Saturday, May 29, 2010

Shark Chronicles 068 - Seal surveys and late-night predations


Not every moment spent at the Oceans research station in Mossel Bay can be devoted purely to the chumming and tracking of great white sharks. In order to fully understand the hunting and feeding behavior of these sharks, it is necessary to spend some time looking at the driving factor behind their actions; the seals (actually sea lions) of Seal Island. Seal surveys are completed anywhere from once a month to once a week, and consist of one, 24-hr long survey period. The end result of one survey will be a complete day’s worth of seal activity, from when they leave the island to feed, to when the stragglers, sluggish with digesting fish, return back to their island home. Over the years, the observations from these seal surveys have shown the researchers at Oceans that the seals are transitioning from very active periods during daylight hours, to almost solely nighttime activity. As a direct result from this shift in activity, the great whites of Mossel Bay have been found to also shift their hunting hours to a more nocturnal schedule. What this means for us dedicated seal surveyors, is the possibility to spot a nighttime act of predation from the great white. I know I speak for more than just myself when I say that this rare opportunity is what drives us to stay awake and vigilant at 3am in the morning, while wearing five layers of clothing and four pairs of socks (and day-dreaming of our much warmer beds on land).

We just completed our most recent seal survey during the hours of Wednesday night and Thursday day. Much like our survey last week (and surveys before, I’ve been told), the seals did not stray from the island during daytime hours but were incredibly active once darkness fell upon the bay. I was fortunate enough to be placed on the nighttime survey period of 1am – 7am, and much like last week, seals were actively leaving and returning to the island throughout the night. Most seals traveled in large groups comprising of 5 or more seals (in order to reduce the odds of being a shark’s dinner), but every now and then a daring seal would take off into the night all by itself. Although I personally find these seals to be amazingly cute, I found myself attentively staring at these individuals, praying for a white shark to breach out of the water and claim it’s dinner. Finally, at 3:36am, a group of 2-3 seals were in the midst of passing by the boat when a great white suddenly breached out of the water and sent the seals flying. The shark was relatively small (~ 2m), and the breach looked somewhat unsuccessful, but I still woke up the entire boat by yelling “BREACH” over and over again until everyone was watching the action. It was the first time that I had witnessed a great white breach, and reliving that moment over and over again in my head was what sustained me for the following four hours of surveying, that and the occasional lone seal setting out to be a possible white shark feast.

Lindsay L. Graff – Mossel Bay, Oceans Research Intern

1 comment:

Andrew said...

I lived and surfed in Mossel Bay for a period during the early 80's and there where very few Great White Sharks in the area then, most had been killed off. It's great to see them making a comeback . Here is a local site devoted to just sharks:
http://www.sharks.org.za