36 



U. S. BUKEAU OF FISHEEIES. 



MUSSEL SURVEY IN UPPER MISSISSIPPI RIVER. 



During the months of July and August, 1920, the Bureau of 

 Fisheries made a study and appraisal of the mussel resources in a 

 portion of the upper Mississippi River, beginning at a point about 

 5 miles above Red Wing, Minn., and extending down through Lake 

 Pepin, a distance of about 80 miles, to Lamoille, Minn. The work 

 was undertaken with reference to recent administrative action on 

 the part of the States of Wisconsin and Minnesota providing for 

 the closure of certain areas for the protection of the fresh-water 

 m-ussels while permitting the fishery to continue in alternate open 

 areas. The data acquired in this investigation are expected to estab- 

 lish a basis for comparison of conditions before and after a period 

 of protection. The investigation was conducted under the Fair- 

 port biological station by Dr. N. M. Grier, with two assistants. Ob- 

 servations were made in five open and five closed areas. 



Many data were secured regarding the depletion of formerly pro- 

 ductive areas of mussel fishery, the diminution in abundance of 

 mussels in different beds being attributed variously to the indirect 

 effects of the construction of wing dam.s as aids to navigation, to 

 excessive fishery, and perhaps in some cases to the dumping of rub- 

 bish in the river in the vicinity of cities. 



The information gained will serve also as an aid to the Bureau 

 in the conduct of mussel propagation for the rehabilitation of de- 

 pleted and protected areas. 



EXPERI]VIENTS RELATING TO MUSSEL PROPAGATION. 



Experiments in retaining in inclosures fish artificially infected 

 with glochidia of the Lake Pepin mucket, Lampsilis luteola^ have 

 been continued in Lake Pepin by Roy 8. Corwin, scientific assistant. 

 It was found in certain experiments that pike perch infected as late 

 as August 19 carried glochidia until the following May, and that 

 mussels during the second year of growth will thrive in an inclosure 

 with a density of 18 mussels to the square foot. Third-year mussels 

 with eight to the square foot flourished and showed an average in- 

 crease in length of more than 100 per cent in one year. 



Artificial infections of the Lake Pepin mucket on pike perch re- 

 tained in a fine-meshed inclosure in the lake yielded an average of 

 833 juvenile mussels per fish. Assuming that these fish bore the 

 usual infection of about 3,000 glochidia per fish, the yield of young^ 

 mussels was 27.4 per cent. This is a much higher percentage than 

 has ever been assumed to result from practical operations in artifi- 

 cial propagation of mussels. 



Dr. L. B. Arey continued his study of the encystment of the 

 glochidia of the fresh-water mussel. It has been established that 

 the tactile response of the glochidium alone is adequate to insure 

 attachment. The view that glochidia regularly attached to the host 

 through a chemical activation by blood, derived from gill hemor- 

 rhages, appears to be untenable. Cyst formation is not initiated or 

 controlled by any vital influence of the glochidium. It has been 

 induced by the application of tiny metallic clips to a gill filament. 



