Jensen et al. The reproductive biology of Lanma nasus in the western North Atlantic Ocean 



735 



W=4 N=19 N=60 W=27 W = 1 



W=5 /V=9 N-2 W = 1 



100 



80 



60 



40 



20 



I 



I 



Sept Oct Nov Dec Jan Feb March April IVIay June July August 



Month D%non-gravid 



 % gravid 



Figure 9 



Relationship of gravid to nongravid adult female porbeagle sharks by month from 1979 to 1999. 



ing the embryos, suggesting recent embryo 

 feeding. One embryo was seen with a whole, 

 undamaged ova capsule protruding from its 

 mouth. The stomach contents of embryos from 

 several litters did not show parts of other 

 embryos, suggesting that adelphophagy (com- 

 petitive embryonic cannibalism), found in the 

 sandtiger shark (Gilmore et al, 1983) does not 

 occur in the porbeagle. The existence of devel- 

 oping runts in several litters and consistently 

 two embryos per uterus reinforces these obser- 

 vations. A slight modification to our knowledge 

 of oophagy would be the possible consumption 

 of the late-fertilized ova capsules that had 

 small undeveloped and decomposing embryos 

 along with unfertilized ova, as mentioned 

 previously. Most gravid porbeagles examined 

 during this study were ovulating and, there- 

 fore, nourishing their embryos. The times at 

 which ovulation ceases, ovary size decreases, 

 and the large amount of yolk in the stomach is 

 consumed, need further definition. 



The mean growth rate of embryos from 

 this study was 11.4 cm per month; however, 

 this is most likely inflated by the lack of larg- 

 er embryos. Combining data from the pres- 

 ent study with previous data from the North 

 Atlantic, which includes later term embryos 

 (Francis and Stevens, 2000), leads to an estimate of 8.15 

 cm per month. The regression of growth per month for the 

 North Atlantic embryos was significantly different from 

 that of the South Pacific population in intercept (time 

 of year) but not in slope (growth rate) (ANOVA P>0.10 

 slopes, P<0.1 intercept) (Fig. 10). 



(NH) FL=22 7 

 r-=0 68 



Sep 



Mar 



Apr May 



Aug 



IVlonth 



Southern Hemisphere 

 Northern Hemisphere 

 NW Atlantic. This study 



Figure 10 



Monthly variation in mean lengths of embryo litters from both hemi- 

 spheres. Data indicated by open circles and closed triangles are from 

 Francis and Stevens (2000) and Francis,'' respectively. 



Neonates and young of the year 



The smallest free-swimming porbeagle examined during 

 this study was 77.5 cm FL (87 cm TL) on 24 May Other 

 records of free-swimming individuals measured in April- 

 June, ranged from 55 to 79 cm FL (mean=71 cm FL, /2=9) 



