10,000-1 



8,000- 



4,000  



2,000- 



MAINE TOTAL 



I/) 



a 



Z 3 ,000  



D 



o 



O 2,400- 



a 



z 



^ 1.800- 



D 



o 



X 



w 1,200- 



CUMBERLAND COUNTY 



TTTT^^^^^jtt^TT 



YORK COUNTY 



hn^ nthj] 



YEAR 



Figure 5. — Landings of soft-shell clams in Maine and 

 Maine's southwestern counties, 1940-67. County totals 

 for 1940-46 from Dow and Wallace (1961) ; Maine totals 

 for 1940-56 from Power (19.38); and county totals 

 for 1947-67 and Maine totals for 1957-67 from Fish 

 and Wildlife Service (1948-68). No totals were available 

 for York County, 1940 and 1943; Cumberland County, 

 1943; and Maine, 1941. Landings in York County in 

 195.5-58 were less than 300 lbs. 



OCCIU-, however, until a certain stage of the 

 warming trend had been reached. 



Similarly, the effects of low temperature may 

 be direct or indirect, short- or long-term. Broek- 

 huysen's (1936) evidence and ideas on tiie dele- 

 terious effects of combined low temperature and 

 low salinity may apply to upper estuaries and 

 semienclosed bays. Since Carcinus consumes 

 considerably more oxygen in dilute sea water than 

 in water of normal salinity (Waterman, 1960), 

 unfavorable temi)erature, salinity, and dissolved 

 oxygen may combine to provide an environment 

 lethal to Carcinus. 



As the species ordinarily seems tolerant of low 

 temperatiu-e, lowered salinity, or low dissolved 

 oxygen when the conditions are niet singly, it is 

 more likely that widespread reduction in numbers 

 results from more complex causes or chronic 

 conditions. Examples might be the ones described 

 in the foregoing section, "Relation of Crab 

 Abundance to Temperatiu-e Change," in ^vhich 

 unseasonable warming brought the normally 

 dormant crabs out into the open where they were 

 later killed by falling temperature, or where an 

 excessively long dormant period, caused by a 

 long, cold winter with heavy icing of the shore, 

 may have been fatal. 



In the northern part of its range, Carcinus 

 maenas is apparently among tlie most responsive 

 of common marine animals to temi^erature 

 change; consequently, the species may be a usefid 

 indicator of changes in the environment that affect 

 associated animals to a less obvious but perhaps 

 no less serious extent. 



ACKNOWLEDGMENTS 



Wardens John F. Anderson, Chester E. Brown, 

 Richard E. Coffin, Bertram E. Davis, Daniel J. 

 Johnson, and Ralph Pinkham of the Maine 

 Department of Sea and Shore Fisheries; Massa- 

 chusetts Town Shellfish Officers Howard L. 

 Anderson and Walter O'Ned; and, especially, 

 retired Massachusetts State Shellfish Officer Daniel 

 B. Pierce sampled with traps in several areas. 

 Biologist Malcolm Richards of the Maine Depart- 

 ment of Sea and Sliore Fisheries assisted in many 

 of the shore surveys. 



LITERATURE CITED 



Broekhuysen, G. J., Jr. 



1936. On development, growth and distribution of 

 Carcinides maenas (L.). Arch. N6er. Zool. 2: 

 257-399. 



344 



U. S. FISH AND WILDLIFE SERVICE 



