Introduction to the Current Problem Facing Fisheries
Bycatch
Fishing vessels discard a large portion of their catch, often dead or dying. They are thrown overboard because they are too small, or have little or no economic value. Most discards are mandatory by federal regulations that require that bycatch be returned to the ocean as unharmed as possible. The measure is intended to prevent wanton overexploitation but bycatch restrictions often not implemented or enforced and even if they are, most fish returned to ocean do not survive. (Turning A Blind Eye)
Fisheries managers failed to monitor bycatch despite being required by federal laws. In order to manage effectively, managers must account for additional fish and wildlife killed as bycatch so healthy fish populations are not overfished, sensitive or depressed populations are not driven to levels below which they cannot recover, and marine ecosystems are not degraded. (Turning A Blind Eye)
High rates of bycatch can have ecological affects such as the alteration of food webs, the shifting predator-prey dynamics, and habitat destruction. Bycatch can lead to overfishing, reduced productivity, and reduced catch levels over the long term. (Turning A Blind Eye)
Nearly 1,000 whales, dolphins, and porpoises drown every day after being tangled in fishing nets and other equipment. Annually, it is estimated that 308,000 marine mammals die unintentionally in fisherman's haul. The study indicates that accidental captures ("bycatch") may be the biggest immediate threat, more than ship collisions and pollution. The IWC banned most whaling in the 1980s but Norway ignores this ban and Japan takes nearly 700 whales a year under a controversial IWC research exemption. Some native cultures are allowed to conduct strictly limited hunts. Commercial fishing advocates point out that cetacean deaths decreased 40 percent in the US in the last decade as new federal laws were enacted and equipment improved. Some measures such as underwater alarms were employed in late 1990s with the help of fishermen. Scientists say some fishermen rush to cut away line and nets wrapped around bodies of dead whales before they can be traced through their equipment. The researchers acknowledge that their methods were very crude (found by multiplying U.S. statistics because mortality figures in remote countries were not available) (Verrengia)
Introduction to Different Fishing Gear and Their Impacts
Precatching Technology
Mobile Gear
Midwater Trawling
Bottom Trawling
Trawling involves one or two fishing vessels towing a large net usually for two or three hours at three or four knots and is used to catch a range of species including orange roughy, hoki, ling, hake, and squid. Recreational fishers are not permitted to use trawl nets. (Starfish)
Dredging consists of fishing vessel towing a rigid steel-framed dredge along sea floor to gather scallops and oysters. (Starfish) Dredging is used for harvesting bivalve mollusks such as oysters, clams, scallops from the seabed using a metal framed basket with a bottom of connected iron rings or wire netting called the chain belly. The lower edge of the frame has a raking bar, with or without teeth, depending on targeted species. Catch is lifted out of the sea by the raking (or teeth) and passes back into the basket or bag. Dredges are generally attached to a towing bar operated from each side of a ship simultaneously. (Fishonline)
Beam Trawls are made more effective by attaching tickler chains (for sand or mud) or heavy chain matting (for rough, rocky ground) that drag along the sea floor in front of nets to disturb fish in the path of the trawl, causing them to rise from the seabed into the incoming net. The trawls range in size from 4 to 12 m (weighing 7.5 tons in air) beam length, depending on the size and power of the ship. (Fishonline)
Demersal Otter Trawls are large, usually cone shaped net which are towed across the seabed. Fish are herded between the boards into the mouth of the trawl where they swim until exhausted. They then drift back through the funnel into the cod-end where they are retained. (Fishonline)
The use of new fish-trawling gear is doing incalculable damage to the seabed, destroying essential habitats for marine life. Every kind of seabed - silt, sand, clay, gravel, cobble, boulder, rock reef, work reef, mussel bed, seagrass flat, sponge bottom, or coral reef can be trawled. For fishing rough terrain or areas with coral heads, trawlers since the 1980s have used "rockhopper" nets with heavy wheels that roll over obstructions. This fishing gear displaces commercial hook and line and trap fishers who fished without degrading the habitat. (Safina)
Bottom trawls churn the upper few inches of the seabed, gouge the bottom, and dislodge rocks, shells, and other structures and the creatures that live there. Much of the world's seabed is encrusted with and honeycombed with structures built by living things. Trawls crush, kill, expose to enemies, and remove these sources of nourishment and hiding places. This makes life dangerous for young fish and lowers the quality of the habitat and its ability to produce abundant fish populations. (Safina)
Trawling commonly affects the top two inches if sediment which is the habitat of most of the animals that provide food and shelter for the fish, shrimp, and other animals that humans eat. In a Gulf of Maine site surveyed before and after rockhopper gear was used many changes were noted including that much of the mud surface was eliminated, extensive colonies of sponges and other surface growing organisms were removed, and rocks and boulders had been moved and overturned. (Safina)
The simplification of the habitat caused by trawling makes the young fish of commercially important species more vulnerable to natural predation. In lab studies of the effects of bottom type on fish predation, the presence of cobbles as opposed to open sand or gravel-pebble bottoms, extended the time it took for a predatory fish to capture a young cod and allowed more juvenile cod to escape predation. A single pass of a trawl kills 5 to 20 percent of the seafloor animals. Georges Bank is swept 3 to 4 times a year, parts of the North Sea are swept 7 times a year, and along Australia's Queenland coast, shrimp trawlers plow the bottom up to 8 times a year. (Safina)
Studies suggest that large increases in bottom fishing from the 1960s to early 1990s likely have reduced the productivity of seafloor habitats, exacerbating depletion from overfishing. At 3 New England sites, studies within and adjacent to areas closed to bottom trawls before and after initial impact found that trawls significantly reduce cover for juvenile fish and the bottom community. In NW Australia, the proportion of high value snappers, emperors, and grouper species that congregate around sponge and soft coral communities dropped from about 60% of the catch to 15%. Less valuable fish associated with sandy bottoms became more abundant thereafter. Studies off Nova Scotia indicate that the survival of juvenile cod is higher in more complex habitats which offer more protection from predators. In another study, the density of small shrimp was 13 per square meter outside trawl drag paths and 0 in scallop dredge's path. (Safina)
Trawling is not uniformly bad for all species or all bottom habitats. A few species do better in clear-cuts, some species do better in trawled than in undisturbed habitats. A flatfish called dab benefits from trawling because its predators and competitors are eliminated and trawl wakes provide them with food. However, most species are not helped by trawling. (Safina)
Communities that live in shallow sandy habitats subject to storms or natural traumas such as ice scouring tend to be resilient and resist physical disturbances. Deeper communities that do not often experience natural disturbances are more vulnerable and less equipped to recover quickly from trawling. Watling and Norse's global review of studies covering various habitats and depths found that many of these were done in relatively shallow waters which are generally more resilient than deeper areas. 0 showed general increases in species after bottom trawling, 1 showed that some species increased while others decreased, 4 indicated little significant change, 18 showed serious negative effects. Watling has said that is trawling stopped today, some areas would recover substantially within months but certain bottom communities would need as much as a century. (Safina)
The Grand Banks study showed trawls making furrows but also smoothing out the sandy bottom, lowering abundance of sea urchins, snow crabs, soft corals, and other epibenthic creatures. The effects were less than expected and overshadowed by natural variability. Recovery took less than a year and no long terms effects were observed. The 1997-1999 Western Bank of Nova Scotia study of gravelly seabed typical of trawling areas made some food organisms such as horse mussels and worms more available as prey items. Physical disruptions were less than on sandy bottom, but lasted longer because gravel bottom is less disturbed by storms. On all banks, trawls did less damage than expected. Harm increased with the size of the bottom organisms and sponges and corals were particularly vulnerable. (Does fish-trawling harm the seabed?)
Research shows that the degree of damage depends on the nature of the seabed and its organisms, fishing effort, and other factors. Sandy bottoms are most resilient; hard bottoms with corals, sponges were least resilient. Detailed sea bed maps are essential to manage human activities in a scientifically sound manner and minimize environmental impacts so Don Gordon says. (Does fish-trawling harm the seabed?)
Sediment clouds
Sediment clouds are generated by turbulence from trawl doors contribute to fish capture. The clouds also add to the total suspended load which can decrease light levels on the substrate and smother benthos once sediment settles. Glatsoff (1964) showed that as little as 1mm of silt settling could prevent spat settlement in Ostrea virginica. Stevens (1987) claimed that high turbidity levels inhibited settlement of Pecten novaezelandiae veliger larvae, depresses growth rates of adults and caused inefficient metabolism of glycogen stores through enforced anaerobic respiration. (J. B. Jones)
Trawl gear can also bring about vertical redistribution of sediment layers. Mayer et al. (1991) showed that heavy chain dredges could mix organic material on the surface with layers below the surface. The organic material removed from the surface metazoan-microbial aerobic chain transfers to an anaerobic system. Churning up the soft bottom (if anoxic) can create anaerobic turbid conditions that are capable of killing scallop larvae. Sediment resuspended from clam dredges in a Maine estuary did not improve the food value of the suspended materials available to filter feeders and actually decreased the food value since filter feeders had to filter more material to obtain nutrients. (J. B. Jones)
Destruction of Non-target Benthos
Cyprina islandica (a large, heavy-shelled bivalve) only formed a large part of the cod and flatfish diet in Kiel Bay after trawling began in the area. Arntz and Weber (1970) concluded that the fish fed on bivalves crushed by the otter boards Medcof & Caddy (1971) and Caddy (1973) confirmed that feeding occurred on exposed and damaged benthic animals in trawl tracks. Stevens (1990) found that trawling caused no observable injuries to crabs. Butcher et al. (1981) found that that scallop dredging in Jervis Bay (Australia) caused little or no damage to the environment. Creutzberg et al. (1987) found that an experimental beam trawl had no effect on the catches of epibenthic animals on a mud substrate but on sandy locations, the number of chains did correlate to the catch. Bull (1986) found that in Golden Bay (New Zealand), after 9 months, the survival of Pecten novaezelandiae spat was better than 20% in an area closed to trawling whereas in an adjacent area open to trawling, the percentage was only 0.8%. (J. B. Jones)
Indirect Effects
McLoughlin et al. (1991) found that natural mortality and indirect fishing mortality rates on scallop beds was much higher on fished scallop beds than natural mortality on unfished beds. 4 to 5 times as many scallops were crushed or damaged as were caught or landed by the scallop gear. McLoughlin et al. saw that within 9 months of starting up a fishery in Bass Strait Australia, that the stock of scallops was almost entirely lost. They attributed it to a suspected bacterial infection resulting from decomposing scallops on the seabed. Saxton (1980) saw a decrease of juvenile fish when the bryozoan beds were removed in Tasman Bay, New Zealand. Sainsbury (1988) found a significant decrease in sponge frequency on the Australian north-west shelf between 1967-73 and 1979. The loss of sponges and alcyonians and gorgonians led to a change in the composition of the catch between those years. The fishes Lethrinus and Lutjanus which were associated with habitats containing large epibenthos and were much decreased. The fishes Nemipterus and Saurida which lived in open sand had greatly increased. A general decrease in diversity can be predicted as long0lived and slow-growing species are removed or killed by human activities. (J. B. Jones)
Conclusion
The removal of macrobenthos has variable effects. In shallow waters where damage is intermittent, recolonisation occurs quickly. Where macrobenthos is substantially removed and recovery is not permitted, the change is permanent (Ex - Sabellaria beds of Wadden Sea and the bryozoan beds of Tasman Bay) (J. B. Jones)
Nonmobile Gear
Purse Seining
The purse seine is a vertically hanging net with floats on its surface line and lead weights on its bottom edge. Attached to the weighted line are rings strung together by a drawstring wire. Ships encircle entire schools with the outstretched purse seine, then they pull the drawstring wire tight to trap the fish inside (AFMA). This method is extremely effective for catching both surface dwelling and mid-water fish, especially tuna, sardines, mackerel, jack mackerel, and herring (Kuznetsov). The Alaska Department of Fish and Game reports that, in the commercial fisheries of Southeast Alaska, purse seines are responsible for 70-90% of the tuna catch alone. Current regulations in Alaska allow purse seining only in specific districts (ADFG).
While fishing companies have practiced purse seining essentially unchanged for the past 100 years, slight innovations in technology have recently made the net even more efficient and, therefore, lucrative. One such example is the "autonomous distance-controlled hydroacoustic system" which, once attached to strategic points along the net and submersed, emanates a low-frequency pulse which frightens fish into the net. This invention consists of a management block onboard the ship as well as the underwater blocks, attached to the net, which emanate the frequencies (Kuznetsov).
One invention analogous to the hydroacoustic system, but used for trawling, is the "towed remote controlled pneumoacoustic system." This machine, which is dragged between ship and trawl, creates a strategically located acoustic field, imitating the acoustics generated by predatory whales. Seeking to avoid the predator, fish congregate in the trawl's catching zone. This method greatly increases the catch without the necessity of altering boats or nets (Kuznetsov).
Sources
Alaska Department of Fish and Game: Division of Commercial Fisheries. "Commercial Purse Seine Fishery." 26 July 2005. 17 Oct. 2007 <http://www.cf.adfg.state.ak.us/region1/finfish/salmon/netfisheries/ps_info.php
>.
Australian Fisheries Management Authority, Australian Government. "Seine." Canberra, Australia. 29 June 2005 <http://www.afma.gov.au/information/students/methods/>.
Kuznetsov, Dr. J.A. "Innovational Projects." Intensification of Multispecies Fishery. Vladivostok, Russia. <imf.fish-net.ru/inpr.htm>.
Traps
Traps are one of the most environmentally friendly fishing methods. They are highly selective, since fishermen can release unwanted fish alive when the traps are hauled up. They also do little to no harm to the ocean floor or other oceanic surroundings, as they are nonmobile. However, there is a huge problem associated with traps - ghost fishing.
In 1995, the FAO deemed ghost fishing to be one of the most seriously negative impacts in the present capture fishery industry (Matsuoka). When traps are lost, from storms or human negligence or otherwise, the vast majority will continue to catch and trap fish or other ocean life for months, or even years. Ghost fishing in some commercial stocks is estimated to be equal to 5-30% of the annual catch levels (Laist). There are already some measures being taken to prevent ghost fishing: the FAO code of conduct states that States should try to minimize catch by lost or abandoned gear, and many countries including Sweden, Poland, New Zealand, and the United States all have gear retrieval programs (Brown).
Gear retrieval programs, however, are not the best way to prevent ghost fishing. A study by Brown and Macfayden indicates that while these programs save fishermen about $32,000 per fleet per year, the time and money spent in retrieving the gear exceeds $65,000. But if these programs are used along with measures that prevent gear loss in the first place, the cost will decrease significantly. Another possibility is to develop new technology that allows for easier and cheaper retrieval of lost nets and traps.
Another measure being taken is the requirement of escape mechanisms. <<INFO>>. If these requirements are made more strict and widespread, then ghost fishing should decrease dramatically.
Unfortunately, there is little data about the effectiveness of escape mechanisms, or even truly accurate data regarding the impacts of ghost fishing on fish populations; most of the numbers discussed above are mere approximations. This is another area in which we can improve
Hook and Line
Alternative Fishing Technologies
Future improvements on beam trawls include electrified ticklers, which are less damaging to the seabed which have been developed but used only experimentally. Square Mesh Panels fitted in the 'belly' or lower panel of the net can reduce the impact of beam trawling. (Fishonline)
Future improvements on demersal otter trawls include increasing the selectivity of trawl fisheries by seperated trawls which exploit the behavioral differences between fish species. For example, cod and plaice segregated into lower compartment of net while haddock are taken in upper part. The mesh size of the two compartments can be altered according to the size of the adult fish being targeted. Selectivity can also be increased by insertion of square mesh panels because unlike traditional diamond shape meshes, they do not close when the net is towed. Discard of immature fish also reduced by increasing the basic mesh size when fishing. Sorting grids are compulsorily fitted in nets in some prawn and shrimp fisheries to reduce bycatch of unwanted or non-targeted species including small prawn and shrimp. (Fishonline)
Most fishing methods target fish for human consumption. Fisheries targeting species for reduction purposes (manufacture of fish oil, meal, etc.) are referred to as industrial fisheries. Fish meal and oil produced almost exclusively from small, pelagic species for which there is little or no demand for direct human consumption. Methods of capture are purse-seining and trawling with small mesh nets (16-32 mm). Industrial species in North Sea and North-East Atlantic include: sandeel, sprat, capelin, blue whiting, Norway pout, and horse mackerel. Fish oil used in products ranging from margarine to biscuits. Fish meal is used in manufacture of pelleted foodstuff for intensively farmed poultry, pigs, and not least, agriculture. The main Impacts of industrial fishing is the removal of large quantities of species from the base of the food chain. (Fishonline)
Policy and Regulation Relating to Fishing Technology
Recommended actions that would simultaneously safeguard the fishing industry as well as the seabed would include no-take replenishment zones where fishing is prohibited which would create healthy habitats supplying adjacent areas with catchable fish where the benefits can be seen within a few years. In New England, fish populations are still low but are increasing in areas where the regional fishery management and National Marine Fisheries Service have temporarily closed to fishing. Fixed-gear-only zones where trawls and other mobile gear are banned in favor of stationary fishing gear such as traps or hooks and lines that don't destroy habitat. What gear is permitted should depend on the bottom composition. Mobile gear allowed on shallow sandy bottom relatively resistant to disturbance but be barred from harder, higher-relief, and deeper bottoms where trawler damage in much more serious. Incentives for development of fish gear should be put in place that do not degrade the habitat on which it is dependent. Fish and fisheries are hurt by perverse subsidies that encourage overfishing, overcapacity of fishing boats, and degradation of habitat and marine ecosystems. Intelligently designed financial incentives are needed to encourage new and more benign technology. (Safina)