damage usually results from shearing of 

 leaders or gangings by the sharp teeth of 

 dogfish. Even wire leaders are sometimes 

 bent or twisted so that they are unusable. 



Continued "gilling" or wox^king of dogfish 

 in a net and the efforts needed to remove 

 them cause rapid abrasion of twines and often 

 result in destruction of nets. When catches 

 of dogfish are large, time in clearing the nets 

 may range from several hours to 2 days of 

 fishing time. Salmon troUers may lose fish- 

 ing time and efficiency while removing dogfish 

 from their hooks and replacing lost gear. 



Loss of historic fishing areas owing to 

 dogfish infestation is one of the important 

 claims of fishermen. The claim is substan- 

 tiated for the trawl fisheries by records of 

 the Washington State Department of Fisheries 

 and the Fisheries Research Board of Canada, 

 Reduced yields and reduced fishing effort 

 on the dogfish- infested grounds off south- 

 west Vancouver Island are clearly shown. 

 K. S. Ketchen of the Fisheries Research 

 Board of Canada has mentioned to the senior 

 author that it has been increasingly difficult 

 to follow abundance trends of groundfish off 

 southern Vancouver Island, because trawl 

 fishermen have been forced from these areas. 

 This situation has also been noted for the 

 Washington trawl fleet, where fishermen re- 

 port having been plagued with dogfish on 40- 

 Mile and Swiftsure Banks during the summer 

 and having been repeatedly forced from these 

 areas. 



Representatives of the local commercial 

 and sports fishing industries estimate that 

 in the Pacific Northwest dogfish cause losses 

 of about $2.2 million due to gear destruction 

 and loss of fishing time, and being forced 

 from historical fishing grounds. 



EFFECTS OF LARGE DOGFISH 

 POPULATIONS ON OTHER SPECIES 



The effects of increased dogfish popula- 

 tions on species of food fish through preda- 

 tion and spatial competition are entirely un- 

 known. That "populations of organisms 



inhabiting a common habitat are in constant 

 flux and react upon each other" (Walford, 

 1958), is a known ecological principle. The 

 predator-prey relationship has received little 

 study in marine fisheries. Walford, however, 

 points out that: (1) members of a population 

 compete with one another for food and space; 

 (2) changes in the combination of environ- 

 mental conditions in an ecological system — 

 such as fluctuation of climate, a shift in 

 ocean currents, the invasion of a new predator, 

 or the sudden infestation of an area by a new 

 species that becomes dominant — all cause 

 changes in the species composition; and (3) a 

 population tends to fill all the space in its 

 sector that meets its peculiar physiological 

 and behavior requirements up to limits set 

 by the abundance of food, predators, com- 

 petitors, and other controlling factors. 



General ecological principles dictate that 

 the increase in dogfish stocks has caused 

 greater competition with and predation upon 

 other species. That dogfish are the dominant 

 groundfish, and are probably exceeded only 

 by herring, in basic stock size off British 

 Columbia has been estimated by Shepard 

 and Stevenson (1956). Their estimate that 

 the basic weight of dogfish stocks exceeds 

 that of all other groundfish combined demon- 

 strates how dominant this species has be- 

 come. 



Walford (1958) states: "The abundance of 

 a stock of a species is greatly influenced 

 by the abundance of species of prey, com- 

 petitors, and predators." The dynamics of 

 ecological shifts are complex, and which 

 species would be most likely to benefit from 

 reduction in dogfish population levels is un- 

 known. Predation of dogfish on food fishes, 

 especially in offshore areas, suggests that 

 food fishes might benefit from a reduction 

 in dogfish numbers. Barraclough (1953) states: 

 "The removal of large numbers of predators, 

 such as dogfish, must of necessity dislocate 

 the economy of the coastwise waters. The 

 exact change in the whole or main popula- 

 tions resulting from vigorous pursuit of this 

 fishery cannot be stated with certainty but 

 the first effects might be expected to in- 

 clude an increase in the forage species, 

 such as herring, and increased opportunity 



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