|A WAVE TOO FAR
(originally published in World Fishing in April, 1998
as "Trawling against demagogues")
by Menakhem Ben-Yami
Criticism of the ways in which humanity is exploiting its marine resources comes in waves. It is vital to counterbalance overexploitation due to greed and ignorance and to spur management. The forcible activities of Greenpeace against indiscriminate whaling were instrumental to international management and the consequent recovery of whale populations. The "dolphin-safe" and "turtle-saving" campaigns and legislation have led to the development and application of purse-seining techniques allowing escape of most dolphins from encirclement by the seine and to the design and introduction of turtle saving devices in shrimp trawls and turtle-save beach sections. They led to reducing East Pacific dolphin mortality and a great expansion of their population, and to saving West Atlantic turtles from possible extinction.
Green organizations are doing also a great job in fighting aquatic and air pollution, and in raising their voices for better and more rational management of natural resources, including commercial fish and marine mammals populations. They've contributed importantly to changing the attitudes of industries, governments, and consumers towards better environmental and fisheries management. In principle, there should be no basic controversy between fisheries and environmentalist lobbies. Both are interested in clean, unpolluted seas and oceans, and in keeping the populations of marine flora and fauna, whether commercially exploitable or not, in the feasibly best condition.
A trade journal like WORLD FISHING may seem a wrong forum to dispute scientists' utterances. Unfortunately, however, some of them are not quite accurate and while they wouldn't pass the muster of peers' review, they do find their way to popular press and various conservationist publications, and are used to propagate rather imbalanced ideas among innocent public. Some otherwise well-intended "green" campaigns are spotted with fallacious allegations that flow one wave too far and crash their arguments on the rocks of the only too often neglected realities.
Such are, for example, frequently repeated complaints about negative effect of trawl gear on sea bed and the associated life. One such account nicely describes how the "sea bottom teeming with invertebrate and plant life..." offers "habitat and nursery and refuge areas for juvenile fish that are otherwise vulnerable to being eaten by larger fishes, and a food source for demersal fish. Some pelagic fish, like the herring swim down to attach their eggs to pebbles on the sea bottom". However, its concluding thesis that "left undisturbed, a rich, biologically diverse community thrived here for centuries, feeding countless humans with the fish and shellfish it produced" is misleading. The biologist quoted should have known that without "disturbing" such communities feeding "countless" people with fish and shellfish would not be possible.
One newspaper feature depicts trawling with quasi-hostile overtones: "...as it churns into these same waters, a hundred-foot-long, steel-hulled trawling vessel powered by a 1,000-horsepower diesel engine the size of a bulldozer's. The combined stench of fuel and dried fish is overpowering. A heavy trawlnet is lowered to the sea floor. Once on the bottom, two iron doors attached to the mouth of the net gouge the seabed, kicking up a plume of sediment that funnels fish into the net. They weigh a thousand pounds apiece and drag a cable designed to stir up mud. The net itself and the massive weights attached to it are pulled along behind. In all, this gear disturbs the seabed as the heavy net sweeps across it - exposing, crushing, scouring and burying the life forms that support the very fish it is harvesting."
Trawling is sometimes compared to a practice called chaining, in which cattlemen stretch a dragchain between two bulldozers to clear unwanted vegetation as quickly and thoroughly as possible. "That's pretty much what trawlers are doing twenty-four hours a day on our continental shelves," a well-known zoologist was reported to say to a journalist. "The impact of logging pales before the destruction of the ocean" an American marine ecologist told a reporter.
"You don't destroy a forest to catch a few squirrels. The oceans are a life-support system, and we are taking the equivalent of bulldozers to its mechanisms without really understanding how they work" - a California-based marine biologist was reported to declare.
Or: "Dragging is a non selective fishing method which captures everything which gets in its way. This leads to a tremendous waste and a dangerous disturbance to the benthic ecosystems of our oceans."
And: "...high-tech fishing gear is causing an ecological crisis... The loss of sea-floor diversity not only endangers the populations of fish we depend on for our food, but also threaten the stability of the planet itself."
Regretably, only too often I scent demagogy-tinged science. The impression is that some otherwise scholarly people poorly understand, misunderstand, or purposely misrepresent the little-known processes which take place on trawled sea bottom. In more extreme cases one gets the impression that some people wish to keep marine ecosystems "people free" or at least "fishers free". Some publications won't stop on blaming overfishing, but put the blame on fishing in general and trawling, in particular. The result is that many members of the public who care about marine environment but not necessarily are able to distinguish rational and scientific from a mystic and demagogic approach to ecology, turn against the industry whose products they demand daily. Those who recognise the fallacious overtones are not always in the mood of starting an argument.
The simple truth is that trawling grounds cover considerable parts of our planet's continental shelf and that the trawl fishery has been producing continually and for many decades some 25 to 30 or more percent and much more than that in money terms, of the world's 80-90M MT marine fish landings. Most of these grounds, if not overfished by excessive effort, are fished by trawlermen who pass over them with their gear from a few to tens of times each year and nevertheless yield continually. How in the world can "destroyed", "devastated", "crushed", and "scoured" habitat produce major yields year after year, decade after decade, and even generation after generation?
True, bottom trawling must physically and biologically affect any virgin benthic habitat. The very harvesting of a part of the main top biomass makes that ecosystem something else. It ceases being "virgin" and becomes a demersal fishery ecosystem with fishing an unseparable component. What happens is that frequently fished sea bottom undergoes a permanent (though mostly not irreversible) ecological change due to both, the effect of fishing gear on the bottom and the intensive harvesting of demersal biota. Trawling grounds are biologically, ecologically, etc., different from a non-trawled or "virgin" bottom areas. If not overfished, their productivity is enhanced by taking off a part of biomass, thus enabling faster production of replacement. Like any other fishery, trawling is removing large, older fish, leaving more food and space available to the younger ones which can now grow faster, reproduce sooner, and actually produce more biomass than a virgin stock. It is absolutely impossible to exploit demersal fish resources by whatever method and at the same time conserve bottom habitat in its virgin form.
Trawling grounds can be compared, with all the biological and ecological differences one can think of, to permanently farmed (and thus changed from its primeval state) areas on the continent. Like overfishing, bad farming can overexploit the soil bringing about desertification, while good farming practices can produce crops on a sustained basis. The same goes for fishing in general and trawling, in particular.
In fact, we know very little how trawling affects production of commercial fish. Its impact no doubt depends on (i) sort of ground and character of the bottom habitat; (ii) underwater weight of the trawlgear; (iii) towing speed (fast towed gear tends to dig less); (4) frequency of trawl passings; (5) the state of the stock. "Destruction", "devastation", etc., are subjective expressions - an over-reaction to the notorious overfishing situations. More to the point would be to ask whether the fish growth rates are affected by repeated trawling of their habitat - a valid question requiring scientific answers resulting from scientific studies. Till then, the only valid position is that where trawl fishery produces sustaining yield, leaving in the sea ssufficient "standing stock", the productivity of the trawl-modified bottom biotope is preserved at an adequate level.
Also, a productive and balanced fishery ecosystem may react in various, unexpected ways to reduction of both, incidental and target species mortalities. High-tonnage biomass not always produces the most valuable yields. Increased overall bio-diversity may actually have some negative side affects. We must accept the reality that we can't attain at the same place and time productive fishery and ecologically diverse and little-disturbed bottom ecosystem. To attain the latter areas closed to trawling must be allocated.
Trawling doesn't necessarily lead to overfishing. It can be well managed employing effort and meshsize controls, escape devices and "windows," aimed and selective capture tactics, seasonal and site closures, etc. Trawl boards and footrope can be rigged to keep the gear off bottom and let certain fish species and sizes to pass to escape underneath.
The description of trawling being "heavy fishing gear bulldozing the sea floor" is an inaccurate over-generalization. Heavy on deck, the gear loses most of its weight approaching neutral bouyancy while in water. Modern trawl boards represent highly efficient hydrodynamic designs that derive their spreading power rather from water flow than from ground shear. Wise fishermen try to waste as little power as possible on ground contact. Some started using foamfilled trawl-boards with a minimum bottom contact. Many codends are designed to keep off bottom, or tend to come off it when filled with fish.
Establishment of "non-extractive areas" or "marine parks" closed to any sort of fishing, and of less limited marine reserves where only mobile fishing gear would be restricted is one way to maintain demersal bio-diversity and perhaps to create breeding tracts from which dense standing stocks would "spill" to neighbouring fishing grounds. Comparative studies on protected areas and trawling grounds might help to find out what really is going on the latter in relation to the former and indicate appropriate management measures.
We have no alterative to influencing and modifying various components of the marine ecosystem as long as we want to live and supply the humanity with the food it needs and, especially, if we want to keep fish-and-chips, tuna salad, fish fillets, and salmon with cream cheese on our daily menu. The issue, therefore is not how to leave marine habitats untouched, but how to exploit marine resources intelligently. So, before bustling over every human effect on ecosystem, let's give the issue a honest examination. Instead of carrying alarms too far, let's spend more time and efforts looking for constructive ways to moderate negative effects of fishing and learn to live with the unavoidable consequences of having on earth six milliard of incessantly procreating people.
A few days ago I received a professionally illustrated and well edited Greenpeace brochure, entitled "It can't go on forever - The implications of the global grab for declining fish stocks." Informed readers who are immune to propaganda would fine among the small-letters text some important information. But who's reading small-letters texts nowadays? The trouble is that the big-letters title of the second "chapter" reads: "Global fishing - An unmitigated disaster..." and that of the fourth one: "Fishing threatens survival of marine wildlife." There's also an eighth "chapter", entitled: "World fisheries - providing food and livelihoods..."
See what I mean ?