LAKE SUPERIOR LIMNOLOGICAL DATA 

 1951 - 1957 



The Great Lakes have long been a challenge 

 to limnologists and freshwater hydrographers. Even 

 now, only modest advances have been made in 

 exploring this largest system of freshwater lakes in 

 the world (Smith 1957), Lake Superior, the largest 

 freshwater lake of the world, has received less at- 

 tention than any other of the Great Lakes, probably 

 because of the problems of special operating and 

 equipment imposed by its great area (31, 820 square 

 miles) and depth (maximum, 222 fathoms). Only 

 recently has this formidable equipment require- 

 ment been met in operations of specially con- 

 structed Great Lakes research vessels by the U. S. 

 Fish and Wildlife Service and U. S. Lake Survey, 

 and of refitted existing vessels by the University of 

 Minnesota (Ruschmeyer, Olson, and Bosch 1957). 



Data presented here were gathered during the 

 operations of the M/V Cisco (Great Lakes Fishery 

 Investigations, U. S. Fish and Wildlife Service- 

 see Moffett 1954 for description) in 1952 and 1953, 

 and the M/V Williams (U. S. Lake Survey) In 

 1956 and 1957. Also included are surface temper- 

 atures obtained from thermographs operated by the 

 staff at the Marquette station of the Great Lakes 

 Fishery Investigations in 1951-1957. This report 

 lists limnological data from these sources, without 

 extensive interpretation, to make the records avail- 

 able to other interested agencies. 



OPERATIONS OF M/V CISCO 



The Cisco was used in an exploratory survey of 

 Lake Superior in August 1952 to collect data for 

 planning the full-season (May-October) study of 1953. 

 After lake trout populations of Lakes Michigan and 

 Huron were depleted following invasion of the sea 

 lamprey (Hile 1949; Hile, Bchmeyer, and Lunger 

 1951), only Lake Superior remained as a source of 

 the life-history information vitally needed for plan- 

 ning future rehabilitation programs. Since the 

 early life history was least known and most impor- 

 tant in establishing a planting program, it received 

 primary attention in the study. Operations of the 

 vessel were guided by requirements for collection 

 of data on lake trout and hence were concentrated 

 in the inshore nursery areas for this species. 



Restrictions imposed by the lake trout study 

 limited but did not preclude the collection of 

 extensive limnological data. Temperature meas- 

 urements with a bathythermograph were made at 

 frequent intervals along routes traveled in 1952, 

 and limited physical and chemical data were ob- 

 tained at selected hydrographic stations. Plans for 

 1953 provided for routine collection of temperature 

 and chemical data at regular intervals between ports 

 of call and fishing locations. Hydrographic stations 

 were established along these transects as time and 

 conditions permitted. Where hydrographic stations 

 were located on routes of travel or at important fish- 

 ing locations, repeat visits were possible. 



The 3-week cruise in August 1952 covered the 

 south shore of Lake Superior east of the Keweenaw 

 Peninsula, Keweenaw Bay, and most United States 

 waters (north and south shores including Isle Royale) 

 from Keweenaw Peninsula to the Apostle Island region 

 (fig. 1). During the 1953 season the lake was covered 

 from the Two Harbors-Port Wing line in the west to 

 the eastern extremity of the lake (figs. 2, 3). The 

 lake was divided roughly into west, central (Keweenaw- 

 Isle Royale area), and east sections. These areas 

 were covered in approximately 2-week cruises on 

 the following schedule: 



Cruise Period (1953) 



Section 



Sections were not given well defined boundaries 

 and some overlap usually occurred in coverage of 

 adjacent sections in succeeding cruises. Restriction 

 of Cruise VUI to the central section was necessitated 

 by adverse weather and Cruise IX was largely de- 

 voted to sampling juvenile, and to tagging adult 

 •lake trout between Marquette and the Keweenaw 

 Peninsula. 



