Kaimmer: Hooking bebavm of Hippoglossus stenolepis 



879 



after initial appearance, more than twice the long- 

 est elapsed time between appearance and first bite 

 for fish that appeared when bottom current was 

 noticeable. 



There were differences in the biting behavior 

 of halibut associated with their direction of ap- 

 proach in relation to bottom current ( Fig. 3 ). The 

 difference was significant (upstream 45^^, side 

 or downstream 257c; x-=33.1. P<0.0125), as was 

 the difference between fish that approached when 

 current was or was not noticeable (current 499c, 

 no current 11%; x^=5.4, P<0.0125). Overall, at- 

 tack rate (bites/fish) was 33-73% over the range 

 of lengths observed (Table 4). Although approach 

 direction in relation to current had a significant 

 effect on attack rate, there was no relation be- 

 tween fish length and attack rate for 41 halibut 

 that had approached upstream. For these fish, 

 the attack rate for fish less than 82 cm (sublegal 

 size) was 467f (11 of 24), and the rate for fish 

 82 cm or larger (legal size) was 47% (8 of 17). 



Direction in relation to the current was noted 

 for 54 departures. Thirty-three (61%) halibut de- 

 parted upstream, 6 ( 1 1% ) departed at right angles 

 to the current, and 15 (26%) departed downstream. 



Postbiting behavior and hooking success 



Almost all bites (95%) occurred while fish were 

 in motion: a fish swam toward the bait, took the 

 bait in its mouth, and continued swimming (rush- 

 ing). In two cases, a lying fish took bait and subse- 

 quently spat it out without rushing. In one case, a 

 lying fish kept the bait in its mouth long enough (20 

 s) to be classified as hooked, but without rushing. 



Rushing behavior was about equally followed in 

 frequency by either spitting the hook (53%) or hook- 

 ing (47%). On average, spitting occurred 10 s after 

 the start of rushing behavior; rushing that did not 

 result in spitting had an average duration of 86 s 

 (Table 2). In two-thirds of the cases where the hook 

 was spat, the fish departed rapidly. Thirty percent 

 of spittings were followed by looping behavior and, 

 in one case, the fish immediately rebit the hook. One 

 "steal" was observed, where the fish swam free from 

 the hook with the entire bait in its mouth. Hooking 

 success (hookings/bite) by 5-cm length group was 

 0-83% and increased steadily with increasing fish 

 size. The difference in hooking success between fish 

 of sublegal (<82 cm) and legal (>82 cm) length was 

 highly significant (38% vs. 71%; x^=4-36, df=l, 

 P<0.025). 



Figure 4 shows observed postbiting behavior tran- 

 sitions, from an initial complete bite by an individual 

 fish through the fourth behavioral transition. Of 50 



1=' 



Rushing 

 47 



Spitting 

 2 



Hooking 

 1 



Biting 



Spitting 

 23 



Hooking 

 20 



Departure 



1 



3rd 



41H 



Figure 4 



Behavior tree describing behavior sequences following an ini- 

 tial complete bite. Numbers at left of rows are the position of 

 behaviors in sequences following initial observation. Numbers 

 in boxes are the total frequencies of each behavior in a row 

 position. Thickness of arrows represents relative numbers of 

 observations for each behavior transition. Because some be- 

 haviors were compromised, not all behaviors have transitions 

 from one row position to the next. 



fish tracked on this chart, 20 ended up departing, 22 

 ended up hooked, and 3 were still interacting with 

 hooks at the end of the fourth behavioral transition. 

 Of the three continuing interactions, one fish lay near 

 bait and two fish rebit baited hooks. Fifty percent of 



