Declining catches of striped bass may not always be due to overfishing. Researchers say a periodic weather pattern in the North Atlantic may be responsible for the low fish numbers. And understanding how it works may help set fishing limits in the future.
The striped bass is in trouble again.
During the 1980s, wildlife managers said these big, full-bodied fish — favorites of anglers along the East Coast — were overfished. So they laid down severe catch limits. The population recovered, and fishing resumed in what is considered one of conservation's great success stories.
But now catches are down again, and some biologists say the problem may not be overfishing this time: It could be the weather.
Brad Burns, who started fishing for striped bass in 1960, says he and his fellow anglers, Stripers Forever, are singing the blues about striped bass.
"What we hear from people that go striped bass fishing — the general trend very decidedly is down," Burns says.
Stripers live in the ocean as well as in estuaries and some rivers. Burns says members have been reporting fewer fish for the past five years. As for the cause?
"Well I don't know," he says, "and I don't know that anybody does."
A New Theory On Fish Levels
But Bob Wood thinks he might. Wood is a biologist with the National Oceanic and Atmospheric Administration. He studies his fish in a boxy little building on the Maryland shore of the Chesapeake Bay. In the semi-darkness, you can make out several vats with bubbling oxygen hoses. Each vat is home to striped bass or white perch, two species that spawn in the bay. This is where Wood's team studies the fish to figure out why striper numbers go up and down.
They thought they had the 1980s crash figured out: "The striped bass crashed because of overfishing," says Wood, "and then it recovered because we closed the fishery."
But now Wood has a new idea that's just taking shape. "This research, at first glance, seems to call that into question," he says.
This idea focuses not so much on fish but on the weather, and especially the Atlantic Multidecadal Oscillation, or the AMO. The AMO is a mashup of wind and ocean currents, a flip-flop that happens every 35 years or so in the North Atlantic.
"Circulation changes in a way that warms the entire basin," Wood explains. "And you can imagine if you warm the entire North Atlantic basin, you're changing the weather because the air and circulation patterns above the ocean are affected."
Ed Martino, a fisheries scientist who works with Wood at NOAA, says when the AMO shift happens, it affects the local weather along the Atlantic Coast.
"You are talking about differences in temperature and precipitation, and therefore river flow or salinity, ultimately all affecting the base of the food chain," says Martino. "It's the way that the climate affects the microscopic plankton." Plankton are tiny plants and animals in the water, and that's what young stripers eat.
Understanding The Weather-Fish Relationship
Here's how Wood and his team think the AMO is messing with fish food. When it's in a warm phase, springtime along the East Coast actually tends to be wet and cool — more rain, more water, more food. In the years following that phase, striper numbers tend to go up. Then the AMO flips — drier springs, less rain, less food. After a lag, it looks like striper numbers start to decline.
Wood says the past 100 years of fishing records show that very trend. And currently?
"It hasn't been so good in say the last five years," Wood says. "And it just so happens this is also the time when the Atlantic Multidecadal Oscillation seems to be switching phase."
Wood suspects it's switching into a "bad for stripers" phase, and he thinks it was also a down cycle that caused the striper crash in the 1980s. When that cycle ended, stripers recovered — not just owing to the fishing limits but because the weather bcame more favorable.
Janet Nye, who studies fish stocks for the Environmental Protection Agency, thinks this research could help fisheries managers.
"We would be able to say, 'OK, for the next 35 years or so we're pretty certain that the AMO is going to be more positive or warm,' and we would be able to say, 'These are the fish that respond favorably to that — you might be able to fish those more,' " she says.
Conversely, fish less in a down cycle, Wood says. "If we know that there is this cycle coming up," he says, "a trend that we are beginning to enter, we can keep that in our heads as we set limits."
If Wood's research is correct, it may take tougher catch limits to bring striper numbers back up again. Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.