Distribution and Ecology of Leptocephali in the Western North Pacific Gyre Ecosystem

Home , Leptocephalus, Leptocephalus (genus), Nettastomatidae

Distribution and Ecology of Leptocephali in the western North Pacific Gyre Ecosystem

Michael J. Miller and Katsumi Tsukamoto

Ocean Research Institute University of Tokyo

Advances in Epipelagic Ecosystem Research Session S5, PICES Yokohama 2006 Outline of Presentation I. Eels and leptocephali - Biodiversity of eels - Reproductive ecology of eels - Unique leptocephalus larva - Ecology of leptocephali in epipelagic zone

II. Research on leptocephali - East China Sea - Kuroshio Extension - Western North Pacific - Connectivity of the WNP Gyre

III. Future Research - Clarify life histories of abundant species - Evaluate migration and recruitment - Develop identification techniques - Ecological significance of leptocephali

Reproductive ecology of most species is poorly known

Spawning locations vary widely from no migration to long distance migrations 4 mm Leptocephali Vary Widely in Size

9 mm 250 mm

Bigger Than Human Beings

Ecology of Leptocephali Feeding Biology is Poorly Known -No zooplankton or large food items ever seen in their guts -Appear to feed on marine snow or discarded larvacean houses

-Gain nutrition at bacterial level Larvaceans filter small particles using gelatinous houses that they discard frequently when clogged

Mochioka and Iwamizu (1996) Ecology of Leptocephali

Leptocephali can Swim A Variety of Pigmentation both Forward and Patterns likely Function as Backwards and are Disruptive Coloration Completely Tranparent to help Avoid Predation Ecology of Leptocephali Leptocephali are found in the upper Epipelagic Zone surface

Growth Rates may vary 0.3 - >1 mm/d 50 m

100 m

Some may vertically migrate deeper during the day 250-300 m? Nemichthys

Leptocephali change during metamorphosis

Triggers of this transformation are not yet known Muraenidae The large size of leptocephali results in large sizes of juveniles that recruit ~ 70 mm to many different habitats Outline of Presentation I. Eels and leptocephali - Biodiversity of eels - Reproductive ecology of eels - Unique leptocephalus larva - Ecology of leptocephali in epipelagic zone

II. Research on leptocephali - East China Sea - Kuroshio Extension - Western North Pacific - Connectivity of the WNP Gyre

III. Future Research - Clarify life histories of abundant species - Evaluate migration and recruitment - Develop identification techniques - Ecological significance of leptocephali Leptocephali are often Abundant but Special Gear is Needed to Collect Them Due to Net Avoidance Techniques for Collecting Leptocephali

Criteria: Large mouth opening nets fished at night to reduce net avoidance

Isaacs Kidd Large ORI Large Mouth Midwater Trawl Ring Net Rectangular Nets (IKMT) 8.7 m2 7.1 m2 6-10 m2 Stations sampled for Leptocephali

s e is ru C 8 NRL MODAS SST 30 Nov 2000 1) East China Sea Sampling in the Kuroshio Current and East China Sea Tansei Maru KT-00-16 2,376 Leptocephali > 45 Species

Higher Catch Over Shelf Marine eels were Spawning Congridae Muraenidae Nettastomatidae Ophichthidae Synaphobranchidae Kuroshio Current

Small Leptocephali < 10 mm > 9 species Clouds

NOAA-14 SST

24 Dec 2000 Distribution of size classes of Gnathophis spp. (Congridae) and Dysomma sp. (Synaphobranchidae) leptocephali

Evidence of Recent Spawning

Evidence of Northward Transport A wide range of sizes Ophichthidae and Muraenidae leptocephali were collected primarily over Ariosoma may spawn the continental shelf after short migration Spawning more over shelf than slope offshore

Absent at stations over shelf Marine eel Spawning Japan in the East China Sea

Congridae Muraenidae Nettastomatidae Ophichthidae China Synaphobranchidae

Clouds

Ariosoma??? Taiwan 24 Dec 2000

NOAA-14 SST Offshore Transport and Currents Sea Surface Chlorophyll/Productivity

Kuroshio Extension

Complex Circulation

North Equatorial Current (NEC)

North Equatorial Countercurrent Sea Surface Chlorophyll/Productivity Offshore Transport and Currents

Kuroshio Subtropical Gyre Recirculation

Possible Counter Currents 3 April 2006 Korea Japan NOAA-14 SST

Complex hydrographic structure 2) Kuroshio Extension

Greatest Abundance

4.6 per tow

68 per tow

KH-06-1 Hakuho Maru Cruise 12 Jan – 13 Mar 2006

36 stations w/ single MOHT tow in upper 100 m 1,368 Leptocephali >39 species of 13 families Leptocephali Collected in 12 Serrivomer Kuroshio Extension and N = 42 Recirculation Region 8

Mesopelagic eels (< 3-5 spp.?) No. leptocephali Nemichthyidae N = 105 0 0 20406080100 Serrivomeridae N = 61 Total length (mm)

8 Nemichthys N = 96 6

2 No. leptocephali 0 0 25 50 75 100 125 150 175 200 225 250 Total length (mm) Leptocephali Collected in Most > 40 mm TL 4 Abundant congrids Kuroshio Extension and 6 Chlopsidae N = 15 Recirculation Region 4

Shelf and Slope eels 2Greatest Number Congridae (12 spp.) N = 1079 ofGnathophis Species 0 Chlopsidae (5 spp.) N = 15 Muraenidae N = 19 Muraenidae (>7 spp.) N = 33 4 Ariosoma major Ophichthidae (2 spp.) N = 3 2 Nettastomatidae (3 spp.) N = 40 Synaphobranchidae (2 spp.) N = 18 0 Saurenchelys stylura

Number of leptocephali 4 AriosomaNettastomatidae sp. 4 Congridae – 4 most abund. spp. N = 20 Gnathophis (>3 spp.) N = 615 2 Ariosoma major N = 249 Bathycongris 0 Ariosoma sp. 4 N = 88 0 20 40 60 80 100 120 Bathycongris sp. N = 93 Total length (mm) Congrid Leptocephali

10050 3020 GnathophisKT-00-16 BathycongrisKT-00-16 4080 N = 477 East China Sea 15 East ChinN = a47 Sea Ophichthidae 20 Nettastomatidae 3060 N = 278 N = 100 10 2040 10 5 No. leptocephali 1020 No. leptocephali No. leptocephali No. leptocephali

00 00 002 2004 4006 6008 8001 100001 120201 140401 16060 002 200 4 400 6 600 8 800 1 10000 120 1201 14040 160 TotalTotal lengthlength (mm)(mm) TTotalotal length (mm)

35050 2030 Ariosoma major 300 KT-00-16 Ariosoma sp. 4 KT-00-16 40 N = 169 N = 57 East China Sea 15 East China Sea 250 Gnathophis Muraenidae ephali 20 20030 N = 983 N = 110 10 15020 10 100 5 No. leptocephali

10 No. leptoc No. leptocephali 50 No. leptocephali 0 0 0 2020 4040 6060 8080 100100 120120 140140 160160 0 2020 4040 6060 8080 100100 120120 140140 160160 TotalTotal lengthlength (mm)(mm) TotalTotal length length (mm) (mm) Proportional Abundance

of Leptocephali in the KH-06-1 Kuroshio Extension

Congridae was Dominant

Some Ariosoma etc. recirculated south

Gnathophis

ColNemichthyidae 2: 105 A. major ColSerrivomeridae 2: 61 ColGnathophis 2: 615 A. sp. 4 A. major Congrids ColAriosoma 2: 249 major Dysomma ColCongridae 2: 215 Gnathophis ColShelf 2: 51 species ColSlope 2: 58 species 3) Western North Pacific

Japanese eel Anguilla japonica spawns in the NEC

Tropical Giant Mottled eel Anguilla marmorata also spawns in NEC Ariosoma major (Congridae) Leptocephali Consistently Collected in NEC Region at Large Sizes (~100 – 300 mm)

A variety of other species have been collected in NEC region Ariosoma major may be abundant in East Asia small sized eels

Their leptocephali are one of the most abundant species in parts of the W. North Pacific

Leptocephali Reach Very Large Sizes Ariosoma major Leptocephali in the NEC Region

Sampling for Leptocephali 7 Cruises 1995 - 2006 1991 transects Large Sized Ariosoma major Leptocephali in NEC Region May to September of 8 different Years

Total Length vs Date of Collection Plot 350 N = 455 300

250

200

1991 150 1995 1998 2001

Total length (mm) 100 2002 2004 50 2005 2006 0 120 140 160 180 200 220 240 260 280 30 April 9 June 19 July 28 Aug 7 Oct Day of year Ariosoma major Leptocephali are Smaller Elsewhere

70 – 110 mm 40 – 56 mm

64 – 239 mm

100 – 300 mm Huang and Qiu (1994) Three Dimensional Structure of Wind-driven Circulation of Subtropical North Pacific. J. Phys. Oceanogr. Ecology of Leptocephali in Kuroshio Gyre Summary Kobayashi et al. 2006 J. Geophys Res. Variety of species get transported offshore into the ? Kuroshio Ext. etc. ? Congrids appear to be the most abundant in Kuroshio recirc. Seasurface Dynamic Height in North Pacific Anguillids and -Two Countercurrents also Present- Mesopelagic eels Whole gyre is used by leptocephali spawn and use but seasonal patterns unknown lower latitudes How many species other than Anguilla recruit back??? 3) Future Research

1) Life histories of eels and their leptocephali -distribution of leptocephali and otolith studies

2) Evaluate larval transport and recruitment mechanisms -how do leptocephali return to adult habitats -how many are lost due to offshore transport 3) Develop species level identification of leptocephali -both morphological and genetic techniques

4) Ecology or “functional biodiversity” of leptocephali -develop conceptual model for significance of leptocephali and eels in marine ecosystems Similar Western Boundary Current Subtropical Gyres

Kuroshio/WNP

Gulf Stream/WNA

Other Research Areas East Australian Current/WSP

Much Awaits to be Learned About Leptocephali in the Epipelagic Layer of the Ocean