72 



Effects of Man's Activity as a Predator on Yields : 



While the assessment community has grappled with technological changes 

 in relation to fishing effort and catch coefficients, virtually no work has 

 been done investigating the effects of that technology on stocks. Although 

 catches themselves serve to reduce stocks, the methods by which catches are 

 made may also have effects on stock abundance. 



• Effects of towing nets on the bottom : This is seen to be an absolutely 

 critical issue by members of the domestic industry. The introduction 

 of ever-larger nets on Georges Bank, sometimes towed by two vessels 

 (pair trawling), may disturb the bottom in such a manner as to reduce 

 food abundance, alter stock behavior, and reduce stock abundance. Al- 

 though many areas of Georges Bank are flat bottom continually swept by 

 strong tides, other areas, particularly those close to the edge of the 

 shelf, contain abundant bottom communities that can be 'swept clean' 

 by a net's passage. The effects of such 'sweeping' activities remain 

 unknown. 



• Relationship between a discard and no-discard fishery : American fishing 

 efforts have been selective in nature, seeking valuable species while 

 throwing others back over the side. Depending on the area fished, such 

 discards can comprise up to sixty percent of the yield from a tow. 



Such discards are almost always dead. Fishermen recognize that discards 

 are a wasteful method of operation, but feel that, however inefficient, 

 such discards are returned to the marine food chain. In fact, a general 

 rule of thumb in the hook-and-line longline fishery is to avoid throwing 

 offal over the side if gear is to be later set on the same bottom. There 

 are indications, in addition, that discards from shucking sea scallops 

 (done at sea while towing a dredge) attract groundfish and, in fact, 

 can even increase their abundance. (81 ) 



Foreign factory efforts, on the other hand, rarely produce any discards. 

 Demersal fish are gutted and the offal thrown into a fishmeal plant. 

 Whereas American fishing vessels are usually followed by flocks of sea- 

 gulls, such is not the case with factory vessels. (82) 



Fishermen feel that such factory operations may have the same effects 

 on the marine environment as does clear-cutting on tracts of forest. 

 They feel that their fishery, although in some senses economically 

 wasteful, is less biologically wasteful than fishmeal operations. 



Specific projects have not been designed to determine the yield impli- 

 cations of a discard as opposed to a no-discard fishery. It is inter- 

 esting to note that Georges Bank produced nearly 500,000 tons a year 

 from the 1920s to the 1960s. All of this production was a discard 



