WHITEFISH FISHERY OF LAKES HURON AND MICHIGAN 



371 



The data of table 43 on the numbers and percentages of gilled whitefish in pound 

 nets and deep trap nets are based on a combination of all nets of similar sizes of mesh 

 irrespective of fishing grounds, depth of water, and the month and year in which the 

 nets were fished. 37 None of these variables was found to affect the percentage of 

 gilled fish. 



Table 43. — Numbers and percentages of legal and illegal whitefish gilled in large-mesh and small-mesh 



■pound nets and deep trap nets, 1931-1932 data combined for all localities and all depths of water 



[The table is based only on the lifts in which gilled fish were counted and separated according to size] 



A larger percentage of both the legal and the illegal whitefish became gilled in 

 large-mesh nets than in small-mesh nets. The percentage of the legal fish gilled in 

 large-mesh nets although small was three times that gilled in small-mesh nets, but 

 the percentage of the illegal fish gilled in large meshes was only slightly above that 

 in small meshes. It may be considered probable that the greater ability of large 

 meshes to gill the larger illegal fish is compensated by the numbers of smaller illegal 

 fish that can pass through the meshes. 



The percentages of gilled illegal whitefish in pound nets and deep trap nets (2.4 

 percent in small meshes and 2.7 percent in large meshes) do not point to gilling as a 

 very important source of destruction of undersized fish in a single lift. Should the 

 same fish be taken repeatedly the risk of death by gilling would be increased. 



BLOATING OF LIVE WHITEFISH IN POUND NETS AND DEEP TRAP NETS 



Another possible source of destruction of illegal-sized whitefish is the bloating 

 (the result of changing pressure) that frequently occurs when nets are lifted. It can- 

 not be stated exactly how serious the effects of bloating may be. It is possible that 

 many fish that are not visibly bloated when a net reaches the surface may have been 

 injured seriously by the change of pressure, particularly if the net was lifted rapidly. 

 On the other hand, visibly bloated fish often appear to make a complete recovery, 

 and swim away vigorously upon return to the water. 



Table 44 shows the relationship between the depth of water from which nets were 

 lifted and the extent of bloating of whitefish of legal and illegal size. The percentage 



Table 44. — Relationship between the depth of water and the bloating of life whitefish in pound nets ami drip 

 trui) mis, l.'i.ll l:i.;_> tlatn combined for all localities 



1 Includes only lifts in which bloated fish were counted. 



* Only 63 percent of the bloated fish were separated as to size. 



17 Fish were considered to be gilled only when it was obvious that they had become enmeshed while the net was actually fishing. Freshly gilled 

 live fish were considered to have become enmeshed during the lifting process, and were not counted; usually they were not injured. 



