキータ科

オイトナ属

オンケア属

コリケウス属

テングウミノミ科

オタマボヤ科

ヤムシ科

ユミウミタル属

ヒドロ⾍綱

n=11 n=10 n=8 n=7 n=7 n=8

Oithona

Oncea

Trachurusjaponicus

Engraulisjaponicus

Triglidaespp.

Sebasticusspp.

Sigmopsgrasilis

Myctophumasperum

Acartiidae

Calanidae

Metridididae

Candaciidae

Aetideidae

Clausocalanidae

Eucalanidae

Scolecitrichidae

Paracalanidae

Euchaetidae

Calocalanidae

Oithona

Oncea

Corycaeus

Platyscelidae

Oikopleuridae

Sagittidae

Doliolum

Hydrozoa

0

1

2

3

4

5

6

7

8

9

10

-24 -23 -22 -21 -20 -19 -18 -17

δ15N

(‰)

δ13C (‰)

Appendicularia

Harpacticoida

Poechilostomatoida

Calanoida

Ostracoda

Cyclopoida

Myctophum asperum

Sigmopsgracilis Trachurus japonicus

y = -0.125 x + 2.86 R² = 0.769

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 5 10 15 20 25Age (days)

abun

danc

e (L

og10

(inds

.))

Survey year Area Survival rate（%）2005〜2009 East China Sea 87.3〜89.9

2019 north Satsunan area 88.3

0

0.1

0.2

0.3

0.4

0.5

0.6

Inner part of the bay Outer part of the bay

* P < 0.05

Mea

n gr

owth

rate（

mm

/day）

Fig. 3 Length-relative frequency of larval and juvenile Trachurus japonicus in the north Satsunan area from 2015 to 2019.

Fig. 4 Larval and juvenile density distribution of Trachurus japonicus at 15 stations in the north Satsunan area from 2015 to 2019.

0.09

0.11

0.13

0.15

2017年 2018年 2019年2017 20192018

n=26 29 135

Fig. 9 Relationship of age and abundance of Trachurus japonicus larvae.

year

Mea

n gr

owth

rate（

mm

/day）

Table 1. Survival rate of Trachurus japonicus larvae in the East China Sea (Sassa et al. 2014) and the north Satsunan area (the present study).

Fig. 5 Comparison of mean growth rate of Trachurus japonicus larvae in the north Satsunan area and East China Sea (bluish area: Takahashi et al. 2014).

Fig. 6 Comparison of mean growth rate (3days before sampling) of Trachurus japonicuslarvae in the inner and outer part of Kagoshima Bay in 2019.

Fig. 7 Prey composition of Trachurus japonicus and other five dominant species larvae by DNA meta-barcoding analysis.

Fig. 8 Mean isotopic signatures of carbon (δ13 C ± SD) and nitrogen (δ15 N ± SD) of Trachurusjaponicus and dominant mesopelagic fish larvae and their main preys.

IbusukiMakurazaki

Kanoya

Kyushu

n Main spawning ground of Trachurus japonicus is located in southern East China Sea.

n It is assumed that T. japonicus spawns in southern East China Sea and larvae and juveniles abundantly recruit into the fishery grounds around Japan (Sassa et al. 2006).

Fig. 1 Red and blue areas are the spawning grounds of the Tsushima and Pacific Trachurus japonicus populations, respectively.

Is the north Satsunan area favorable as the nursery ground?Yes: The values of abundance, mean growth rates and survival ratio were equivalent to the data of previous studies in East China Sea.Ø Feeding habits were different between T. japonicus and the other dominant fish larvae.Ø There are no strong competition for prey items between T. japonicus and the mesopelagic fishes.The importance of the mouth of Kagoshima Bay in the north Satsunan areaØ Mean growth rate was significantly higher in the inner part than the outer part.Ø Copepods density of the inner part is higher than outer part (not displayed data). Ø The oceanic water sporadically inflows into Kagoshima Bay during the winter and spring months,

leading to a massive upwelling and phytoplankton bloom (favorable feeding conditions).ReferencesHattori S (1964) Studies on fish larvae in the Kuroshio and adjacent waters. Bull Tokai Reg Fish Res Lab 40: 1–113. Sassa C, Konishi Y, Mori K (2006) Distribution of jack mackerel (Trachurus japonicus) larvae and juveniles in the East China Sea, with special reference to the larval transport by the Kuroshio Current. Fish Oceanogr 15: 612–619Takahashi M, Sassa C, Nishiuchi K, Tsukamoto Y (2016) Interannual variations in rates of larval growth and development of jack mackerel (Trachurus japonicus) in the East China Sea: implictionsfor juvenile survival. Can J Aquat Sci 73: 155–162Sassa C, Takahashi M, Nishiuchi K, Tsukamoto Y (2014) Distribution, growth and mortality of larval jack mackerel Trachurus japonicus in the southern East China Sea in relation to oceanographic conditions. J.plankton Res 36: 542–556

n Meanwhile, Hattori (1964) suggested that the north Satsunan sub-populatonmay recruit into the fishery grounds in Pacific coast of Japan and substantially support the fishery resources of T. japonicus.

n In this study, we clarified the early life history of T. japonicus and evaluated the importance of the north Satsunan area as the nursery grounds for T. japonicus.

n=30 92

×

×

2015

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2018

×

×

2017

×

2016 2019

×

0 <1 <10 <100 <1000(inds./1000m3)