Stevenson et at: Interactions between fisheries and early life stages of skates in nursery areas of the Bering Sea 
1 1 
Table 2 
Viability of egg cases of skates identified by observers aboard commercial fishing ves¬ 
sels in the eastern Bering Sea from November 2014 through November 2017. Viable 
egg cases contained a yolk mass or an embryo in some stage of development. Mean per¬ 
centages of viable egg cases are presented with standard errors (SEs) in parentheses. 
Species 
Empty 
Viable 
Viable (%) 
Total 
Bathyraja parmifera 
976 
979 
50.1 (2.4) 
1955 
Bathyraja aleutica 
259 
88 
25.4 (3.8) 
347 
Bathyraja interrupta 
157 
46 
22.7 (4.8) 
203 
Bathyraja lindbergi /maculata 
153 
61 
28.5 (6.7) 
214 
Bathyraja minispinosa 
92 
36 
28.1 (6.9) 
128 
Bathyraja abyssicola 
16 
7 
30.4(7.9) 
23 
Bathyraja taranetzi 
6 
3 
33.3 (16.7) 
9 
Raja rhina 
4 
0 
0 
4 
Bathyraja trachura 
2 
1 
33.3 (33.3) 
3 
Amblyraja hyperborea 
1 
0 
0 
1 
Total 
1666 
1221 
42.3 (1.8) 
2887 
Approximately 42% of egg cases assessed by observ¬ 
ers were classified as viable, although viability propor¬ 
tions were not uniform across species or gear type. For 
most species, viability proportions ranged from about 
20% to 30% (Table 2), but the proportion for egg cases 
of Alaska skate was significantly higher (P<0.0001). 
Among gear types, over half (53.9%) of egg cases as¬ 
sessed on longline vessels were classified as viable (Ta¬ 
ble 3), but the percentages of egg cases that were vi¬ 
able for the 2 types of trawling gear were significantly 
lower (P<0.0001). The sample sizes for several species 
and from boats using pot gear were too low to provide 
credible estimates of viability. 
Most of the egg cases identified by observers as 
B. parmifera, B. aleutica, or B. interrupta were con¬ 
centrated near the 6 nursery areas designated as 
HAPC. Egg cases of Alaska skate were the most 
broadly distributed, with high concentrations caught 
near the Bering 1, Pribilof, and Pervenets sites (Fig. 
3A). Additional high concentrations were reported in 
the northern part of Pribilof Canyon and the south¬ 
ern part of Zhemchug Canyon. Egg cases of Aleutian 
skate were concentrated near the Bering 2 and Per¬ 
venets sites, with very few reported in other areas 
(Fig. 3B). Egg cases of Bering skate were encoun¬ 
tered primarily near the Pervenets site, although 
some were also reported near the Bristol site and 
farther south in Bering Canyon (Fig. 3C). Observers 
identified large numbers (20 or more) of egg cases 
of Alaska skate in 18 separate hauls, but egg cases 
of Aleutian skate and Bering skate were recorded in 
large numbers much less frequently (1 and 2 hauls, 
respectively). The other 2 taxa that were identified 
in moderate numbers (B. minispinosa and the taxon 
for individuals that could be B. lindbergi or B. macu- 
lata) were reported primarily from the southern rim 
of Bering Canyon, near the eastern Aleutian Islands. 
Table 3 
Viability by gear type for egg cases of skates identified 
and assessed by observers aboard commercial fishing 
vessels in the eastern Bering Sea from November 2014 
through November 2017. Viable egg cases contained a 
yolk mass or an embryo in some stage of development. 
Mean percentages of viable egg cases are presented 
with standard errors (SEs) in parentheses. 
Gear type 
Empty 
Viable 
Viable (%) 
Total 
Longline 
861 
1008 
53.9(2.7) 
1868 
Bottom trawl 
697 
178 
20.3 (2.2) 
876 
Pelagic trawl 
106 
35 
24.8 (4.5) 
141 
Pot 
2 
0 
0 
2 
Total 
1666 
1221 
42.3 (1.8) 
2887 
Discussion 
The results of this study indicate that the egg cases of 
a variety of skate species are regularly encountered in 
the commercial fisheries of Alaska. These encounters 
are most common in the canyon areas of the EBS, near 
the shelf break, at depths favored by skates for egg 
deposition (Hoff, 2008, 2010). Therefore, fisheries for 
relatively deepwater species, such as the arrowtooth 
flounder, Greenland halibut, Pacific cod, and sablefish, 
are more likely to encounter egg cases of skates than 
fisheries for relatively shallow-water species, such as 
walleye pollock and small flatfish species. 
A somewhat surprising result of this study was the 
relatively high number of egg cases of skates reported 
on vessels fishing with longline gear. It is clear that a 
trawl sweeping the seafloor would collect the egg cases 
