Table 6. — Size composition of recruit class samples in percent. 



Carapace 



size (mm; 1949-50 1950-51 1951-52 1952-53 Average 



the summer and fall, is in all probability a major source 

 of natural mortality through the consequent predation 

 by finfish and may be a principal cause of the esti- 

 mated 28 to 36 percent natural mortality rate as- 

 sociated with this size class of lobsters. 



Recent declines in the available supply and relative 

 abundance of legal lobsters appear to be related to 

 several factors. The decline in the frequency of 

 moulting — or, at least, of the percentage of lobsters 

 moulting each year — has reduced the volume of lob- 

 sters entering and passing through the legal size range. 

 The length of time from egg to minimum legal size — a 

 minimum of 4 yr and probably 5 to 7 yr for the 

 majority — would appear to preclude prior to 1973 the 

 effects being evident of unfavorable temperature or 

 other environmental conditions on the supply of larvae 

 and subsequent stock recruitment. Attenuation of time 

 from larval to legal minimum has probably increased 

 the mortality rate, since mortality is a function of time 

 as well as of growth. 



A third possibility is that of trap efficiency and the 

 number of times during the lobster year that lobsters 

 have to be exposed to trapping in order to provide an 

 adequate sample of fishing mortality. If it requires 130 

 trap hauls per legal lobster per year when tempera- 

 tures are optimum in order for the recruit class to sup- 

 ply 85 percent of the catch (660,000 traps at 9.15°C to 

 produce 22 million lobsters), then at 7.5°C approxi- 

 mately 900,000 to 950,000 traps would be required to 

 produce the same number of exposures. With lower 

 temperatures lobster foraging activity declines; there- 

 fore, to provide compensating exposure to trapping 

 would require increasing the number of traps. 



"Trap exposure" and "trap haul" represent some- 

 what differing concepts. Although 75 percent of the 

 annual catch consists of recently moulted lobsters 

 produced by "trap hauls," the number of times these 

 lobsters are "exposed" to trapping by reason of enter- 

 ing and leaving or remaining in traps or passing by will 

 vary with foraging activity and shelter seeking. Pre- 



sumably during low sea temperature years more traps 

 will have to be set more times by fishermen to provide 

 an equivalent proportion of opportunities for each 

 lobster to be caught. 



G. Disease, Pollution, and Predation. 



Although there is no significant evidence to support 

 the assumption and, in fact, all data indicate an oppo- 

 site interpretation, factors other than seawater tem- 

 perature and fishing effort may have caused the fluctu- 

 ations which have periodically occurred in the supply 

 of lobster. Among those factors are diseases, para- 

 sites, natural predators, and pollutants. 



The factors causing death of lobsters in the ocean 

 are not completely known, and the relative importance 

 of those which are recognized is very much in doubt. 

 Recognized as killers of lobster are: predation by fish, 

 cannibalism, starvation, and predation by man (fish- 

 ing). Possible but probably extremely rare in open 

 water, is death by asphyxia (lack of oxygen) or chemi- 

 cal poisoning. These occur occasionally in commercial 

 storage and handling of lobsters. In the "wild" state 

 there are remarkably few diseases and parasites of the 

 lobster. None of these is known to cause significant 

 mortalities except under conditions of storage. 



The most virulent disease is gaffkaemia, popularly 

 called "red tail." The common name stems from an 

 erroneous correlation of red pigmentation of the un- 

 derside of the tail with infection. In fact, a wide varia- 

 tion of such pigmentation exists normally and is inde- 

 pendent of the presence of the bacterium Gaffkya 

 homari* (now Pediococcus hoinari. Opinion 39. Re- 

 jection of the generic name Gaffkya trevisan. Int. J. 

 Syst. Bacteriol. 21:104-105.) 



Gaffkaemia customarily develops in lobster pounds 

 where lobsters are held for extended periods under 

 adverse conditions. The causative organism, a tetrad- 

 forming encapsulated micrococcus, Gaffkya homari, 

 reproduces in the blood until it is virtually a pure cul- 

 ture in the terminal stages. 



Lobsters in the terminal stages of gaffkaemia are 

 characterized by extreme weakness, a tendency to col- 

 lect at the edges of a lobster storage pound in the 

 shoalest water, and blood which lacks blood cells and 

 does not readily clot. The behavior suggests that as- 

 phyxia might be critical in terminal stages. 



More recent studies of gaffkaemia indicate that once 

 established, the infection passes inevitably through the 

 stages of infection to death. Contradictory indications 

 exist in lobster pounds, where rates of infection among 

 stored lobsters may soar in late summer and early fall. 

 If no action is taken by the poundkeeper, evidences of 

 infection decline with dropping temperatures and dis- 

 appear by early winter. Losses in such situations may 

 be inconsistent with the apparent degree of seasonal 

 infection. 



Gaffkya homari can be demonstrated in bottom sed- 

 iments of lobster pounds, and at the height of the 



