How Many Fish In The Sea?

October 7, 2007

Release from: Molly Murray
The News Journal

From the wheelhouse of the First State, Captain Michael J. Garvilla pushes a throttle and begins the process of lowering a single net into Delaware Bay.

It is a picture-perfect morning -- "right slick cam," as a waterman might say. The water tower of Lewes glows silver in the distance, and the black shape of icebreakers, installed decades ago to prevent ice from flowing down the bay, lie just ahead.

For 20 minutes, Garvilla and a team of state fishery scientists and technicians wait while the net -- always pulled into the tide -- drags along the bottom.

On deck, Garry Glanden slowly advances the net back onto the reel. He stops from time to time to let the scientists remove a small shark, a whelk or another creature caught in the upper reaches of the mesh. It doesn't look like much of a catch and then you see and hear the mother lode -- hundreds of fish writhing in the bottom of the net.

There are spot, weakfish and skates, sharks and sponges. Croaker prattle like Gatling guns. There is a puffer fish, so tiny it looks like it could slip into your pocket like a quarter, and a summer flounder, shaped like a dinner plate. There are the lumpy back of an oyster toadfish and the fan-shaped pectoral fins of sea robins. It makes a weekend angler wonder, why, after years of hook-and-line fishing in Delaware Bay, you catch so little when there is so much here?

These surveys, done month after month, year after year, are like pieces of a puzzle with which scientists and environmental regulators construct a deeper understanding of the creatures inhabiting the Delaware River and Bay and Rehoboth and Indian River bays.

Data from these journeys into the sea determine when commercial and sport fishing on some species must end, when it can expand and how many pounds in a particular year or season the state's small group of commercial fishermen can harvest of such restaurant fare as blue crab and striped bass.

On this survey along the bay bottom near Lewes, one thing is clear: this is not a great trawl, said Stewart Michels, a state fisheries biologist. Michels expected more, based on years of monitoring the late summer and early fall fishes of Delaware Bay.

'Trends over time'

The trawl surveys of 2006 were pretty good -- above-average catches of summer flounder, weakfish Atlantic croaker, scup, spot, white perch and striped bass. In all, state fisheries scientists tallied 47,500 fish, from 57 species. There were thousands of invertebrates, too. But the bulk of the catch -- 84 percent -- was just six species.

With each trawl, Michels and others who study the diversity, size and dynamics of fish populations in Delaware get more data and more clues into the mysteries of this unseen world.

"The value of this survey is looking at the trends over time," he said.

At this instant, it gives fisheries officials a snapshot of what is going on just off Lewes Beach near the mouth of Delaware Bay on one beautiful September morning.

The trawl surveys provide volumes of data, but often, the data raise more questions than answers. Take, for instance, weakfish -- once Delaware's dominant commercial fish catch.

In 2005, commercial landings were at the lowest level in Delaware Bay since 1970. In 2006, weakfish were the second-most abundant catch by number in the Delaware Bay large trawl survey. But for recreational anglers, it's almost impossible to catch a keeper these days, 13 inches long or longer.

Or consider Atlantic croaker. They were all but non-existent in commercial and recreation catch data from the 1980s. Michels said summer wind and temperature probably play a big role in abundance. These days, they are among the most abundant of fish in the trawl surveys.

Trawl surveys have provided scientific data from the Delaware River and Bay and the Inland Bays for more than four decades.

In 1958, Carl N. Shuster Jr. was working at the University Marine Lab in Lewes -- the precursor to the University of Delaware College of Marine Studies. Shuster would go on to become the world's most renowned researcher of horseshoe crabs. A sanctuary for horseshoe crabs at the entrance to Delaware Bay is named in his honor.

At the time, though, Shuster and two other researchers were interested in the fish and ecological conditions in the Delaware Estuary.

Between August 1958 and February 1960, they conducted trawl surveys at 16 sites. In all, they found 66 species. They concluded that 41 of the 66 species depended heavily on bay anchovies, silversides and the host of bottom dwelling creatures called benthic invertebrates.

The scientists also found the richest diversity of young fish in the "luxuriant growth of intertidal plants."

But mostly, they pointed out what they didn't know.

"We lack truly comprehensive data on the biological, physical, chemical and geological characteristics of the waters as they were 100, 50 and even 10 years earlier," they wrote in a 1962 paper. "The lack of a suitable yardstick by which to measure these changes will be more apparent as the trend of unnatural ecological changes continues in estuaries."

Even today, Shuster sees the same key issues facing the Delaware estuary.

Ask him if there is trouble at the base of the food chain and he says no.

"What is more important is the loss of habitat," he said. It is especially true with horseshoe crabs, which depend on sandy beaches for spawning, he said.

Scientists trying to rebuild the population are "missing the boat," he said. "The problem may well be with the loss of spawning habitat."

Wide changes

When they first published their study, the scientists pointed to the potential for environmental changes in the estuary and found that deforestation and land-use changes had already resulted in higher temperatures in the water that ran off into the Delaware River. The warmer water, they wrote, had less capacity to hold oxygen. High loads of silt and nutrients, along with industrial and domestic pollution, would cause additional changes in the ecosystem and pose a threat.

The scientists weren't far off in their predictions, Michels said. Pollution did cause serious problems for fish, especially in the Delaware River. Each spring into summer, there was a dead zone -- where oxygen levels dropped dramatically -- that blocked the successful passage of large schools of spawning fish into the fresher waters of the estuary.

That dead zone disappeared as Philadelphia and Wilmington cleaned up sewage discharges going into the river. But the legacy of industrial pollution continues, complete with fish consumption advisories.

As for the lush beds of underwater vegetation that early researchers found, they still exist. Bart Wilson, a scientist with the state Coastal Management Program, has been working on a survey of the Delaware River and Bay bottom. He has found beds of wild celery, a plant that grows underwater, up near Marcus Hook.

Further south, turbidity is too high to support underwater vegetation, he said. But "we definitely found a whole bunch in the Delaware River."

From the earlier study, there were changes the scientists didn't foresee.

Dredging the shipping channel in the river has increased salinity, said Dewayne Fox, a fisheries biologist and assistant professor at Delaware State University.

Fox said fisheries biologists have for years grappled with the questions of why some fish species thrive while others don't.

A species Fox and his graduate students study is the Atlantic sturgeon -- once an important commercial species in the Delaware River. These days, the fish is so rare researchers often have difficulty finding fish to study in the estuary.

Most fish have the capacity to reproduce at astonishing rates. A single 12-pound female striped bass, for example, produces 850,000 eggs a year. A larger female, at 55 pounds, will produce as many as 4 million eggs in a spawning year.

There can be huge population swings due to slight changes in water temperature, wind direction, predation or food availability, Fox said.

The state's juvenile surveys of young fish turned up few Atlantic croaker in the early years of juvenile sampling. In 1982 and 1983, they didn't catch a single baby croaker in a 16-foot trawl net in the Delaware Estuary. By 1984, they started to see more fish, then less -- and then, in 1992, saw a juvenile population explosion. Ten years later, juvenile croakers were among the most abundant fish caught in the estuary during the juvenile trawl survey. The numbers dropped dramatically in 2003, rose and dropped again in 2005.

Spot have a similar wild ride on the data sheet. And young weakfish, though consistently abundant in the estuary, show similar, though less dramatic, annual fluctuations.

At each stage in fish development, there is a tremendous amount of mortality, Fox said: "There's a million things that can go wrong."

Changes in the summer winds might be behind the fluctuations in croaker, Michels said. Species such as blue crabs and croaker, in the earliest stages of life, depend on wind to blow them back into the estuary.

A new approach?

What's happening in Delaware Bay is just a paragraph in the larger fisheries story.

"Here, we're just looking at Delaware Bay," Michels said.

A question fish managers are beginning to look at is whether an estuary can have high levels of several species of predatory fish -- say weakfish, striped bass and bluefish -- at target population levels at the same time. They are big fish, important recreationally, but are not the apex predators in the bay. Sharks take that honor, and the shark relative -- the ray -- can also have an impact, Michels said.

Now, rather than looking at fish by species management plans, fish managers are starting to consider an ecosystem approach, examining how species relate to one another. For instance, researchers are beginning to look at how striped bass and menhaden interact in an ecosystem.

"It would be great if we could integrate all of these species into a glamorous model," Michels said.

But the inner workings of the relationships of fish, forage and habitat are extremely complex, he said.

A close look, but questions remain

On the First State, Michels, Mike Greco, another environmental scientist, and fisheries technicians Nate Rust, Jordan Zimmerman and Glanden move quickly, sorting the catch by species. Spot, spot, spot, spot. Croaker, weakfish, ray, windowpane flounder, shark. Each species goes into a different bucket. There are hundreds of fish in this haul. The bounty is tallied, weighed and measured, and most of the fish are quickly thrown back into Delaware Bay.

A bucket of fish is weighed and then emptied onto a measure board. Rust and Zimmerman shout out length measurements: "185, 150, 190, 200." Glanden makes tally marks next to the length.

The young weakfish and summer founder get special treatment, as the ear bones -- otoliths -- are removed.

Back in the lab, researchers will take cross-sections of the bones to get an idea of the age of the population.

Michels said the cross-sections allow researchers to read the rings on the otoliths like a forester reads rings on a tree trunk.

In one haul, there are hundreds of bits of data -- species composition, salinity, water temperature, water depth, size, age and weight. Dozens more tows like this one, along with trawls using smaller mesh nets in the Delaware Estuary and the Inland Bays, add thousands more bits of data.

Individual species managers keep a close eye on species of interest, but there has been little work on the big picture of Delaware Bay. When a researcher notices something out of the ordinary, he remarks, "You know that there's something going on out there."

But what?