Kendall and Nakatani: Early life history of Theragra chalcogramma in Shelikof Strait and Funka Bay 



131 



OOE ISO ODE ISO OOE r70 OOE 160 OOU 170 OOW 160 OOW tSO OOW 140 OOU 130 OOW 



I ' l I I I I I I I ! I I t I I I I 1 I I I I I I I I I I Ill 



158 OOW 1S7 OOW ISe OOW ISS OOW 1S4 OOU 153 OOW 152 



40 OOH 

 56 30N 



Figure 1 



Location of Funka Bay, 

 Japan, and Shelikof Strait, 

 Gulf of Alaska. Insets are 

 enlargements of the areas 

 with pertinent bathymetry. 



trated in a small area of deep water (> 250 m) near Cape 

 Kekurnoi (Fig. 1) (Kendall and Picquelle 1990). 



Field surveys of adult walleye pollock in Funka Bay 

 and Shelikof Strait show that fish congregate and 

 migrate to a particular part of their range just prior 

 to the spawning season. Final migration to a restricted 

 spawning area takes place quickly. In Shelikof Strait, 

 hydroacoustic surveys show that the fish separate into 

 vertical strata, presumably by sex (females below 

 males) and readiness to spawn (Muigwa 1989). 



Although the fish move to the spawning area as a 

 large group, spawning itself is by pairs. Behavior of 

 spawning walleye pollock has been investigated using 

 captive fish from Funka Bay (Sakurai 1982, 1989), as 

 well as from Puget Sound, Washington (Baird and 011a 

 1991). The shallow tanks used by Sakurai (1989) may 

 have prevented some of the vertical aspects of spawn- 

 ing behavior observed by Baird and 011a (1991). 

 Although no such studies have been conducted on fish 

 from Shelikof Strait, similarities between the behavior 

 of fish from near the eastern (Puget Sound) and 

 western (Funka Bay) extremes of the species distribu- 

 tion may indicate that spawning behavior varies little 



geographically. In experimental tanks, the fish form 

 loose aggregations near the surface. Males frequently 

 follow other males and females. Sakurai (1989) related 

 male-male interaction to the agonistic behaviors 

 associated with dominance; Baird and 011a (1991) con- 

 sidered the male's following behavior as a searching 

 behavior for potential mates. Sakurai (1989) also 

 observed courtship displays by males toward prospec- 

 tive mates. At the onset of a spawning, a female would 

 swim down with a male following her. The male then 

 made contact with her by rubbing his ventral surface 

 first against her dorsum or side and then he swam 

 beneath her, with their two vents in contact. Other 

 males occasionally followed the pair closely and also 

 made contact with the female. During vent-to- vent con- 

 tact, the male rubbed his body rapidly against the 

 female's abdomen, and presumably gametes were 

 released at this time (they could not be seen in the 

 water, but were found in the tank overflow within an 

 hour). Most spawning took place in evening or morn- 

 ing twilight (Baird and 011a 1991). 



Female walleye pollock characteristically spawn a 

 number of batches of eggs over a fairly short period 



