Open Letter. The Great White Shark Mystery – I think Not!

By admin on Sep 16 in Local news, SAPFIA news.

Available at: https://www.fishingindustrynewssa.com/2020/09/11/letter-the-great-white-shark-mystery-i-think-not/  . [Accessed 14th September 2020].

“We caught the Orcas predating on the broadnose sevengill shark, also an apex predator… Later, they were found to have predated on Great Whites in Gansbaai.” So says a marine biologist, aquarist and commercial diver from the Two Oceans Aquarium in Cape Town. Great Whites raise a lot of interest but there is nothing mysterious about them according to the following letter written by a professional commercial and game fisherman.

Dear Editor,

My interest was tweeked by your recent article on Great Whites and together with the somewhat unbelievable rumours doing the rounds, I decided to investigate a bit further. It helped that I number amongst my close friends from the past, Brian, who virtually developed shark cage diving to what it has become today, and several involved scientists.

First, are Great White sharks a mystery?’ We know so little about Great Whites but that does not make them mysterious. It merely indicates our lack of knowledge about them!

Great Whites line up with other problems that are far more serious such as Covid 19, global warming, and an over-populated planet. We don’t have enough knowledge about how to deal with any one of these issues.

Ultimate Apex predator

Great Whites are the probable ultimate Apex predator in the biodiversity of the South African inshore fishing environment.

With that term comes my first long standing problem. If it is an Apex predator, what predates it? Why, over the past three years, has their sudden disappearance from areas like False Bay and Diaz Island almost become the norm?

False Bay has always been a known congregation area for Great Whites since I first started fishing there as a child. We always believed it was the seals on Seal Island that were high on their menu of choice, but today we know this is not the case. Like most predators, including humankind, convenience plays a large part in deciding what we eat.

Diaz Island

Some 20 years ago, Diaz Island became one of the finest venues for shark cage diving in the world. Then three years ago it suddenly changed when all the sharks – 90% or more Great Whites – took off to who knew where.

Slowly they returned, but then did the same disappearing trick six months later This time, in a panic, the operators hit on the idea of attracting another species, the Bronze Whalers (Bronzies).

The Bronzies were often seen to have a go at the large chunks of fish used to attract the Great Whites to the cages containing the underwater spectators, before giving way to them with wise alacrity. With no competition any longer, the operators then used to initially attract over 50 at a time.

Then came the commercial shark longline boats and ski-boats to once again spoil the fun. More importantly, to destroy a niche industry that attracted extremely well-off overseas tourists.

The overriding question still remained! Why were the Great Whites leaving and to where?

Killer whales (Orcas)

About 18 months ago, a strange story started doing the rounds. My first reaction was to respond, “Not killer whales (Orcas).” After more than 60 years at sea, I can assure you that Great Whites probably do not appear on their menus, except in the very extreme exception.”

Although capable of prodigious migration for whatever unknown reason, they are an inshore species with a probable chosen diet of fresh (live) fish. Ask any line fisherman, diver and spear fisherman. Seals may come next, where they are readily available, though in many of the places where they are encountered, the seals are not there.

Orcas are normally deep-sea inhabitants. There is absolutely no proof whatsoever that they have decided to change that habitat.

Eye In The Sky. Interacting With The Wild

The game fisherman experience

Game fishermen have always occasionally encountered them, as I have, prodigious distances off Cape Point on the tunny grounds. Usually they are in the company of porpoises, seals and mainly yellowfin tuna, who all frequently hunt bait fish together.

The Orcas, it appears, love both fresh tuna and porpoise (dolphin) meat!

That they left False Bay because they were being harassed and eaten – at least in part, by “Port” and “Starboard”,** believe it or not being a pair of killer whales; (i.e. by Orcas) – is an unlikely story.

I fished False Bay, both semi-commercially and on a recreational basis from 1954 until the 1980s. In all that time I only encountered Orcas just inside the mouth twice!

Down Memory Lane…Tuna Giants put Fish Hoek Bay on the Map

Intelligent sea mammal

Orcas, found in all the oceans of the world, have a reputation of being one of the most intelligent of all sea mammals. That is why they are targeted by marine and sea parks for training and display.

They are family-oriented, so are normally found in small or medium size pods of as little as two up to 50 individuals. They appear to decide on a chosen diet, frequently hunting as far as possible for whatever species of sea life that represents.

There are many strange stories of their chosen feeding habits, such as tipping up or down ice floes to dislodge back into the water whatever is on top of them. Another is their oft encountered action of jumping onto sandbanks to either grab a seal or chase it back into the water.

So, whilst being accepted as normally occupying near offshore coastal waters, a couple’s willingness to enter inshore shallow bays or waters is not so surprising.

During my line fishing days, Great Whites regularly fluctuated in numbers. Some years they hardly bothered us by stealing our fish off our lines. At other times they almost seemed to shoal, and you had to up anchor and move well away or no hooked fish would reach the boat!

Nor would it have been pollution, which is still only a minor problem sometimes inshore. Neither would it be one of my pet theories that is badly under rated by the scientists – human disturbance.

Research not conclusive

I repeat I do not know of any logical reason. If the study in False Bay from 2000 to date resulted in no firm indication, let alone finding, I think we should all accept that research on them is still in its infancy.

Please also discount trophy targeting and inshore protective nets. Both have been on a continuous decline for the past 30 years, the latter intentionally. As for the former, it has always been a totally insignificant activity to have had any meaningful affect on their population level.

I may not be up to date on landing levels of Great Whites by shark longliners (only two or three have been active since licences were granted some years back) or any other longliner. Surprise, surprise, there also does not seem to be reliable stats from the Department of Environment, Forestry and Fisheries. This is partly due to Fisheries reporting less than one hooked Great White per set.

I also dispute there is an annual aggregation of Great Whites off the south-east coastline at this time of the year.

There are no more fish or seals there than anywhere else from Cape Town to Port Elizabeth. It is more likely that our extraordinary mild winter weather, and the relaxation of “lockdown” regulations, have resulted in far more people and surfers in the water.

Great Whites have always been inquisitive. Ask the divers – again.

Shark Study. Genetic Research Sheds Light on Managing Local Species

Great Whites Heading for Extinction

Sardine run

Port Elizabeth to Durban is a different story. The sardine run, when the inshore water cools down, is a spawning migration of one of the most important parts of the maritime inshore food chain. Everyone joins in, including the sharks.

Bumper Sardine Run a Feast for All to Enjoy

Their tendency to move north-eastwards is unsurprising anyhow, let alone the now almost inarguable fact of “Port” and “Starboard’s” chosen diet as they clearly patrol the coast seeking their prey.

It has also been surmised that in the absence of Great Whites a substitution of species has occurred with the Bronze Whaler (Carcharhinus brachyurus), and Cow (Seven Gill—Notorynchus cepedianus) sharks taking their place as the next two Apex predators behind the Great White.

Predation substitution is a common marine environment occurrence. However, I find it personally difficult to grant the Sevengill the status of an Apex predator, though a predator it is.

So the Apex predator Great White is now out-apexed by what is probably the ultimate Apex predator of the oceans. Not a fish but a mammal, though normally, but not always we now know, present in different oceanic environments. A pack of them is known to even attack whales!

** Why are they named “Port” and “Starboard”? The reason is that male Orcas have uncommonly high single dorsal fins which can stand up as much as two and a half metres in a fully grown adult. This pair always swim side by side with each fin always flopping outwards every time. There has been some conjecture that they may be a male and a female. This is unlikely as the female’s dorsal fin is not as tall and curves backwards without flopping to the side.

Available at: https://www.fishingindustrynewssa.com/2020/09/11/letter-the-great-white-shark-mystery-i-think-not/  . [Accessed 14th September 2020].

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