Posted on Thursday, 16 February 2012
In this next edition of six blogs we will be celebrating the magnificent marine wildlife that can be found in False Bay. The feature will highlight the mega predators of False Bay, their dependence on the bay and interconnectivity with other species within the bay. I will also talk about seasonality, the Bay’s unique aspects and any human impact facing these animals within the Bay.
In 1488, Bartholomew Dias named the Cape Point Peninsula "Cabo Tormenentoso" or the "Cape of Storms". In 1580, Sir Frances Drake described the Cape as "The most stately thing and the fairest Cape we saw in the whole circumference of the earth." Indeed, whatever the feeling, the spectacular entrance of Cape Point to False Bay’s western peninsula elicited an emotional response from all that sailed past it’s shores. What many an early sailor did not comment on was the fact that False Bay is home to some of the world’s most famous marine predators and has an abundance and diversity of wildlife that is seldom matched anywhere.
Today several centuries later False Bay’s waves wash the shores that are home to 3,5 million Cape Town residents, yet despite this massive human presence this bay amazingly still boasts a treasure trove of apex predators and prey. To understand what makes this bay attractive to so many of the world’s greatest marine predators it is important to understand the uniqueness of the False Bay’s environment.
With a water temperature range of 12-23 degrees Celsius the bay attracts predominantly temperate water species but does at the high end also attract subtropical species and at the low end attract cold water species, a situation mirrored in only a few locations globally. The most comparable area being the coast off central California.
Starting from the bottom up , False Bay is home to 7 endemic species of anemone. A family with a cosmopolitan diet from plankton and crustaceans, to small fish showing just how diverse the prey base must be to support these unique creatures. Over 200 species of seaweeds have been recorded in False Bay alone. The seaweed richness in False Bay is attributed to the variety of habitats in the bay and the bio geographic position of the bay, as an overlap region between the seaweed floras of the warm-temperate Agulhas region and the cool-temperate Benguela region. Amongst many oddities, the bay’s reefs are also home to the Double Sash Butterfly fish, the only butterfly fish to occur in both the Indian and Atlantic ocean. Many other species found in False Bay are at the end of their ranges and False Bay therefore is the last place that these species can be seen. Examples of these include the Dusky Shark, Smooth Hammerhead and Ragged Tooth sharks, although on rare occasions under the right conditions these species do venture onto the peninsulas western seaboard. The list of unique marine attributes goes on, suffice to say that above the water the situation is no different with Cape Point’s Cape of Good Hope Nature Reserve being the smallest but richest of the world's six floral kingdoms, comprising a startling 1 100 species of indigenous plants. You are literally bombarded with an unbelievable profusion of life no matter where you look be it above or below the water.
It is no surprise then that with all this diversity and density that this bay is home to an impressive array of predators, both big and small.
Indeed if you look at the definition of a predator being, "an organism that lives by preying on other organisms", then I would need several pages to merely scratch the tip of the ice berg as predators in False Bay are so abundant in so many forms. The bay is a veritable marine coliseum of combat and all that enter the bay must compete.
The bay’s honour’s list is impressive with a few worthy mentions being Africa’s largest island bound seal colony at Seal Island numbering over 60 000, Africa’s largest fixed land based penguin colony at Boulders Beach, one of South Africa’s largest cormorant breeding colonies on the Cliffs adjacent to Smitswinkel Bay and arguably along with Dyer Island and Mossel Bay the worlds greatest concentration of Great White Sharks. Add to this a seasonal abundance of Southern Right Whales, a semi resident population of Brydes whales, migrating Humpbacks and other whales and an annual influx of at least 5 species of dolphin.
Indeed one of the dolphin species, the Common Dolphin, sometimes form schools of over 1000 individuals. If this wasn’t enough there are also a multitude of marine bird species, including threatened species such as bank and crowned cormorants and African oyster catchers. After winter storms the bay can be home to many open ocean birds including shearwaters, skua’s , petrels and occasionally albatross amongst others. Quite simply False Bay is a naturalist’s paradise.
Seasonality and the ever changing tapestry of conditions plays a huge part in what predators are to be found in the bay at any one time and to understand this the bays mega fauna needs to be looked at during the different seasons.
Certainly from the amount of press they receive Great White Sharks at Seal Island are the most talked about predators commonly encountered in False Bay. Due to the wide range of temperatures and habitats the bay attracts a vast array of large shark species from Great Whites, Ragged tooth, Bronze whalers, Hammerheads, Seven gills and Common threshers to occasional visitors to the bays entrance such as Mako and Blue sharks. Less known but equally interesting are the small species such as the Puff adder and Brown shy sharks as well as the Leopard and Striped cat sharks that usually hunt amongst the kelp. All of these species are in fact endemic to the West and South coast of South Africa and Namibia. Slightly larger are the Spotted gulley, Black spot and White spot Smooth hound and Soup fin sharks which all congregate seasonally in different areas within False Bay. Smooth hound and Soup fin sharks were up until the mid nineties still abundant with massive schools numbering thousands of individuals being found in areas such as Wolfgat, Roman Rock, Black Rocks and Rocky Bank. Sadly these sharks have been heavily fished particularly in the past two decades and now occur in far smaller numbers.
Apart from the Seven Gill cow sharks the predominant reason the larger sharks come into False Bay in summer is to dine on the huge shoals of Sardine, Anchovy, Mullet, Maasbanker and Squid that routinely mass within the confines of the bay as well as feeding on larger bony fish and smaller sharks which also feed on the bait fish. The 2.5 - 3.0m long Seven Gill cow sharks are primarily scavengers and will feed on a range of prey from molluscs, crustaceans and small fish to scavenging seal carcasses. Indeed these prehistoric looking sharks are truly the masters of their kelp forested world and are rightfully now becoming a major diving attraction in the Millers point area. The popularity for divers to see these sharks alive once again highlights the value of non consumptive uses of our shark resources.
During the summer months of October to March the concentration of most of False Bay’s larger sharks is generally focused close inshore off the bays Northern beaches of Fish Hoek to Gordon’s Bay where the summers onshore winds create a perfect feeding environment for the mullet and other baitfish which feed off the Annaulus (a microscopic type of algae) blooms which discolour the water brown. The concentrations of bait fish then attract the sharks and other large fish such as Kabeljou, Elf, Leervis, Yellowtail and others. Interestingly the very water that people often think is sewerage is in fact the most productive in the bay and is teeming with life. It is not surprising that with decades of experience that the trek fishermen who make their daily catches off the bay’s beaches target this water and often catch the sharks with their target fish. Fortunately for the sharks most of the educated trek fishermen release the sharks knowing that these animals are vitally important within the bays food chain. What is also evident in these net catches are the high numbers of Rays , Sand sharks and Chimaeras, all of which are closely related to sharks but typically occupy different niches and have different prey to the big shark species. Sharks and rays that have been tagged in the nets have been found to travel the whole way up to the beaches of Kwa Zulu Natal showing not only how far they travel but just how important False Bay is that they make these vast migrations to this area. By mid to late summer the species composition of predators is changing. Bait fish such as maasbanker are becoming more evident in False Bay’s inshore areas. With the influx of these fish comes another spectacular predator to the fray, the Thin tail Thresher shark. Although notoriously difficult to get close to underwater due to it’s shy nature these sharks do get caught in the nets especially around December to January when they move into bays such as Fish Hoek and off the beaches of Muizenberg to the Strand.
With their small mouths, massive eyes , purple blue dorsal colours, patchy white ventral sides and ridiculously long tails these are remarkable creatures to behold. These sharks stun their prey with sjambok like strikes of their tails and are occasionally seen jumping several feet into the air. By February water temperatures are peaking in False Bay reaching the 22-23C mark and species diversity is huge. Occasionally sub tropical species such as Kingfish, Barracuda and even Wahoo are caught in the bay and just outside it’s entrance and the bay is throbbing with hunters of all forms. Often terns, gannets and shearwaters raucously scream their excitement as below them the water churns into frothy spray as hungry game fish charge into shoals of baitfish, accompanied below by excited sharks.
The real possibility for eco-tourism enthusiasts to see Great white sharks, various Whales, Dolphins, Seals, Penguins and other marine birds all in one mornings outing.
With the coming of March and April the waters start to cool as the winds start to shift more into the West and North West producing more offshore days coupled with generally smoother seas. These conditions are generally not conducive to algal blooms and the near shore shark concentrations tend to disperse with species such as bronze whalers now focusing more on large shoals of Anchovy and Sardine which become noticeably more evident in the middle of False Bay as the waters cool down. Density , not diversity is now the key feature of the bay.
The cooling of the waters also sees a shift in great white shark movement back to Seal Island. These apex sharks now start preparing to target young of the year seals that have been generating large fat reserves from feeding on their mothers energy and fat rich milk for the past 5-6 months and will be starting to go offshore and feed for the first time.
The massive shoals of sardine and anchovy also herald the arrival of other predators in the form of huge schools of common dolphin sometimes numbering over 1000 animals in a single mega pod. Assaulting the shoals from the air are thousands of Cape Gannets who plunge into the water at speeds exceeding 120kmph and can dive to depths of at least 20m. Indeed the gannets hit the water so hard that if you are close to them underwater the concussion of the strike goes right through your body, almost like standing next to a tank being fired, it really is quite a thrill. The gannets have travelled from the islands around Saldahna and Lamberts bay to come to the bay to feast. Other feathered warriors are the Cape cormorants who travel in flocks numbering in the tens of thousands forming a snaking black blanket of whirring bodies. The gannets dive from high whilst the cormorants simply slip under water and assault their prey anyway they can.
Joining the frenetic banquet are the bays semi resident Brydes whales who with their sleek 15m long bodies lunge mouth agape into the shoals of bait fish who have nowhere to hide. Indeed False Bay has it’s very own scaled down version of the sardine run each year, yet little attention is given to this phenomena in this area as everyone heads up to the wild coast.
During the 2009 and 2010 season the activity was of such an epic nature that another predator came to dine in the bays bountiful waters. For 16 years and over 1500 trips into the bay we had never encountered an orca in the area although there had been a handful of reports. Offshore sightings were however fairly regular so we always had hope. Suddenly a change occurred and during the past two seasons we have seen 5 different pods. What is even more spectacular is that they appear to come into False Bay primarily to hunt dolphins. All but one of our sightings have taken place during the Autumn months when dolphin activity has been at it’s peak.
Whilst on our way to watch one of the worlds most famous natural predation events, that of great white sharks breaching through the air in pursuit of Cape Fur seals our Simons town shark cage diving guests were treated to the mind blowing spectacle of watching well organised Orca pods hunting the schools of 500-1000 dolphin. On one occasion the Orcas were hunting dolphins and the Great White Sharks hunting seals concurrently within a few hundred meters of each other. Quite simply an unrivalled situation where the oceans two greatest predators hunted literally within a stones throw from each other. What was also fascinating was the fact that the Orcas often had company, Cape fur seals!
In many other parts of the world seals form a large part of the orcas diet, yet here in False Bay we saw the orcas swim under , around and even had rafts of seals float above them while the orcas fed on the dolphins. Indeed it appears that these Orcas were dolphin specialists.
By mid June we had our last Orca sighting as the massive shoals of bait fish had moved off and with them the mega pods of dolphin. False Bay’s waters had cooled to between 13.5C - 15.0C and a small but voracious predator had arrived in mass, the Snoek. Forming an important part of the commercial hand line fisheries catch each year these massive shoals of Barracuda like fish aggregated well inside False Bay feeding on the last shoals of Anchovy that still lingered around.
This feast of fish is a magnet for the seals who steal fishermen’s catches or catch their own and for sub adult and adult seals this easy meal is one they can‘t miss. What this means is that large groups of seals head off from Seal Island in the direction of the snoek and fishing fleet each morning, or if the Snoek are not around the seals go in search of bait fish. Within these groups of outward bound seals are the young of the year who are now accompanying the adults for the first time after months of suckling their mothers fat rich milk.
Like all super predators the great white sharks are ready for this exodus. The sharks now actively patrol Seal Island during the daylight hours knowing full well that these young seals will often return alone. The young seals are not strong enough yet to have kept up with the adults and probably broke away from the outward bound groups to feed on more easily caught prey than Snoek. Seal Island is now the staging ground for an epic showdown of brute power and athleticism in the form of the sub adult great white sharks against the agility and dexterity of the young seals.
For the next 4 months from May to August Seal Islands seemingly docile waters will see in the region of roughly 600-800 Great White shark predatory events with an almost equal amount going the way of the shark being successful or it’s wily prey escaping. Sights of Great White sharks breaching 10ft out of the water with seals clamped across their jaws or seals evading death by the narrowest of margins are often witnessed. Each predatory event is a life and death struggle.
This spectacle is truly one of natures greatest to witness in terms of sheer in your face predatory power and efficiency versus agility and the instinctual drive to survive. Weather conditions play a large part in the sharks ability to catch seals, with cloudy and choppy conditions favouring the apex predator and clear, calm conditions being to the preys advantage.
As with all great concentrations of predation there are the other less obvious avian benefactors, on land it is the vultures, at Seal Island it is the Kelp Gulls. At the Southern point of the island the gulls sit in mass, akin to a gathering of undertakers, knowing that this is the best vantage point from which to watch for predation. Gobbling up scraps of flesh or stringy entrails, the predations bring a harvest of their own for these efficient and raucous aerial gangsters.
By August the young seals have become wiser and return in larger better organised groups more capable of detecting and evading their attacker. They are also stronger and fitter and as such pose a far more difficult meal to catch. After four months of heavy feeding the Great Whites have had their fill and are in excellent condition and as the springs South East winds begin to blow these super sharks begin to move to the inshore area of False Bay as conditions change to favour their near shore existence.
From Fish Hoek to the Strand these Great White Sharks slowly patrol the outside of the surf looking for other smaller sharks and fish to prey on. They are also perhaps using the warmer water trapped inshore by the now predominantly onshore winds coupled with highly oxygenated water from the surf to help them digest food and save energy. Whatever the reason these sharks are certainly not scouting for human prey. What must be considered though is that with the rampant exploitation of smaller inshore shark species that great whites are known to feed on, the great whites may be needing to cover more ground than ever before to find their regular prey. The probability to come into contact with humans is therefore logically likely to be greater than before and is likely to increase unless measures are taken to reduce the fishing of these prey species to a well regulated few rather than an unregulated many.
At about the same time as the great whites move shore wards the Southern Right whales appear in False Bay in mass. These 18m long giants come into the bay to mate and calve and share pretty much the same sandy beach environment as the great whites. Indeed it is not uncommon to see great whites and Southern Right whales within a few hundred meters of each other and lucky shark cage diving guests on charter boats might well see breaching great white sharks, dolphins and Southern Right whales all on one trip during late August and early September.
By the end of September the False Bay’s waters are starting to get churned by the regular South - South East winds that lash the Northern parts of the bay. Warm water starts to spill over the Agulhas banks and the first few tendrils start appearing off Cape Point and occasionally snake into the bay. Action wise the focus is now once again off the beaches, particularly Muizenberg to the Strand area where massive 3m long female Bronze Whaler sharks laden with their precious cargo of pups actively feed on the bait fish before migrating further up the coast dropping their pups off Southern and Eastern Cape beaches. A profusion of life starts to filter across the bays reefs and shoals of game fish such as Yellowtail, Elf and Kabeljou once again return to their summer haunts.
As the sun’s first rays bathe the bay in gold comes the real possibility for eco-tourism enthusiasts to see Great white sharks, various Whales, Dolphins, Seals, Penguins and other marine birds all in one mornings outing. The amazing thing is that you need not dive or even get wet to see them.
Indeed few places of earth can be so diverse in species, abundant in density , beautiful in scenery and yet be surrounded by so many people. False Bay truly is South Africa’s Serengeti of the Sea where the oceans greatest predators still rule the waters and the abundant shoals of prey still precariously wonder through the waves.
Hopefully in time to come the same amount of attention will be given to this marine wonderland as it’s terrestrial counterparts and people from all around the world will flock to see it’s riches and help preserve it‘s resources.