Bottom Tending Gear Used
in New England
by
Ronald Smolowitz
Coonamesset Farm, East Falmouth, Massachusetts
(from Effects of Fishing Gear on the Sea Floor of New England Link to publication page)

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. 
 

Image of New England marine ecosystem
Figure 1: MARINE LIFE CYCLE
drawn by Robin Amaral
Figure 2 is an artist's rendition of the New Bedford style scallop dredge, with the top removed to better illustrate the gear. Although removing the dredge top is not a management proposal for scallop fishing, large mesh twine tops are being explored as a means of reducing finfish bycatch in the scallop fishery. Scallop dredges are commonly defined by the width of their frame. Most of the vessels tow two 15-foot dredges or two 13-foot dredges. The front of the steel frame is called the bale and usually rides off the sea floor' except in hard rocky bottoms where it might hit. The bottom of the aft part of the frame is called the cutting bar. It rides about four inches off the bottom. In a flat area, it remains off the bottom, but in areas with sand waves, for example, the cutting bar hits the tops of the sand waves and tends to knock them out. 
 
Link to diagram of scallop dredge
Link to Scallop Dredge diagram
The sweep chain is attached to each end of the dredge frame at a reinforced bottom pad called the shoe, which is basically a short dredge runner. The chain sweeps back in an arc to which the bottom of the ring bag is attached. There is a club stick at the very end of the ring bag that is responsible for maintaining the bag's shape, especially during handling on deck. The ring bag drags on the bottom. A scallop fishing vessel working an area repeatedly for a long time will tend to flatten out the sand waves. 

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. 
 

Link to Otter Trawl diagram
Link to Otter Trawl diagram
The doors and other parts of trawl gear have been designed to generate mud clouds, because mud clouds tend to herd fish into the path of a trawl and keep them in that path. As mentioned above with scallop gear, there are concerns now about the impact of sediment resuspension. In addition, trawl gear used to be smaller and towed at lower speeds. In New England, the primary target was haddock, which meant towing over a particular type of bottom and leaving other bottom types unfished. By using larger trawls, higher speeds, and mixed-species targets, fishermen are now trawling the whole ocean in a general sense. Habitat that once remained untouched by mobile gear in the past now is being fished. Bycatch problems with trawls are often generated by the man agement regime, with species by species management and the gear clearly tends to resuspend sediment. From a management perspective, concerns about trawls relate to the fishing power of the gear, species selectivity, size selectivity, and bottom disturbance. In my opinion, it would be good to develop low impact bottom trawls and to define critical habitat in which it might not be appropriate to use 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. 
 

Link to Gillnet diagram
Link to Gillnet  diagram
Gillnets in the past were made of inefficient twine materials-twine made of natural fibers such as cotton. In many cases fishermen had to fish the gear only at night to make it efficient, and the vessels were not able to handle all the gear that was needed. Gillnetters used to need three sets of gear. A vessel had to have one set fishing, one set in transport, and one set on the beach, drying. Now we have very efficient materials monofilament and multifilament synthetic mesh, as well as high net numbers. The main issues surrounding gillnets have to do with marine mammal entanglement and fishing power. Gillnets have many positive attributes because they are able to target fish by size and to be selective for certain species. In general, the gear is considered habitat friendly compared to towed gear. In my opinion, the key issue with gillnets is fishing power, or the number of nets that an individual vessel is allowed to fish. Marine mammal entanglement concerns are also related to net numbers. Reducing net numbers will also address another concern-inappropriate fishing strategies, whereby gillnetters leave nets out to occupy bottom and prevent other users from fishing on that bottom. Figure 5 illustrates the design of lobster traps. The entrance head usually allows lobsters very easy access into the front part of the trap, or the kitchen. From the kitchen there is a long sloping head to the second part of the trap, the parlor. In the parlor there is an escape vent to allow small organisms, such as small lobsters and crabs, to escape from the trap. Lobster traps can be fished singly or strung together in trawls. Single traps are often used in rough, hard bottom areas where trawl strings tend to foul on bottom structure. They are fished in trawls on flatter types of bottom. The process of hauling a trawl drags the traps over the bottom. The amount of bottom that is affected by a single string of traps during the setting and hauling process is not significant. However, if one multiplies that effect by the three million traps being hauled several times a week, a significant cumulative effect is possible. 
 
Link to lobster pot diagram
Link to Lobster Pot diagram
During colonial days, lobsters were so abundant that they were harvested with hoop nets and spears. Eventually, lobstermen started using single parlor traps in the inshore waters. As lobsters became more scarce and longer sets further off-shore were needed, the two-compartment trap was developed. This trap design could contain more lobsters for a longer time. In most cases, the bycatch from lobster traps is released in good condition, so bycatch is not a major issue. The escape vents offer pretty good size selectivity. An important concern with lobster traps, currently, is whale entanglement in the buoy and string lines. Figure 6 illustrates bottom longline hook gear. One of the interesting things about hook gear is how much its fishing effort has decreased. At the turn of the century, a fishing schooner might have quite a few dories on board which could be handling 16,000 hooks and hauling them twice a day. Thus it fished 32,000 hooks daily. Today, hooks are used mostly on small coastal vessels that set around 500 hooks per day. A few vessels in New England gear up with 10,000 to 15,000 hooks. In other places in the world, 40,000 hooks automatically hauled and set daily is not out of the question. The new circle hooks are a little bit more efficient than the old "J" hooks. In general, I donít think there is any direct impact on habitat by hook gear, though there may be some indirect effects on the habitat from the selectivity of the gear. 
 
Link to Longline diagram
Link to Longline diagram
In conclusion, the definition of overfishing is a key concern from a habitat standpoint, in my opinion. Overfishing is currently defined in the Federal Register as the rate of fishing mortality that jeopardizes the long term capacity of the stock to produce the largest average annual catch on a sustained basis. Overfishing must be defined in measurable parameters, according to national standard one of the Magnuson-Stevens Fishery Conservation and Management Act. Measurable parameters include fishing effort, catch and catch rates, and abundance estimates. Numbers are an excellent aid to reasoning, but it is an increasingly common error to use only the numbers available and to fail to quantify the rest of the situation. An important part of the rest of the situation is fish habitat. Because impacts to habitat can not be quantified, they tend to be ignored. 

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. 

 
 
Link to gear effects directory