350 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Distribution of legal-sized whitefish. — In May the average numbers of legal white- 

 fish taken in 111-120 feet and in "deep-water" (more than 120 feet) lifts were above 

 those of the single lifts from 81-90 and 101-110 feet. In June, however, the average 

 catches of the nets from the deeper water were exceeded by the catch of the 6 nets set 

 in 101-110 feet. The 5 lifts in shallow water (41-70 feet) averaged only 9.0 and 9.8 fish 

 for the two intervals involved. The largest average lifts in July occurred at depths of 

 81-90 feet (43.2) and 91-100 feet (37.3). However, the average number of fish in 

 lifts from 111-120 feet was almost three times that of lifts from the 101-110 foot in- 

 terval. The single lift in shallow water (41-60 feet) was again small (7.0 fish). The 

 depth from which the largest lifts were made in August was shallower than that in 

 July (71-80 feet). It is to be noted also that the average numbers of fish taken in the 

 shallow water far exceeded the corresponding averages for June and July. In August, 

 again, the catch of nets set at 111-120 feet was well above that of nets set at 101-110 

 feet. This agreement between the July and August data suggests that in late summer 

 whitefish may be concentrated at more than one depth. 30 The September data cover 

 only two intervals of depth. In this month the average number of legal whitefish per 

 lift from 111-120 feet was twice that of nets from 101-110 feet, and in both intervals 

 the numbers were relatively large, suggesting a return of the fish to deep water. 



The data offer some evidence of an onshore movement of legal whitefish as the 

 summer progresses. In May concentrations were greatest in the deepest water (beyond 



110 feet). In June a general shift seemed to have occurred to waters between 80 and 



111 feet deep, in July to waters of depths between 70 and 101 feet, and in August to 

 depths between 60 and 91 feet. 



In the averages for the entire season the number of legal fish per lift increased from 

 shallow water to a maximum of 84.2 fish at depths of 71-80 feet. Beyond this depth 

 interval there was a continuous decline in the average number of legal whitefish per lift. 31 



Distribution of illegal-sized whitefish. — The data on the bathymetric distribution of 

 illegal whitefish bear considerable resemblance to those of legal fish. In both size groups 

 the average number of fish per lift was greater at 111-120 feet than at 101-110 feet in 

 every month but June. Furthermore, both groups appear to undertake an onshore 

 movement as the summer progresses. A difference is found between the vertical distri- 

 bution of legal and illegal whitefish in the greater abundance of the latter group in 

 shallow water. 



The averages for the entire season show heavy concentrations of young whitefish 

 in the intervals: 41-60 feet, 81-90 feet, and more than 120 feet. These fish were least 

 abundant in depths of 71-80 and 101-110 feet. These averages, however, are influenced 

 by the shift in concentrations. The monthly figures indicate a heavy concentration in all 

 depths beyond 80 feet in May, between 80 and 111 feet in June, between 80 and 101 feet 

 in July, and in 81-90 feet in August. In September the number again increased in the 

 111-120 foot interval. A comparison of the seasons' averages reveals that the maximum 

 concentration of illegal whitefish (81-90 feet) was in water 10 feet deeper than the 

 maximum for legal fish (71-80 feet). However, legal fish did not share the inshore 

 abundance of the smaller whitefish. 



SAGINAW BAY AEEA (OSCODA, EAST TAWAS, AND BAY PORT) 



A total of 223 lifts of pound nets and deep trap nets was examined in the Saginaw 

 Bay area. Despite this large total, the distribution of the lifts leaves certain depths 

 of less than 91 feet poorly represented (table 25). With the exception of a few lifts on 

 northerly and easterly courses out of Oscoda, the deep-trap-net lifts were made on the 

 grounds of district H-A. (See fig. 4.) Most of the pound nets observed were in the 

 neighborhood of East Tawas. The Saginaw Bay area differed from the Alpena-Ossineke 

 grounds in the relatively high abundance of legal, as compared with illegal, fish. 



30 The evidence for more than one "concentration depth" is not strong (particularly for legal whitefish) in the Alpena-Ossineke data. The sug- 

 gestion is brought out here because of the later conclusive evidence that there are two concentration zones in northeastern Lake Michigan (p. 353). 

 No good evidence of a concentration at 111-120 feet was found in other Lake Huron waters. 



31 The September data obscure the presence of two concentrations of legal whitefish. If the September data are excluded the average numbers 

 of legal whitefish per lift become 18.7 at 101-110 feet and 30.3 at 111-120 feet. 



