90 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



of Lake Michigan water into Green Bay is charac- 

 terized more by surges than by a regular movement. 

 Surges into the bay result primarily from seiche 

 action set in motion by wind and pressure changes 

 over Lake Michigan. The resultant currents in 

 tlie bay cause a tremendous amount of mixing. 

 In the northern passages the sequence of inflow, 

 mixing, and outflow result in a great amount of 

 water excliange between the bay and the lake. 

 Evidence of a high degree of exchange in the 

 northern area is found in the relatively clear. Lake 

 Michigan-type water that lacks the deep green 

 color produced by dense phytoplankton growth 

 characteristic of the remainder of the bay. Def- 

 inite lines of demarcation cannot be made on this 

 basis, however, because of mixing of water masses. 

 Clear lake water is sometimes observed in the 

 Sturgeon Bay area, but here a sharp line of demar- 

 cation is usually present between the two types of 

 water. This condition indicates that little mixing 

 occui-s before the lake water is returned with an 

 outgoing surge through the canal. 



In addition to water movements propagated by 

 currents and water-level changes in Lake Michi- 

 gan, the water in the bay itself is subject to indig- 

 enous seiches and currents caused by local condi- 

 tions. The systems operating simultaneously in 

 lake and bay, as they must most of the time, result 

 in extremely complex and irregular water move- 

 ments. 



The water level in Green Bay is subject to 

 almost continuous chaiige. A change of a foot an 

 hour is not uncommon and occasionally a drop of 

 several feet in the southern end of the bay strands 

 fishing boats in shallow harbors. Although a 

 complex resonance pattern is characteristic of 

 water-level charts of Green Bay, peaks occur at 

 intervals of about 12 hours. The peaks show no 

 relation to the movements of the moon. Typical 

 spacing of the peaks within the 24-hour period can 

 be completely disrupted by severe storms after 

 which a new system is established with peaks 

 occurring at different hours of the day but again 

 at 12-hour intervals. 



Some of the effects of water movements on the 

 water temperatures in Green Bay will be shown 

 later in a discussion of the distribution of lake 

 lierring. 



ECONOMIC IMPORTANCE OF THE 

 FISHERY 



Green Bay supports one of the most productive 

 commercial fisheries of the Great Lakes and the 

 lake herring is a major contributor to the catch. 

 Hile, Lunger, and Buettner (1953) showed that on 

 the average 28.8 percent of the total pounds of all 

 species taken in the State of Michigan waters of 

 Green Bay consisted of herring. In 1952, the last 

 year for which complete statistics and values are 

 available, the lake herring catch of Green Bay 

 (both Wisconsin and Michigan) amounted to 

 9,121,600 pounds and had a value to the fishermen 

 of $456,080. This catch represented 94.1 percent 

 of the production of this species in all of Lake 

 Michigan and 38.7 percent of the lake herring 

 production of all United States waters of the Great 

 Lakes. 



The commercial production of the lake herring 

 in Green Bay is characterized by wide annual and 

 seasonal fluctuations. The catch in Michigan 

 waters of Green Bay ranged from 1,515,000 to 

 11,850,000 pounds (average 5,841,000 pounds) 

 from 1891 to 1908 (Hile, Lunger, and Buettner, 

 1953) and averaged 82.4 percent of the total 

 pounds of all species taken. In a later period 

 (1929-49) there was a marked drop in the produc- 

 tion to between 160,000 and 2,668,000 pounds 

 (average 1,070,000 pounds) which contributed an 

 average of 29.9 percent to the catch of all species. 

 The production of lake herring in Michigan and 

 Wisconsin waters during the years for which 

 reliable records are available for both States 

 (table 2) show wide variation seasonally and 

 annually. Fluctuations of the catch are influ- 

 enced primarily by weather, availability and 

 abundance of other species with higher market 

 value, and the abundance of lake herring itself. 

 Thus, the causes of fluctuations are difficult to 

 ascertain, but the great difference between the 

 1891-1908 and 1929-49 data on the Michigan 

 waters of Green Bay (82-percent drop in average 

 production) shown by Hile, Lunger, and Buettner 

 indicates that the population must be subject to 

 wide variations. The present study, however, has 

 been conducted in years (1948-52) when total 

 production has been high and relatively stable 



