Lauth et al,: Timing and duration of mating and brooding periods of Pleurogrammus monoplerygius 



565 



6 8 



Temperature (°C) 



10 



12 



Figure 3 



Plot of results from laboratory experiments in which 

 Atka mackerel (Pleurogrammus monopterygius) eggs were 

 incubated in a series of controlled incubation tempera- 

 tures. The best fit relationship of days to first hatching 

 as a function of temperature (°C) is represented by the 

 equation, coefficient of determination (r^), and the line 

 drawn through the data points. 



Incubation model 



Water temperatures varied by area and time of year; 

 daily averages were generally highest during the spawn- 

 ing and hatching periods from late summer to early 

 winter, and higher near Amchitka and Tanaga Islands 

 compared to Seguam Island (Fig. 4). During the period 

 1 July to 15 January, average daily water tempera- 

 tures from Amchitka and Tanaga Islands reached a 

 maximum of 6.21°C during October and a minimum of 

 4.17°C in January (Fig. 4A). Average daily water tem- 

 peratures were generally lower and more variable for the 

 same period at Seguam Island, ranging from 4.00°C in 

 June and January to 4.66°C in August (Fig. 4B). The 

 mean and standard deviation for all daily average water 

 temperatures for the period 1 July to 15 January was 

 5.22 ±0.16°C for Amchitka Island and 4.34 ±0.50°C for 

 Seguam Island. 



Amchitka Island Spawning started from late-July to 

 early August, peaked from mid-August to early Sep- 

 tember, and ended in late September (Fig. 5). Some of 

 the egg masses collected at Amchitka Island were at 

 an advanced stage of development; therefore hatching 

 began about the same time that egg masses were col- 

 lected in mid-October and was completed by early to 

 mid-December. 



Tanaga Island Assuming the same incubation tem- 

 peratures as Amchitka Island, calculated spawning and 

 hatching dates for Tanaga Island were about a half- 

 month later than Amchitka Island (Fig. 5). Spawning 



Q. May Jun Jul Aug Sep Oct Nov Dec Jan Feb 



0) 



< 6 



May Jun Jul Aug Sep Oct Oct Nov Dec Jan 

 Month 



Figure 4 



Pooled average daily temperatures (°C) from histori- 

 cal time series data collected from (A) Amchitka and 

 Tanaga islands, and (B) Seguam Island. The dark lines 

 represent the average daily water temperature and the 

 lighter lines, the standard deviation. The dashed lines 

 represent the low and high average daily water tem- 

 peratures chosen for the incubation model. 



commenced from early to mid-August and ended in late 

 September or early October. Hatching began in early 

 November and ended by late December or early January. 



Seguam Island Spawning and hatching dates for 

 Seguam Island were the latest among the three areas 

 sampled (Fig. 5). Spawning began in mid-August, peaked 

 in mid-September, and ended in early-October. Hatching 

 commenced in mid-November and ended from early to 

 mid-January. 



All areas and temperatures combined For all areas 

 combined, spawning began in mid- July, peaked in early 

 September, and ended mid-October (Fig. 6). Hatching 

 immediately followed the end of spawning, peaked in 

 early December, and continued until late January. 



