Sharks having a whale of a time?

Take 50,000 humpbacks and assume annual mortality of 1.5%. That's about 750 dead whales a year somewhere across their migratory range.

An adult humpback weighs roughly 25-30 tonnes. Mortality will include calves and juveniles, so use a conservative average carcass weight of 20-25 tonnes.

That gives roughly 15,000-19,000 tonnes of dead whale biomass a year.

Perhaps a third of an adult humpback's mass can be blubber. On those assumptions we're talking of something of the order of 5,000-6,000 tonnes of extremely energy-rich blubber each year, as well as thousands of tonnes of muscle and organs.

Obviously not all those whales die off NSW or Queensland, and sharks don't get all the carcasses.

But the scale is interesting.

Experimental estimates of great-white metabolism suggest 30 kg of whale blubber could provide around 15 days' energy for a roughly one-tonne white shark.

That means about 730 kg could supply a year's energy.

So 6,000 tonnes of blubber contains the energy equivalent of more than 8,000 one-tonne great-white "shark years".

The sharks plainly don't get anything like all of that.

But give them just:

1% = energy for ~80 large whites