Walking the Beaches – Grand Baie

Much of the rock around Mauritius’ coast is black, volcanic and almost impossible to touch in the middle of the day with all the heat it had absorbed.  Exposed to the rain and washed by high tides, the outcrops are rounded but deeply pitted but rarely covered in algal growth.  White limpet like shellfish clamp on to the sides, and winkles amble across the wetter portions.  The contrast between the black rocks and the white sand could hardly be greater.

As we passed the resorts, the sand became cluttered with their paraphernalia; large palm leaf sunshades, line after line of loungers and small glass tables for your drinks, a volleyball court here, assorted watersport equipment there, and from time to time a beach bar blaring out music.  Although the beach is public, these resorts de facto own just by occupying the space with their bric-a-brac.

Then there were the boat ramps – huge concrete slabs descending gently into the water.  The main fault with these was that sand would be trapped on one side and prevented from moving onwards around the bay; the longshore drift of schoolboy geography powering the process.  On the downdrift side the sand would continue to be moved away but nothing replenished causing holes in the beach, exposed rock and threatening the coastline behind from accelerated erosion.

The distance around the east side of the bay into town was barely a kilometre, but noting down all these features took time.  Eventually we met what we expected to call the centre of town, where a rather ugly shopping mall had been constructed by Grand Baie’s main road junction and traffic lights.  It was dominated by high class boutiques selling essential items like handbags, silk wraps, Persian carpets and hifis.  Beyond this point we had to scramble over the waste pipes of a couple of establishments on the sea front, more boat ramps and then a strip of more formal institutional type buildings.  We realised our skewed perception of Grand Baie was wrong – we had been passing through the tourist centre up to now, here was the true town centre, if indeed you could say Grand Baie had one at all.  Religious constructions of various types, police station, town council building and some normal shops selling things you might actually need.  What was still missing from Grand Baie was anything old.  Even the mosque and Catholic church were modern in construction; no earlier than the 1950’s.  And indeed that is Grand Baie’s history.  Despite one of the most extensive and sheltered bays on the whole island, its shallow and difficult entrance made it unsuitable in sailing ship times, and the small fishing village was just at the end of the huge sugar plantations for most of the last three centuries.  As tourism started to develop in the 1950s the village grew both with people who found the area attractive to live in, and for those to service the growing population.  The next stretch of the walk revealed just that activity,

Walking the Beaches – The First Boat Survey

Jeremy was very clever to find a highly motivated, organised, intelligent and willing partner from the University of Mauritius,  We visited his office at the Reduit campus in the middle of the island and he not only offered his expertise but gave the services of a number of students who were willing enough to drop over the side of a small boat and explore the substrate in the lagoon.

We decided Grand Baie was the best place to start our field survey.  Not only was it close to Calodyne, but it was an intensely busy bay and the smallest of the pressure zones.  I had prepared the initial interpretation from some satellite imagery back at the house and chosen  a route around the bay where we could investigate all the patches I had identified.  By using the GIS to mark those locations, their coordinates could be uploaded into a GPS and then it was a matter of sailing around the bay guided by the unit.  I found this relatively easy to do using the GOTO function on the GPS – it warned you how far you way from your destination and in which direction.  Fairly quickly I learnt that you could read the currents and wind by looking at the water surface and if we approached from the direction of the current we got a good chance of standing over the spot we wanted.  In most of the bay the current was fairly mild so the boatmaster could use the engine to fight against the current and keep us stable over the patch of sea.  It helped in Grand Baie that we had found a glass bottom boat.  Glass bottom boat tours are common around many of the touristy areas to give visitors a chance of seeing under the water without getting too wet.  They helped us enormously as I could keep the map and survey materials dry.  Our colleagues from the University of Mauritius  were very keen to keep popping in to the water to take a look around.  With over a hundred points to survey we could not spend huge amounts of time analysing each frond of coral, but we did want to ensure that we were not overgeneralizing, so we did allow them early on to investigate any new cover class in a bit more depth.  In particular we were keen to record where algal growth had choked the coral, or for any evidence of bleaching, an aptly named process where the animal parts of coral migrate out of the rocky skeleton, effectively taking the colour out of the coral.

On the first day in Grand Baie we made slow progress.  It took time to explain the methodology to the new field workers, and also we were trialling it ourselves for the first time, so we had to see what was necessary and what could be streamlined.  But although the bay looked complicated on the satellite image, large areas of the central portion were a grey sandy bottom with occasional mats of seagrass or algae and could be covered quickly.  The slight colouration differences on the image proved not to be a substrate issue but related to the depth of the water.  Around the fringes of the bay and at its mouth was the reef itself and on the satellite image this looked like a myriad tapestry of shapes and colours.  Even here ,with a bit of understanding of the morphology of coral reefs, one can see the patterns repeated time and time again; the head reef, the long thing parallel lines where countless waves have ground a path through, the scattering of patch reefs behind.  Once these classes of substrate have been confirmed by the field survey, over 80 percent of the job is complete.  The challenge is to seek out the exceptions to those rules – different textures or colours on the image that do not conform to this morphology.  Usually the solution to those teasers are fairly obvious once seen, which shows the value of spending time on the boat.

The sands and the seagrass beds and even most of the coral patches were easy enough to navigate over, but coral reef has a tendency to try and grow up to the light and much of the reef was too shallow for the boat to go over, in some places even breaking the surface.  We had to be extremely careful if we needed to get in amongst the sharp reef heads to investigate deeper water beyond.  Over our numerous trips, our captains varied in their courage levels, or maybe it was their boat was uninsured, I never dared ask.  Even when I would show them print outs of the satellite image and demonstrate a clear way in (and more importantly out ) of the reef they would be sceptical.  Their experience had told them that reef bad, deep water good – why would anyone want to navigate a boat against that hard jagged thing that could rip your bottom apart on your way out.  Indeed we had many nervous moments when all you could hear was the scratching of reef against the fibre glass and the sucking of teeth from our captain.

Our surveying had to extend out into the open water beyond the bay and too look at the forereef.  Out here we were still not in the ocean but the incredible lagoon that surrounds almost the whole of Mauritius.  The waves were larger and the currents stronger here, and it took all the skill of the captain to be able to still navigate to our survey locations and hold the boat still while we observed under the water.  I’ve got better at keeping my nausea to a minimum in small boats, but this started to affect me; Jeremy was looking the worse for wear and he retreated into the depths of his rain jacket and lowered his wide brimmed hat over his eyes.  We did not spend too long out there but there was nothing difficult about the interpretation in the open water; it was a mixture of hard reef and rubble kicked up by the wave energy.  Anyway, on the satellite imagery much was obscured by the white foam and breaking waves themselves so I could not do much with any mapping.  So we headed back to the shore.

Walking the Beaches – Jeremy

Jeremy had not been on the original project team  – indeed I did not know of his existence when I had been here for the first two months.  Our original survey expert had not been able to go through with the project and Jeremy was known to our team leader.  He had arrived a few days before me so I turned up at the house in Calodyne with him already settled in.  It’s always a mouth gulping  moment when you meet someone for the first time with whom you have been forced to work for a long period, but after a day or two of pleasantries, a few beers, exploration of our mutual pasts and a few terrible joke telling sessions, we found ourselves comfortable in each other’s company.  As the next few weeks progressed I grew to like Jeremy enormously – very passionate and sound over his work, meticulous over contract arrangements but also generous to other’s opinions and relaxed about working arrangements and incredibly good company.  Those qualities proved supremely important given the tasks we had to do.

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We set about thinking through our strategy for field work and the resources we needed.  The survey needed to be two sided.  We wanted to get out in the lagoon in each area and determine both the substrate and any other environmental factors.  Substrate would be complexes of hard or soft coral, seagrass beds on sand, and rocky or sandy bottoms.  The environmental factors could include turbidity or algal growth on the substrate.  To complement this we had to walk the entire coast of each pressure zone to document what the coastline was like.  We needed to see whether it was naturally a sandy or pebbly beach, a rocky area or cliff, or whether some sort of coastal protection in the form of gabions, walls or rocks had been placed.

In theory it sounds ok.  The practicalities on the marine side were we needed to hire several boats. It is difficult to get inshore boats to sail around the whole island given the nature of the lagoons,  so we had to pick local guides in each area. We required people who could do the survey for us, with our guidance, and we needed a strategy.  I had done several interpretations in the Caribbean and worked out a method – to use the imagery first to delimit areas that looked the same, and try and categorise from your previous knowledge which of the types it was, then you would head out in a boat and try and find those areas and see if your first guess was right.  In theory, if your first guess was right you could just go round reaffirming that your initial interpretation was always correct, but if you found something different at your location, you had to start working out what that classification was, what it looked like on the image and why it was different from the other class you first thought of.