Figure 4. — Bubbles in the gill separators of a lobster. A. Major 

 artery" along the edge of the gill separator, with a large bubble. B. 

 Sinus of the separator, showing a diffuse system of smaller bubbles. 

 Both are at the same scale. 



algae. Mussels setting on lobster gills frequently cause 

 mortality. 



Predation upon lobsters other than by man is proba- 

 bly most important in early life, especially during lar- 

 val stages, and gradually becomes less important with 

 increased size except when lobsters are confined to- 

 gether, as in traps. At any age or size the most hazard- 

 ous time for a lobster is the period after moulting, 

 before the new shell has hardened. Since larval stages 

 float free in the water, they may be attacked by squid 

 and by mackerel, pollock, and other surface-feeding 

 fish. After the fourth moult the lobster goes to the 

 bottomand seeks shelter. Thenceforth, it is the prey of 

 cunners, sculpins, cod, cusk, hake, dogfish, sea 

 robins, pollock, wolffish, and other fish found near 

 bottom. 



Lobsters not only need to avoid other fish, but other 

 lobsters as well. In such an artificial home as a hatch- 

 ery, one or two fourth-stage lobsters may be the only 

 survivors of thousands started unless the water has 

 been kept in motion to prevent cannibalism. Larger 

 lobsters in traps are more likely to become victims of 

 other lobsters immediately following moult. 



Probably the most important predator on popula- 

 tions of commercial size lobsters is man. There is good 



reason to believe that in those areas which are inten- 

 sively fished as many as 85 to 95 percent of the com- 

 mercial size lobsters are caught or die naturally each 

 year. In some locations even the higher figure may be 

 exceeded. 



Occasionally severe storms cause lobster mor- 

 talities. Evidence of this is furnished by lobsters in 

 shallow inshore areas being washed ashore in traps 

 and stranded by the ebbing tide. Small lobsters also 

 are found in storm-loosened kelp and rockweed that 

 has been stranded above mean high water. 



Members of the Department's scuba team have re- 

 ported many unbuoyed traps with entrapped lobsters. 

 With the magnitude of annual trap losses and the dura- 

 bility of synthetic fibers, lobster losses from this 

 source, both in terms of mortality and of removal from 

 the fishery, may become of major significance if they 

 have not already. 



III. POPULATION DYNAMICS 

 A. The Available Biomass. 



Considered collectively, the total lobster population 

 of Maine and its contiguous waters consists of au- 

 tonomous colonies dispersed about attractive ecologi- 

 cal areas. Those lobsters of the biological supply 

 which fall within the limits imposed by legislation con- 

 stitute the legal supply. This supply is of paramount 

 interest to fishermen, for a portion of these lobsters 

 together with those illegal lobsters which enter and 

 remain within traps and other fishing devices during the 

 course of the calendar or lobster year make up a third 

 supply — the available supply (i.e., those lobsters 

 which are available for catching). The biological abun- 

 dance of legal lobster can be estimated within ± 10 per- 

 cent from effort-yield and temperature-yield data. 



The most probable error in assuming an identity be- 

 tween relative abundance and the legal supply would 

 involve the presence of islands of unfished lobster 

 stocks, located in isolated rocks and shoals within or 

 on the edges of the heavily fished bottom. Such a pat- 

 tern would require careful planning to detect. It is, 

 however, a pivotal issue in interpreting the meaning of 

 other determinations. 



Since the fishery appears to be carried on at a rela- 

 tively high order of intensity, 90 percent or more, the 

 legal supply is largely dependent upon those previ- 

 ously sublegal lobsters which became legal as a result 

 of moulting and comprise the recruited supply. For 

 biological and meteorological reasons, it is assumed 

 that the available portion of the biological supply var- 

 ies seasonally and geographically as well as by sex, 

 age, and probably other factors. It is now becoming 

 increasingly evident that nearly all of the available 

 legal population is being caught each year. In refer- 

 ence to "legal" size lobsters there are several compel- 

 ling arguments for an increase in the minimum legal 

 size of lobsters to 3'/i in. (88.9 mm) or more. Taylor 



12 



