564 



Fishery Bulletin 105(4) 



Archival tags Two archival tags were retrieved from regular diel 



Seguam Pass in September 2000, and one each in Sep- season from 



tember 2001 and January 2001. It was evident from the B). During 

 depth data of two tags that Atka mackerel males made 



250 

 



50 



100 



150 



200 



250 

 



4 June 2001 



Mean nesting depth = 1 17 m 

 Mean temperature = 4.5 °C 



B 



1 2 Dec 2000 

 Mean nesting depth = 99 m 



li-i. 



Mean temperature = 4.9 °C 



50 ^ 



100 



150 - 

 200 - 



250 



Mean nesting depth = 1 17 m 

 33 days 



Mean temperature = 4.6 "C 



H 1 1 1 h- 



50 ^ 



100 

 150 

 200 



250 



D 



33 days 



Mean nesting depth = 1 1 5 m 

 Mean temperature = 4.5 °C 



Jun 



— I — 

 Jul 



-+- 



-(- 



Aug Sep Oct 

 Month 



Nov 



Dec 



16 

 -- 12 



- 8 

 -- 4 



16 



+ 12 

 8 

 4 

 



16 

 12 



Figure 2 



Plots A-D show the depth and temperature data of archival tags from 

 four captured male Atka mackerel (Pleurogrammus monopterygius) that 

 were originally tagged and released in July 2000. The calendar year 

 for plot A is 2001, and for plots B-D is 2000. All four males exhibited 

 periods of limited vertical movement consistent with nesting behavior. 

 An arrow points to the start of nesting behavior in plot A and the end 

 of nesting behavior in plot B, and plots C and D have brackets delin- 

 eating the nesting periods and the length of nesting behavior (days) 

 is indicated above the brackets. Mean water depth and temperature of 

 nesting behavior periods are also presented along with average daily 

 water temperature represented by the lower black line in each plot. 

 Periods with frequent and repeated diel vertical migrations outside the 

 arrows and brackets are consistent with non-nesting behavior. 



vertical movements during the nonbreeding 

 mid-December through May (Fig, 2, A and 

 the breeding season from June to Decem- 

 ber, the behavior of all four tagged males 

 was characterized by an extended period 

 of time on the bottom and very limited 

 or no vertical movement (Fig. 2). It was 

 assumed that these periods corresponded 

 with nesting behavior. The earliest date 

 within a year that such nesting behavior 

 was observed was 4 June (Fig. 2A) and 

 the latest was 12 December (Fig. 2B). The 

 male in Fig. 2A was at liberty for 406 days 

 and exhibited 89 days of limited vertical 

 movement before being captured. The male 

 in Fig. 2B displayed nesting behavior for 

 141 consecutive days, — the longest unin- 

 terrupted time period for all tagged males. 

 Also unique to the male in Figure 2B was 

 a depth shift from 125 to 92 m on 14 Sep- 

 tember followed by a continuation of nest- 

 ing behavior until 14 December (89 days). 

 Three of the four males displayed nesting 

 behavior shortly after being released (Fig. 

 2, B-D), but two of these males (Fig. 2, 

 C and D) abandoned the behavior after 

 only 33 days, whereas the other male (Fig. 

 2B) shifted depth and continued nesting 

 behavior. Males in Figures 2B and 2D also 

 showed unexplained and periodic ascents 

 and descents during periods of presumed 

 nesting behavior. 



The average depths where male nesting 

 behavior was displayed ranged from 92 

 to 117 m and the water temperatures at 

 those locations ranged from 4.5° to 4.9°C. 

 Water temperatures varied by a maxi- 

 mum of 2.6°C during these periods. 



Laboratory incubation experiments 



In 2004, ten egg masses were fertilized 

 and all were incubated successfully at 

 the ASLC. The first spawning event for 

 the captive Atka mackerel was recorded 

 on 27 July, and the last was on 13 Octo- 

 ber. For 2005, the first and last spawning 

 dates were 13 July and 12 October. The 

 average temperature for each of the four 

 treatments was 3.89°, 5.04°, 7.03°, and 

 9.85°C. The incubation time of 74 days at 

 6.15°C from Lauth and Blood (2007) was 

 also used in the analysis. The best fit of 

 the data was a logarithmic function with 

 a negative slope (Fig. 3). Total incubation 

 time (D,) was a function of the natural 

 logarithm of incubation temperature (t) 

 with days to first hatching ranging from 

 44 days at 9.85°C to 100 days at 3.89°C 

 (Fig. 3). 



