Keeping alive an ecosystem

ON THE BAY

Management: To keep the Chesapeake Bay healthy, scientists need to better understand how its species interact.

August 27, 2004|By Tom Horton | Tom Horton,SUN STAFF

ALL our best and most valued food fishes are only menhaden in another shape," W. K. Brooks, an eminent bay fisheries scientist, said in 1903.

He understood how the oily little menhaden, also known as pogy, bunker, bugfish or alewife, were a mainstay in diets of so many top-of-the-food-web piscivores.

But for much of the 101 years since, managers allocated harvests of menhaden as if only one consumer - the fish oil and fish meal industry - need be assured its slice of the pie.

That is beginning to change as recent downturns in the bay's menhaden - for reasons unclear - are linked to nutritional stresses in striped bass.

It's clear that the rockfish must get a cut of the menhaden action too; also bluefish and speckled trout, not to mention summering ospreys and fall and spring migrating loons.

Even larger possibilities loom for more smartly managing menhaden. They feed by filtering bay water, sopping up by the billions of pounds each year the algae with which the modern bay is overburdened. Allowing more of them to grow larger could have significant water-quality benefits.

Viewing the whole bay

Menhaden cry out for the kind of enlightened fisheries management that considers their value to the whole bay ecosystem. And they are hardly alone.

Oysters have become the poster child for species whose role in keeping the bay clean and productive exceeds their value on the half shell. They filter and cleanse the water, and the reefs they form are favored habitat for 57 species of fish.

Similarly, the eggs of horseshoe crabs that spawn on beaches around Chesapeake and Delaware bays are critical replenishment for a variety of migratory shore birds. A species once considered good only for bait and fertilizer is now key to hemispheric bird populations.

Blue crabs, eating darn near everything, including one another, and eaten in turn by hordes of other species, are well documented as critical in the greater Chesapeake scheme of things.

But they may also play a less obvious role in protecting bay marshes. Recent research in marshes of Virginia and Georgia indicates that a dearth of blue crabs can allow one of their prey, the unassuming little periwinkle snail, to expand enough to overgraze and destroy salt marshes.

This bears more study, but similar interaction has occurred on coral reefs in the Caribbean. Disease killed off spiny sea urchins, allowing the algae that they normally kept grazed down to overrun the corals.

In a twist on this, destruction of sea otter populations in the Pacific northwest allowed one of the otters' prey, the sea urchin, to explode in numbers, devastating kelp beds.

Fully comprehending all the ways each species fits in the Chesapeake's ecosystem is not rocket science - it's a darn sight more complicated. But scientists and fisheries managers know enough to make a start at true ecosystem management, and it's past time they began.

Declining harvests

Traditional management, regarding species as if they existed in a vacuum, has seen annual commercial harvests of bay seafood fall from above 300,000 metric tons during the 1950s to about 250,000 tons during the 1990s - and plummet just in the past decade to 200,000 tons.

And there has been a decline in diversity. Just two species, blue crabs and menhaden, make up about 80 percent of the tonnage today.

The state-federal Chesapeake 2000 agreement that guides bay restoration calls for ecosystem-based management plans for a handful of bay species by 2005.

A roadmap for devising such plans, Fisheries Ecosystem Planning for Chesapeake Bay, has been assembled by the bay's leading fisheries scientists, many of whom donated their time.

The 360-page document, available from the National Oceanic and Atmospheric Administration, should dispel notions that the bay has been "studied to death." Of 22 major bay species, basic information needed for ecosystem management is lacking for half, the report says.

The tiny bay anchovy, for example, is so abundant at times it may supply the bulk of annual nutrition for some of the bay's birds and larger fish. Yet we know little about what causes huge periodic fluctuations in their numbers.

Maybe we don't need more study and smarter management of the bay's fishes. Maybe it's just been a run of bad luck that we reduced shad to 1 percent of their historic catches, striped bass to 10 percent, oysters to the point of collapse, blue crabs and menhaden to historic lows.

Maybe it's just coincidence that only four of 22 major bay species are at healthy or high levels of abundance.

Maybe I'll put my faith in more study and management, as if nature mattered, too. The NOAA report is a good start on getting there.

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