catches of lake trout were usually small, and, 

 of the total drags, trout were caught at a catch 

 rate of only 5-1/2 pounds per 1/2-hour drag 

 for all depths. Lake trout are an ecological 

 associate of chubs, and of the 251 drags that 

 contained either chubs or trout, one-half con- 

 tained a combination of both species, one-third 

 contained only trout, and one-sixth contained 

 only chubs. Because adult lake trout, except for 

 spawning, do not gather in large schools, they 

 would not be a primary target species for 

 trawling. Moreover, during trawling, most 

 immature lake trout can be effectively avoided 

 by fishing at selective depths. 



Catch rates, number of trout per drag, and 

 average weight of trawl -caught lake trout 

 varied with depth. An analysis of three depth 

 zones showed the following: 



4 to 12 fathoms --In this zone the catch rate 

 and number of trout taken were very small 

 (2.2 pounds of lake trout and 1.7 trout per 

 1/2-hour drag). The average weight of trout 

 was 1.3 pounds. 



13 to 27 fathoms --In this zone the catch rate 

 and number of trout increased to 5.7 pounds 

 and 7.3 trout per 1/2-hour drag, whereas the 

 average weight of trout decreased to 0.78 

 pounds. Within the zone, the catch rate was 

 highest at 20 fathoms. 



28 fathonns and deeper - -This zone took 

 primarily very small trout with an average 

 weight of 0.41 pounds per trout. The catch rate 

 and number of trout taken were very high at 

 30 fathoms (16.4 pounds and 38,3 trout per 

 1/2-hour drag) and decreased sharply with 

 depth. At 50 fathoms, the catch rate was 1.5 

 pounds and 2.9 trout per drag. No trout was 

 taken deeper than 55 fathoms. 



Figure 10 shows the average individual weights, 

 number of trout per drag, and catch rates by 

 5 -fathom depth intervals for all lake trout 

 captured during the study. 



Maximum concentration of small trout 

 varied several fathoms from cruise to cruise 

 and in different geographical areas; however, 

 few concentrations (15 pounds or more per 

 drag) were taken deeper than 35 fathoms. 

 Once a concentration was located, an adjust- 

 ment of fishing depth of several fathoms 

 effectively avoided the concentration. This 

 avoidance was demonstrated north of Cornu- 

 copia when the Kaho made a comparison drag 

 side by side with the experimental commercial 

 trawler Nichevo using the same size net, 

 vessel speed, towing direction, and drag dura- 

 tion. The Nichevo fishing in 33 fathoms caught 

 only 12 trout, and the Kaho fishing in 28 fathoms 

 caught 150 trout. Both vessels caught com- 

 mercially significant amounts of chubs in 20 

 minutes, but the Nichevo' s catch was 34 percent 

 greater. 



Concentrations of trout (catch rates over 15 

 pounds per one-half hour) were located only 



15 20 25 30 35 4C 



DEPTH (FATHOMS) 



n 



n 



JZL 



DEPTH (FATHOMS) 



r-i [—1 n 



n 



n n 



DEPTH (FATHOMS) 



Figure 10. — Distribution of trawl-caught lake trout by 

 depth in Lake Superior. A. Average individual weight 

 of lake trout by depth. B. Number of lake trout captured 

 per 1/2-hour drag at each depth Interval. C. Catch 

 rates of lake trout (pounds per 1/2-hour drag) at each 

 depth Interval. The data above are for all drags during 

 the study. 



in the following areas: southern Keweenaw 

 Bay, the east shore of Keweenaw Bay off Pt. 

 Abbaye, Keweenaw Bay off Portage Entry, 

 several localitites between Grand Traverse 

 Bay and Bete Grise Bay, off Ontonagon, off 

 the Porcupine Mountains, in the south channel 

 off Madeline Island, and north of Cornucopia. 

 Thirty-six drags in these areas took nearly 

 60 percent of the total pounds of trout caught 

 by the Kaho in Lake Superior. It is noteworthy, 

 that of the 36 drags, 21 were in 28 to 37 

 fathoms, 7 in 20 to 22 fathoms, only 3 deeper 

 than 38 fathoms, and 5 at other depths. 



The total catch of lake trout was insigni- 

 ficant. During the study, the Kaho made ex- 

 ploratory drags at preselected areas and 

 depths and used a smaller size mesh (l-inch 

 stretched measure) in the cod end than would 

 be used by a commercial trawler. Although 



14 



