240 
Fishery Bulletin 106(3) 
Habitat use 
Analysis of trawl catch data and depth soundings 
showed that the nursery site had little benthic struc- 
ture or habitat diversity and the bottom was generally 
200 - 
-S 120 
o 
Cohort 3 
2004 
2005 
1 1 1 
3 June 27 July 1 1 Sept. 
17 Nov. 16 Jan. 
Nursery sampling date 
1 1 1 
18 April June 7 July 
Figure 5 
Mean embryo total length (±1 standard deviation) at each sampling 
date for each cohort from the length-frequency data for the Alaska 
skate ( Bathyraja parmifera). Growth rates were estimated from 
the slope of the linear relationships for each cohort. 
_Q 14-1 
E 
LU 12- 
10 - 
4- 
80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 
Julian date 
Egg deposition 
l,ll Jl I , i llliH 
Feb Mar April May 
June July 
Month 
Aug Sept 
Figure 6 
Estimated time of hatching (top) and egg deposition (bottom) frequency for all 
embryos measured from the Alaska skate ( Bathyraja parmifera) nursery site. 
Hatching and egg deposition dates were determined from the average growth rate 
of 0.2 mm/day and an estimated hatching size of 224 mm total length. The x-axis 
indicates the Julian date (top) and the corresponding month (bottom). 
flat, and composed of sandy mud. The trawl samples 
within the nursery did not contain any attached ben- 
thic invertebrates that would have constituted a unique 
habitat. Bottom depths varied by only several meters 
throughout the nursery site (145 to 150 m) and the 
average bottom depth was 149 m, weighted by 
egg case density. Bottom temperatures at the 
nursery index site varied little throughout the 
year, ranging between a low of 4.1°C in June 
2004 and April 2005, to a high of 5.0°C in 
July of 2004. The mean bottom temperature 
for the 14-month study period was 4.40°C 
±0.327°C. 
The Alaska skate was widely distributed 
across the eastern Bering Sea shelf and the 
immature stages used a different portion of 
the habitat than that used by newly hatched 
juveniles and mature adults. Juvenile skates 
were distributed along the outer continental 
shelf (100-200 m) and overlapped in distribu- 
tion with mature adults (Fig. 8). Immature 
Alaska skates were distributed mainly in the 
middle and inner shelf regions and were found 
less on the outer shelf. A model lifetime move- 
ment pattern for the Alaska skate indicates 
an ontogenetic shift in habitat use in which 
there is a cyclical movement across the shelf 
after hatching to the shallow inner shelf, fol- 
lowed by a return to the outer 
shelf as maturity is reached 
(Fig. 8). 
Discussion 
Recent advances in elasmo- 
branch biology have stressed 
the importance of identifi- 
cation and conservation of 
nursery sites for oviparous 
elasmobranchs (Ellis et al., 
2004) . Understanding habitat 
requirements for skate repro- 
duction may be critical for 
successful management plans 
for these vulnerable species. 
The results presented here are 
the first reported dynamics of 
a skate nursery with regard 
to reproductive patterns and 
habitat use. 
Because of their inherent 
low fecundity and slow growth 
rates, skates may reproduce 
with distinct seasonal pulses, 
over protracted periods, or 
in some cases continuously 
throughout the year (Temple- 
man, 1982; Sulikowski et al., 
2005) . Results from previous 
