So on my last day in S. Africa we had the privilege of meeting with marine biologist Alison Towner at Marine Dynamics who presented, Predator vs Predator, a presentation on the attacks of orca (killer) whales on great white sharks in the Gansbaai area (The peak season for seeing great whites is about March to September). This was a very unique and interesting presentation because this is a problem that has been seen in places such as the Farallon Islands but not in the False Bay area. This has really hurt & affected the great whites in the area and is something that researchers are now looking into. The researchers use the dorsal fins of sharks to identify them because they are like fingerprints - unique to each animal. Sharks, like many animals, release a death hormone when they are killed and this plays a big part in the disappearance of sharks after an attack.
Great whites became a protected species in S. Africa in 1991 and so when a great white washes ashore dead for any reason it has to be reported to the S. African government where they will come retrieve the animal, preform a necropsy, take samples from the shark, and do research on it to try and figure out a cause for the death.
Whereas, great white sharks are a common marine animal in bay, orcas are not common to the area.
Orcas are typically seen out at seen in the deep ocean but not in the bay area - between 2011 and 2016 only 5 sightings have been recorded by researchers (April 2011, Aug 2012) and it was the on the third & fourth sightings 2 male orcas with completely collapsed fins were seen. These sightings were on Oct 30 & 31 of 2015 when they were given the names of "Port" & "Starboard" and they did not enter the bay area. In 2016 6 orcas were seen alongside a pod of common dolphins. At none of these times did the orcas seem to be affecting the sharks in the area.
This year there has been a major shift in the activity of the orcas. Port & Starboard were first seen coming into the shallows of the bay on Feb 8 and were seen circling the shark cage boats. Then on Feb 9th the first deceased great white, a 2.7 meter juvenile female, washed ashore at Pearly Beach with no obvious marks after which they had 23 days of no shark sightings in Gansbaai by any cage diving vessels. The government was called and they took the great white for necropsy and research. This was only the 2nd time they had a period were they did not seen sharks and the 1st was in 2016 when there were issues with the water such as low temperature, red tide bloom, and low oxygen levels. Then on April 19th they two orcas were seen again circling a cage dive ship but as they left a boat was able to follow them. After this visit the area went 6 days without seen any shark activity around the cage diving vessels.
On May 1 they were seen again and on May 3 the 2nd deceased, a 4.9 meter female, white shark washed ashore at Franskraal Beach and because of her size they were able to keep the shark there for dissection after they called in Dr. Malcolm, the top researcher and shark necropsy doctor, to come in from Port Elizabeth to perform the dissection. This shark was a large shark and the dorsal fin was matched to a female known in the area as Khaleesi (last seen in the bay area in June 2016). The dissection was conducted on May 4th with wounds obvious of an orca attack. This female was 1.1 tons WITHOUT the liver so that is how they knew she was a big girl. Tissue samples were taken and sent to the government and also for genetic testing. The liver of a great white is the largest organ and very high in nutrients and is know the be what orcas eat from the great white along with the testis from the male great whites. Orcas kill humpback whales for their tongue because it's so high in nutrients as well.
On May 4th a deceased 3.6 meter male washed ashore at Franskraal Beach and because Dr. Malcolm was already on location the government allowed this animal to stay on location for it's necropsy. Since this shark's dorsal fin was so badly degraded they had to use the caudal fin pigmentation for identification. This shark was also missing its liver and several other organs. The dissection was performed on May 5th in which they found orca teeth indentations on both pectoral fins.
The 4th deceased shark, a 4.1 meter male, was discovered on May 7 at Struis Baai. The government was informed but because the research team was now "experienced" at doing necropsies (Dr. Malcolm had left) they were allowed to keep it and perform the necropsy there. All samples, including the fins being cut off, jaws taken out, vertabrae cleaned and counted, and the spiral valve which is also counted, were counted and sent to the government for research and testing.
Finally, a break! Great whites were beginning to be seen since April on May 13th and things seemed to finally be getting better. There was an increasing number of sharks being seen and coming back around.
During this time Port and Starboard are seen coming in and out of the bay. There was discussion among the researchers about tagging the orcas but tagging seems to hurt and affect the whales in such a negative manner that the researchers could not justify tagging them. Especially since these two orcas have completely collapsed dorsal fins, causing them to be initially thought as humpback whales. When asked what causes the dorsal fin collapse we were told it could be from a number of reasons such as ill health/stress. a genetic disposition, or even a physical issue. They know that captive orcas have fallen dorsel fins but these two have fully collapsed causing them to be easily identified.
With the 6th sighting of Port and Starboard in Gansbaai, the 5th deceased white shark is found on June 24th at De Gruis Beach. It is a 4.1 meter shark but was is the most degraded shark carcass they have seen. The dissection was conducted on June 24. Again the research group was able to perform the necropsy with permission from the government.
After the 5th great white was found the area was followed by 45 days of no great white sightings BUT other types of sharks and stingrays were seen. What the researchers are seeing though is that their research seems to be following that of patterns seen in the Farallon Islands. This is causing more research to be done and patterns to be examined between the sharks and their environment. Also trying to figure out the cause for orcas to come into the shallows and the bay area where great white typically live. The question becomes is it a competition for a food source like cape fur seals? Are they intentionally targeting the great whites? How will this affect the marine environment in the bay?
Great whites became a protected species in S. Africa in 1991 and so when a great white washes ashore dead for any reason it has to be reported to the S. African government where they will come retrieve the animal, preform a necropsy, take samples from the shark, and do research on it to try and figure out a cause for the death.
Whereas, great white sharks are a common marine animal in bay, orcas are not common to the area.
Orcas are typically seen out at seen in the deep ocean but not in the bay area - between 2011 and 2016 only 5 sightings have been recorded by researchers (April 2011, Aug 2012) and it was the on the third & fourth sightings 2 male orcas with completely collapsed fins were seen. These sightings were on Oct 30 & 31 of 2015 when they were given the names of "Port" & "Starboard" and they did not enter the bay area. In 2016 6 orcas were seen alongside a pod of common dolphins. At none of these times did the orcas seem to be affecting the sharks in the area.
This year there has been a major shift in the activity of the orcas. Port & Starboard were first seen coming into the shallows of the bay on Feb 8 and were seen circling the shark cage boats. Then on Feb 9th the first deceased great white, a 2.7 meter juvenile female, washed ashore at Pearly Beach with no obvious marks after which they had 23 days of no shark sightings in Gansbaai by any cage diving vessels. The government was called and they took the great white for necropsy and research. This was only the 2nd time they had a period were they did not seen sharks and the 1st was in 2016 when there were issues with the water such as low temperature, red tide bloom, and low oxygen levels. Then on April 19th they two orcas were seen again circling a cage dive ship but as they left a boat was able to follow them. After this visit the area went 6 days without seen any shark activity around the cage diving vessels.
On May 1 they were seen again and on May 3 the 2nd deceased, a 4.9 meter female, white shark washed ashore at Franskraal Beach and because of her size they were able to keep the shark there for dissection after they called in Dr. Malcolm, the top researcher and shark necropsy doctor, to come in from Port Elizabeth to perform the dissection. This shark was a large shark and the dorsal fin was matched to a female known in the area as Khaleesi (last seen in the bay area in June 2016). The dissection was conducted on May 4th with wounds obvious of an orca attack. This female was 1.1 tons WITHOUT the liver so that is how they knew she was a big girl. Tissue samples were taken and sent to the government and also for genetic testing. The liver of a great white is the largest organ and very high in nutrients and is know the be what orcas eat from the great white along with the testis from the male great whites. Orcas kill humpback whales for their tongue because it's so high in nutrients as well.
On May 4th a deceased 3.6 meter male washed ashore at Franskraal Beach and because Dr. Malcolm was already on location the government allowed this animal to stay on location for it's necropsy. Since this shark's dorsal fin was so badly degraded they had to use the caudal fin pigmentation for identification. This shark was also missing its liver and several other organs. The dissection was performed on May 5th in which they found orca teeth indentations on both pectoral fins.
The 4th deceased shark, a 4.1 meter male, was discovered on May 7 at Struis Baai. The government was informed but because the research team was now "experienced" at doing necropsies (Dr. Malcolm had left) they were allowed to keep it and perform the necropsy there. All samples, including the fins being cut off, jaws taken out, vertabrae cleaned and counted, and the spiral valve which is also counted, were counted and sent to the government for research and testing.
Finally, a break! Great whites were beginning to be seen since April on May 13th and things seemed to finally be getting better. There was an increasing number of sharks being seen and coming back around.
During this time Port and Starboard are seen coming in and out of the bay. There was discussion among the researchers about tagging the orcas but tagging seems to hurt and affect the whales in such a negative manner that the researchers could not justify tagging them. Especially since these two orcas have completely collapsed dorsal fins, causing them to be initially thought as humpback whales. When asked what causes the dorsal fin collapse we were told it could be from a number of reasons such as ill health/stress. a genetic disposition, or even a physical issue. They know that captive orcas have fallen dorsel fins but these two have fully collapsed causing them to be easily identified.
With the 6th sighting of Port and Starboard in Gansbaai, the 5th deceased white shark is found on June 24th at De Gruis Beach. It is a 4.1 meter shark but was is the most degraded shark carcass they have seen. The dissection was conducted on June 24. Again the research group was able to perform the necropsy with permission from the government.
After the 5th great white was found the area was followed by 45 days of no great white sightings BUT other types of sharks and stingrays were seen. What the researchers are seeing though is that their research seems to be following that of patterns seen in the Farallon Islands. This is causing more research to be done and patterns to be examined between the sharks and their environment. Also trying to figure out the cause for orcas to come into the shallows and the bay area where great white typically live. The question becomes is it a competition for a food source like cape fur seals? Are they intentionally targeting the great whites? How will this affect the marine environment in the bay?
Comments
Post a Comment