By Dr Deborah Robertson-Andersson.
If you woke up in Hout Bay on the 20th of November 2011 it would have been to the calls of seagulls yelling “mine, mine, mine”, thousands of seals barking in the bay and the excited calls of fishermen and general public scooping up buckets of sardines.
Later that afternoon people were crowding the beach catching thousands of Sardines using anything that came to hand. My own son ran down to the waters edge after school and caught 4 sardines with his bare hands. You could scoop them up with buckets, a sarong was very effective and of course there were the professional fishermen with their throw nets. I have lived in Hout Bay for over 25 years and can only remember one other morning like this one.
I knew that there was a large presence of sardines inshore as I had seen it earlier in the month while out at sea doing research. We came across a huge shoal of sardines that was being targeted by seals and dolphins. Ten minutes after watching the feeding frenzy I was awarded my first sighting of killer whales (Orcas) off the South African coastline.
The killer whales around our coastline are dolphin specialists and moments later the shoal parted and a dolphin, followed closely by a whale came flying out of the water. I had yet to see a killer whale in the wild and I was rewarded not only by seeing a small pod of five animals but a hunt as well.
The presence of the sardine shoal was first noticed by Koeberg at the beginning of November as they found large numbers of them in their harbour. We saw them frequently around Table Bay after the 15th of November, from then they were noticed in Blouberg, Hout Bay and Kommetjie, with a portion of the shoal being forced ashore by predators in Hout Bay from the 20th of November.
By the 4th of December they were still being kept in the Bay and were slowly being picked off by predators. It was quite comical to see birds that were so full they couldn’t take off and seals who barely moved a muscle when fish swam past their noses. It was great to see all the seals sunning themselves behind the shoal which was trapped between them and the beach.
In the mornings huge flocks of kelp gulls, terns and cormorants would wheel up into the sky before plummeting down in to the ocean. After gorging themselves, the birds would float overnight on the water in huge “rafts” behind the shoal thus preventing them from moving out of the bay.
On the 4th of December a portion of the shoal had become trapped in the harbour and high tide saw thousands of them swimming into the Sea Rescue base via the slipways. That meant that Sunday morning’s training included a portion of cleaning the base slipways to remove the fishy smell and scales.
Sardines (Sardinops sagax) together with Anchovy, Engraulis encrasicolus (until recently referred to as E. capensis), are the main open ocean fish resources around our coastline and constitute more than 80 % of the total national pelagic purse-seine catch.
The sardines off South Africa can also be found in the deep waters off Japan, Australia, and California in waters between 14 to 20 °C. Sardines are small silvery fishes that grow very quickly to reach a length of just over 23 centimetres, which they reach in about two years living on average for three years. They have a single dorsal fin located over the middle of the body, a forked tail fin and a keel of large spiny scales along the belly. Because of their small size, they group together when threatened as a natural defence mechanism.
When thousands of them group together, they form a shoal and act together as a collective, constantly swimming and rearranging themselves in dazzling patterns to disorient predators. Sardines are filter feeders, sieving plankton (both phytoplankton (plants) and zooplankton (animals) from the water as it passes between their gills. Pretty much every other creature in the sea dines on sardines, positioning them near the bottom of the food web.
An adult dusky shark was found with 621 sardines in its stomach, while a bronze whaler shark can swallow 20 sardines in a single gulp. Other predators include dolphins, penguins, cape fur seals, other sea birds and of course man.
South African sardines range from Southern Namibia near Lüderitz, to Richard’s Bay on South Africa’s northeast coast. Sardines in South Africa are under stress and the sardine population in the southern Benguela has undergone substantial fluctuations in size over the past 50 years. Sardines have been fished commercially in South Africa since the 1940s, and processing plants grew rapidly on the west coast, with most of the sardines in tomato sauce originating from the Cape.
The numbers caught and processed increased up to the early 1960s, peaking at around 400 000 t in 1962. But in 1968 the fishery collapsed as a consequence of overfishing, to around 40 000 t annually. The population then recovered steadily during the 1980s and 1990s, partly due to increased fishery control measures and better environmental conditions (increased upwelling in the Northern Benguela).
Since 2001, however, most of the sardine population has been situated on South Africa’s south coast, far from processing facilities. The fisheries and processing plants are now moving to the South coast and this is having disastrous consequences for the work force on the West coast. At the same time the numbers of sardines have continued declining. Four hypotheses explaining the change in the distribution and numbers of sardine have been proposed: (i) over fishing on the West coast; (ii) changes in the environmental conditions on the West coast (an increase in low oxygen waters) (iii) a decrease in successful spawning due to less favorable spawning areas on the South coast (iv) and disease (particularly Sardine herpes virus which was responsible for crashing the Australian sardine population).
One of theses relates to Evanne Rothwell’s question posted on the 03. Dec, 2011
“While cleaning sardines from the Hout Bay sardine run, I noticed that out of about 30 fish, only about 6 had roe in them. Does this mean that there were only about 6 females, or are the roe not developed in many of them?
Data from the last 25 yrs show that the sardine stock is currently under stress and that significant changes in size distribution and maturity have occurred. Sardine larger than 26 cm total length are virtually absent in the current stock. In the past, larger sardines (over 20 cm) were mainly females. Larger females spawn more and lay larger eggs which have a better chance of survival.
Sardines prior to 1968 became sexually mature for the first time between 20.8 – 21.4 cm total length. Before the 1968 collapse less than 3 % of the sardines were one year old fish. The mean fish length was 25.5 cm and sardine reached the age of up to 11 yrs. Between 1952 and 1967 most of the sardine stock comprised of fish that were between 1 and 2 years old and the mean fish length had decreased to about 21 cm. Sardine started spawning around 19.5 cm for males and around 21 cm for females. Now we see an onset of spawning around 14–17 cm.
As older females have more metabolic reserves and can invest more energy into reproduction the smaller female size has resulted in the reproductive output of the sardines decreasing by 25 %. Scientists have also worked out that for every cm that a female sardine increases the number of times she can spawn per year increases by 50– 70% with each 1-cm increase in length. So a large female sardine (26.2–27.3 cm) can produce at least five times more eggs than that of medium-small female (22.6–23.7 cm).
So to answer Evanne Rothwell’s question yes there probably were only 6 females in the sardines you caught as they were generally all small, and the smaller size means that they can’t produce as many eggs. The smaller size probably meant that many of them weren’t sexually mature which is also why the roe had not developed in many of them. In addition those sardines will probably spawn in more Southey locations which are generally unfavorable in terms of egg and juvenile survival. All of this coupled with increased pressure from predators (including man) and disease means that the chances of us seeing number of sardines anything like those prior to 1968 are very slim indeed.