Ecology and Fishery Biology of Holothuria fuscogilva in the Maldives, Indian Ocean (Echinodermata: Holothuroidea)

Norman Reichenbach, Liberty University

Document Type Article

Published in the Bulletin of Marine Science, 64:103-113.

Abstract

The ecology of Holothuria fuscogilva was assessed in three habitats in the Republic of Maldives: marine grass beds, island gaps and lagoon floor. In the lagoon floor habitat, H. fuscogilva was the dominant sea cucumber with relative abundances ranging from 70 to 94.9% in the two atolls studied. In one island gap area the median density (biomass), movement and growth rate were 29 ha[sup-1] (21 kg ha[sup-1]), 2 m d[sup-1] and 0.29% d[sup-1], respectively. Based upon the weight distributions in the three habitats, H. fuscogilva appears to recruit to shallow marine grass beds, then migrates to deeper waters such as island gaps. It then moves to the deep waters of the lagoon floor, as it approaches sexual maturity (1.5 kg TW), where it matures and reproduces. Growth slows as the animal matures and individuals with total weights of 5000 g or greater were estimated to be at least 12 yrs old. Based upon micro and macroscopic examination of extracted gonads, mature individuals from the lagoon floor were found primarily from August through May. Spawning of both male and females was observed between December and March or essentially the N. east monsoon season in the Maldives.

Exploitation of tropical sea cucumbers for processing into beche-de-mer, a delicacy in several Asian countries, has resulted in over harvested sea cucumber populations in many countries (Conand, 1990, 1991). This is particularly true for the more valuable species such as the prickly redfish, Thelenota ananas, white teatfish, Holothuria fuscogilva, and sandfish, H. scabra (Adams, 1993; Joseph, 1992).

In the Republic of Maldives, an atoll nation in the Indian Ocean southwest of Sri Lanka, a ban on the use of SCUBA to collect sea cucumbers was recommended (Joseph, 1992). The ban, which was implemented by the Ministry of Fisheries and Agriculture, was designed to take pressure off the spawning stocks of the T. ananas and H. fuscogilva. Despite the value of H. fuscogilva to the beche-de-mer fishery (Conand, 1990), little is known of its ecology except in New Caledonia (Conand, 1981, 1989, 1993).

The taxonomic status of H. fuscogilva has been recently questioned as being a synonym of H. nobilis (Rowe and Gates, 1995). In the Maldives, Joseph (1992) described two varieties of the teatfish, the white and black forms. He noted the white form occurred in waters from 3 to 30 m deep and the black form in shallow water about 3 m deep. This corresponds well with data collected in other locations (Conand, 1990) as well as our findings. I found the black teatfish, adults and juveniles, on the marine grass beds and adults were only found on the reef crest and slope to about 10 m in depth. In contrast, white teatfish juveniles were only found in the marine grass beds and the adults were found on the sandy lagoon floors typically 30 to 40 m in depth. The white teatfish, H. fuscogilva, was formally described and differentiated from the black teatfish, H. nobilis by Cherbonnier (1980). In my research I retained the name H. fuscogilva to describe the white teatfish.

The objective of this study was to acquire baseline ecological data on H. fuscogilva in order to advance the protection of this species in the reef ecosystem. Data were collected on H. fuscogilva (1) abundance, (2) weight class distributions, growth, and movement, and (3) reproduction.