The changing behaviours of ocean predators

Whales and sharks around the world are displaying bizarre changes in behaviour as theories around food shortages circulate. But is something more sinister to blame?

A wave of braver behaviour

Reports are building of sharks and orcas (killer whales) around the globe displaying changes in behaviour, suggesting they are becoming braver and more brazen in their approaches to survival. With the help from drones, footage is emerging of sharks swimming in shallow waters amidst a rise in shark attacks. Orcas are attacking other predators with an unprecedented ferocity that usurps their vociferous reputation.

Anyone interested in marine conservation must have noticed the surge in social media posts regarding changes in behaviour patterns of whales and sharks around the globe. As the evidence against these possibilities mounts, governments all over will need to listen to the experts who are monitoring varying changes in behaviour patterns as they could highlight more significant concerns in our oceanic ecosystems.

There has also been an upsurge in human attacks by sharks in various places around the globe over the last few years. As sharks venture into shallower waters, they are coming into contact with more and more surfers who to their untrained eye, look temptingly like seals or turtles.

Predators to prey

Great whites are no longer the top predator

Great white sharks have been heralded as the kingpins of oceanic predators, thanks to films like Jaws. Their size and strength make them formidable killers and they have long since been believed to be at the top of the food chain. No longer happy with playing second fiddle to great whites, the ferocity of attacks on sharks and whales has placed orcas firmly ahead of great white in recent months.

The last month has seen three great white sharks carcasses wash up around Gansbaai, South Africa. One, a 4.9m behemoth female, had clearly met with a powerful opponent. All were found with wounds under their pectoral fins. All were missing their livers.  One was also found without its heart.

When necropsies were performed on the sharks, experts were convinced orcas were responsible for the attacks due to the surgical-like precision with which the squalene-rich livers were removed. Each liver contains about 60kgs of nutrient-rich goodness that orcas require – over a quarter of their 200kg daily requirement.

Orca predation of great whites is rare – the last recorded incident was in 1997 in the San Francisco area. So, why three so close together? Experts have yet to offer theories about this bizarre bout of frenzied attacks which are not the only ones to happen in recent months.

 Unparalleled attacks

Just last month, in Monterey Bay, California, a grey whale and her calf were relentlessly attacked with all the ferocity a group of orca could administer. The killings reportedly lasted a mere 4 minutes – a quarter of the time orcas usually take to kill another whale. The frequency of the group’s attacks in the area has been hailed as unparalleled to normal orca attacks.  



Orca attacks are brutal and ferocious

Also off the Monterey Bay coast, in December 2016, two young orcas orchestrated an attack on what was believed to be a sevengill shark, devouring it quickly. They were thought to be offshore orca, which usually hunt and eat below the surface and are rarely seen.

Opportunistic hunting or desperately hungry

People have feared attacks by great whites who have yet to call a truce with surfers around the world. Attacks are often sensationalised but the fact is shark attacks are on rise. This is hardly surprising as sharks are being sighted more and more in shallower waters. The question is why?

Are sharks losing their food sources further out to sea and travelling towards shore to find other sources? Sharks are not known to hunt humans and in most cases, they release their victims after the first bite. 

Over-fishing around the world and climate changes killing off fish, has to be affecting those higher up the food chain. With less food to eat, hunting behaviours will need to be adapted and sharks will have to widen their hunting territories.

Sharks are swimming dangerously closer to shore

                   

 Facing adversity

With orcas taking the great white’s place at the top of the food chain, they appear on the surface to be free from threat. Unfortunately, this is not true.

Orcas have faced huge adversities in recent years. In 2015, a shortage of wild salmon led some experts to have concerns about their survival if food shortages didn’t improve. Whilst changing sea temperatures don’t seem to affect orcas – they can survive in warm or cold waters – other changes in oceanic ecosystems could create issues for them.

At the beginning of May, Lulu the killer whale was found dead off the coast of Scotland. She was found to have record-breaking levels of the toxic pollutant PCB (polychlorinated biphenyls) – a manmade substance.  Her blubber contained 95mg of PCB per kg – more than 100 times the estimated safe limit!  Lulu’s small pod had not produced a calf for almost 20 years. Normally, killer whales produce a calf every few years.

Orcas are clever and sociable mammals; they work together in teams when hunting and rearing young. The correlation between the dangers in the Scottish waters and the pod’s lack of rearing a calf should be looked into as the coincidence is… well, too coincidental.

Orcas are clever and sociable mammals

There then is human rubbish. With several giant gyres in the planet’s oceans, all marine wildlife will be affected at some point. Much needed pressure on the UN and governments across the globe is being wielded but not enough is being done.  The more we spoil our oceans, the more we spoil our own chances of survival, not just those of predatory species in the ocean.

The survival instinct

Animals constantly evolve and change to suit their surroundings – as changes are made, so they change. Could orcas and sharks be using their survival instinct to change their behaviours in the face of some of their biggest threats to date?

Sharks need to eat only 0.5 to 3% of their body weight per day.  This is surprising for their size and eating preferences. If this is the case, how much has their food supply shrunk if they are heading closer to shore? Are we responsible for far more of the ocean’s problems than we think?

Could orcas be changing their feeding habits?

Being apex predators, issues facing many other species will eventually also affect orcas and sharks. As fish, seals and whales face their own adversities, collectively all these adversities will affect those at the top of the food chain, too. Perhaps, their survival instinct is to try to limit these threats by changing their feeding habits to feed on species less affected, thus limiting the effect on themselves.

It’s certainly food for thought.