130 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



OCTOBER 21 -2S 



Figure 15.— Vertical distribution of lake herring taken in 

 oblique sets of gill nets in 60 feet of water. The full width 

 of the panel for each time period is 100 percent. 



OCTOBER 22-25 



Figure 16. — Vertical distribution of lake herring taken in 

 oblique sets of gill nets in 90 feet of water. The full 

 width of the panel for each time period is 100 percent. 



(fig. 15) and at 90-foot stations (fig. 16) are given 

 as unweighted mean percentages for all stations 

 where lake herring were caught. 



Despite the concentration of lake herring in the 

 upper 15-foot stratum at 60-foot stations (E and 

 G) in early May (67.9 percent, fig. 15), evidence 

 at 90-foot stations where nets were fished on the 

 same and other dates in early May (table 41, fig. 

 16) suggests a possibly random distribution. In 

 late May the lake herring were concentrated in 

 the top 15-foot stratum at both 60- and 90-foot 

 stations (69.0 and 87.1 percent); most of the 

 remaining fish were at the 15- to 30-foot level 

 (29.0 percent at 60-foot stations and 9.7 percent 

 at 90-foot stations). Lake herring exhibited a 

 strong tendency to move into water deeper than 

 30 feet in June (84.5 percent at 60-foot stations 

 and 98.7 percent at the 90-foot station); the 

 tendency toward concentration below 30 feet was 

 still greater in July (94.4 and 99.3 percent at 60- 

 and 90-foot stations). Lake herring were present 

 in fair numbers except in deepest water (75 to 90 

 feet) in October but showed a decided tendency 



to be concentrated in the upper 30 feet (74.6 and 

 66.8 percent at 60- and 90-foot stations). 



The general seasonal trend in vertical distribu- 

 tions from May to October may be summarized 

 as follows. The first change was from a variable 

 pattern in early May to a pelagic distribution in 

 late May. In June and July the lake herring 

 had descended to depths greater than 30 feet and 

 by October they had resumed the pelagic habitat 

 with the greatest concentration between the 

 surface and 30 feet. 



The distribution of lake herring during the 

 spawning period in November and December has 

 been brought out in the discussion of spawning 

 activity. Distribution during winter and early 

 spring is subject of much speculation. The few 

 observations that have been made lead to the 

 conclusion that schools of lake herring may be 

 found at any depth. 



The vertical distribution of lake herring showed 

 no relation to temperature, except in the avoid- 

 ance of water with temperature near or above 

 20° C. In early May when the water was rela- 

 tively cool (3.2° to 7.6° C. at stations where lake 

 herring were caught) and varied little with depth 

 (table 42), the distribution of herring was largely 

 random (table 41). Late May temperatures are 

 available for only the shallow-water stations (A 

 and B); the surface temperatures at these loca- 

 tions were 14.1° and 14.5° C. and bottom tem- 

 peratures were 13.0° and 11.6° V. 



Although the lake herring had moved toward 

 greater depths in June, it cannot be assumed that 

 increasing water temperature near the surface was 

 the cause. The temperatures from the surface to 

 30 feet were between 12.3° and 15.1° C. (total 

 range at all stations) — not greatly different from 

 those at stations A and B in late May. The lake 

 herring continued to be concentrated below 30 

 feet in July. During this month water tempera- 

 tures at less than 30 feet (fig. 17 and table 42) 

 usually were within the range of 18.3° to 21.5° C. 

 (the range from 15.6° at 20 feet to 18.6° at the 

 surface on July 24 represents a transitory situation 

 following a severe storm). Since these July tem- 

 peratures from the surface to 30 feet were mostly 

 near or above the values considered critical for the 

 lake herring (see p. 128), it is probable that tem- 

 perature conditions held the lake herring in greater 

 depths in July. This view is supported by the 

 absence of lake herring at shallow-water station A 



