Ambush at South Pass: At Fakarava Atoll in French Polynesia, spawning is an even more boisterous affair. Around the full moon in July, thousands of camouflage groupers head for South Pass, a narrow channel just 100 metres ufabet wide and 30 metres deep that connects the central lagoon to the open ocean.
Ambush at South Pass
Twice each day, water rushes through the pass as the lagoon fills and drains with the tide, and it is here that male and female groupers congregate to spawn, the females noticeably bigger, with their bellies swollen with eggs.
After a few trial runs, when a few pairs leave the group in sudden bursts of speed to release their eggs and milt, this sparks the dramatic main event. At its peak on the outgoing tide, when thousands of fish spawn at roughly the same time, the water turns into a dense ufabet white fog. Fertilised eggs are flushed out to sea by the strong current, but this mass-spawning event is what the local sharks have been waiting for.
Hundreds of grey reef sharks crowd into the pass, and they come because the groupers are so intent on spawning that they can be picked off with ease. They sweep in at high speed and grab the spawning fish before they have time to escape.
Sharks flash past this way and that, as their targets rocket up towards the surface. Large blacktip and sicklefin lemon sharks swim in from the ocean and join the fray, and such is the mayhem even great hammerheads have been known to prey upon the sharks that are themselves hunting the groupers.
That there are so many sharks here is a bit of a biological puzzle. On average, 600 grey reef sharks are found here throughout the year, but numbers can vary between 250 in summer to as many as 700 of these 2-metre-long predators in winter. It is the highest concentration of grey reef sharks in the world, and there should not be enough food to maintain such numbers.
Scientists studying the sharks estimate that the population requires about 90 tonnes of food a year to stay healthy, but there is only about 17 tonnes available, so for most of the year the sharks must travel away from the ufabet channel and seek food elsewhere. However, for a couple of months in winter they don’t. They stay put, and they can do so because of the groupers.
Like the delivery van arriving with the groceries, upwards of 17,000 camouflage groupers congregate in the channel. They come from all over Fakarava Atoll and nearby islands, some travelling from reefs as far as 50 kilometres away, and they represent a sudden influx of about 30 tonnes of available food.
And even when the groupers have left, the sharks can turn their attention to the surgeonfish, parrotfish and several other species that also gather here to spawn. All these reef fish supplement the shark’s normal diet, explaining why so many sharks are seen here.
Fakarava is unusual in that it has not been overfished. Just ten fishermen catch reef fish for subsistence, and the sharks are protected because French Polynesians revere them, so the grouper population has remained healthy. Significantly, on coral islands where overfishing has reduced populations of reef fish, including groupers, the shark population has also often suffered.
The sharks at many of these places, of course, have been caught for their fins, decimating populations, but this research is showing that a ban on shark fishing alone might not be sufficient to protect them. The coral reef fishes that form these spawning aggregations must be protected too. Without them, there would not be so many sharks, and sharks are vital to the health of the coral reef community.