Table 8. — Average survival— days per lobster (three experiments 

 combined). 



Metal 



Natural 

 seawater 



Artificial 

 seawater 



Copper 



Zinc 



Aluminum 



Lead 



Stainless steel 



Control 



waters adjacent to the shore or to tidal rivers where 

 upstream sources may contribute toxic materials. 



Organic materials or chemicals which impose a high 

 rate of dissolved oxygen depletion are other survival 

 threats to the lobster. These may include such diverse 

 substances as sawdust, sulphite, and other chemical 

 wastes from paper mills; domestic sewage; fish offal or 

 chicken waste from processing plants; or mass mor- 

 talities of fish in tidewater and storm-loosened kelp 

 which has been stranded in shallow and relatively 

 warm water where decomposition is rapid. Even nor- 

 mally high seawater temperatures of summer acceler- 

 ate organic processes and decrease dissolved oxygen. 

 "Calico" lobsters have bright yellow spots, which 

 may appear on the carapace or dorsal surface of the 

 tail. With dissection, each yellow spot (which is usu- 

 ally raised above the surrounding shell) is found to be 

 underlain by a pustule located between the endoderm 

 and mesoderm. •* The pustule apparently does not pre- 

 vent shell formation at moult, but does prevent the 

 deposition of the red and blue pigments. The condition 

 is a slowly developing one, occurring endemically in 

 isolated areas. It does not develop in the periods of 

 storage, and its effect on survival in the wild is un- 

 known. Such lobsters can be held in captivity for many 

 months with neither appreciable mortality nor visible 

 change in development of lesions. 



There is a class of infections which appear to de- 

 velop at the site of wounds. They probably are caused 

 by the same organism which infects claw plug wounds. 

 Under conditions of long-term storage, pustules de- 

 velop around the plugs, occasionally enlarging until 

 the claw shell is eroded through from the inside. The 

 contents of the pustule contain bacteria which are 

 lethal if injected into the lobster's bloodstream. 



Some lobsters have brown spots of varying sizes in 

 the membrane on the underside of the tail. On close 

 examination, each of these spots is found to surround 

 a wound or puncture of the membrane. As the lesions 

 develop, the membrane may erode, and loss of body 

 fluids may occur. The condition varies from minor to 

 lethal. Its contribution to natural mortality is un- 

 known, but possibly significant. 

 These diseases are far more damaging to lobsters in 



■•This was a special fmding by D. M. Harriman. 



captivity than in nature. In captivity lobsters are much 

 more crowded, there is more opportunity for infection, 

 and the weakening influences of the environment tend 

 to reduce the lobster's resistance to disease. 



Fresh water is often fatal to lobsters. Lobster tissue 

 and blood are of about the same concentration as the 

 surrounding seawater, and the lobster kidney is not 

 able to maintain the internal concentration as the out- 

 side water becomes fresh. Therefore, as the salt con- 

 tent decreases, the lobster tissue takes up water to 

 maintain the same concentration. If the water be- 

 comes too fresh, cells become so distended that they 

 burst. With the organization of the body damaged, the 

 lobster dies. The degree of freshness which a lobster 

 can tolerate depends upon the rate of change in salin- 

 ity, the temperature, and the amount of available ox- 

 ygen. Seawater in the Gulf of Maine is normally about 

 32"/oo salt. Lobsters begin to show symptoms of fresh 

 water poisoning at approximately 20"/oo salinity, or 

 about two-thirds the concentration of seawater. 



At times lobsters are overcrowded in pounds or 

 floating cars. The supply of oxygen is then consumed 

 and the lobsters are suffocated. Tanks using recircu- 

 lated seawater are sometimes overloaded with the 

 same results. 



More often in tank systems, either using water 

 pumped directly from the ocean or using recirculating 

 water, a condition called "gas disease" (Harriman, 

 1954) causes trouble (Fig. 4). This disease occurs 

 when too much nitrogen is dissolved in the water by 

 the pump. Bubbles form in the lobsters, weakening 

 and killing them. This condition is similar to the 

 "bends" among human divers. Gas disease is more 

 likely to develop in crowded tanks and in extremely 

 warm or cold weather. 



If the factors influencing the severity of the several 

 lobster hazards are reviewed, it is found that in almost 

 every case temperature is mentioned. The heavy 

 losses of lobsters in warm water often raises a ques- 

 tion, "How high a temperature can lobsters stand?" 

 Lobsters have been successfully held in water of 30° to 

 38°C, and are often found on warmwater shoals. Any 

 condition causing weakness in the lobster, however, is 

 aggravated by high temperatures. Temperatures above 

 18°C are likely to give trouble in practical holding situ- 

 ations. 



A sudden and drastic change of temperature or sa- 

 linity, even within the tolerable range, will also 

 weaken lobsters and cause death. Resistance to any 

 given cause of weakness or death depends largely 

 upon the suddenness of exposure, degree of exposure, 

 and the number of such causes active at the time. Low 

 oxygen combined with gas disease is far more deadly 

 than low oxygen or gas disease alone, and the same 

 relationships hold for other weakening conditions. 



In addition to these frank pathogens, there are other 

 organisms apparently commensal with the lobster. 

 These include the mussel, barnacles {Balanus 

 balanoides), and, even in pounds, kelp and filamentous 



11 



