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CHAPTER ONE

INTRODUCTION

1.1   BACKGROUND TO THE STUDY

Holothuria scabra, or the sandfish, is a species of sea cucumber in the family Holothuriidae. It was placed in the subgenus Metriatyla by Rowe in 1969 and is the type species of the subgenus. Sandfish are harvested and processed and eaten in several coastal communities all over the world. Sea cucumbers are marine invertebrates and are closely related to sea urchins and starfish. All these groups tend to have radial symmetry and have a water vascular system that operates by hydrostatic pressure, enabling them to move around by use of many suckers known as tube feet. Sea cucumbers are usually leathery, gherkin-shaped animals with a cluster of feeding tentacles at one end surrounding the mouth. The sandfish is greyish-black on the upper side with dark-coloured wrinkles but paler on the underside. It grows up to four centimetres long, is broader than it is high and has a pliable skin. It is covered by calcareous spicules in the form of tablets and buttons. In many areas the fisheries have declined over the years because of over fishing, so ranching, aquaculture and hatchery rearing are being attempted (FAO, 2005).

Sandfish stocks are being increased in some areas by being bred in tanks at hatcheries. Spawning is induced by temperature shock and the fertilized eggs incubated for a day. The auricularian larvae that hatch from the eggs are fed on microalgae for nine days after which time they develop into doliolarian larvae. These are fed on diatoms and after five days settle as pentactular larvae onto diatom-coated plates. Juveniles are grown on in tanks and may reach one to two centimetres in three months. They are then moved to larger ponds for a few months before being released into suitable habitats for ranching or restocking (Adams, 2008). Sea ranching is a culture method whereby juvenile animals, generally produced in hatcheries but could also be wild-caught, are introduced into the natural environment and allowed to grow without containment structures. The environment provides the animals with everything they need and no additional feed is required (Adams, 2008). Sea ranching of sandfish where hatchery-produced juveniles are placed on the sea bed and allowed to grow to marketable size, is being trialed in the West African sub-region.

Juvenile sandfish are produced in hatcheries. sea cucumber ranching is only viable if the culture area is closed to commercial trawl fishing while the animals grow and if the animals remain in the specified culture area until harvest. Sandfish are normally harvested by hand either by diving or hand harvesting at low tide in shallow water. Aquaculture, in a variety of forms, is needed to redress the problem of low yields from inshore invertebrate fisheries including the sandfish (Bell, 1999). Aquaculture can be used to increase productivity in a way that the cultured juveniles can be released into the wild to restore stocks to levels at which they provide substantial, sustainable yields. This process is known as “restocking”. This phenomenon occurs when the natural supply of juveniles fails to reach the carrying capacity of the habitat, even when there are great numbers of breeding adults. Other important features of the sea ranching and restocking sandfish in Nigeria are that it causes little damage to the environment, and does not conflict with the subsistence food requirements of villagers (Dalzell, Adams and Polunin, 1996).

The method being developed for the restocking of sandfish involves the propagation of juveniles in hatcheries for release in the wild. Other methods for restocking sandfish have been proposed, including collection, rearing and transplantation of postlarvae; induced fission; and translocation of adults. However, these methods are not suitable for the large-scale restocking of sandfish. Collection of wild juveniles is not practical because they are difficult to find, even though the settlement habitat of postlarvae has now been identified (Mercier, Battaglene and Hamel, 2000; Hamel et al., 2001). In addition, their abundance is likely to be limited as a result of overfishing, and methods for collecting them at settlement would still involve the use of aquaculture facilities for grow-out. Induced fission is not considered to be an option as it only works for a few generally lower-value species of sandfish and is a slow and labour-intensive way to increase numbers. Finally, the translocation of adults would only be effective where their propagules are retained, and at best would benefit some localities at the expense of others. The methods that have been developed for the propagation of juvenile sandfish can be adopted in Nigeria.

1.2   STATEMENT OF THE PROBLEM

There is now general recognition that the fastest way to restore the productivity of severely depleted sandfish for the benefit of the coastal communities in Nigeria may well be to rebuild the stocks by releasing cultured juveniles, and to combine this intervention with other forms of management that will protect the released animals until they, and their progeny, replenish the population to a level at which it can be managed sustainably through sea ranching and restocking. However, as a means of maximizing the productivity of sandfish in Nigeria where there is recruitment limitation, sea ranching and restocking can be the best approach which is to be examined in this study.

1.3   OBJECTIVES OF THE STUDY

The following are the objectives of this study:

1.  To examine the process of sea ranching and restocking of sandfish in Nigeria.

2.  To examine the prospects of sea ranching and restocking of sandfish in Nigeria.

3.  To identify the limitations of sea ranching and restocking of sandfish in Nigeria.

1.4   RESEARCH QUESTIONS 

1.  What is the process of sea ranching and restocking of sandfish in Nigeria?

2.  What are the prospects of sea ranching and restocking of sandfish in Nigeria?

3.  What are the limitations of sea ranching and restocking of sandfish in Nigeria?

1.5   SIGNIFICANCE OF THE STUDY

The following are the objectives of this study:

1.  The results from this study will reveal how Nigeria can tap into sea ranching restocking of sandfish being practiced in other advanced countries for the purpose of economic development especially the coastal communities.

2.  This research will be a contribution to the body of literature in the area of the effect of personality trait on student’s academic performance, thereby constituting the empirical literature for future research in the subject area

1.6   SCOPE/LIMITATIONS OF THE STUDY

This study will cover the process, prospects and limitations of sea ranching and restocking of sandfish in Nigeria with special focus on the coastal communities.

LIMITATION OF STUDY

Financial constraint- Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet, questionnaire and interview).

Time constraint- The researcher will simultaneously engage in this study with other academic work. This consequently will cut down on the time devoted for the research work.  

REFERENCES

Adams, T. 2008. Coastal fisheries and marine development issues for small islands. In M.J. Williams, ed. A roadmap for the future for fisheries and conservation. ICLARM Conference Proceedings No. 56: 40–50.

Bell, J.D. 1999. Aquaculture: a development opportunity for Pacific Islands. Development Bull., 49: 49–52

Dalzell, P., Adams, T.J.H. & Polunin, N.V.C. 1996. Coastal fisheries in the Pacific Islands. Oceanogr. Mar. Biol.: an Annual Review, 34: 395–531.

FAO. 2005. The fishery resources of Pacific Island countries. Part 2. Holothurians, by C. Conand. FAO Fisheries Technical Paper, 272.2. Rome.

Hamel J.-F., Conand, C., Pawson, D. & Mercier, A. 2001. The sea cucumber Holothuria scabra (Holothuroidea: Echinodermata): its biology and its exploitation as bêche-de-mer. Adv. Mar. Biol., 41:129-223.

Mercier, A., Battaglene, S.C. & Hamel, J.-F. 2000. Settlement preferences and early migration of the tropical sea cucumber Holothuria scabra. J. Exp. Mar. Biol. Ecol., 249: 89–110

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