– Rea Borcherds

Diamonds or rock lobsters? – A presentation by Allan Heydorn: Saturday 20 May 2017

Dr Allan Heydorn held his audience captive on Saturday evening 20 May when he recounted his role in a historic expedition in 1964 to a near mythical undersea mountain to search for diamonds.

Vema Seamount is an isolated flat-topped undersea mountain rising up from the deep Atlantic Ocean Basin to approximately 26 – 30m below the surface. It was discovered in 1959 by the American research vessel ‘Vema’ and lies approximately 550 nautical miles west of Lambert’s Bay. Ever since its discovery, oceanographers and marine biologists dreamt of exploring this unique undersea territory. Amongst others there was a vision of treasure in the form of diamonds as theoretical westward extensions of the Olifants- and Orange River diamondiferous rock formations on the South African mainland cross at the position of Vema. This prompted diamond magnate Sam Collins to fund an expedition to explore the seamount in 1964. For the purpose, he made available a diamond prospecting vessel, the ‘Emerson K’, to carry a team of oceanographers and geologists to carry out a survey of the peak.

As a fisheries scientist (and diver, trained by the SA Navy), Allan Heydorn was invited to participate. He accepted enthusiastically but took a bet (for a case of beer) with his geological colleagues that no diamonds would be found, but rather rock lobsters. He hypothesised that as a result of the ocean current configuration of the South Atlantic Ocean, phyllosoma rock larvae from the mid-Atlantic Ridge islands, Gough and Tristan da Cunha, could be carried to the seamount. Therefore, if rock lobsters were to be found on the seamount, the species would be Jasus tristani, and not Jasus lalandii, which occurs in the waters of the South African West Coast.

The first divers to descend from the ’Emerson K’ into the unbelievably clear, cobalt blue waters were geologists, intent on checking for the presence of diamonds. Over and above they collected large quantities of sediment by means of the ship’s massive air-lift. These contained a number of large beach-rounded pebbles which indicated that Vema Seamount must have been an island during the glacial period some 70 000 years ago, when surf pounded its shores. The air-lift also brought up many biological specimens. These were carefully sorted and annotated on the ship and later described by UCT scientist Colin Berrisford, who is well-known in Betty’s Bay. Colin published a comprehensive scientific article on the biology and zoogeography of the summit. He was present to hear Allan’s talk.

However, of diamonds there was no sign on Vema Seamount.

When Allan’s turn came to dive, he discovered a huge and thriving population of rock lobsters as he had expected. To his joy, they belonged to the species Jasus tristani. This supported his hypothesis about transport of larvae from the mid-Atlantic Ridge region to Vema by ocean currents.  He had won his case of beer!


The discovery of this virgin population of rock lobsters triggered a massive fishing effort on the seamount by a flotilla of fishing boats, mainly from South Africa. The limited population was over-exploited to the extent that within three years it was depleted. During those three years Allan analysed the commercial catches from Vema which were brought back to Cape Town processing factories. He recorded drastic changes in both the sex and size composition of the catches, which explains why fishing on the seamount became unprofitable. In his view, repopulation of this rock lobster stock will take many years because settlement of larvae carried by ocean currents from the mid-Atlantic Ridge is a slow and random process.

This is where our local area of the Kogelberg comes into Allan’s story. He pointed out how a similar process of gross over-exploitation of both rock lobster and perlemoen stocks is currently taking place right here, in the waters of the Kogelberg Biosphere Reserve, which are supposed to be protected as a proclaimed MPA (Marine Protected Area). Protective legislation is not being implemented properly and sexually immature perlemoen and rock lobsters are being caught resulting in progressive declines in the local stocks of both perlemoen and rock lobsters. Worse, this is leading to serious changes in the ecology of the inshore waters inter alia, because the grazing of kelp by perlemoen has been drastically reduced.

Allan explained that if this situation continues, eventual stock extinction can well occur with serious consequences for the delicate overall ecology of our nearshore marine environment.  He concluded his talk with a plea for a governmentally driven strategy that will provide sustainability. He handed over to Richard Starke, to present proposals drawn up by the Kogelberg Biosphere Reserve Company, in an attempt to curb over-exploitation in our local waters.

Richard described a somewhat radical, but in his opinion feasible, scheme by which local communities could benefit, rather than illegal poaching syndicates and factories concerned only with generating profits through exports. The proposal includes proclamation of a limited ‘no-take’ zone in which all marine species can procreate without any human intervention. Fishing should be limited to locals only, and to nine months of the year, and the total national annual catch (TAC) should be lowered from 2000 to 1000 tons. Richard pointed out that in comparison to commercial catches and poaching, recreational fishermen do not have a significant impact on local stocks. A key aim would be to ensure that catches from the KBR region are marketed locally and not exported. This would benefit local industries, and promote tourism to the area. A radical scheme, indeed, but one with many positive and attractive aspects.

The interesting evening was rounded off by the presentation to Allan and his wife, Helene, of a well-deserved certificate of appreciation. It read:

The Botanical Society of SA wishes to express sincere appreciation to Helene and Allan Heydorn – legendary champions of the natural world. We thank you!”, signed by the Executive BotSoc Director, Zaitoon Rabaney.

As a postscript to the lovely evening, in a warm email to Merrilee, Allan pays tribute to his wife, Helene, who to this day still edits scientific papers for the CSIR:

“Then came the wonderful surprise of the BotSoc Certificate of Appreciation to Helene and me – thank you so much! I am particularly glad that Helene’s name is first on that certificate. There is not a report which I produce which she does not edit for me – more often than not with suggestions for improvements to the contents – and that has happened for close on 60 years. And she needs to delve deeply into her resources of patience when I spend hours in front of the computer, usually forgetting all about meal times etc. So she deserves this recognition and that certificate means a great deal to both of us.”