Mavis Grind is the narrowest point of Shetland, at only 33m wide, this small strip of land (called an isthmus) separates the Atlantic Ocean to the west and the North Sea to the east. It is said that Vikings used to drag their ships across Shetland at this point as a short cut across the island. Although it’s unlikely you’ll see a Viking dragging his ship across now, you might be lucky enough to spot the occasional otter scurrying across the road, as well as the odd diver!
The dive is on the Sullom Voe (east) side, where a small shore allows access into the voe. Sullom Voe is Shetlands longest voe at 12km long. Mavis Grind is at the south-west corner of the voe and is about as far from the open sea as you can get in Shetland. The voe is poorly flushed, with ‘the narrows’ reducing the flow in and out of this part of the voe even further. Most of the live is found above 20 meters on this dive, a trip deeper reveals that much of the voe is naturally anoxic below 30m, with patches of Beggiatoa (white bacteria) on the surface of the mud.
Before I first dived Mavis Grind I had been warned that there was ‘nothing there’ and was best avoided except for taking in trainees when it was too windy to go anywhere else. However, one of my friends who had been before was very keen and insisted it was in fact quite interesting. So it was with some trepidation that I went to see what Mavis Grind had to offer. I quickly realised that Mavis Grind is what would be classed as ‘muck diving’ in the tropics, with a narrow band of kelp quickly giving way to thick mud. It took me a few minutes of thinking ‘where’s she taken me now!’ to realise my friend was right, the mud is home to a large variety of life as are the rocks that protrude out of the mud. Although the water can be quite clear the mud is easily stirred up and the conditions can quickly deteriorate to only a few inches of visibility after a few ungraceful fin kicks, quite unlike Shetlands normally clear and sediment free waters.
Although there are a few different directions to explore my favourite dive at Mavis Grind is on a wall that loops out from the voe edge into the bay. It stretches from a depth of 8m out to a depth of 20m before curling back towards the shore. It harbours a variety of life and at the right time of year you can see literally hundreds of nudibranchs. This has led us to give it a Lembeh (Indonesia) inspired nickname ‘nudi falls’.
The violet seaslug (Flabellina pedata)
It came as a bit of a surprise when I first found this rocky reef, I thought I’d try going right instead of my normal left. The seabed slopes gently downwards parallel to the road and much like any other Mavis Grind dive it starts with oodles and oodles of mud with the occasional large rock jutting out. Hermit crabs are common on the mud and sea squirts adorn the rocky outcrops.
The mud slopes steadily down when at approximately 8m a rocky reef looms out of the gloom on the left. Starting at a mere 30 cm high it slowly grows as it heads down into deeper water to a more impressive 4 -5 m wall. This vertical wall is dominated by the sea squirts with numerous indents and cracks home to a variety of life including sponges, dead mans fingers, crabs, shrimps, butterfish and scorpion fish. The most eye catching part of this dive is the sheer number of nudibranchs that can be found covering the wall and crawling over the sea squirts. Due to their abundance it’s not hard to find couples pairing off and then subsequently laying eggs. There are several different species to find including the lined polycera (Polycera quadrilineata), the lined Coryphella (Coryphella lineata), the orange club seaslug (Limacia clavigera) and the violet seaslug (Flabellina pedata).
The lined polycera (Polycera quadrilineata)
Eventually the wall snakes back towards the shore and starts to shrink before finally disappearing into the mud. There are a few things to look out for on the journey back to the shore. The green sea urchin (Psammechinus miliaris), with its beautiful pink and green spines is on the wall top and there are several species to spot in and on the sediment such as the tube anemone (Cerianthus lloydii), hermit crabs (Pagrus bernhardus) with a hydroid (Hydrocantha echinata) providing a fluffy covering and the hermit crab (Pagrus prideaux) with the pink and white spotted cloak sea anemone (Adasmia palliata). Often seen scuttling across the mud are harbour crabs (Liocarnus depurata) and occasionally edible crabs (Cancer pagrus). Rocks and small boulders litter the muddy slope which are always worth investigating as they are home to squirts such as the gas mantle sea squirt (Corella parallelogramma) and more sea slugs. In the shallows the kelp fronds harbour nudibranchs such as the solar powered seaslug (Elysia viridis) and small fish such as the two spot goby (Gobiusculus flavescens) and small lump suckers (Cyclopterus lumpus).
Hermit crabs (Pagrus bernhardus) with a hydroid (Hydrocantha echinata) providing a fluffy covering
Overall its a very enjoyable dive offering many photographic opportunities and can just about be dived in any weather conditions.
The solar powered seaslug (Elysia viridis)
The lined Coryphella (Coryphella lineata)