Where have all the old fish gone?

There are plenty of fish in the sea, they say. But a study published Thursday in the journal Current Biology indicates the well-worn reassurance may need a new caveat, one that echoes Matthew McConaughey’s infamous line in Dazed and Confused (“I get older, they stay the same age…”). Here’s the 2017 update: There are plenty fish in the sea, but they’re getting younger and younger.

A team of scientists at the University of Washington looked at 63 fish species across five ocean regions and found that most populations are missing their elders, and that decline is likely a result of commercial and recreational fishing. On average, the researchers found 72 percent fewer “old fish” than would likely be swimmin’ around with fish dentures if they had never faced threats from the fork and the knife.

“The only rule of thumb is that when you stop killing fish, they continue to get older.”

Of course, “old” is relative, even in fish populations. A Pacific cod, for instance, can live up to 18 years, whereas a rockfish can clear 100-plus. But across the board, fish populations are skewing younger. Pacific hake on the West Coast, Walleye pollock from Alaska, and Atlantic cod from Europe are some of the hardest hit. Regionally, the Southeast and West Coast of the United States showed the clearest youthward trends. Alaska seems to be the most geriatric-friendly region, for what it’s worth.

It’s hard to tell exactly how much fishing has impacted these populations, though researcher Lewis Barnett has studied marine reserves where fishing isn’t allowed and notes that demographics tend to even out in the absence of fishing boats. “The only rule of thumb is that when you stop killing fish, they continue to get older,” he says. Makes sense.

But why should we care if fish are getting younger? Fewer grandparents around to read their fingerlings One Fish, Two Fish, Red Fish, Blue Fish doesn’t necessarily spell environmental catastrophe. Turns out the reasons for conserving older populations are kind of hard to pin down. And that means it’s never been a regulatory priority.

Especially when the environment is changing, you want to have that variation and diversity.

The common argument that started in the early 2000s was that old fish were inherently more productive, that they produce offspring that are inherently more fit,” Barnett says. But though scientists have proven old fish do lay more eggs, they haven’t actually been able to demonstrate that those eggs hatch more often or breed sturdier babies.  

Shouldn’t old fish pass down good genes, since they’ve clearly escaped more fish hooks than the young bucks? And they must provide some kind of wisdom to the community. Can’t they lead the youngers to safe egg-laying spots and show the hatchlings how to look out for a lure?

Maybe. But none of this has really been proven. “We don’t know a whole lot about the genetic side and behavior,” Barnett says.

Old fishes’ biggest selling point may be that they behave just a little differently from younger fish. They lay their eggs in different places, swim further into deeper waters, and get pregnant at different times. Which means they diversify the behavior of the population as a whole. Their presence is an assurance that a whole school of fish (literally) doesn’t put all its eggs in one underwater basket. Especially when the environment is changing, you want to have that variation and diversity,” says Barnett.

Young fish are pretty well protected—recreational fisheries institute minimum size limits, and commercial equipment isn’t designed to catch juveniles—but similar protections haven’t really been introduced to protect bigger, older individuals. To make matters worse, fish aren’t even measured by individual size; rather, a population is measured by its total biomass. According to mainstream measurements, three juvenile cod and one big guy look exactly the same.

But Barnett says he hopes the conversation around fish age will change soon. “That’s our next frontier, really, is trying to shape the discussion on how to make age structure feed back more directly into the fisheries’ management process,” he says.

Maybe soon, fishermen will start throwing granddaddy rockfish back in the water. It’d be nice to know the ocean is full of nice old folks, regardless of whether or not their babies are smarter.

H. Claire Brown is a senior staff writer for The Counter. Her work has also appeared in The Atlantic, The Guardian, and The Intercept and has won awards from the Society for Advancing Business Editing and Writing, the New York Press Club, the Newswomen's Club of New York, and others. A North Carolina native, she now lives in Brooklyn.