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Fishery Bulletin 90(4). 1992 



Based on the foregoing observations, it appears that 

 up untO 1990 at least most of the mature, nonovigerous 

 females in St. Michael's Bay did not extrude. Rather, 

 they resorbed the lipovitellin accumulated in the ripen- 

 ing oocytes, and many then proceeded to molt. Resorp- 

 tion of the ripe ovary has been associated with un- 

 favorable holding conditions near the expected time of 

 extrusion (Templeman 1940) but appears to be common 

 in the wild as well (Ennis 1984b). Resorption occurs 

 when the molting and reproductive cycles are out of 

 phase, and molting is due to occur within 3 or 4 months 

 after egg extrusion (Aiken and Waddy 1976, 1980ab). 

 These cycles are normally synchronized by temperature 

 and photoperiod regimes to ensure that when a female 

 lobster extrudes eggs in one summer, it will not molt 

 until after the eggs have hatched sometime the follow- 

 ing summer. 



In their experiments on the effects of winter tem- 

 perature and photoperiod on spawning, Aiken and 

 Waddy (1989) found a high incidence of resorption 

 among mature females held at high temperature 

 throughout the winter, particularly when a short-day 

 photoperiod was maintained throughout the summer 

 (55% resorbed). Onset of a long-day photoperiod in 

 spring was necessary to trigger spawning among 

 females held at high winter temperature. The incidence 

 of spawning was high ( >90%) among those held at low 

 winter temperature, even without onset of a long-day 

 photoperiod in spring, and only a few resorbed. 



These results do not explain the high incidence of 

 resorption among female lobsters in St. Michael's Bay 

 where they are exposed to environmental conditions 

 well outside the foregoing experimental treatments. 

 From mid-November to mid-May, the bottom temper- 

 ature is near or below 0°C and the bay is frozen over 

 for most of this period. Visual acuity of lobsters at very 

 low light intensity has not been described. It seems 

 unlikely, however, that sufficient light would penetrate 

 a layer of snow-covered sea ice underlaid by low-salinity 

 water (from continuous river discharge and slow mix- 

 ing under the ice) for lobsters to detect a light:dark 

 cycle. This combination of very low temperature and 

 near continuous darkness for 5-6 months from late 

 autumn to spring is probably the main cause of the high 

 incidence of ovary resorption that has prevailed among 

 female lobsters in St. Michael's Bay. 



Most of the ovigerous females collected in St. 

 Michael's Bay had extruded quite recently. The re- 

 mainder were old-egged females that spawned the 

 previous summer. Apparently, many females that ex- 

 truded lost the entire clutch of eggs before the follow- 

 ing summer. Massive but incomplete loss of eggs was 

 also observed. Of 9 ovigerous females collected in 

 Indian Arm in 1987 and 1988, 5 had numbers of eggs 

 ranging from 7 to 334. Only one of the 21 ovigerous 



females collected in 1989 and 1990 had just a few 

 hundred eggs. The overall incidence of ovigerous 

 females, particularly those with new eggs, increased 

 substantially in 1989 and 1990 and especially in 1991. 

 At Goose I., no ovigerous females at all were included 

 in samples until 1989, 4 years after they were trans- 

 planted. This indicates a high degree of acclimation or 

 physiological adjustment to environmental conditions 

 in St. Michael's Bay on the part of females, resulting 

 in much less resorption of ripe ovaries and much more 

 extrusion in recent years. However, loss of the entire 

 clutch of eggs appeared to be still quite prevalent. 

 Ovigerous females sometimes lose their entire clutch 

 of eggs by molting (Ennis 1984b). This may have been 

 a more common occurrence in later years, which could 

 explain the near absence of tiny clutches compared with 

 the high incidence observed in 1987 and 1988, and 

 would also be consistent with a high incidence of new 

 shells and advanced setai development among females 

 in 1989 and 1990. Despite some physiological adjust- 

 ment resulting in more extrusion, for most females the 

 molting and reproductive cycles continued to be out of 

 phase. 



Embryonic development in lobsters proceeds slowly 

 at temperatures below 6°C, and hatching can be 

 delayed by as long as 6 months if temperature remains 

 at 2-3°C throughout spring, summer, and autumn, 

 although it will eventually occur, even at that tem- 

 perature (Aiken and Waddy 1986). Perkins (1972) 

 found that advanced embryos will develop more slow- 

 ly than less advanced ones when held at the same 

 temperature. In one specimen with 29-week-old eggs 

 on 10 January held at the Boothbay Harbor Laboratory 

 under local water conditions, there was no measurable 

 development for an 18-week period starting in early 

 December. Over most of the period, temperature 

 ranged from 0.1°C to 1.5°C. 



In St. Michael's Bay, bottom temperature drops 

 below 6°C by mid-October, below 3°C by mid-Novem- 

 ber, and below 0°C by late November. Of the old-egged 

 ovigerous specimens from there, which are presumed 

 to have extruded the previous summer, there was one 

 with 0.8 yolk remaining when examined at the end of 

 June, three with 0.7 remaining around 20 July, and 

 three with 0.5 remaining in mid-August. Possibly some 

 of these females carry their eggs through a second 

 winter and may represent the ones observed in our 

 samples with sufficiently advanced development for 

 hatching to occur before the end of summer (i.e., 

 hatching 2 years after extrusion rather than the usual 



1). 



Only 6 of the 17 old-egged ovigerous females col- 

 lected in St. Michael's Bay from 1986 to 1991 had less 

 than half the yolk remaining in the eggs when exam- 

 ined. Four of these would likely have been ready for 



