I will address how we create wealth from the marine environment by harvesting the larger animals that live amongst the rocks and mud and eat the little critters. Basic wealth is created by only a few industries-farming, fishing, forestry, mining, and idea creation. All other human endeavors are built upon this wealth. Our task is not only to create wealth from our New England marine ecosystem in a sustainable manner, but also to enhance the production of this wealth. As a starting point, we need to know how we currently harvest this wild crop and what sustainability issues are associated with the harvesting tools. Key among these issues are bycatch and habitat impact, which are in fact closely related. I will briefly describe the principal bottom tending gear used in the region and indicate the points of impact with the bottom.
Bycatch is a combination of the target and nontarget species. In many cases, the nontarget benthic organisms are discarded. In the past these organisms were referred to as trash by scientists and fishermen alike. I remember filling out trash logs on the data sheets on fisheries research cruises. It is interesting how our view of the world changes. I suggest that as our knowledge of ecosystems matures, some of todayís bycatch will become classified as weeds, to be controlled, and some will become prized targets.
In many cases, bycatch is defined by regulations. Certain fisheries
are only allowed to catch a particular species. One important point is
that bycatch is not always bad and that making gear selective for species
or spcies complexes is not always good. Figure I illustrates the complexity
of a typical local ecosystem and presents a real case scenario from Nantucket
waters. There is a fishery for tautog, a hook and line fishery. The tautog
are known to feed on the green crab, which are known to feed on the small
bay scallop larvae. A few years ago fishermen overfished the tautog, and
there was a population explosion of the green crab. The green crab then
fed on the incoming scallop spat, and the scallop fishery collapsed. In
this case, a very selective fishery for the tautog had negative ecological
consequences on another fishery. It might have been better in the long
run to have a less selective fishery with some bycatch mortality of the
crabs in balance with the tautog harvest. This may have resulted in better
production and a more balanced ecosystem. When we think about habitat,
we need to be aware that the issues are broad and complex, and that the
solutions are not as simple as they may appear.
For hard bottom scalloping, in addition to tickler chains that run from side to side between the frame and the ring bag, there are also chains that run from front to back, known as rock chains (Figure 2). On rocky bottom, fishermen put a lot of rock chains in to prevent boulders from getting into the ring bag.
Underwater video of dredges being towed at speeds of five knots show that the chains do not dig into the bottom. They skip over the surface and hit it periodically. The chains tend to pop up organisms like starfish that are on the bottom. Some digging into the sand must take place, because at times burrowing clams end up in the dredges.
In the past (mostly before 1975), scallop dredges were relatively light gear limited in width and structural strength. The vessels were smaller than at present, so they were limited in the seasons they could fish. They had lower horsepower, so they could not tow the gear over many types of hard bottom and substrate. There has been an expansion in dredge size and weight and strength, and the horsepower of scallop vessels has increased. This enables the vessels to tow faster and to get into types of bottom that they were not able to tow in formerly.
Current issues related to scallop dredging include bycatch of monkfish, flounders, lobsters, and benthic organisms. Selectivity of the dredge is now controlled by the size of the rings. Current regulations require rings of 3.5" diameter. With larger rings, fewer bottom organisms come up in the dredge bag. However, this does not mean that they are not disturbed by the gear. Another key issue related to the gear is the impact scallop gear may have on the bottom. There is an indication that working the bottom with scallop gear resuspends sediment. Sediment impacts might cause some damage and mortality to small scallops. Fishermen have also noticed that working the bottom may increase the production of scallops from year to year. This might be the result of spreading out the scallops and/or somehow controlling predators.
The next type of gear I will review is the bottom trawl (Figure 3).
Trawl doors, which function to keep the net open laterally, tend to leave
a groove on the bottom, depending on the hardness of the substrate. They
could dig in as much as 10- 15 cm. There are many different types of ground
gear that can be used on the sweep of bottom trawls, from simple drop chains
to sweeps made of six-inch roller cookies to large bobbins to rollers.
The overall impact to bottom habitat of each type of rig is not necessarily
obvious at first glance. For example, fishing hard bottom gear with large
rollers allows many bottom organisms to escape unharmed under the net.
There are spaces between the rollers on the sweep that allow small fish
and organisms to escape. On the other hand, this rig allows the net to
be towed over substrate that would normally support many organisms that
grow vertically and would otherwise remain unaffected by mobile gear.
Bottom set gillnets used in New England are diagrammed in Figure 4.
An individual gill net is usually 300 feet long. Usually 10 to 20 nets
are tied together in a string, and a fishing vessel might fish 5 to 20
strings. Groundfish gillnets are currently limited to 80 or 160 nets per
vessel, depending on target species. In temperate regions like New England,
few questions have been raised about habitat impacts of gillnets, per se.
There is concern about ghost fishing after nets are lost and what impact
that has on organisms on the bottom. In more tropical regions, there is
concern about damage to coral when hauling and setting strings of gillnets.
Scientists have not been able to quantify substrate alterations, sediment resuspension, destruction of benthos, and alteration of behavior. Fishery managers tend to forget that they are dealing with living organisms. In my opinion, the habitat impacts of fishing may insidiously keep ecosystem production depressed by an undetectable amount by chronic sublethal effects on reproduction and feeding. These effects are indetectable because they are masked by the overall fishing effort. I would propose to replace the rate of fishing mortality definition with cumulative fishing impact, and to describe and quantify, where possible, all gear impact on ecosystem productivity.
Finally, discussions about habitat in a management context usually focus on closed areas. It is interesting that the term closed areas is used instead of managed areas. Closed area is automatically a pejorative term for commercial fishermen. The biggest problem at present with closed areas is that they cannot be enforced effectively. They are also difficult to reopen mainly because the reasons they were closed in the first place do not vanish. For example, if these areas were closed in order to protect habitat, any gain would then be lost as soon as the area was reopened. There are also questions about how to allow access into a newly opened closed area. One proposed solution is to allow only fixed gear in areas that might be critical habitat. One advantage to this approach is that it could be self-enforced by the passive gear users. The benefits inside these areas could be harvested to create basic wealth, which might provide incentives to move the industry toward habitat-friendly gear types. Another possible solution involves farming strategies. Fisheries depend on natural sets of animals, with no control over where they set. It might be beneficial to set commercially important animals in the types of habitat that are most appropriate for towed gear.