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HABITAT PREFERENCES OF GROUPER SPECIES

Introduction

From five weeks of research in the Wakotobi Marine Reserve, Indonesia, research has been conducted on the habitat usage of groupers found in the region. The Bajo community set up a voluntary No Fishing Zone to allow the associated fish stocks recover from years of over-exploitation. Indonesia is the fourth largest country in the world and 70% of its population relies on fish as a main protein source. Fishing areas such as that off Hoga are therefore vitally important to be preserved and this study will as part of a major research programme deduce vital information on the viability of the grouper stocks within the area.

Groupers play a major role in the fishery with over 200 species commercially caught from around Hoga alone – this makes up half of the total known species in the world.

Aims: To understand if there is a habitat or habitats that are grouper species specific.

Objectives:

To survey various parts of the reef and recording the microhabitat in which the different species of grouper are found.

To investigate whether there any size correlation between/within species at different reef zones by estimating and recording the size of the species discovered at each particular site.

To investigate whether different species behave differently at various parts of the reef by recording the activity, body posture and direction that the grouper is facing when resting..

Methodology

Firstly, a keen eye is needed for identification of groupers and coral growth forms, found within the Sulawesi region. This will involve speaking to members of staff and consulting textbooks that outline the species found in this region. A few check dives are used prior to data collection to emphasise this point. Prior to data collection, dive buddies are organised with one using the standardised Line Intersect Transect technique (Loya 1978; Marsh et al 1984) with slight modification to look at a one metre square transect. The now Modified Line Intersect Transect technique (MLIT) is like its predecessor, used to assess the sessile benthic community of coral reef.

Upon descent in buddy groups consisting of a minimum of two people, surveying can begin. One diver notes the environmental/site characteristics, and the fish present within the locality of grouper found and if possible subjects this to species level. Site characteristics involves analysing cloud cover using the Oktas method, depth, vertical and horizontal visibility, and current (English, S et al 1997). The diver responsible for conducting such surveying is usually the one not using the MLIT.

Using the Modified LIT

Prior to the laying of the MLIT, a grouper needs to be located. This involves random sampling on parts of the reef with respect to the ecological zones present. To survey groupers correctly and precisely, it is generally agreed that those to be sampled are found perching and not swimming as they may be passing through an area of the reef they are not usually associated with. When a potential sample grouper is located, the MLIT diver firstly notes: (i) the species of grouper; (ii) the size of the individual; (iii) its activity including body posture with respect to the reef and any interactions it has with the reef during the time the area is sampled; (iv) the time the individual was encountered; (v) and at what depth it was encountered.

The diver responsible for the use of the MLIT, firstly lays down a 1 meter line horizontally over site where grouper was found. This line is subdivided into ten centimeter intervals, the first interval being at ten centimeters. Where the grouper was located perching, the fifty centimeter interval on this line is placed over it. Secondly, another one meter line is laid yet this time vertically across the previous line laid. Specifically, the vertical line is laid over the horizontal intervals i.e. at the first horizontal interval, the vertical line is laid so it intersects at the first ten centimeters. To ensure that a one meter square is laid correctly, the vertical line is laid with the fifty centimeter position on this line intercepting the horizontal line at a specific ten centimeter interval (see figure 1). It must however be noted that the horizontal intervals start at ten centimeters whilst the vertical line starts at 0. When the one meter square has been laid and is torque, surveying can begin. This involves recording the growth forms on the substrate. At each ten centimeter interval the diver records the life form which is present beneath it, such as soft coral, rock or hard coral. Life forms recorded are done so using the known AIMS method of abbreviations such as; (i) SC is Soft coral; (ii) MA is Macroalgae. Upon completion of dive, recorded data is transferred to a database/spreadsheet prior to analysis.

Preliminary results

Initial analysis has shown that the small Epinephelus merra (Honeycomb grouper) is primarily located to the reef flat and marginally to the reef crest, whereas larger species like Cephalopholis argus and cyanostigma are strictly confined to the reef slope and never observred anywhere else.

Report

A final year dissertation report entitled Grouper habitat preferences will be completed by James Gilks, University of Aberystwyth by May 2003.