Exploring the last frontiers: Reef pinnacles on the Agulhas Bank

Bathymetric map of part of the studied area on the Agulhas Bank showing Martha’s Reef, 12-Mile and Alphard Bank. So far, very little bathymetric information is available on the two additional research sites, 45- and 72-Mile Bank (therefore not shown here). The Ellen Khuzwayo is a R100-million purpose-built 43-metre research ship. The “Ellen” can work up to 200 nautical miles offshore with a steaming range of 2 500 nautical miles and can remain at sea for up to 20 days. She accommodates eight scientists and a crew of 13.

The Agulhas Bank represents the centre of the South African fishing grounds.

The bulk of reef-associated species, many of which are severely overexploited, are caught here.

To date, research activity has focused on the inshore rocky reefs and the trawl grounds on the bank. Rocky reefs further offshore have long become uneconomical to exploit and information on these un-trawlable areas is therefore scarce and anecdotal.

These reefs consist of relatively shallow (20 – 70 metres) rocky banks and pinnacles between 20 and 150 km offshore, whose remoteness qualifies them to serve as potential spawning grounds and as a natural refuge for many fish and invertebrate species that are elsewhere on the verge of extinction.

A 15-day cruise on the research ship Ellen Khuzwayo presented the first opportunity to sample these offshore banks systematically. Headed by Dr Sven Kerwath and Chris Wilke from the linefish section of Marine and Coastal Management, the host organisation of the SAEON Egagasini Node, a multidisciplinary group of eight scientists were tasked to develop and test methods suitable for monitoring fish and invertebrates. Amongst these methods, diving surveys (where possible), linefishing, fishtraps and longlines proved to be particularly useful and new insights on distribution and biology of important marine resources were gained.

The team of technicians and scientists originating from many different institutions worked together to make the cruise a success. Dr Albrecht Götz from the SAEON Elwandle Node played a vital role in the team by developing a relational database to capture all the data from the different sampling activities. The data gathered during this voyage is currently being written up into a manuscript for a short communication, which will be submitted to the African Journal of Marine Science.

Building on the foundation laid during this voyage, the researchers hope to continue this work during their next cruise in the 2008/9 summer season, when additional attention will be turned to further developing suitable invertebrate sampling methods for an ecosystem approach in fisheries management.

The Ellen’s engine room hosts two main diesel engines, three diesel generators and a thermal desalination plant for freshwater extraction at sea.	Crew and scientists participate in one of the regular safety drills at sea.	The Ellen’s bridge is equipped with state of the art cruise and operational controls enabling scientists and crew to synchronise their activities at all times.
Research dives were carried out from two small rubber-ducks deployable from the Ellen.	Subantarctic skuas (above), Great shearwaters, Whitechinned petrels, Shy albatrosses and Yellow-nosed albatrosses were common visitors squabbling over offal.	A close-up of the diverse invertebrate reef cover supporting a rich fish community at around 36 metres on Twelve-Mile Bank.
An underwater scene from the Alphard Banks. In warm and clear water more than 60km offshore, some pinnacles on the bank rise to depths of around 25 metres.	The sharks were dissected at sea immediately after capture.	Soupfin sharks give birth to up to 50 live pups every three years.
Standardized linefishing methods were used to target demersal reef fish at depths beyond SCUBA diving capabilities.	The demersal longlines set over offshore reefs mainly yielded medium-sized shark species such as soupfin and smooth-hound.	Some of the reef fish attracted by the longlines were subsequently attacked by sharks.
A fishtrap is recovered by the crew.	Fishtraps are very effective when targeting a broad spectrum of demersal reef fish including catsharks.	Crew and scientists enjoy a fish and boerewors braai with (non-alcoholic) beer after a long day at work.