Along the South African coastline, there has been an enormous increase in mussel biomass and cover along the west coast and dramatic decrease along the east coast. The reasons for these changes are associated with the arrival and proliferation of the invasive mediterranean mussel (Mytilus galloprovincialis)flourishing on the west coast, whereas human exploitation of the brown mussel (Perna perna) is the cause for the decrease on the east coast. This has led to major changes in the community structure of our rocky shores. My study is set to investigate whether or not Mytilus galloprovincialis has a significant impact on species composition, diversity and richness of rocky shore species.

Mytilus galloprovincialis, probably introduced in the late 1970’s, is already the dominant mussel throughout the Cape west coast of South Africa. This is mainly due to its rapid rate of growth and a high fecundity, as well as an enhanced tolerance to desiccation (Van Erkom Schurink & Griffiths, 1990). Its presence has resulted in an overall increase of standing stock and vertical extent of mussel beds. Before the arrival of Mytilus, the mid to low intertidal zone of the Cape west coast was largely occupied by the slow-growing indigenous mussel Aulacomyaater and by limpets, particularly Patellagranularis (Griffiths et al., 1992). Only in the lower littoral can Mytilus be out-competed by the indigenousChoromytilus meridionalis, as it has a very low silt-tolerance.

 

The brown mussel Perna perna is abundant along the southern Africa coastline, from the Cape Peninsula to Mozambique. Extensive exploitation of this resource takes place on the Transkei coasts and Kwazulu Natal, where mussels form a significant proportion of the annual protein intake of the indigenous coastal population (Lasaik & Dye, 1989). This exploitation has rapidly increased in recent years due to human population pressure (Hockey& Bosman, 1986). Due to this extensive exploitation, the cover and biomass of Perna perna on the east coast has decreased accordingly. The implications of mussel (biomass and cover) increase and decrease on rocky shore communities needs to be established. This is a unique situation in which the west coast of South Africa is experiencing a major increase in mussel biomass whereas the east coast has drastically been stripped of its mussel cover.

My study includes sampling locations such as Swakopmund (Namibia), Groen Rivier (West coast), Cape Peninsula, Gansbaai (South coast), Port Elizabeth, Port St. Johns (Transkei), Salt Rock (KZN) and Cape Vidal (KZN). At these locations transects ranging from the low to high shore are set up, in which quadrats of mussel bed are collected. From these we

Wendy Hammond, Zoology Department, UCT

E-mail: whammond@botzoo.uct.ac.za

"TO THE USA – AND BEYOND"

Our visit was funded under a United States Government grant associated with the Exchange Support Fund of the Binational Commission between the Republic of South Africa and the United States of America to give students an opportunity to be exposed to fisheries science elsewhere than South Africa.

OBJECTIVES OF THE TRIP

We started our travels with a visit to sunny Miami and the South East Fisheries Science Centre. The South East Fisheries Science Centre is one of the four branches of the National Marine Fisheries Service (NMFS) / NOAA (National Oceanic and Atmospheric Administration) situated in Miami made up of about 100 staff members, including researchers and economists. This centre conducts multidisciplinary research and provides scientific information for fishery conservation, fishery development and utilisation, habitat conservation, and protection of marine mammals and endangered species. NMFS is the agency that enforces laws and plays an active role in managing fish and marine mammals that migrate between the United States and other countries. It also measures the social and economic effects of fishing practices and fishery regulations. We had an opportunity to make contacts and give short seminars on our research projects to PhD students and researchers at University of Miami Rosenstril School of Marine and Atmospheric Studies.

Next stop Lake Arrowhead for the CALCOFI conference. The annual California Co-operative Oceanic Fisheries Investigation was established about 50 years ago to monitor the status of the California Current System. About 73 people attended, including scientists, researchers, and students. It was snowing unlike Miami. The conference was divided into three parts:

status of the fishery, including fishery landings and population biomass estimate

the symposium about ecosystem-based management, looking at effects of climate change on fish habitat and ecology

poster session on Thursday evening

From here we headed off to San Diego and the South West Fisheries Science Centre. This is the second branch of National Marine Fisheries Service and is responsible for developing techniques and carrying research on California fisheries and providing Pacific Fishery Management Council with that information. PFMC is made up of a balanced number of members including scientists, fishermen and the public. It is this council that in responsible for making fishery management decisions. It was a great pleasure to meet Dr. Paul Smith who invented a CalVET net that I used to collect fish egg samples. He is currently a fisheries biologist and a member of NOAA.

 

The next item on the itinerary was the Scripps Institution of Oceanography. It is both a research institute and a department offering courses in physical, chemical, geological and biological oceanography as part of the University of California. It is situated nicely close to the beach. Saturday the 4^th of November we went to a cruise on the Pacific Ocean with first year graduate biological oceanography students of Dave Checkley and Lisa Levin from the Scripps Institution of Oceanography. The purpose of the trip was to provide students the opportunity to experience a day at sea working on the SIO research vessel New Horizon and to observe and participate in sampling relevant to biological oceanography.

Here we learnt that there are two important fishery sectors in the US, recreational and commercial. The commercial fishery is not as important as in South Africa, especially since the collapse of sardine fishery in early 50s; agriculture took over and is still dominating in terms of the economy. Squid is the most important resource in terms of landings and generating revenue of the California region. Most of it is exported to China and some is sold as fresh fish in markets or frozen for bait. This fishery is new and its management is based on monitoring the number of eggs and landings. In Miami, the shrimp fishery is the biggest in terms of landings and revenue.

 

Sadly our trip came to an end at this point and we left the US for South Africa to relate our adventure, which could not have been possible without financial assistance from the U.S Binational Commission Exchange Programme and NRF. We would like to also thank Coleen Moloney, Carl van der Lingen and also Dr. Brad Brown and Prof. Dave Checkley, our hosts who took us around most interesting parts of the U.S. We really enjoyed ourselves; everyone was very kind and caring and made us feel at home.

Nandipha M. Twatwa (Ntwatwa@sfri.wcape.gov.za)

and Terence Jayiya (Tjayiya@sfri.wcape.gov.za)

Zoology Department, UCT

"Catsharks and Californians"

I moved to Cape Town, South Africa in February 2000 from Westlake Village, California. I studied at the University of Arizona for five years, where I attained my BS in Biology (and two minors, one split minor in chemistry, physics and math and the other in French). I have always known that I wanted to study marine biology, but it wasn’t until I was fortunate enough to experience a dive with four mantas (Manta birostris) in the Gulf of California, Mexico, that I decided that I wanted to study elasmobranches.

So, here I am in beautiful South Africa studying catsharks at the University of Cape Town. I am currently in my second year of the Master’s program and my research involves the age, growth and consumption rates of four species of catshark. This includes the pajama shark (Poroderma africanum), leopard catshark (Poroderma pantherinum), puffadder shyshark (Haploblepharus edwardsii) and dark shyshark (Haploplepharus pictus). All are endemic to southern Africa and generally occur in the intertidal zone (P. africanum and P. pantherinum have been found down to 100m and 256m, respectively), which is where I collect and study these sharks.

 

On a typical collection day, a group of divers and I will SCUBA or snorkel at a selected study site, armed with bait bags filled with pilchards and ‘shark nets’ that I’ve made from shade cloth and nylon rope. The first step is to tie a bait bag to some kelp, mush it up a bit to release the juices, and wait. Usually within five minutes, the sharks are attracted by the scent and are in easy reach of capture (not to worry, the largest of the four species reaches about 1m). Using one hand to open the bag and the other to handle the shark (this can prove difficult with the larger specimens as they are muscular and quite strong!), the sharks are placed securely in the sack. On a good day, we can capture up to 30 sharks! After the dive, they are taken back to the university in an aerated tank and then released into a large tank in the department’s small aquarium.

 

Here is where the research begins. My main goals are to age and to conduct consumption rate experiments with these sharks. Although these sharks are common to South African shores, there is still much to be learned about them. The age and growth portion of my experiment involves extracting vertebrae from each species. After processing them (cleaning, cutting and mounting on slides), the vertebrae are placed under a microscope where growth bands radiating from the centra can be seen (much like the rings in trees). Two types of bands are apparent: hyaline and opaque (dark and light). Each band pair is believed to represent one year of growth. Because the sharks are small, their vertebrae are also small and it is often difficult to ‘read’ the bands under the microscope. Therefore, the question of whether or not the pair of bands represents one year has yet to be answered.

 

Before I use these sharks for the age portion of the experiment, I analyze how quickly they digest certain prey items in a consumption rate experiment. Previous research only gave prey items information, therefore from this data, I chose three types of prey that I could feed the four shark species: blood worms (Arenicola loveni), klipfish (Clinus superciliosus) and crabs (Plegusia chabrus and Carcinus maenas). The sharks readily eat the worms and fish, but are reluctant with the crabs. I am still on the search for a hard-shelled animal the sharks will eat! I feed the sharks a piece of food that roughly equals one percent of their body weight, after an allocated time period, the sharks are finally dissected. The remaining food (if any) is weighed to see how much has been digested.

 

Both the age and growth and consumption rate analyses are important components in understanding more about catsharks. Combined with extensive diet and population studies, the impact these predators have on their environment can be determined.

Alison Dainty, Zoology Department, UCT