A 317 manatee count at one Florida warm water outflow beat every earlier tally that winter, where what the number tracked was the cold front rather than the size of the population

A manatee is a tropical animal living at the northern limit of where it can survive.

It is large, which helps, but it carries almost no insulating fat and runs a metabolism far slower than a mammal of that size normally would.

So it cannot burn its way out of a cold snap.

Below roughly 68 degrees the animal starts losing heat faster than it can replace it, and the damage that follows is slow rather than sudden.

Skin lesions, digestive shutdown, a failing immune system. Days and weeks, not hours.

Warmth is the only defense.

The crowd is a thermometer

This is the part that gets read backward. A big gathering at a warm water site looks like abundance and is nothing of the kind.

When the water outside is tolerable, the animals spread out across the estuary and feed where the grass is, which is exactly what you want them doing.

When a front drops the water temperature, they abandon the food and pack into whatever is warm, and the tighter they pack the worse the conditions outside have become.

So the count at any one refuge rises and falls with the weather and not with the number of animals in the state.

A low morning at the canal in January is good news, because it means the estuary outside is still habitable. A very high one is the opposite.

The tally measures air temperature.

A canal with a viewing deck over it

The site is an industrial discharge channel on the Florida east coast, where a generating station takes in water to cool its machinery and returns it a few degrees warmer.

Beside it the utility built a free public center with an observation deck and cameras above and below the waterline, open daily from the middle of November to the end of March.

Nothing about the plant was designed for wildlife. It just happens to produce the one thing a cold manatee cannot get anywhere else nearby.

The animals come back to it year after year, and calves born into the habit learn the location from their mothers rather than finding it themselves.

That is what makes the arrangement harder to unwind than it looks.

Habit becomes inheritance.

Four mornings that went 66, 34, 160 and 317

Staff count by eye from the deck in daylight, tallying every animal visible in the plume at one moment.

The season ran all over the place. A cold snap at the start of January brought 66, a second one on the sixteenth brought just 34, and a late January front pushed the morning tally to 160.

Then on February 10 a stronger front arrived and the count reached 317 animals, which staff described as the highest single day figure of the season.

Those are observations, not a census. A manatee that surfaces twice in different places can be recorded twice, and one resting just under the surface may not be recorded at all.

Nobody on the deck is pretending otherwise. The figure is a careful tally of what was visible at one moment from one vantage point, and it is reported that way.

Statewide context comes from aerial work rather than decks, and it is unforgiving about how much of this population now depends on industry.

Counting is an estimate.

Where the comparison numbers go wrong

The temptation with a figure like 317 is to set it against the biggest number anyone remembers, and that is where most of the errors creep in.

The largest documented single count at the main Brevard County plant refuge is 957 animals, recorded in January of 2010, in the way that a counted rescue or a single count turns into a round legend.

Figures in the thousands for that site do not appear in the published record. The same statewide analysis found 48.5 percent of all manatees counted in winter surveys were sitting at power plant outfalls.

That analysis ran in the habitat study covering surveys from 1999 to 2011.

Half the population is on a meter.

What a crowded canal costs

The hard number from the same winter is not the crowd. It is what the cold did to the animals that did not reach warm water in time.

Florida recorded 35 cold stress losses between January 1 and the end of February, against a five year average of 13 for that window, so the season ran at nearly three times normal.

The species is listed as threatened rather than endangered, and the warm water it depends on comes from plants that will not run forever, which the local coverage did not get into.

A warm water outflow held 317 animals for a morning.

The cold that put them there did the rest.