2.8 million eels on one seamount: the deep is still a blank map

How do you lose track of millions of animals? Apparently, quite easily, as long as they live deep enough. A team of Australian scientists has estimated, for the first time, the size of a gathering of deep-sea eels that forms every year around a seamount off Tasmania. The number at its peak: about 2.8 million individuals.

What the count says, and what it doesn't

According to the Spanish edition of Gizmodo, the study puts that peak accumulation at between 2,557 and 3,547 metric tons of eels. The animals are not spread evenly over the mountain. As Martín Cid's Latin American edition describes it, they pack into dense swarms at one particular depth on the western side, over deeper, flatter ground. Orange roughy, a long-lived deep-sea fish that shares the seamount, stays on the steep slopes.

The coverage we've read points to reproduction as a possible explanation. We would stress "possible." Some outlets say the phenomenon may be related to breeding, and the Gizmodo headline says science doesn't know why. We haven't seen the paper itself, so we can't say how it was published or how firm the number is. Treat 2.8 million as an estimate with a wide error bar, not a census.

The surprise isn't the eels, it's the blind spot

The reflex is to be amazed by the size. We would rather be uneasy about the timing. This gathering recurs every year, at a recurring place and depth, and it was only now that someone put a figure on it. The animals didn't just show up. We hadn't looked.

The numbers about seamounts suggest this is no exception. Wikipedia's entry cites estimates of around 100,000 seamounts at least a kilometer tall, and a figure approaching a million if smaller ones are counted. We suspect that only a small fraction of those has had anything like the attention this one just got. If one peak off Tasmania can hide a swarm of this scale, it seems reasonable to ask what the rest are hiding. Other recent reports point the same way, including a seamount off Canada's Pacific coast where scientists found millions of eggs on a volcano that had been considered extinct.

Map first, exploit later

Here is where we take a position. A concentration like this is a gift for science: a place where a hard-to-study group of animals gathers in a predictable spot. It is also, for anyone with a net or a drill, a very obvious target. Dense, predictable aggregations are exactly what makes a fishery efficient, and exactly what can make a population fragile if the aggregation is a breeding event. If the animals are indeed there to reproduce, then removing them in bulk would hit the next generation, not just the adults.

We are not claiming anyone is planning to fish these eels. Nothing we've read says so. Our point is about order of operations. In our view, the sequence has too often been: find it, exploit it, study what is left. With the deep ocean the sequence should be reversed. First map the seamounts, count what lives there and find out when and why it gathers. Only then decide what, if anything, can be taken.

There is also a lesson for how we read stories like this. "Science doesn't know why" can sound like a failure. We think it's the honest starting point. The most useful thing this finding does is shrink our confidence in how complete the picture of the ocean is.

Our recommendation is simple. Treat this seamount as a reference site: monitor it, repeat the count and learn what the eels are doing there. And treat the other seamounts as unread chapters, not as empty space waiting for a use.