Why are some areas on the bottom of the ocean teeming with life while others are like a watery desert? Trawl fisherman and part-time collaborative research participant Marshall Alexander points out that biologically rich areas are regions that have been “worked” or dragged over. This, claims Alexander, increases productivity and hence fish abundance. Pose the same question to researcher Michele Dionne, and she will tell you that this “patchy” phenomenon is a complicated issue involving natural disturbances (such as storms) and predator and prey dynamics overlapped with human activities all of which vary in time and space.
With funding from the Northeast Consortium, a group of scientists and fishermen from southern Maine are working together on a research project to get to the bottom of this question. The project takes advantage of fishermen’s expertise and combines it with a research scientist’s approach.
The project focuses on benthic (bottom) habitats in relation to juvenile fish distribution and is trying to find a link between substrate type (such as gravel, fine clay, mud or rocky bottom), fish abundance, and human activity. As management changes from a single or multi-species regime to an ecosystem-based approach, fishermen are becoming increasingly worried about more and bigger area closures. The project will collect baseline information about the bottom habitat associated with juvenile groundfish such as cod, Pollock, flounder and haddock and measure the effectiveness of area closures as a management tool and help define essential fish habitat (EFH). The principal investigators in this project are Wells National Estuarine Research Reserve (NERR) researchers Michele Dionne and Rich MacKenzie and fishermen Vincent Balzano, Marshall Alexander, Kenneth Young, Pat White, Pete Innis, and Canoopy Nieuwkerk.
On a calm, sunny day in August, Alexander’s 54-foot dragger DE DEE MAE II meets up with the F/V NORTH STAR to go over the sampling strategy for the day. Balzano, captain of the NORTH STAR, is geared up for beam trawling. The beam trawl is used to collect juvenile groundfish. Balzano and his fellow research partners Jim Dochtermann and Fred Dillon are going to catch juvenile groundfish along a ten mile transect ending offshore over Jeffreys Ledge in the Gulf of Maine. Jeffreys Ledge is known to be an important feeding and spawning area for groundfish, and is located approximately 20 miles off the coasts of New Hampshire and southern Maine.
Meanwhile, Alexander and Mackenzie arrive equipped with a sediment profile imager (SPI camera) and a bottom grab sampler aboard the F/V DE DEE MAE II. Their job is to collect sediment samples and take pictures of the sea floor and the animals that live there such as worms, clams, and shrimp.
In addition to documenting bottom structure and comparing it to juvenile groundfish usage, the project participants are also studying the impacts of coastal development on the Saco, Kennebunk, Webhannet and Piscataqua River estuaries. “There’s not much data available on the near-shore groundfish assemblage” says Mackenzie. “Southern Maine is particularly important because the growth rate of the coastal population is so high.” During the summer, the coastal population in southern Maine expands by an order of magnitude. MacKenzie points out that this boom “really underlines the need to start documenting habitat change now.”
The group is using state-of-the-art technology to look at the bottom. The SPI camera penetrates the bottom layer and takes detailed photos of the sediment from top and profile views at depths up to 20 cm and can distinguish objects as small as a grain of sand.
After arriving at the first station, the SPI camera is lowered to a depth a few feet above the sea floor. While the camera dangles over 400 feet below, MacKenzie displays streaming video of the bottom of the ocean on his laptop computer on deck. MacKenzie excitedly points out a burrow made by a worm and shows a dozen archived photographs of anemones, clams, and shrimp.
Along with sediment and juvenile fish samples, these images are used to characterize bottom habitat and predator and prey communities. “In the last five years, people have started to understand the importance of bottom type on juvenile fish populations,” says MacKenzie.
MacKenzie’s data will “ground truth” earlier studies by revealing sediment composition and texture and mud-dwelling organisms in their natural state. These images from the SPI camera can be compared to maps of the seafloor made by acoustic techniques.
While steaming back to port, Alexander elaborates on his theory about bottom trawling and fish productivity, suggesting that trawl fishermen are in fact stimulating fish productivity. “I think all the dragging they’re doing down here [in the western Gulf of Maine] is keeping the fish here. It stirs up the bottom and provides food for the fish.” According to Dionne, Alexander’s observations fit right in with a basic ecological principle called the intermediate disturbance hypothesis. This hypothesis basically states that if you disturb a community a little, more species will be able to coexist, and you’ll have higher diversity. By “resetting the clocks of succession,” no single animal is allowed to dominate a particular area, explains Dionne.
Alexander has been fishing for 30 years, but with increased fishing restrictions, he has embraced cooperative research as another mode of business. Although cooperative research is a change of pace for him, it is an experience that he believes all fishermen should try. “Fishermen should be mandated to go out with scientists and scientists with fishermen; so that they can see how the other side works.”
In the future, the project participants would like to expand the sampling area and ensure long-term data collection. “You can’t do a habitat study in two weeks” insists Alexander. So far, it is too early to make any conclusions about juvenile fish usage and habitat type, as there are many factors that may affect juvenile groundfish distribution such as prey availability, human impacts, and physical structure. As MacKenzie put it “there are so many variables that if you tweak one thing, you could affect the whole system.”