NOTE Jones and Ugland: Reproduction of female Squci/us acanthus 
689 
25 
20 
1 1 
* 
15 
* l l * f 
♦ 
m 
l 
10 
5 
0 ^ — ' — ' — 1 — ' — 1 — ' — ’ — ' — ' — > — ' — ' — ' — ’ — ' — >— 
ASONDJ FMAMJ JASOND 
Month 
Figure 6 
Length of the embryos during their second year of devel- 
opment for the combined 1987 and 1997 sample. 
Fecundity was within the bounds found elsewhere in the 
northeast Atlantic (Aasen, 1961; Gauld 1 ). Free-living em- 
bryos showed the same increase in number per length in 
1987 and 1997, but the level was significantly lower in 
1997 (on average one less embryo per unit of length). In 
addition the fish were shorter and heavier in 1997. How- 
ever, these results must be taken with some caution be- 
cause of the large variability in the data. 
A small sample size and annual variability in both em- 
bryo production and food availability may have contrib- 
uted to the lower fecundity in 1997. With regard to the 
sample sizes (31 and 38 fishes), it is emphasized that the 
covariation between the number of free-living embryos 
versus length was rather low. Although the differences be- 
tween 1987 and 1997 were statistically significant, the 
overlap was so large that caution must be used in inter- 
pretation of the data. 
Reproduction cycle and embryonic growth 
In the Oslofjord, fertilization occurs from October to Febru- 
ary and parturation from October to December. Research 
in other areas has shown that the pregnancy lasts 22-23 
months (Ford, 1921; Gauld 1 ). Thus, the duration of preg- 
nancy in the Oslofjord (18 to 24 months) seems to have a 
greater variation than these observations. This variation 
may have been caused by the sample from the Oslofjord, 
which included dogfish that were fertilized early in the 
fertilization period, as well as dogfish that were fertilized 
towards the end of the fertilization period. This, in turn, 
indicates the possible minimal and maximal duration of 
pregnancy. 
Behavioral factors may influence pregnancy duration, 
as well. Some dogfish may inhabit cooler water for longer 
periods of time than other dogfish, which may increase the 
duration of their pregnancy. 
The differences in the embryo growth rate during their 
second year of development may be related to the water 
temperature. Hickling (1930) found that females migrate 
from deep to shallow water as pregnancy proceeds. This 
migration pattern exposes the embryos to different tem- 
perature levels that may influence embryonic growth, as 
found in Newfoundland by Templeman (1944). Embryos 
outside of Newfoundland had an average growth rate of 1. 1 
cm/month and a 24-month pregnancy period (Templeman, 
1944). Outside of Woods Hole, Hisaw and Albert (1947) 
found an average growth rate of 1.3 cm/month and a preg- 
nancy period of 20-22 months. Nammack et al. ( 1985) stat- 
ed that the lower sea temperature outside of Newfound- 
land could be a possible reason for this difference. 
In phase 1, growth is slow and corresponds to a period 
of low water temperature (winter and spring). As females 
begin to migrate towards shallower water, they encounter 
warmer water (summer and fall). The increased growth 
rate in phase 2 is therefore most likely related to an in- 
crease in water temperature. 
Acknowledgments 
We would like to thank P. A. Johansen for making the col- 
lection of the sharks possible, as well as giving us valu- 
able suggestions. We thank scientists and personnel of the 
biological station in Drpbak and H. E. Karlsen for the use 
of equipment associated with age determination. We are 
also particularly grateful to T. R. Wiley and H. Zidowitz for 
their comments on the manuscript. 
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