A transferable predator avoidance reaction may 

 account for the conditioned and naive coho salmon 

 acting as a homogeneous group in the present 

 study. Conditioned coho salmon had learned to 

 avoid torrent sculpins through some unknown 

 mechanism. Apparently the naive fish behaved as 

 conditioned individuals through visual clues re- 

 sulting in mimicry. O'Connell (1960) noted 

 mimicry in sardines in a conditioned response ex- 

 periment where unconditioned replacement fish 

 performed in unison with the school of conditioned 

 fish from the first trial. Kanid'yev et al. (1970) 

 indicated that the consensus of Russian workers 

 was that sight played the main role in developing 

 the predator avoidance reaction and that rein- 

 forcement is maximal for fish that are observers. 



Sculpins commonly cohabit streams with and 

 prey on young salmon. Growth of salmon to a size 

 too large for sculpins to successfully prey on effec- 

 tively removes them from this predator predation. 

 The maximum size of coho salmon that a torrent 

 sculpin can catch and eat in laboratory conditions 

 is much larger than those that are normally 

 preyed upon in nature. This indicates that al- 

 though growth is effective in limiting torrent 

 sculpin predation on coho salmon, other factors 

 are equally important. Among salmon, the coho 

 has a well-developed innate predator avoidance 

 response (Patten 1975). The response apparently 

 can be reinforced by experience with fish predators 

 and this conditioning probably increases their 

 early survival in streams. 



Acknowledgments 



I thank J. R. Heath and other personnel of the 

 City of Seattle Water Department who granted me 

 use of the flume site within a secured area. 



Literature Cited 



GlNETZ, R. M., AND P. A. LARKIN. 



1976. Factors affecting rainbow trout (Salmo gairdneri) 

 predation on migrant fry of sockeye salmon (Oncorhyn- 

 chus nerka). J. Fish. Res. Board Can. 33:19-24. 

 KANID'YEV, A. N., G. M. KOSTYUNIN, AND S. A. SALMIN. 



1970. Hatchery propagation of the pink and chum salmons 

 as a means of increasing the salmon stocks of Sakha- 

 lin. Vop. Ikhtiol. 10:360-373. (Transl. J. Ichthyol. 10: 

 249-259.) 



O'Connell, c. p. 



I960. Use of fish school for conditioned response experi- 

 ments. Anim. Behav. 8:225-227. 

 PATTEN, B. G. 



1962. Cottid predation upon salmon fry in a Washington 

 stream. Trans. Am. Fish. Soc. 91:427-429. 



1971a. Predation by sculpins on fall chinook salmon, On- 

 corhynchus tshawytscha, fry of hatchery origin. U.S. 

 Dep. Commer., Natl. Mar. Fish. Serv., Spec. Sci. Rep. Fish. 

 621, 14 p. 



1971b. Increased predation by the torrent sculpin, Cottus 

 rhotheus, on coho salmon fry, Oncorhynchus kisutch, dur- 

 ing moonlight nights. J. Fish. Res. Board Can. 28:1352- 

 1354. 



1972. Predation, particularly by sculpins, on salmon fry in 

 fresh waters of Washington. U.S. Dep. Commer., Natl. 

 Mar. Fish. Serv., Data Rep. 71, 21 p. 



1975. Comparative vulnerability of fry of Pacific salmon 

 and steelhead trout to predation by torrent sculpin in 

 stream aquaria. Fish. Bull., U.S. 73:931-934. 



Benjamin G. Patten 



Northwest and Alaska Fisheries Center 

 National Marine Fisheries Service, NOAA 

 2725 Montlake Boulevard East 

 Seattle, WA 98112 



DESCRIPTION OF MEGALOPA OF 



SNOW CRAB, CHIONOECETES BAIRDI 



(MAJIDAE, SUBFAMILY OREGONIINAE) 



Chionoecetes bairdi Rathbun, a brachyuran crab, 

 occurs on the continental shelf from Puget Sound 

 in Washington State, northward into the Bering 

 Sea, and westward along the Aleutian Islands. 

 The species has been taken as deep as 474 m 

 (Garth 1958), but adults commonly occur at depths 

 less than 190 m. Chionoecetes bairdi may be quite 

 abundant in inshore areas throughout its range 

 and has become an important subsistence and 

 commercial species because of its large size and 

 accessibility. It supports an extensive fishery in 

 the Bering Sea and Gulf of Alaska for three 

 nations — the United States, the Soviet Union, and 

 Japan. 



The range of C. bairdi overlaps that of three 

 other species of Chionoecetes: C. tanneri Rathbun, 

 C. angulatus Rathbun, and C. opilio (O. Fab- 

 ricius). Chionoecetes tanneri ranges from Mexico 

 north to the State of Washington, and commonly 

 occurs between 370 and 1,630 m on the outer 

 slopes of the continental shelf (Garth 1958). 

 Chionoecetes angulatus occurs throughout the 

 range of C. bairdi, but C. angulatus occurs on the 

 lower slopes of the shelf edge between 730 and 

 2,980 m (Garth 1958). Chionoecetes opilio occurs 

 only in the Bering Sea, and its distribution is often 

 sympatric with C. bairdi. Two other species of 

 Chionoecetes occur in the western Pacific Ocean, 



459 



