Hoff: A nursery site of Bathyra/a parmifera in the eastern Bering Sea 
237 
Skate length (TL, cm) 
Figure 2 
Length frequency for all Alaska skates (Bathyraja parmifera ) for all trawl samples 
combined from the nursery site in the southeastern Bering Sea. The vertical 
dashed line on each graph indicates the skate length at 50% maturity (male, 
91.75 cm; female, 93.28 cm) for the eastern Bering Sea Alaska skate population 
as determined by Matta and Gunderson (2007). 
trends of increased abundance (skate density) in the 
nursery area during summer months of June and July 
in 2004 and 2005 respectively, and few skates were 
found during the nonsummer months of January, April, 
September, and November (Fig. 3). 
Stomach analysis of the Alaska skate revealed wall- 
eye pollock to be the predominant prey consumed (81% 
by weight, n=195), followed by other fish species includ- 
ing flatfish, salmon, and unidentified fishes (14.6%), 
and invertebrate species (snow crabs [ Chionoecetes spp.] 
and shrimp that represented the third most important 
component by weight [4.4%]). Seasonal diet analyses 
revealed that feeding occurred throughout the year and 
that skates in advanced reproductive states (gravid) 
nearly always contained full stomachs. 
Embryo length-frequency analysis 
Embryo length-frequency modal shifts showed a mini- 
mum of three cohorts developing simultaneously during 
all sampling periods. The mean length of each cohort 
increased slightly at each subsequent sampling and 
showed a natural progression of development over time, 
and individual cohorts appeared and disappeared as 
time progressed (Fig. 4). 
The length data showed that a cohort appeared dur- 
ing the November 2004 sampling and persisted dur- 
ing the April, June, and July 2005 sampling periods. 
The approximate developmental period was 180 days 
from egg deposition (June) until the length samples 
revealed the presence of the cohort (November). The 
long period of early development was similar to that 
of the small spotted catshark ( Scyliorhinus canicula ) 
(Ballard et al., 1993) and the clearnose skate ( Raja 
eglanteria) (Luer et al., 2007); for these two species, it 
takes approximately 15-16% of the early developmen- 
tal period before an embryo is visible at 8 to 10 mm. 
This finding was similar to that for the Alaska skate; 
the smallest embryo visible at 15 mm had taken ap- 
proximately 14% of the development period to reach 
this size. 
Cohorts 1, 2, and 3 showed no difference in linear 
growth rates throughout their size ranges (test of 
slopes F=32.11, P=0.129; Fig. 5). The estimated daily 
growth rates (slopes) obtained for the cohort length data 
ranged from 0.18 to 0.22 mm/day (mean: 0.20 mm/day 
[Table 2]). The distribution of expected birthdates and 
egg deposition dates from the embryo length frequen- 
cies revealed that although there is continuous hatching 
and egg case deposition throughout the year, the peak 
hatching event occurs during fall and winter months 
(October to February: Fig. 6A) and egg case deposition 
peaks during spring and summer months (June to Au- 
gust: Fig. 6B). 
From average growth rates of 0.20 mm/day, an embry- 
onic development period of 3.5 years to reach 224 mm 
