THE ROLE OF A MANGROVE AREA AS A NURSERY GROUND FOR LARVAE

1993 Fiscal Year Final Research Report Summary

• Project/Area Number: 04660213
• Research Category: Grant-in-Aid for General Scientific Research (C)
• Allocation Type: Single-year Grants
• Research Field: General fisheries
• Research Institution: TOKAI UNIVERSITY
• Principal Investigator: SAWAMOTO Shozo TOKAI UNIVERSITY, INSTITUTE OF OCEANIC RESEARCH AND DEVELOPMENT, 海洋研究所, 助教授 (90119678)
• Project Period (FY): 1992 – 1993
• Keywords: MANGROVE AREA / FISHES / GUT CONTENTS / ZOOPLANKTON / CRUSTACEAN LARVAE / IRIOMOTE ISLAND / UDARA GAWA

Research Abstract

The role of a mangrove area as a nursery ground for larvae was studied at Udara gawa in iriomote Island in September-November, 1992 and August, 1993. The research was carried out five times in the periods. Sampling site was placed at a creek in the area where water depths were ca 50 cm during neap tides while they were ca 120 cm during spring tides. Muddy bottom emerged even at the neap tides when water was lowered. Water temperature and salinity varied with tidal cycles. Fishes were caught with a net during the day and at night in ebb tides of neap and spring tides. A total of 323 individuals in 16 species of 13 families was sampled. Among them four species were found in every sample and were composed of 71 % of the total catch. These were Zenarchopterus duncheri (Hemiramphidae), Apogon amboinensis (Apogonidae), Yongeichtys criniger (Gobiidae) and Chelon macrolepis (Mugilidae). Z.duncheri was supposed to spend in the mangrove area because its small specimen (29.1 mm TL) and mature specimen (> 100 mm TL) were sampled. Organisms in the digestive tracts of the four fishes were varied each other. Preys of C.macrolepis were algae and detritus, those of A.amboinensis were gammarid amphipods and planktonic copepods, those of Y.criniger were polychaets and meiobenthos. Z.duncheri, fed on insects mainly ants, might not connect with detritus. Most of the prey organisms of those fishes were found in the zooplankton smaples. Preys were diverse including crustacean larvae in August, while limited in November. This would be caused by lowering water temperature by November. Several kinds of decapos crustaceans were fed by fishes at newly hatched zoea and advanced stages. Udara gawa mangrove area is supposed to be a nursery ground for larvae including fishes from August to November.