Follow one spawning site on the Great Barrier Reef through a season. Press the steps in order and watch the fish. The counts come from a scientist who watched this site off Cairns[1], the closure dates from Queensland's own fishing rules[2], and the sources are at the bottom.
On the spawning site
7coral trout
An ordinary day: 7The most she counted: 128on about 18,300 square feet
Closed in 2026
the new moon, on Queensland's clock
In 2027: October 26 to 30 and November 25 to 29.
What the fish wait for
the water is below 75°F
The big idea: coral trout crowd onto the same patch of reef at the same new moons every year, so they are easy to catch then. Queensland bans catching them for five days at the October and November new moons so they can spawn.
Where "about 7" and "128" come from: Melita Samoilys counted the coral trout on one spawning site at Scott Reef, off Cairns, from 1990 to 1993. From January to July the mean of her 12 counts was 6.58 fish, drawn here as 7. The most she counted was 128[1]. 128 ÷ 6.58 = 19.45, so about 19 times as many as on an ordinary day. She measured it another way too, against what she calls the pre-spawning densities: up to 13 times in 1990, 19 times in 1991, 16 times in 1992 and 14 times in 1993. By that measure 1992, the year of the 128, was 16 times[1]. Her own densities agree: 6.58 fish on 1,700 square meters is 3.87 per 1,000, and 128 is 75.3 per 1,000, the figures she gives[1].
Where "about 18,300 square feet" comes from: the site measured 1,700 square meters[1], and one square foot is 0.09290304 square meters, so 1,700 ÷ 0.09290304 = 18,299 square feet[6].
Where "75°F" comes from: the season began once the water rose above 24.00°C after winter[1], and 24.00 × 1.8 + 32 = 75.2°F[6]. She gives the line, not the winter's temperature, so the panel's tube only shows the water below the line or above it.
Where "about 5 days" comes from: the fish gathered around lunar days 28 to 3, where day 1 is the new moon, and each gathering lasted 4.7 days on average and 7 at most; her summary says "an average of 5 d"[1]. She saw 94 spawning rushes, the fish spawning in pairs. Each evening's spawning lasted about 33 minutes on average, and across all her evenings it ran from 41 minutes before sunset to 19 minutes after; 68% and 82% of the evening gatherings at her two reefs were on a rising tide, and in 1990 fusiliers ate the eggs of 27% of rushes[1]. She called the fish's predictability the reason they are vulnerable to overfishing, and the reason closures can protect them[1].
Where the 2026 dates come from: Queensland's fisheries page lists two five-day closed seasons for coral reef fin fish, October 8 to 12 and November 6 to 10, 2026, in tidal waters from the tip of Cape York down to latitude 24°50′ south[2]. The 2023 statement puts that line near Bundaberg, lists the fish it covers (cod and grouper, coral trout, emperor, fusilier, parrotfish, surgeonfish, sweetlip, tropical snapper and sea perch, and wrasse), and says October and November "have been shown scientifically to be the most effective months"[3]. NASA puts the new moons at 3:50 pm on October 10 and 7:02 am on November 9, 2026, world time[4]; Queensland's clock is 10 hours ahead[5], which makes them 1:50 am on October 11 and 5:02 pm on November 9. Both fall on the fourth of the five days, and so do the new moons of 2025 and 2027[2][4].
What the counts do not tell you: they come from one site at one reef off Cairns, counted from 1990 to 1993. At nearby Elford Reef her site was 3,200 square meters and the most she counted there was 59[1]. Other reefs and other years will differ.
The drawing is not to scale. The site is drawn as an oval on top of a reef, and the fish are drawn far bigger than the reef around them. Every coral trout drawn is one fish counted, but where each one swims, how fast they arrive and leave, the 6 spawning rushes drawn, the fusiliers coming for the eggs of one of them, the boat and how dark the sea gets after sunset are this drawing's own choices, and so is how full the panel's tube looks. The moon is drawn as it looks from Queensland. In real life the crowd broke up each morning and gathered again after 1 pm[1]; with the days sped up, the drawing keeps it together. Both new moons are drawn filling to 128, the most she counted, in 1992; her biggest gatherings at Scott Reef ran from 63 to 128[1]. The sunset plays at 360× real speed: the hour from 41 minutes before sunset to 19 after (41 + 19 = 60 minutes) in 10 seconds, so every rush drawn falls inside her limits; the days in steps 3, 5 and 6 are sped up and do not pass at an even speed, and steps 1 and 2 are not timed to real life.