.32 

 .30 



.28 

 .26 

 .24 



.22 



.20 



.18 



.16 



.12 

 .10 

 .08 

 .06 

 .04 

 .02 



' 



1966 1967 1968 



Figure 3. — Accumulations of pesticides in lobsters. 



in fresh-caught lobsters, (up to 1.373 ppm), we as- 

 sumed that insecticides are a major contributing factor 

 in unexplained pound or tank-stored lobster mor- 

 talities. 



Toxic levels for lobsters or other marine animals are 

 unknown except under limited laboratory conditions. 



It is probable that tolerance varies among individual 

 animals (as well as by species), and with other factors 

 also, including temperature, salinity, and dissolved 

 oxygen. 



Detergents and other cleansing agents carried into 

 seawater from household and commercial laundry 

 facilities are also toxic to lobsters and may locally be a 

 significant contributor to the "natural" mortality rate. 

 Oil spills in Casco Bay have decreased the survival 

 and marketability of lobsters. 



Physical alteration of the environment by coastal 

 dredging and filling, the destruction of tidal flats and 

 coastal marshes and the damming of estuaries are all 

 practices which have adversely affected lobster abun- 

 dance by reducing the food supply and creating toxic 

 conditions. One such well-documented harbor dredg- 

 ing occurence in 1959 resulted in a 32-fold increase in 

 the mortality of stored lobsters within the period of a 

 week. 



Of those metals which have been evaluated copper 

 causes the highest rate of mortality among lobsters. 

 Although natural seawater contains this metal in 

 measurable amounts, any appreciable increase in the 

 copper content of water in which lobsters are held 

 usually causes mortality of the animals. Temperature 

 of the water appears to be an important factor in the 

 rate of mortality from copper poisoning. 



Among other evaluated metals naturally occuring 

 along the Maine coast, zinc is probably the second 

 most toxic. Since several toxic metals are used in in- 

 dustrial operations, pollution from these sources may 

 very well be building up a lethal barrier for lobsters in 

 some inshore areas. For this reason, mining in areas 

 where metallic residues might be carried into tidewater 

 poses threats to the lobster resource. 



A summary of experiments measuring the relative 

 toxicity of metals to lobsters is shown in Table 8, in 

 which natural seawater and artificial seawater were 

 both used to evaluate metals. 



In these experiments four lobsters were placed in 

 each tank containing about 182 liters of water. Air was 

 bubbled through a hardwood plug to provide aeration 

 and circulation. 



The lobsters in the control seawater tank demon- 

 strated their hardiness in the absence of crowding. In 

 the first experiment the seawater controls lived 74 

 days in water temperatures ranging from 15° to 32.2°C. 

 Death was caused when one lobster moulted, and the 

 oxygen demand of the fouling reduced oxygen to lethal 

 levels. Salinity of the water at this time had risen to 

 over 80%o because of evaporation. 



The probability of such a limitation to lobster survi- 

 val being ultimately developed in the inshore waters is 

 very great when the various harmful materials are con- 

 sidered. Metals from either industry or mining, 

 detergents from household or commercial use, insec- 

 ticides, hydrogen sulfide from marsh or harbor dredg- 

 ing and other organic sources, and oil spills are all 

 serious threats to lobster survival, especially in those 



10 



