372 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



of bloated fish (legal and illegal fish combined) in the lift rose consistently as the depth 

 of water increased. No fish were bloated in nets (mostly pound nets) set at depths of 

 60 feet and less. At depths of 61-80 and 81-100 feet slightly less than one-half of 

 one percent were bloated. The percentage of bloated whitefish increased to 1.08 in 101— 

 110 feet, and rose still further to 1.70 percent in deep water (more than 110 feet). 



The data on the percentages of the legal and of the illegal whitefish that were 

 bloated reveal that both sizes of fish share the general trend toward increased bloating 

 with increase in the depth of the water. The greater percentage of bloated legal fish at 

 61-80 feet in comparison with the percentage at 81-100 feet constitutes the only 

 exception. At all depths beyond 80 feet relatively more of the illegal whitefish than 

 of the legal whitefish were bloated. This difference was probably due to the thinner 

 body wall of the younger fish. The averages for fish taken at all depths show that 

 0.63 percent of all legal fish and 1.17 percent of all illegal fish were bloated. 



The bloating of live whitefish was probably an unimportant source of destruction 

 of undersized individuals. Only 1.17 percent of all illegal fish were bloated and the 

 maximum percentage of bloated fish at any one depth was 2.08 (deep water). How- 

 ever, the repeated capture of undersized fish would increase the risk of injury or death 

 through bloating. 



DEAD WHITEFISH IN POUND NETS AND DEEP TRAP NETS 



Commercial fishermen opposed to the use of deep trap nets contended that confine- 

 ment in this type of gear was fatal to whitefish and that dead illegal fish were very 

 numerous in the lifts. The data of table 45, which show the number and percentage of 

 dead fish (exclusive of dead gilled fish) at three different depths and the percentages of 

 the legal and of the illegal fish found dead at these same depths, do not, in general, sup- 

 port this contention. 



Table 45.— Relationship between the depth of the water and the numbers and percentages of dead whitefish 

 in deep trap nets in Lakes Huron and Michigan, 1931-1932 data combined for all localities in 

 each lake 



1 Includes only lifts in which dead fish were counted. 



: Only 72 percent of the dead fish were separated as to size. 



Almost 4 percent of the undersized whitefish were dead in the Lake Huron deep trap 

 nets lifted from depths of 80 feet or less. However, at that time (1931-19321 

 relatively few deep trap nets were fished in such shallow water. Less than 1 percent 

 of the illegal whitefish were dead in nets lifted from greater depths. The average per- 

 centage of the undersized fish found dead in the lifts of all deep trap nets observed 

 in Lake Huron was slightly above 1 percent. The percentage of the dead among the 

 legal whitefish in Lake Huron deep trap nets was small (average, 0.38 percent) and 

 showed little variation with the depth of the water. 



The percentages of both the legal and the illegal whitefish found dead in deep trap 

 nets were much smaller in Lake Michigan than in Lake Huron. The shallow-water lifts 

 (80 feet and less) in particular had relatively few dead fish as compared with nets 

 from the same depth in Lake Huron. The percentages of dead whitefish in Lake 



