Specific activities (dpm/g) are also much greater in the canyon axis, 

 indicating that enhanced scavenging rather than preferential deposition of 

 particles containing these isotopes accounts for these differences. The 

 greater inventories of isotopes found in Lydonia Canyon suggest that this 

 environment has a greater potential for scavenging dissolved contaminants than 

 noncanyon areas. 



Canyon Fisheries 



Several commercial species (lobster, Jonah crab, red crab, witch 

 flounder, four-spot flounder, white hake, squirrel hake, ocean pout, and 

 tilefish) are found in high abundance in the heads of submarine canyons, due 

 in part to the wide variety of low relief, three-dimensional habitats. 

 Fishing methods directed toward these species include traps and long- line 

 (baited hooks) gear. Mobile gear (trawls, dredges) is not used in the 

 canyons, so there is no physical damage to the habitats as has occurred in 

 historic fishing areas on the shelf and slope. Submarine canyons therefore 

 function as refuges ("home territory") for a number of commercial species and 

 their food organisms. All of these species are mobile and, with the exception 

 of tilefish which are very faithful (endemic) to a given tunnel or grotto 

 shelter, are likely to move out of the canyon head or along the rim or wall if 

 subjected to any stress. The most mobile (migratory) of these species, the 

 lobster, is known to undergo extensive seasonal migrations inshore, offshore, 

 and along the shelf. Approximately 75 percent of the offshore lobster catch 

 and 95 percent of the tilefish catch emanates from the submarine canyon 

 populations. 



POSSIBLE IMPACTS 



As in the previous section, information capsules are presented for topics 

 that are likely to be considered in relation to environmental impacts of 

 petroleum activities. 



97 



