Fishermen cooperating in this project v;ere provided ivith col- 

 lecting jars containing a 10 percent forraaldelTj'"de solution. 

 Attached to these jars were tacs requestinr; the follovdnc infom- 

 ation: Date of capture, specific locations of capture, nain catch 

 i.vhere sea lampreys were talcen or species to which attached, depth 

 at which nets were set, name of boat captain, and the na;":e of the 

 vessel. These lishermen were visited regularly and frequently TJith 

 the result that accurate collection data were the rule rather than 

 the exception. All specimens were e::ajnined in the laboratory for 

 length, weight, and degree of maturity. Total length vra.s obtained 

 to the nearest tenth of an inch using a raeasuring board; v;eight 

 was balanced to the nearest gram upon a Chatillon scale. Degree of 

 maturity was estiiiiated by e::arp.ination and rieasureiiiont of the gonads. 

 The vd-dth and thickness of this single, nedian organ was measured 

 to the nearest half -millimeter with dividers and a steel rule; the 

 point of meas-'arement was always one-third of the length of the 

 gonad from its anterior tip. 



Distribution in Lalce Huron and its 



northern conne cting waters 



Based upon data obtained vath the samples froi.i this laJ:e, and 

 upon repeated interviews with fisheiTien operating in these waters, 

 it is nj observation that parasitic sea la-':pre3's are present through- 

 out '±10 length and breadth of the lalce, that the parasitic popula- 

 tion is greatest in -0110 northern thrce-fourtlis of this water c;:- 

 pan.:-e (fron the neighborhood of Ilast Tawas, Michigan, north), and 

 that the majonum concentration is present in three contiguous areas: 

 the northwestern extremity of Lake Huron, in the Straits of Mackinac, 

 and in the northeastern extension of Lalce Ilichigan. A comparable 

 concentration also seems to have developed in the v;aters of -the 

 Detour- Passage (Figure 61).). 



Sea lampreys were recovered in Lalce Huron at depths ranging 

 from 2.$ to 5U0 feetj they were comm-only found, depending on the 

 season, at depths of 10 feet to the majcimui'ii noted. The shallovrast 

 capture made was a sea lamprey which was taJcen attached to a north- 

 ern channel catfish caught by gillnetting through the ice over the 

 shoals in Saginaw Bay. At the other extrene, several individuals 

 were captured attached to chubs gillnetted at the depth indicated. 



Seasonal variations in -bhe ease rdth wliich specimens were ob- 

 tained in the different fisheries and observations made by the con- 

 meicial fishermen indicate that there is some systematic change in 

 the bs.thj'metric distribution of sea lampreys at different times of 

 the jeriT. During the months of Hay and J^'one, chub f?shermen, oper- 

 ating in deeper waters of the lalce (200 to $(X) feet) encounter th^ 

 most lampreys J inshore fishermen, trapping or netting for "ivhitefish, 

 suckers, perch, etc., in the same season find relatively fewer 

 lampreys. During the summer months there is a general shift and 

 sea lamoreys and lamprey-scarred fish become more abundant in the 



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