233 
Abstract — A nursery site for the 
Alaska skate (Ba thy raja parmifera) 
was sampled seasonally from June 
2004 to July 2005. At the small nurs- 
ery site (~2 km 2 ), located in a highly 
productive area near the shelf-slope 
interface at the head of Bering Canyon 
in the eastern Bering Sea, reproduc- 
tive males and females dominated 
the catch and neonate and juvenile 
skates were rare. Seasonal samples 
showed summertime (June and July) 
as the peak reproductive time in the 
nursery although some reproduction 
occurred throughout the year. Time- 
series analysis of embryo length fre- 
quencies revealed that three cohorts 
were developing simultaneously and 
the period of embryonic development 
was estimated at 3.5 years and aver- 
age embryo growth rate at 0.2 mm/ 
day. Estimated egg case deposition 
occurred mainly during summertime 
and hatching occurred during winter 
months. Protracted hatching times 
may be common for oviparous elas- 
mobranch species and may be directly 
correlated with ambient temperatures 
as evident from a meta-data analysis. 
Evidence indicates that the Alaska 
skate uses the eastern Bering Sea 
outer continental shelf region for 
reproduction and the middle and inner 
shelf regions as habitat for immature 
and subadults. Skate nurseries may 
be vulnerable to disturbances because 
they are located in highly productive 
areas and because embryos develop 
slowly. 
Manuscript submitted 26 November 2007. 
Manuscript accepted 21 February 2008. 
Fish. Bull. 106:233-244 (2008). 
The views and opinions expressed or 
implied in this article are those of the 
author and do not necessarily reflect 
the position of the National Marine 
Fisheries Service, NOAA. 
A nursery site of the Alaska skate 
{Bathyraja parmifera ) in the eastern Bering Sea 
Gerald R. Hoff 
Email address: jerry.hoff@noaa.gov 
Alaska Fisheries Science Center 
National Marine Fisheries Service, NOAA 
7600 Sand Point Way NE 
Seattle, Washington 981 1 5 
Elasmobranchs are of growing concern 
worldwide because they are threat- 
ened by increased fishing and habi- 
tat disturbances (Musick et al., 2000; 
Stevens et al., 2000). Characteristic 
life history traits of these fish include 
slow growth rates, late maturation, 
low fecundity, and long life-spans, all 
of which make them extremely vul- 
nerable to increased fishing-induced 
mortality (Dulvy, 1999; Frisk et al., 
2002). Species with these life history 
patterns depend on high juvenile sur- 
vival and recruitment for population 
stability. An adequate understanding 
of reproduction dynamics and habitat 
requirements are lacking for most spe- 
cies, yet these may be the most criti- 
cal biological criteria for successful 
reproduction. 
Oviparous species such as skates 
(Rajidae) use nursery areas for egg 
deposition, embryo development, and 
hatching (Hitz, 1964; Hoff, 2007). 
They produce relatively large colla- 
gen egg cases (Knight et al., 1996) 
which contain a large yolk mass and 
developing embryo. The egg cases are 
deposited directly onto the seafloor 
and embryos develop independent of 
maternal care (Hamlett and Koob, 
1999). The embryonic developmental 
period is unknown for most species 
of skates, but evidence indicates that 
it may exceed one year for temperate 
and deepwater species (Berestovskii, 
1994). 
The Alaska skate (Bathyraja par- 
mifera) represents >95% of estimated 
skate biomass on the eastern Bering 
Sea shelf (20 to 200 m) (Lauth and 
Acuna, 2007), and estimates of bio- 
mass and population numbers have 
indicated nearly a fourfold increase 
since 1975 (Hoff, 2006). Skates at 
all life stages are encountered in the 
shelf environment and the species 
range is limited to depths of <400 
m on the slope (Hoff and Britt, 2003, 
2005; Stevenson et al., 2007). The 
Alaska skate reaches a large size 
(135 cm) and can be locally abun- 
dant (Hoff and Britt, 2005). Its dis- 
tribution pattern and accessibility 
in relatively shallow waters make 
the species a likely candidate in 
target fisheries, and its life histo- 
ry characteristics make it suscep- 
tible to population decreases (Matta, 
2006; Matta and Gunderson, 2007). 
A nursery site for the Alaska skate 
was identified in June 2004 (Fig. 1) 
where significant numbers of skate 
egg cases were previously reported 
by commercial fishing crews and 
fisheries observers. The nursery ex- 
ists in an area that has been heavily 
fished for walleye pollock ( Theragra 
chalcogramma) and Pacific cod ( Ga - 
dus macrocephalus) for many years, 
and the site is frequently disturbed 
by bottom trawls. 
Understanding reproductive char- 
acteristics and essential habitat 
requirements are necessary to ac- 
curately predict population stability 
under changing conditions for elas- 
mobranch species worldwide. The 
recent discovery of a nursery site 
for the Alaska skate allowed a first 
look at the reproductive details of the 
species. Specifically, this study esti- 
mates the timing of egg deposition 
and duration of embryonic develop- 
ment through length-frequency mode 
tracking from a seasonal sampling of 
embryos. In addition, the habitat of 
the Alaska skate is examined with 
respect to nursery site use and life- 
stage distribution patterns. 
