Tuesday, March 26, 2013

Chesapeake Bay Fish Controlled by Climate

A pretty long but decent article from Chesapeake Quarterly, the publication by Maryland Sea Grant, on how the Atlantic Multidecadal Oscillation, the multidecadal scale movement of temperature patters across the Atlantic Ocean, controls the success of common fish in the Chesapeake Bay, including Striped Bass:

Taking the Long View: The Fall & Rise & Fall of Stripers & a Lot of Less-famous Fish
How many striped bass could be coming next year has befuddled scientists for decades. Their sudden and unpredictable boom years can turn out twice as many offspring as the year before, sometimes three times as many, sometimes 10 times as many. More than 30 years ago, biologists Don Heinle and Joe Mihursky came up with a clue: cold, wet winters bode well for a striped bass boom year.

Bob Wood came at the issue from a different angle. Before he was a fisheries scientist, he was a climatologist who spent a lot of time looking at huge, noisy data sets jammed with multiple variables. If certain weather patterns brought on boom years for stripers, perhaps those same patterns were also bringing boom years for other species at the same time. "I thought the patterns in nature are not one fish at a time," says Wood. "If there is an environmental signal, it is probably not going to pick out a single fish."

To probe all his data, Wood tried a statistical technique called Principal Component Analysis. Designed to dig out patterns buried in the data, this analytic tool uncovered an unexpected connection: whenever fish that spawned in the Bay did well, fish that spawned in coastal waters did poorly. And vice versa: whenever coastal spawners did well, Bay spawners did poorly.

Wood discovered another surprise in the data: these patterns lasted for several decades. Boom years for stripers, for example, seemed to come in bunches, and so did bust years. And the pattern affected a lot of fish: The Bay spawners include species like alewives, blueback herrings, white perch, yellow perch, shad, and, of course, stripers. The coastal spawners who come in from the continental shelf include spot, croaker, hardhead, weakfish, drum, and, of course, menhaden.
OK, lets cut to the chase, what it is it?
In the year 2000, Bob Wood got his doctorate and the Atlantic Multidecadal Oscillation (or AMO) got its name. This ocean cycle brings several decades of warming waters followed by several decades of cooling waters in the Atlantic basin. A dozen years after it was named, the AMO remains loosely described and its effects widely debated.

The temperature swings can be small, but the cycle seems to have far-reaching effects. An earlier warm phase of the AMO has been tied to the Dust Bowl of the 1930s and the droughts of the 1950s. Since the early 1990s, the AMO has been in a warm, positive phase — and we've seen twice as many big hurricanes, including Isabel, Ivan, Katrina, and Sandy. We've also seen some boom years for new stripers.

When Bob Wood began reading about the AMO, his inner climatologist came alive again. "When I saw that it had cycles, I said 'Wow!' Then I looked at the statistical correlations," he says, "and it was amazing." The recent ups and downs of the AMO seemed to correlate with the ups and downs of fish populations in the Chesapeake.
 But this was the part that caught my eye:
Summer trips were usually the worst for Wood, a tall slender student with dark hair, a dark beard, and a delicate stomach. When the trawl boat would make a haul down near the mouth of the Bay, the deckhands would dump the catch on the big, sloshing culling table, and Wood would go to work sorting fish — with ocean swells rolling under the boat, with diesel fumes hanging over the deck, with jellyfish tentacles slapping at his face. Picking through the flopping fish, he'd try to figure out which were larval anchovies or alewives, yellow perch or white perch, which were white mullet, satinfish shiner, bigeye scad, or bighead sea robin.

When it got bad, he'd go over to the side of the boat and throw up. Then he'd lie down on the deck, summer or winter, and wait until the next trawl was done. When the net came up, he'd scramble up and take his place at the table again. He always went back to the table. When it got worse, when he got dehydrated and went greenish in the face, the captain put him ashore. He left him on a dock down near Norfolk and called the lab to come pick him up. This only happened once, but it made Wood a legend around the lab.
He's one of them.  The green ones.  I've seen a few.  I've been sick, but never green...

Anyway, it's a good article.  Read the whole thing.

No comments:

Post a Comment