Winter’s Bounty: As ‘breach season’ rolls in…

As we move from the end of autumn towards the beginning of winter in South Africa, we are also drawing ever nearer to “breach season”.

Mossel Bay is a well-known white shark aggregation site on the Southern Cape coast and we are lucky to have these beauties present year-round. Although we see a spectrum of sizes, it is interesting to note that 80% of our white sharks are between 2 – 3m. This means that most of our white sharks are feeding predominantly on fish and smaller elasmobranchs. It is only around the 3m-mark that white sharks begin to target marine mammals, such as Cape fur seals.One of the sites that we sample in Mossel Bay is at a Cape fur seal island colony that is roughly 800m from the shore. Despite the small size of this seal colony (est. 5000 individuals) it still represents a valuable food source.

A white shark attacking a Cape fur seal in Mossel Bay, South Africa

Below is a graph representing the average number of white sharks sighted per unit effort (SPUE), in this case per hour, for each season.This graphical representation of the data highlights a distinct peak in abundance during the winter months.

 

Insight into the life-history of this seal species shows that the winter months coincide with the time seal pups leave the island to forage offshore for the first time. The lack of experience in predator-prey games make these seal pups an easy target for white sharks. Thus it’s easy to see why, during winter, the mean number of sharks seen per hour is 1.57 in comparison to the average of 1.3 sharks per hour across the four seasons.

Over the past few weeks white shark activity has increased drastically at the seal colony.Although we are still seeing the 2-3m sized white sharks, there appears to be a greater proportion of individuals that are over the 3m-mark utilising this area.

As we move into winter and the environmental conditions favor the ambush-strategies of white sharks stalking Cape fur seals, it is certainly a very exciting time to be out at sea!!

Rabi'a Ryklief

Shark Chronicles 040 - Retrospective

As a 3-monther, SAMPLA has not only become my home, it has become a way of life. Aside from the routine tasks and daily duties, more so than learning the skills required to run a boat or conduct scientific research, SAMPLA has helped me to realign my interests and reminded me why I decided to pursue marine biology in the first place.

At a previous intern's farewell braai, Ryan once said something to the tune of "the one thing I hope all of the interns can take away from this experience is to find what truly inspires them in life, whether that be sharks, oceans, or something completely different." Well Ryan, I think you all have succeeded more than you know in helping all of us further realize and experience our personal goals and aspirations. It has been an honour to work with everyone here at SAMPLA, the directors, the office staff, and of course the other interns who have all encouraged me to pursue this crazy dream I have of saving the world, no matter how daunting or impossible it may seem.

It has been such a welcome change to be surrounded by people equally as passionate and crazy about the ocean and conservation as I am, comforting to know that there are people who care enough to make a difference. As a self-proclaimed science dork, its always fun to find others who get as excited about things most people would cringe at. Who else would root for the adorable, innocent baby seal to be ripped apart by a shark if not a SAMPLA intern? Who else could rework the lyrics to classics by the likes of Bob Marley and the Police to sing about chumming if not a SAMPLA intern? Who else can say they wrestled a Great White shark and lived to tell the tale if not a SAMPLA intern? At the risk of sounding overly sentimental, I can honestly say this is one of those experiences that will stay with me forever.

In short, I hope to express my sincere appreciation and say thank you for making this experience to everyone I have met over the course of my 3 months here. As amazing as it is to see Great White sharks on a daily basis, SAMPLA truly is a product of its members. I look forward to working with you all in the future! And watch out for me on National Geographic/Discovery Channel, I have big aspirations…

Simone Lewis-Koskinen (SAMPLA intern)

Shark Chronicles 039 - The ocean, the other SAMPLA director

SAMPLA crew were still feeling the flip side of exciting research this week. The murky waters left by the previous week’s storm prevented any visibility. Onshore winds persisted the entire week, preventing any sediment to settle. As dirty river runoff continued, it became evident after several days of unsuccessful chumming, that the sharks do not enjoy brown seas. Only a few sharks were sighted throughout the week however with poor visibility on their side, most of us on the bait rope experienced the humbling feeling of often losing the bait.

Finally by Friday, the sea began to clear. The winds had died down and the swell eased. This enabled us to complete a seal survey in beautiful conditions from Friday to Saturday morning. It became clear that the seals were preparing for the mating and pupping season as very few were travelling to and from the island. With this comes the uneasy feeling that the non-resident sharks of Mossel Bay may soon move on, searching for other food sources.

Even with so little movement of seal, we were called for a not moving stranded seal close to the Mossel Bay point. We ran there thinking we were going to face a baby seal. With surprise we found an adult Cape fur seal, most likely weakened by the rough sea. After checking that no serious wound was there, it was great to see the seal clamber back into the ocean and duck beneath the waves.

The major realisation this week was that the fun, exciting research that occurs most days in Mossel Bay is not governed by the directors, the interns or the institute of SAMPLA; it is ultimately the ocean itself. Luckily the unique geographic and climatic characteristics of Mossel Bay provide beautiful conditions the majority of the time.

Riley Elliot - SAMPLA intern

Shark Chronicles 030 - A for Effort

The theme for SAMPLA’s progress this week is A for effort. Attempts to track the recently tagged shark Xena (formerly known as Bitey) as well as attempts to conduct 24-hr seal surveys were thwarted by bad weather and sick interns. Nevertheless, the birthday celebrations for SAMPLA director, Stef, could not be hindered by rough seas nor invading bacterium!

As our often quoted birthday-man-director, Stef, likes to say, “Tomorrow is a brand new day,” and with a brand new day came a brand new name for the shark of the hour, Bitey. The general rule of thumb in shark naming is that the crew on the boat who tags the shark gets to name it. Stef, Christine, Vicky and Nico were the lucky crew to have this honor but what they lacked in decisiveness they made up for in many, many potential names for the newly tagged 3.5m female shark, hence the name change to one more fitting. Bitey was therefore renamed Xena (after the warrior princess) to better reflect her characteristic battle scars, the large wound on her left side and her unique parasites, which are hair like in nature.

Tracking the rambunctious Xena proved tricky not only because of her way-ward swimming habits but also because of the weather. So just like last week, the SAMPLA crew had to abandon tracking efforts. Weather not only hindered white shark studies but two different attempts to conduct 24 hr seal surveys as well. Though the diurnal observations were completed, by the time the nocturnal portion of the surveys were underway the sea conditions once again cut SAMPLA’s work short.

This isn’t to say however, that a little rain and a brisk wind keeps the SAMPLA team from completed its task. On the contrary, the crew can complete work in these conditions with their eyes closed! Assuming one eye is slightly open to properly record observations. What truly made the week a challenge was that half the interns came down with a flurry of illnesses which took most of them out of the running for tracking and seal surveys.

In the midst of all this came the fateful date of Tuesday, September 16. The birth of SAMPLA director Stef. There is no intestinal bacterial infection or gale wind strong enough to keep the celebrations subdued. During the 2am crew switch for the only 24hr seal survey (conducted earlier in the week) that was fully completed, Stef’s birthday became official and so did the chocolate cake brought in for him.

The week has ended with slow intern-recoveries and a sunny weekend. Tomorrow is not only “a brand new day”, it’s a brand new week that brings the same tenacious work effort but new chances to track Xena as well as opportunities to fully complete a 24 hr seal survey.

Vicky and Nico (SAMPLA interns)

Shark Chronicles 029 - Seal in a box

On Sunday September 14, 2008, a stranded seal thought to have come from the Southern Antarctic islands washed up in Mossel Bay. The seal was a first year seal, and was not in the best condition after its long journey thousands of miles from home. The seal was reported to director Stefan Swanson, who has extensive knowledge of marine mammals and seal populations. The seal was then picked up and put in a box to be taken to the SAMPLA household until it could be cared for.

A few hours later, SAMPLA interns Christine, Tricia, Alessandro, and director Stefan brought a certain large box which began to make small growling noises. The seal in a box was brought down to the dockside, where Stefan gave the students a lesson in seal anatomy. Christine, Tricia, and Alessandro learned how the gender of seals is determined, as well as the aspects of seal’s anatomy that identified it as a distant visitor, such as the enlarged eyes and white fur on the chest. In addition, the size of the canine teeth identified it as a young-of-the-year seal. After this lesson, Stef returned the under-nourished seal to the harbor, where it could forage in relative safety and hopefully regain its strength before its long swim back home.

Shark Chronicles 017 - Seal scat collection

The first time you cruise around Seal Island and get a good smell of the 4,500 seals your nose wrinkles but eventually you get used to the smell.

Just recently SAMPLA scientist Stephen Swanson and two students (Antonin and Sophie), together with the help of the Mossel Bay Police went to the island in order to collect scat samples for Marine and Coastal Management. Marine and Coastal Management uses the scat samples to determine the health as well as the diet of the resident seals. Determining the health of the seals is important because in such a dense population of animals disease and parasites could spread quickly.

Stepping on the island there was a small, smelly stampede: thousands of seals fled to the water for refuge from these intruders. Others crowed around the far side of the island while a few individuals stood their ground and challenged the SAMPLA team for the right to stay on the island.

The team tried to keep their distance from the animals because such a large animal could do some real damage to a small person if it felt threatened.

While walking around the island looking for suitable scat samples the team kept their eyes open for wounds that were caused by sharks or people. One bull had a noticeable wound in its back flippers caused by a shark, and one female had a line around her neck.

However, other than that the seals seemed to be in good shape from what the team could see. Now we wait for the analyses from the MCM lab.