for growth in competing predators, such as 

 salmon, lingcod, and halibut." 



Elimination or reduction in numbers of 

 predators or competitors from an area has 

 been described by Rounsefell and Everhart 

 (l^^SS) as being desirable when "because of 

 their abundance and predacious habits they 

 are limiting the abundance of more desirable 

 species." These authors further state that 

 "when a fish population becomes unbalanced 

 or becomes undesirable in the ecology of 

 an area, it may be necessary in the interest 

 of good wildlife management to control it." 

 We cannot, however, at this time state that 

 these principles are necessarily applicable 

 to dogfish, for the limiting effect of dogfish 

 on more desirable fishes is unknown. 



METHODS OF CONTROL 



Eliminating or decreasing dogfish damage 

 can be achieved through (1) reducing the 

 numbers of dogfishes or (2) developing and 

 using chemicals (repellents or deterrents) 

 to protect gear and catches. 



Reducing Dogfish Numbers 



Most control measures proposed are aimed 

 at minimizing dogfish damage through reducing 

 their numbers. Presumably decreased gear 

 loss and damage would follow stock reduction, 

 but whether or not such decreases would be 

 directly proportional to the reduction in stock 

 is unknown. 



Reducing the size of dogfish concentrations 

 (mass) can be accomplished only by removing 

 dogfish at a rate exceeding the increase of 

 population through recruitment and growth. 

 A study of the history of the dogfish fishery 

 in Hecate Strait indicates that an annual fish- 

 ing mortality of 10 to 15 percent may be 

 adequate to initially effect a material re- 

 duction in stock sizes. Assuming that the 

 Shepard and Stevenson (1^56) estimate of pOO 

 million pounds of dogfish off British Columbia 

 is reliable and assuming further that an addi- 

 tional 2(X1 million pounds may exist off Oregon 



and Washington, we estimate that from 80 to 

 120 million pounds of dogfish may have to be 

 removed during the first several years to 

 decrease substantially the cumulative popula- 

 tion level. Such quantities could be removed, 

 conceivably, by: (1) selective poisoning or 

 (2) intense fishing effort. 



Prospects for selectively poisoning dog- 

 fish : — From what we know about the selective 

 toxicity of a number of chemicals, we could, 

 possibly, develop a selective poisoning tech- 

 nique. 



Selective poisoning is based upon behav- 

 ioral or biochemical differences among 

 animals. Poisons, to be effective, must 

 be absorbed by the animal tissues and must 

 produce an effect on a particular bio- 

 chemical system in the animal. Thus, we 

 could conceivably poison sharks without 

 harming other more valuable fishes by 

 finding and using (1) as bait some sub- 

 stance that would be eaten by sharks but 

 not by other fishes and (2) as a poison 

 dissolved in the water some substance that 

 would interfere with a biochemical system 

 present in sharks but absent in other marine 

 organisms. 



Since behavioral (feeding) and biochemical 

 differences do exist between sharks and bony 

 fishes, development of a selective poison 

 seems chemically feasible. But, even as- 

 suming that the price of such a poison, in 

 commercial lots, were reasonable, spread- 

 ing the poison and seeing that the dogfish 

 ingested or otherwise absorbed it in lethal 

 amounts would be extremely difficult. A better 

 prospect seems to be development of an 

 intensive fishery. 



Prospects for developing a fishery : — To 

 rejuvenate a fishery for dogfish that would 

 be sufficiently intensive to bring about the 

 required 10- to 15-percent initial mortality 

 would require (1) a bounty system with an 

 attractive reward, (2) a large vessel-charter 

 system, or (3) development of a high market 

 demand for dogfish or dogfish products. In the 

 first two instances. nearly continuous 



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