tures have followed the same downward trend 

 as the annual means, the decreases have been 

 greater during the winters. Lauzier (1965) has 

 shown that air and sea temjjerature trends similai- 

 to those recorded at Boothbay Harbor have 

 occurred at various points along the western 

 north Atlantic Coast from Atlantic City, N.J., to 

 Halifax, Nova Scotia, and stations over the 

 Scotian Shelf. The sea temperature trend at St. 

 Andrews, New Brunswick, is of ])articular interest 

 because the station is on Passamaquoddy Bay, 

 a part of the Bay of Fundy where observations 

 were made on crab abundance, and because the 

 general trend is similar to that at Boothbay 

 Harbor. The jjeak of the warming period at vSt. 

 Andrews was in 1951, and the temperature de- 

 clined rapidly after 1954. 



RELATION OF CRAB ABUNDANCE TO 

 TEMPERATURE CHANGE 



Past records in different areas have indicated 

 that the green crab suffers frona extrenae or sudden 

 decreases in temjjerature and ap])arently prospers 

 in periods of increasing temperature. Broekhuysen 

 (1936), working near Den Helder, Netherlands, 

 found that the development of the eggs of this 

 species was most successful witliin an optimum 

 range of water temperature and salinity and that 

 a combination of low temjierature and low salinity 

 adversely affected egg development and probably 

 the development of adults as well. 



Glude (1955) associated increases in green crab 

 abundance with the increase in sea-water tempera- 

 ture — especially winter temperature — and specu- 

 lated on ways in which temperature could affect 

 the crabs. He also pointed out that Goucher (see 

 footnote 1) had recorded an increase in green 

 crabs at Essex, Mass., between 1926 and 1933 

 (a period of warming) ; an abrupt decrease of 

 crabs after the very severe winter of 1933-34; 

 and an increase in abundance again from 1944 to 

 1951, coincident with the most recent warming 

 period. 



Taylor, Bigelow, and Graham (1957) discussed 

 the changes in distribution and abundance of 

 numerous marine animals during the period when 

 information on abundance and temjjerature has 

 been available. They mentioned that too little 

 was known about the life history of the green 

 crab to say what environmental factors affected 



it so favorably, but that the \\inter temperatures 

 of the mid-1950's seemed sufficiently high to 

 accoimt for the northward extension of its range. 



Waugh (1964) and Crisp (1964), investigating 

 the effects of the severe winter of 1962-63 on 

 marine life in southern England and North Wales, 

 respectively, found heavy mortality among adidt 

 green crabs, but smaller individuals seemed less 

 affected. During most of January and February 

 1963 the water temperatiu-e was about 5° C. 

 below normal, often reaching well below 0° C. 



Along the Maine Coast, the most drastic and 

 noticeable decreases in crab abundance were 

 during the winter of 1955-56. Mean monthly 

 water temperatures at Boothbay Harbor for 

 December 1955 (4.9° C.) and January 1956 

 (3.4° C.) were the coldest in 8 years. These con- 

 ditions occurred at a time when crab abundance 

 was near an alltime high and when fishermen 

 and others had been alerted to the threat of the 

 green crab. Thi-oughout 1956, I received numerous 

 reports attesting to a decrease in the numbers 

 of crabs seen along the shore or taken in lobster 

 traps during the summer. Of greatest interest 

 were the reports of dead crabs during the winter. 



On the Skillings River, in Hancock, Maine, 

 clam diggers observed that green crabs became 

 very active during a thaw in January and were 

 out in the open on the clam flats. The temperature 

 dropped suddenly, and shortly thereafter many 

 dead crabs were found along the shores. This 

 area is near the trapping location at Trenton, 

 where catches dropped sharply from 1955 to 

 1956. 



A lobsterman reported that when the ice broke 

 u]) in Blue Hill Bay in 1956 he saw large numbers 

 of green crabs washed up along the South Blue 

 Hill shore. 



Another lobsterman reported many dead green 

 crabs during the winter of 1955-56 at Herrick Bay 

 in Brooklin, Maine. During the following sum- 

 mer, he found the crabs far less numerous in his 

 lobster traps there. 



At Sams Cove, Bremen, Maine, in January 1956, 

 BCF biologists saw hundreds of dead and d3dng 

 green crabs on muddy bottom at 0.3 to 1.2 m. 

 below mean low water. Heavy ice cover prevented 

 us from examining much of the bottom, but we 

 found crabs lying on the bottom at a time when 

 they woidd normally be buried. We do not know- 

 when the conditions occurred that killed the 



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U. S. FISH AND WILDLIFE SERVICE 



