From the viewing platform at The Pass, the onshore wind is fierce. I brace myself and scan the sea, as if this hour were my turn on the watch of a ship. Ahead I see the blows of five or six humpback whales. Next, their great splashes. The whales are aware of each other and much more. For all that I am a puny human landlubber, I want to be as aware. So I augment each observation with a kind of sixth sense: some trained imagination.
Humpbacks see ahead through water up to eleven metres. More importantly, they listen with their sonar, feeling with their sensitive skins to know the ambience of a marine place. They know there is a container ship in the area 24 hours before they can see it.
A plane flies overhead. I know when I snorkel I can hear aircraft. I try to ‘hear’ for myself the whales’ soundscape. The steady rocks, the breaking surf, the rising tide. The continental shelf falling away. In every direction, the crowd scene of marine life. The constant hum of mechanical traffic.
To starboard are now seven or eight terns. Small, flashing white as they dip in and out of the water and circle back. Five black cormorants leave the straggly tree next to me. They join in, bobbing up and diving down into what must be a school of small fish. The fish must be moving to port because the birds shift along as they hunt.
Dolphins appear, but I can only spot them in that top metre or two of water. They rise and dive, herding and hunting. Seven gannets arrive, soaring and plunging. From wherever they were, they noticed the frenzy. Every sea creature around must know too. This, I reflect, is also the time of fish schooling. Silver bream and tarwhine haunt the surf and inshore reefs, spawning near the openings of waterways. Great white sharks need to eat at least one good-sized bream each day. If they can get a fat seal pup instead, they are good for about three days.
Sharks are known to be in the area. I scan intently, but I don’t see any. They explore or attack from below. Human pilots or noisy drones can only spot them when they rise up to the top two metres of water.
Beyond the glare on the water to the port side are some breaks with surfers. Maybe they are safer if they and their boards were striped white? They would look like sea snakes, which sharks fear. Or would an orca pattern be more convincing?
Orcas hunt sharks, as well as whales. A pod was seen up at the Gold Coast last week. I don’t spot any today, but I know sightings are collected online by the Australian Orca Database.
Like sharks, dolphins, seabirds, sea snakes and whales, orcas are top predators. To bring all the marine animals into one dynamic picture, many scientists use the great Trophic Level Index. They rank the diets of different animals and then connect it all in one food web.
Top predators score 3.4–4, the highest numbers. All these animals jostle each other, influencing each other’s lives. Whales bring babies into shallower water, where sharks find it harder to attack. Sharks avoid areas where orcas are hunting. How will it all play out here?
Add squids as predators in that top group. Rays? Their score is around 3. Just below that, at 2.5, are the schooling fishes. Think of small sharks: 3, like rays. But along the entire NSW coast, six of seven shark species are extirpated (locally extinct). What happens when so many animals exit at some level?
Perhaps other animals find the new gap a ‘release’ and fill it. Is this what humpbacks are doing? Many other whales are not recovering from former hunting, leaving ‘gaps’. Meanwhile, humpbacks are currently increasing by 11 per cent each year.
The lower score, around 2.0, is for any oysters and pippi. They, like zooplankton, eat at the lowest level. Their diet is phytoplankton, the marine photosynthesisers.
But ‘who eats whom’ is only chapter one. It’s changing even as I look. I take a deep breath of sea air. Its perfume is dimethyl sulphide, created by marine bacteria and viruses as they decompose phytoplankton. Are microbes in chapter two? Meanwhile, these microbial byproducts are tossed by wind into the upper atmosphere. There, they act as a core around which clouds are formed.