What Does the Seafloor Say?
On June 1, 1999, the research vessel Albatross IV set out on a ten-day cruise of the eastern Georges Bank. Built in 1962 for the National Marine Fisheries Service’s (NMFS) biological lab at Woods Hole, the Albatross IV is specially equipped to collect information on the distribution and habitat of groundfish and sea scallops in the Northwest Atlantic Ocean.
Georges Bank is the southernmost part of a chain of huge shoals that extend from Newfoundland to southern New England, on the edge of the North American continental shelf. They were one of the world’s richest fishing grounds until the last decades of this century, when overfishing on a massive scale brought many fish populations, including cod, haddock, herring, and scallops, to the brink of commercial extinction. “In the last ten years a huge amount of biomass has been removed,” says Dr. Jeff Cross, Chief of the Ecosystem Process Division of the Northeast Fisheries Science Center of the National Marine Fisheries Service. “Some areas were trawled several times a year.”
A Unique “Before and After” Opportunity
The Albatross IV cruise was designed to take advantage of a unique window of opportunity. In 1994, two areas of Georges Bank were completely closed to fishing and scallop dredging in order to give juvenile groundfish a chance to survive and grow. [link to G3-Trawling takes a Toll] In 1999, half of what had been designated Closed Area II was about to be reopened to scallop fishing. The Albatross IV cruised primarily within Closed Area II and the surrounding waters to monitor the resilience of the ocean bottom by comparing the areas closed to fishing, which had been untouched for four and a half years, with grounds outside the boundaries. Researchers designed a study which paired 48 stations in and out of the closed area.
Dr. Cross had observed that inside the protected area scallops were far larger, 7 to 12 per pound compared to 20 to 30 per pound outside. “The ones outside the area never have a chance to grow,” he explains. “This is a new area to get a lot of attention from scientists. There is good evidence that in areas where animals use rocks for shelter, it takes years for this kind of habitat to recover.” The underlying objective of the current study is to provide accurate scientific information on which to base sound management and legislation decisions. “We're trying to characterize the habitat from a geological and a biological point of view,” explains Page Valentine, a geologist with the U.S. Geological Survey. ‘When we’ve obtained some baseline information about the different kinds of habitat, their function, their use by certain species, we can provide it to managers of the fisheries. Then they can determine how the bottom is going to be utilized. Right now,” he continues, “so little is known about the function of these habitats and their distribution that it's hard for the managers to make decisions.”
Sampling the Ocean Bottom
“We’re interested in biodiversity and we want to get a handle on what goes on down there, because we don't really know. And basically the only way to do it, except for using a submarine or a remote operated vehicle, is to bring part of it up,” explains Dave Packer of the NMFS. Working on the sea bed is far more difficult than on land, and scientists are restricted in how much information they can gather while at sea. The research is designed to produce an overall portrait of the different types of bottom habitats and the organisms they support. Monitoring the sea floor is an ongoing process that ideally requires constant updating, since environmental change and fishing patterns can greatly affect the growth rates of many species, setting up a complex feedback loop.
The crew sampled the ocean bottom using three different techniques:
an otter trawl
This standard trawling gear consists of a large net pulled along the ocean bottom. The upper edge is held up by floats and the net is kept open by giant wooden or steel planks on either side, called otter doors. In this study, a 15-minute haul was made at each station, and the catch from the grab counted, weighed and measured. The scientists also looked at the fish's stomachs in order to make a direct correlation between what the fish are eating and what kind of animals actually live there. “We want to understand the food chain because a lot of what lives in and on the bottom is basically fish food for many of our managed species,” explains Packer. “A lot of the various trawls and nets that the fishermen put out have the potential to disrupt that bottom habitat. And you know, if you destroy the food web down there or disrupt the food web, you're gonna eventually be hurting the fishes that you're trying to catch.”
a Seabed Observation and Sampling System (SEABOSS)
This system uses two video cameras (one pointing forward and one downward), a 35mm still camera focused on the ocean floor, and an instrument called a grab sampler. As the Albatross IV drifts for 20 minutes, the apparatus “flies” above the sea floor, videotaping it in real time. At the same time, representative still photographs are taken and samples of the top few centimeters of sediment collected. The samples are used to determine grain size, and the images serve to quantify the distribution of different microhabitats and their relationship to fish. “Much of the fish that is harvested here off the East Coast are groundfish, which live on the bottom for most of their lives. So the nature of the bottom is really very important to them, as a source of food and of refuge from predators,” says Valentine. “It's really their environment, so it's really a requirement for fisheries management to know what factors are altering it, and actually forming it.”
a Smith-McIntyre a spring-loaded bottom sampler
This is a metal frame with two jaws that snap together when they hit bottom. It collects one -tenth of a square meter of bottom—mud, rocks, or sand—as well as the tiny animals, mostly invertebrates, that live in or on the bottom: worms, crustaceans, sand dollars, scallops and other mollusks. “We sift out all the sediment to leave just the animals behind, identify them, count them and weigh them, to get an idea of the actual community structure: how many animals there are and who might be eating whom, because we know the life histories of a lot of these animals,” says Packer. Different types of bottom are home to very different communities, and some are highly diverse, “especially areas that are mixtures of both sand, mud and larger boulders and rocks. They provide habitat for young fish and they provide habitat for the invertebrates upon which the fish feed,” he explains. Other instruments also measured water temperatures and salinity.
Back to the Lab
When the Albatross IV returned from its research cruise, the various samples--the images, VanVeen grab samples, marine organisms preserved in formalin, and feeding ecology data--were turned over to the NMFS laboratory in Woods Hole, Massachusetts, for analysis, while sediment core samples went to the NMFS’s Howard Laboratory in Highlands, N.J. “Probably within 6 to 9 months we will know if we see a difference between the two areas, and an indication of whether or not the change is significant,” says Cross. “It’s a snapshot, but a significant one,” says Dr. Peter Auster, science director of the National Undersea Research Center at the University of Connecticut, who also participated in the cruise.
And Back to the Ocean
The information gathered and analyzed from the June 1999 cruise will provide the scientists with one data point in time. More data points, on shorter time scales, are needed for a more complete portrait of the sea bed’s condition. Since frequent assessments aren’t logistically or financially feasible, the idea is to pick key areas and habitats and use that information as a guide for management. Within two months of Closed Area II's reopening for scallop fishing, 145 vessels had removed a total of 3.1 million pounds of scallops. That constitutes one-third of a total allowable catch of 9.4 million pounds, and the season extends to the end of the year. The NMFS has a cruise planned to the same area for June, 2000, at least six months after the scallop fleet has departed. As in 1999, the crew will assess the number of fish, the number of invertebrates, and the appearance of the habitat. “We’ll see what’s there that wasn’t and not there that was, and then we’ll combine all this information for a second data point,” says Cross.
“How quickly do these habitats recover from trawling and dredging?” asks Cross. “That’s the crux of the issue. How quickly do animals come back, does the structure of sediments return to their former structure? If recovery takes six months to a year, then that gives you one option for managing. If it takes a decade that that’s a whole different issue.” Studies have shown that communities in sandy habitats recover more quickly than those in gravel or hard-bottom habitats, where organisms are more long-lived and disturbed less often. It’s a complex equation, into which the timing and nature of fishing efforts also need to be factored. “In addition, we need to understand the linkages between sea floor habitats and economically important fishes,” says Auster. “More fundamentally, we need to view fish and fish habitat as components of regional biodiversity.”
What Lies Ahead for Georges Bank?
For the first time in 30 years, there are some signs of recovery of groundfish on Georges Bank. Growing awareness of the impact of trawling on marine ecosystems and of the need to preserve marine habitat is leading to more research and more effective legislation, such as the 1996 Sustainable Fisheries Act. One fisheries management concept is area rotation, in which certain places are closed for the amount of time it takes for stock to regenerate or the habitat to recover. However, Auster points out that, unlike in the case of crop rotation, “we’re not talking about planting anything. We’re talking about altering a natural system and assuming that during the period when we’re not altering it, the system will return to a state that’s economically productive.” Studies like the one conducted by the Albatross IV will help establish where and at what intervals area rotation might be effective.
Some areas of Georges Bank remain completely closed to fishing. On paper, however, the only reason is to give cod, haddock and yellowtail populations time to recover, “not for conservation or habitat integrity or biodiversity. Once those particular fish populations have recovered, then there is all the rationale in the world to open them up. Is that something we want to do?” asks Auster. He proposes a larger-scale priority. “If we start managing for maintenance of biodiversity--as opposed to looking at fisheries and biodiversity as two totally different objectives--then sustainable fisheries should be a natural outcome.”