Site by N.E. Stolpe

Number 1
June 24, 1998

Link to NJ Fishing Consumer Alert page Link to NJ Fishing Consumer Alert page

The next anti-fishing “Frontier”

In a Planet Watch piece in the June 15, 1998 issue of TIME magazine David Bjerklie identifies bottom trawling as an aquatic Armageddon, quoting the National Audobon Society’s Carl Safina’s sound bite friendly term for it - “scorched earth fishing.” Mr. Bjerklie’s somewhat lopsided coverage cries out for an attempt to put bottom trawling and related fishing activities into a real world perspective. This perspective is one that he and many of the people intent on remolding the public view of fishing unfailingly ignore.

How much of the ocean’s bottom is impacted by trawling?

Oceans cover about 70% of the earth’s surface. Their mean depth is 3795 meters. Almost 90% of the world’s ocean waters are deeper than 1000 meters (see table below). Because of primarily technological limitations, bottom trawling is for all practical purposes limited to waters that are generally much less than 1000 meters deep (While not documented, probably 75% of the bottom trawling done off the East coast of the U.S. is in waters less than 200 meters deep). Even if bottom trawling were as “destructive” as Mr. Bjerklie and Dr. Safina would like us to believe, it doesn’t require a particularly rigorous analysis to determine that it isn’t about to turn a large part of the sea bottom into a biological desert.

Depth Interval
All Oceans
from Table 5 Percentage area of depth zones in the oceans (Kosinna, 1921)
(from The Oceans, Their Physics, Chemistry and Biology; H.U. Sverdrup, M.W. Johnson and R.H. Fleming; 1942; Prenttice-Hall, Inc. )
Making some reasonable assumptions (necessitated by a chronic lack of data pertaining to what real fishermen are doing in the real ocean), we estimate that there are 2,500 trawlers fishing in the Atlantic EEZ (in Fisheries of the United States 1992 the National Marine Fisheries Servicereported that in 1990 there were about 7500 documented commercial fishing vessels from Maine to Florida. We are assuming that 1/3 of these are engaged in the ocean trawl fishery). If each of these boats is using a net with a 100 foot opening (the few Boeing 747-swallowing nets in use [Link to 747 quotes] are balanced by the much smaller ones used by most trawlers), and tows that net for ten hours a day at 3 miles an hour, and fishes for 200 days a year, in a year the entire fleet will have covered about 300,000 square miles of bottom. Coincidentally, that is a reasonable approximation of the area of the EEZ off the East coast. That means that, were the fishing effort evenly distributed, each square foot of bottom would get fished over once every year.

But fishing effort isn’t evenly distributed. Some areas are, for physical or administrative or regulatory or political reasons, beyond the reach of the fishing fleet. In some areas, the fish just aren’t there. So, in reality we have a situation where small, localized areas - Georges Banks off Cape Cod, for example - are, because of their accessibility and their suitability for producing and/or attracting and holding large concentrations of marketable fish, heavily fished. Other areas are fished lightly if at all. So in reality a small proportion of the only 10% of the total ocean area that could be fished by bottom trawls actually is. That leaves in excess of 90% of the ocean seabed intact - at least as far as working fishermen are concerned - and performing all of those biological functions that ocean bottoms are so important for. Dr. Safina’s “scorched earth fishing” doesn’t seem a large-scale conflagration. Maybe a brushfire, but read on....

Can we harvest fish and shellfish from the world’s oceans without changing the ocean environment?

Of course we can. Just as we could have harvested plants and animals from the North American continent in a manner that might have been acceptable to Dr. Safina and Mr. Bjerklie. That’s what the Native Americans did for centuries (give or take the odd brush fire they might have set). If either of these “scorched earth” proponents was in charge of agricultural policy, however, we wouldn’t be supplying the protein needs of several hundreds of millions of people today. Maybe a million or two, but that would take an awful lot of deer, squirrels, bunnies, roots, bark and berries. Modern terrestrial food production technology - we also call it farming - entails a certain amount of interference with the natural world. Generally that interference is along the lines of clearing the land of trees and rocks and weeds and other “natural” impediments, preparing and treating the soil, etc., etc., etc. (A process not far removed from that of intensive trawling on the ocean bottom.)

This is what keeps us, a lot of us, in Big Macs, Fritos and Pop Tarts - and most of the "organic" produce that is so popular today. Would Dr. Safina actually refer to modern agriculture as “scorched earth farming” and campaign for it’s elimination? Would Mr. Bjerklie carry on in TIME magazine about it? They might respond “but there’s a difference.” But is there?

Modern bottom-tending fish harvesting gear has been in intensive use in some areas for generations. It is used there because it is an efficient method of getting fish from the ocean floor to the consumer. It definitely changes the character of the bottom. If it is done effectively, however, it demonstrably doesn’t destroy the area’s capacity to produce the fish being harvested. That’s why the fish, and the fishermen, keep coming back. Of course the system can get out of balance, just as - witness the Dust Bowl - agricultural systems can. But as long as well over 90+ percent of ocean bottom is undisturbed by trawling and producing new recruits - the fry, fingerlings, larvae, eggs, cysts, etc. that are the equivalent of seed - and as long as the mesh size of the trawl nets in use allows smaller fish and invertebrates to pass through, no bottom, no matter how heavily trawled, is being turned into a lifeless, unproductive “desert.”

From: Ecosystem Effects of Demersal Fishing: A European Perspective by S.I Rogers, M.J. Kaiser and S. Jennings (in Effects of Fishing Gear on the Sea Floor of New England edited by. E. Dorsey & J. Pederson, Conservation Law Foundation, 1998)
Note: The following was taken from the Conservation Law Foundation report to show that, when it comes to the impacts of bottom tending gear, the scientific community seems to agree on little other than the fact that much more work needs to be down before any conclusions can be drawn. While there are those like Dr. Safina who believe that any disturbance of the "natural" sea bottom should be prohibited automatically, there is a sizeable and growing body of work describing the actual results of those disturbances and,  as is shown in the following, these results aren't necessarily detrimental to the fish stocks.

The references to other papers have been omitted. Copies of the full report (MIT Sea Grant Publication 98-4, ISBN 1-892787-00-8) are available from the Conservation Law Foundation at 62 Summer Street, Boston, MA 02110 (phone 617 350-0990)

"The direct effects of trawling on target species is clear and has resulted in high levels of fishing effort on most of the important European stocks. The development of the heavy beam trawl in the 1960s allowed  the introduction of a targeted flatfish beam trawl fishery in an area of the southern North Sea that had already experienced constant otter trawling effort for many years previously. Another  important direct effect of fishing is that it has provided food for other species in the ecosystem by  discarding unwanted bycatch and by killing benthic animals in the  passage of the gear.

Recent studies of long time-series of data, some taken in research vessel cruises before the first World War, have revealed patterns in fish abundance which cannot always be associated with the deleterious effects of commercial fisheries. One group that is considered vulnerable to the effects of increased fishing effort are the elasmobranchs, which generally  have low fecundity and high age and length at maturity. However, not all species appear equally sensitive, and those with a relatively low length at maturity such as the starry ray, Raja radiata, have proved to be resilient. Survival experiments using fish bycatch taken from beam trawls have shown mortality rates of up to 40% for Raja neavus, compared with higher rates of 60 to 90% for dragonet, Callionymus lyra, and for plaice and dab, Limanda limanda.

In the 1960s and 1970s an increase in growth rate was reported for both plaice and sole which could not be related to changes in temperature, but which did coincide with increases in both beam trawl effort and eutrophication in coastal waters. There is some evidence that eutrophication has enhanced populations of polychaetes and brittle stars in coastal waters, thereby increasing the food supply for fish. Some of the most important consequences for the production of demersal benthic organisms result from the presence on the sea bed of (1) damaged or dead organisms resulting from the passage of the trawl and (2) discarded target and non-target species (bycatch). It is estimated that 475,000 mt of fish, offal, and benthic invertebrates are discarded in the North Sea annually. Kaiser and Spencer observed 35 times as many fish aggregating over a recently beam trawled line compared with adjacent unfished areas, which implied that fish moved into areas of disturbance. Similarly, gadoids were observed to aggregate around newly disturbed pits in sandy sediments. Analysis of plaice and sole growth rate confirmed that increases for intermediate plaice size classes (15-30 cm) may have been due to a combination of beam trawl and eutrophication effects because of the spatial overlap of these effects and of these fish size classes. Increases in mean length at age for sole since the 1960s was significantly correlated with increased beam trawl effort. Although the small mouth size of sole suggests that this species may not be able to benefit directly from damaged benthos, the longer term effect of trawling would tend to encourage smaller opportunistic benthic invertebrates, which form a large part of its diet. As the fishery operates outside the 12-mile limit, these effects would tend to benefit older individuals.

Dietary analyses of gurnards (Trigla spp.) and whiting (Merlangius merlangus) caught on recently beam trawled and undisturbed areas also revealed that both species consumed significantly greater numbers of the amphipod, Ampelisca spinipes, within the fished area. This amphipod constructs a tube that protrudes from the surface of the sea bed, which makes it vulnerable to contact with bottom fishing gear. Interestingly, gurnards normally eat large prey items such as shrimps, Crangon spp., and swimming crabs, Liocarcinus spp., but preferentially selected A. spinipes when feeding within the trawl tracks.

This switch in diet implied that large numbers of amphipods were made available to predatory fish as a result of trawling. Adult queen scallops, Aequipecten opercularis, do not occur in the diet of whiting under normal circumstances. However, the distinctive orange gonads of these bivalves were recorded in whiting stomach contents after trawling, indicating that these molluscs had been damaged by the trawl. Large numbers of the bivalve A. islandica are damaged by trawling at times of intensive otter trawling in Kiel Bay, and at these times this species is common in the stomach of cod, Gadus morhua. 

Similar responses to fishing disturbance were also recorded for dab, which were attracted to animals damaged by the trawl within 20 minutes of its passage and increased to three times their former abundance after 24 h. In addition, the diet of dab captured in the trawled area consisted mainly of the oral discs of the brittle star, Amphiura spp., in contrast to those in adjacent undisturbed areas, which consumed only brittle star arms."

Then there are natural bottom disturbances:

A sea surface wave with a height of ten meters (not an excessive height in storms off our coast - see Sebastian Junger’s The Perfect Storm Link to The Perfect Storm review) can induce a particle velocity of 40 centimeters per second 100 meters under the surface (see the table below). This approximates the velocity (actually 49 cm/sec) 2 meters under a wave with a height of one meter. Dive six feet beneath a three foot high wave and you’ll know that a lot of water is being moved pretty rapidly down there. A 30 foot wave can have the same effect 300 feet deep, and most of our bottom trawling is done on shallower bottom. Can a trawl cause as much disturbance of the bottom in these shallow waters as a run-of-the-mill Nor‘Easter? More importantly, is anyone comparing the impacts?

Period Length
Velocity at surface Velocity at 2 meters Velocity at 20 meters Velocity at 100 meters
2 312 6.2 0.25
4 624 25 1.0
10 1561 156 7
220 (cm/sec)
16 2498 396 10
from Table 60 Velocities of water particles at different depths in surface waves of different periods, lengths and heights
(from The Oceans, Their Physics, Chemistry and Biology; H.U. Sverdrup, M.W. Johnson and R.H. Fleming; 1942; Prenttice-Hall, Inc. )

And hook-and-line fishing:

The anti-swordfish consuming campaign that we reported on a few issues back [Link to FishNet on Swordfish Boycott] is still hanging on. As part of that campaign, Audobon’s Dr. Safina contributed an op-ed piece to the New York Times on April 14 titled Fish Market Mutiny. In it he railed against longlining (fishing in which baited hooks on long leaders are suspended at intervals of hundreds of feet from horizontal “long lines” designed to follow the edges of productive offshore water masses - because that's where the fish are).

We’ve always assumed a fish hook was a fish hook, whether attached to a long line with a working fishermen standing in oilskins at the end or dragged behind a half a million dollar yacht with a retired CEO in a - sort of - equivalent position (only strapped into a $5,000 fighting chair and holding a $2,000 fishing pole). They all have similar effects on the creatures that are unfortunate enough to eat them. With the intention of putting the longlining “threat” into a realistic perspective,  we’ve done some hook to hook comparisons.

The East coast U.S. pelagic longline fleet - those boats that fish in the EEZ off the Atlantic states for tuna, swordfish, mahi mahi and shark - numbers less than 200 vessels. They fish an average of 600 hooks each for under 100 days a year (personal communication from Blue Water Fishermen's Association). Assuming 200 boats, 100 days and 600 hooks, that’s 12 million hook-days (one hook in the water for 1 day) a year for an entire fleet that is being treated as the scourge of the ocean, right in line with Dr. Safina’s "scorched earth" bottom trawlers.

Thanks to the National Marine Fisheries Service’s statistics people [Link to NMFS Recreational Trips document (Adobe Acrobat format)note: this is a link to an Adobe Acrobat PDF file. You must have the Acrobat Reader plug-in installed to access it] we found that in 1995 sports anglers on the East coast were estimated to have made slightly over three million trips fishing from party and charter boats, 18 million trips fishing from shore, and 18 million trips fishing from private and rental boats. Assuming an average of three hooks per angler (extensive personal observation would bear this out), that’s almost 120 million hook-days. It’s difficult to imagine how in any rational world one user group can be made the target of an international campaign backed by reputable environmental organizations when another group, using the very same gear but with a total effort an order of magnitude greater, can be ignored completely. It brings to mind the pop song popular back in the Eighties titled “Who’s zooming who?”

What’s really going on?

There are some valid questions about the possible environmental impacts of seafood harvesting techniques that have been in use, and taken for granted, for generations. These are being looked at. When it comes to issues of ocean quality, fishermen have been in the lead in identifying problem areas and in coming up with solutions for longer than many of today’s environmental organizations have been in business. If you are a working fisherman today you realize that when it comes to estuarine, coastal or ocean habitat degradation, it isn’t your job that’s at risk, it’s your way of life. There are definitely more than enough real habitat-related issues of far more significance than bottom trawling impacts to keep us all busy.

So why put the “doom and gloom” machine into motion because of the yet-to-be identified effects of fishing techniques that have been in use for generations - and in use, we have to emphasize, on a very small part of the sea floor - and that are in all probability minimal compared to “natural” processes like the storms that occur every year? And why proclaim that the use of a particular technology by one group is completely unacceptable while ignoring the impacts of that same technology used by a far larger group? It almost seems as if these “causes” are being manufactured. If that’s the case, we can only ask why?

- The Oil Slick -
Recipient of a Clinton Administration Environmental Heroes Award and, according to a New York Times profile on June 23, 1991, not an admirer of anyone who enjoys a fish dinner Link to reference in FishNet #7, Sylvia Earle, Ph.D. is the Pew Trust’s Link to Capitol Research Center Foundation Watch web page on PewSeaWeb “voice for the oceans.” Among other things, she is listed on the SeaWeb website Link to SeaWeb bios page (Dr. Earle's is ca 1/4 down) as serving on the Boards of Dresser Industries, Inc. Link to Dresser Industries websiteand Oryx Energy, Inc. Link to the Oryx Energy website
>>>>>>>>>>  <<<<<<<<<<
(Follow this link Link to Wall Street Journal article on Pew Trusts & the mediato an interesting review of the Pew Trust's media outreach program)


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