Conceptual model of habitat restoration for Gobies in Tokyo Bay, Japan

Transcription

1 Conceptual model of habitat restoration for Gobies in Tokyo Bay, Japan Keita Furukawa 1, Tomonari Okada 1, Satomi Kamimura 1 and Yoshida 1 1 National Institute for Land and Infrastructure Management, Yokosuka, Kanagawa, Japan Tokyo Bay is an enclosed, mostly populated, and intensively used bay in Japan (Furukawa and Okada, 26). The inner bay catchment area has a total population of some 2 million. The concentration of population and industries in the catchment area of Tokyo Bay has brought remarkable changes to its coastline. Surrounded tidal-flats have been reclaimed by land fill, and only few natural tidal flat are remaining (98% of coastal line are covered by constructed structures). Furthermore, water quality of the bay is degraded (frequent red-tides, several times anoic water upwelling and occasional fish kill are occurred by eutrophication). Goby (Acanthogobius flavimanus) has nest in soft saline bed in 6-8m deep water in winter, and hatched larvae swim up to upstream limit of estuarine environment and settle on sandy shallow bed in spring. It becomes 6-8cm in early summer and growing up to 1-2cm in autumn. These seasons are ideal for easy fishing for public. Most of senior residents not only Tokyo bay, but also almost all around Japan, had eperience of goby fishing in childhood. So, it can be said as one of vanishing culture for coastal residents in Japan. Preliminary census for Gobies shows possibility of limitation, degradation and discretization of coastal habitats for Gobies. Some river mouth is serving marginal habitat of Gobies. Nevertheless, bay side of the habitat is affected by hypoic water intrusion from bottom layer. Furthermore, in the canal network that is remaining water bodies of tidal-flats that reclaimed, life cycle of Gobies seems to be adopted by discretized environment. Some of them are not having marginal habitat, but they stay in the same place for long period. A detail eamination for life-cycle of Gobies and determination for environmental status for shallow, canal, intermediate and deep area has been done, and watershed scale conceptual models were established. Since Gobies in Tokyo bay seems to have two groups which spawning in winter (conservative model) and spawning in early summer (alternative model), two different models are proposed. For conservative model, there are three negative pressures for Gobies habitation i.e. 1) lack of habitat for juvenile in canal, 2) fishing pressure in canal, and 3) low DO in intermediate and deep area during summer. For alternative model, 1) lack of habitat for nesting, 2) food shortage in intermediate area, and 3) low DO are found. Contact Information: Keita Furukawa, Research Coordinator for Coastal and ine Affaires, National Institute for Land and Infrastructure Management, Nagase 3-1-1, Yokosuka, Kanagawa, Japan, Phone: , Fa: , furukawa-k92y2@ysk.nilim.go.jp

2 Goby: Acanthogobius flavimanus Tokyo Bay Environment Map Winter. - ch Spring. - e Summer y. Mahaze 真鯊 Autumn.. Environment Map of Tokyo Bay ch 21 International and Environmental Division Ports and Harbors Bureau Ministry of Land, Infrastructure, Transport and Tourism ine Environment Division, National Institute for Land and Infrastructure Management The annual Water Quality Survey in Tokyo Bay have been conducted since 28. In 211, total of 139 institutions and organizations took part in the survey and conducted investigations at a total of 82 points, including places in the bay and in rivers. These annual survey are aiming to promote interests of public to the bay, reporting present status of bay water quality including discharged rivers, and reveal bay water contamination mechanisms. Hypoic and Anoic water in the bottom of the bay during early summer to late autumn is a one of biggest concerns for the bay environment. Especially, living resources such as fish, shellfish, and benthos are severely damaged during hypoic and anoic events. Goby (Acanthogobius flavimanus) has nest in soft saline bed in 6-8m deep water in winter, and hatched larvae swim up to upstream limit of estuarine environment and settle on sandy shallow bed in spring. It becomes 6-8cm in early summer and growing up to 1-2cm in autumn. These seasons are ideal for easy fishing for public. Most of senior residents not only Tokyo bay, but also almost all around Japan, had eperience of goby fishing in childhood. So, it can be said as one of vanishing culture for coastal residents in Japan.

3 Present Situation of Tokyo Bay Action Plans for Bay Renaissance The Committee (ision Maker) Secretariat of the Committee (ision Making Process) Represented by Bureau Managers of Related Ministries and Local Governments (3) Represented by Section Chief of Related Bureau (3) Photo by Prof. Ishimaru, TUMST Photo by KRT, MLIT WG1: Land WG2: Sea WG3: Monitoring Red tide (Algal broom) Blue tide (Anoic Water Upwelling) Tokyo Bay Renaissance Project, 28th ch 23 :1 years action plan Goal: Restore the beautiful coastal environment for enabling pleasant use and sustaining biodiversity as a wealth of capital. Fish Kill on 23 (due to Anoic Water) Photo by Mizuo, Yokohama City Institute for Env. Res. 1km Surface Area: 1km 2 Ave. Depth: 1m River Discharge: t/year Load of N: 1.11 t/year Tokyo Bay is an enclosed, mostly populated, and intensively used bay in Japan (Furukawa and Okada, 26). The inner bay catchment area has a total population of some 2 million. The concentration of population and industries in the catchment area of Tokyo Bay has brought remarkable changes to its coastline. Surrounded tidal-flats have been reclaimed by land fill, and only few natural tidal flat are remaining (98% of coastal line are covered by constructed structures). Furthermore, water quality of the bay is degraded (frequent red-tides, several times anoic water upwelling and occasional fish kill are occurred by eutrophication). Present Tokyo Bay Based on Chart W9, JCG

4 Edo-Mae: Originated in Tokyo Bay Fishing on Tidal Flat Photo by Y. Sawada: Goby fishing boats at Tokyo bay in 196s Fleet for Goby Fishing Photo by T. Hayashi, Chiba Museum Clam shell correcting 1km Utase Towing Sail Boat Sushi Tokyo Inner-bay Fisheries Records Image of Landsat No. TM Superpose of geographical map of 18s and fisheries zone map of 198 Tempura Fukagawa Bento (Lunch Bo) Nori Harvesting

5 Preliminary census of Gobies: Where are you? Preliminary census for Gobies shows possibility of limitation, degradation and discretization of coastal habitats for Gobies. Some river mouth is serving marginal habitat of Gobies. Nevertheless, bay side of the habitat is affected by hypoic water intrusion from bottom layer. Furthermore, in the canal network that is remaining water bodies of tidal-flats that reclaimed, life cycle of Gobies seems to be adopted by discretized environment. Some of them are not having marginal habitat, but they stay in the same place for long period. Number of Fish Hooked Acanthogobius flavimanus as an indicator of the Bay Environment y.2. Abundunce rate Abundunce rate Hiyama, e Winter.. Autumn Body Length Body Size (cm) Body Size (cm) y.. Summer 1. - ch. - ch Winter Schematic image of Gobies Lifecycle 2 Nesting Holes in 28 Ｎ 生息孔数 1 St.6 朝潮運河 1 St.4 夢の島 Nesting Holes in 29 St.1 ' St.9 St St.3 有明北 St.2 お台場 St.8 1 St. 1 号地 In 28 凡 例 Size of Nest 生息孔口径 St.7 ' St.7 St.1 羽田 St. 2 > cm以上 cm 3 cm 3- cm 3cm未満 1 St.3 St km In 29 凡 2 St.6 ' 2 2 St St 例 Size of Nest 生息孔口径 1 1 St < 3 cm Monitoring by participants 1 ind. / hour Ｎ > cm cm以上 3 cm 3- cm 3cm未満 1 1 < 3 cm 2 km Possible change of Nesting Pattern: Do they adapt change of environment? Fishing events for Goby Census

6 Conceptual Model for Gobies: What should we do? 7 Air Temperature (deg C) St. Surface 1 St.11 Surface 1 St.2 Surface 3 Azume B. Water Temperature (deg C) 3 Tukuda B. St. 2 2 St. Bottom 1 St.11 Bottom 1 St.2 Bottom St St DO (mg/l) A detail eamination for life-cycle of Gobies and determination for environmental status for shallow, canal, intermediate and deep area has been done, and watershed scale conceptual models were established. Since Gobies in Tokyo bay seems to have two groups which spawning in winter (conservative model) and spawning in early summer (alternative model), two different models are proposed. For conservative model, there are three negative pressures for Gobies habitation i.e. 1) lack of habitat for juvenile in canal, 2) fishing pressure in canal, and 3) low DO in intermediate and deep area during summer. For alternative model, 1) lack of habitat for nesting, 2) food shortage in intermediate area, and 3) low DO are found. 4 St. Bottom 4 St.11 Bottom 3 St.2 Bottom Classification of Life Stage 6 Habitat Creation COD (mg/l) 4 St. Bottom 3 St.11 Bottom 2 St.2 Bottom 1 Intermediate 7 6 Number of Fishing Boats Environmental Status Classification of Area Tidal Pond Enough light & Suitable Temperature Firm foundation & Inundation.-. Dissolved Oygen Supply Fishing Management Registration, Guidance Moving to point Scaling Temp. is High Lack of habitat Fishing pressure Fishing pressure No mud bed Hatching Temp. is too low Hatching? e y-..-. Too shallow Hatching Relatively low fishing pressure No mud bed Hatching NG Temp. is low Start fishing Intermediate Data recording y-. Fishing pressure Too shallow Public involved fishing census Closing Remarks.-e Catch! Conservative Model (Hatching at Winter) Needs control of fishing pressure Intermediate NG Alternative Model (Hatching at Early Summer) Needs hatching area restoration Integrated Model: Watershed size