The need for long-term data


Research: Information gathered for decades, and independently of fisheries, paints a more accurate portrait of the Chesapeake's crab population.

March 09, 2001|By Tom Horton | Tom Horton,SUN STAFF

IT WAS 1954, and down on Virginia's York River, a young fisheries scientist named Willard Van Engel began wading waist-deep through the eel grass beds, pushing a modified dip net before him, to see what he could see about the Chesapeake blue crabs living there.

In the spring of 1968, up the bay in Maryland, George Abbe, a biologist with the Philadelphia Academy of Natural Science's Patuxent River laboratory, began another crab survey, fishing a few dozen pots near the new Calvert Cliffs nuclear plant.

Neither man's crab harvests would have impressed a waterman, but the crab data their efforts generate to this day are proving invaluable to preventing the collapse of the Chesapeake blue crab population.

Such long-term, repetitive, boring, unsexy monitoring is a large underpinning of the unprecedented proposals by Maryland and Virginia to jointly reduce fishing for crabs.

If I could go back to the 1950s, when the bay was in better shape, and make a single change to maintain its health, it might be this:

Institute excellent, comprehensive monitoring of the estuary's vital signs, from sea grass beds, to fish and shellfish, to the oxygen in its depths.

We wasted so much time arguing, as the bay declined between the 1960s and the 1980s. Was it natural cycles or unnatural downtrends? Were things really worse than in the past? Were human or natural causes to blame?

The dearth of reliable, long-term data meant that many hard decisions were postponed long past the time for action.

The power of long-term monitoring was illustrated in the 1970s, when scientists chanced upon forgotten 1930s studies of the Patuxent River in the attic of a laboratory.

The studies proved that vital oxygen levels in the river's water really had been higher in previous decades. The data were critical in rescinding weak pollution control plans that would have ruined the river.

Had long-term data about the bay's submerged grasses and other keystones of a healthy system been gathered since the 1950s, we'd be much closer to restoring North America's greatest estuary.

With blue crabs an economic mainstay of bay fishing, and a virtual public icon to boot, one might think there'd be an abundance of information about them.

Governments have published the number of pounds and bushels of crabs harvested from the bay for about 115 years. But monitoring catches is a flawed way of tracking the health of any species.

Commercial crabbers take only certain sizes, which can change over time as legal limits change. Crab harvests change subject to market prices for crabs and for alternate species like rockfish; they also change as fishing gear and techniques change.

Such data make comparisons between past and present shaky, and at best tell you only what's being caught, not what's out there.

A "fisheries-independent" study like George Abbe's, which is not dependent on commercial harvest data, shows the problems of looking only at catches ("fisheries-dependent" data).

Abbe never varies his gear or fishing effort or fishing location, and counts all sizes of crabs caught each year in his 30 crab pots.

His 34-year study, which was begun to measure any adverse impacts of Calvert Cliffs, has shown that male crabs in the bay are getting smaller over the decades.

"It's not so much that I'm catching fewer crabs as I'm catching fewer big crabs," says Abbe, 57 and hopeful that he'll continue to crab for several more years.

Heavy fishing is simply taking most male crabs (considered more desirable than females) soon after they reach the five-inch legal size (male crabs easily reach six inches and, more uncommonly, eight or nine inches, if allowed to grow).

Smaller crabs mean a waterman might actually show the number of bushels of crabs he caught as unchanged over the years, Abbe says; but because more crabs are required to fill a bushel, the catch data would conceal that more crabs are being caught.

Another wealth of data illuminating the crabs' true, imperiled status results from 46 years of the Virginia survey that evolved from Van Engel's early dip-netting. He and a colleague expanded the study, dragging nets along 45 miles of the York River behind an old "draketail" workboat.

Van Engel, 85 and retired, still participates in bay crab science. His survey now covers several rivers and the open bay. It has documented an 80 percent to 85 percent drop since 1991 in the number of crabs old enough to spawn, says Rom Lipcius, a Virginia crab ecologist.

"The data suggest something environmental happened in 1991 that substantially reduced the crabs going into the spawning stock," he says.

It's another example of why we need "fisheries-independent" data. Watermen might not be catching many more crabs or fishing harder than in 1991, but the depleted spawning population can't stand as much pressure now.

In 1990, a third key data collection was begun. Each winter, Maryland and Virginia sample the crabs on the bottom at 1,500 spots baywide. This provides the best look yet at how many crabs -- it fluctuates annually from a few hundred million to several hundred million -- are there for the next summer's harvest.

This winter's survey foretells another lean year. The proposed 15 percent cuts in harvests might have to be bigger.

No one will thank the data collectors for such news. But without the scientific management they make possible, we'd be risking the bay's greatest remaining harvest.

Baltimore Sun Articles
Please note the green-lined linked article text has been applied commercially without any involvement from our newsroom editors, reporters or any other editorial staff.