Biology and Ecological Niches in the Gulf of the Farallones 



Continental Slope Communities 



Tom Laidig 



In the shallow coastal areas of the Gulf of 

 the Farallones, as in other regions of the 

 world, fishing pressure has increased and 

 numbers of fish have decreased over the 

 past few decades. As many fish stocks have 

 declined, some fishermen have been forced 

 to look elsewhere to fill their nets. 



Traditional fishing grounds in the gulf 

 have been located on the Continental Shelf, 

 a rather flat, relatively shallow area of the 

 sea floor adjacent to the coast. At a depth 

 of about 600 feet, the bottom starts to drop 

 off more rapidly on what is called the Con- 

 tinental Slope. It is on upper and middle 

 parts of this steeper slope that the new fish- 

 ing grounds have been established. Because 

 the fish inhabiting these deeper waters are 

 less understood than those in shallower 

 water, there is a danger of overharvesting, 

 which could threaten the long-term viabil- 

 ity of these newer fisheries. 



The deep waters of the Continental 

 Slope are characterized by nearly freezing 

 temperatures, extremely low light condi- 

 tions, and very high pressures. Because 

 of the cold, organisms that live at these 

 depths have slower metabolisms they eat 

 less frequently, are slower in digesting 

 their food, and move and grow more 

 slowly. They also attain greater ages than 

 their counterparts that live in shallower 



waters some deep-sea rockfish live more 

 than 70 years. 



Many of the animals living in the perpet- 

 ual darkness of the Continental Slope have 

 developed light-producing organs. These 

 serve various functions, such as communi- 

 cating with members of their own kind (as 

 in courtship), attracting food (like attracting 

 moths to a flame), and avoiding being eaten 

 (flashing a light in a predator's eyes can 

 give an animal a chance to get away). 



Another adaptation to the darkness is 

 an absence of color diversity. With no 

 light, colors have little function. Therefore, 

 animals living on the Continental Slope 

 are generally a dark color, like black, 

 brown, or red. Among the fishes, rockfish 

 and thornyheads are dominantly red. Red 

 objects appear black at depth, allowing red 

 organisms to blend in with their dark sur- 

 roundings. 



The water pressure on the sea floor at the 

 top of the Continental Slope is more than 

 10 times higher than at the surface, and at 

 the bottom of the slope the pressure can 

 be more than 100 times higher than at the 

 surface. To compensate for this high pres- 

 sure, organisms have a large percentage of 

 water in their tissues, bones, and shells that 

 replaces other substances, such as gases and 

 calcium. Owing to the high water content of 



their tissues, many larger, older fish caught 

 from deeper waters are limp and soft when 

 brought to the surface. 



Fishes living at different depths on the 

 Continental Slope have different life his- 

 tories. Species living near the top of the 

 slope produce pelagic (open-ocean) young 

 that spend the first few months to years of 

 life swimming in the upper water column 

 and then settle out in relatively shallow 

 water and migrate downslope as they grow 

 and mature. Dover sole, sablefish, and rock- 

 fish have this type of life history; however, 

 most species living deeper, such as rattails, 

 deep-sea soles, and slickheads, have young 

 that live in the same depths as the adults. 



Relatively few species occur at all or 

 most depths on the Continental Slope. Spe- 

 cies occupying one depth commonly are 

 replaced by similar species at other depths. 

 An exception is the eel-like hagfish, which 

 is found at all depths on the slope. 



Productive commercial fisheries operat- 

 ing today on the Continental Slope off 

 California's coast catch Dover sole, sable- 

 fish, deep-living rockfishes, and thorny- 

 heads. Many of these fishes occupy similar 

 habitats and generally are caught together. 

 One increasingly active fishery is for rat- 

 tails, a deep-living fish with a large head 

 and a long tail that tapers to a point. 



One major fishery of note is for hagfish, 

 the skin of which is used to make what are 

 sold as "eel skin" wallets. Hagfish are not 

 true eels but are a primitive group of fish that 

 have no bones or jaws. Instead of bones, they 

 have cartilage, and instead of jaws, they have 

 a large sucker-like mouth similar to that of 

 a lamprey or a leech. Once attached, hagfish 

 use a tongue with many tiny teeth to dig into 

 their prey. Once inside, the prey is eaten from 

 the inside out. Besides its unique method 

 of eating, the hagfish has another interesting 

 trait it produces copious amounts of slime, 

 probably used to discourage predators, which 

 gives the fish its nickname, the "slime eel." 



Except for fishing activities, the Con- 

 tinental Slope and its communities of 

 fish and invertebrates are still virtually 

 untouched by humans, offering scientists 

 the opportunity to study a generally undis- 

 turbed natural system. New methods, such 

 as viewing animals and their habitat by 

 underwater video cameras in submarines 

 and in remotely operated vehicles, have 

 been particularly productive in providing a 

 new understanding of fish and invertebrates 

 living on the slope. In the Gulf of the Faral- 

 lones, scientists are using these methods to 

 collect data at increasingly greater depths, 

 providing critical information needed to 

 better protect these areas from overuse. 



56 Biology and Ecological Niches in the Gulf of the Farallones 



