Hoff: A nursery site of Bathyra/a parmifera in the eastern Bering Sea 
241 
Figure 7 
Relationship between rearing temperature and days to hatching determined from 
21 published studies and 13 oviparous chondrichthyan species. Open circles rep- 
resent values from the literature and the shaded circle is estimated embryonic 
developmental period for the Alaska skate ( Bathyraja parmifera) in the pres- 
ent study. The hatching time of the Alaska skate was not used to determine the 
equation parameters. See Table 1 for data sources. 
studies have shown that the 
Alaska skate is reproductively 
active year-round and that 
peak egg production occurs 
during summer months (Mat- 
ta, 2006; Matta and Gunder- 
son, 2007). A distinct summer- 
time pulse of egg deposition 
was evident from the nursery 
site seasonal skate abundance 
data, and distinct cohorts of 
embryos were present in the 
nursery throughout the year. 
Embryonic development of 
the Alaska skate was estimat- 
ed to take over 3.5 years from 
egg deposition until hatching, 
and as a consequence multiple 
cohorts were developing simul- 
taneously at the nursery site. 
Embryonic developmental rates 
are most likely coupled with 
environmental temperatures 
and produce a Q 10 effect where 
there is an exponential change 
in metabolic processes as tem- 
perature changes (Schmidt- 
Nielsen, 1997; Charnov and 
Gillooly, 2003). The sensitivity 
of the developmental period to temperature increases 
is significant; if one uses the regression equation pa- 
rameters, a mean increase of 0.5°C in environmental 
temperatures could decrease the developmental period 
of the Alaska skate by nearly 16% (~6 months) and 
there would be stronger effects as greater temperature 
changes occurred. This has dramatic implications on 
what influence climate change may have on the shelf- 
slope environment, and skate reproduction and recruit- 
ment. The dramatic increase or decrease in recruitment 
success due to environmental changes may become an 
important model parameter for stock assessments and 
management plans for elasmobranch species. 
For the estimate of growth rate for the Alaska skate 
in this study, linear growth was assumed during the 
developmental period and an effect of environmental 
temperature on growth rate was not considered because 
environmental temperatures varied little during this 
study. These variables recognizably may influence daily 
growth estimates and therefore the length of develop- 
mental period, however averaging across three years of 
cohorts may provide an accurate estimate of the rela- 
tively long developmental period for the Alaska skate, 
as well as for other oviparous species in cold waters. 
Linear growth during embryonic development for the 
size range reported here for the Alaska skate was simi- 
lar to that for the clearnose skate from approximately 
18 mm through hatching (Luer et ah, 2007). 
Site selection criteria for skate nurseries are as of yet 
unknown, however areas of high biological productivity 
may be a requirement for nursery sites because of the 
protracted reproductive activity and energy require- 
ments of adults. The Alaska skate nursery site is in a 
region of high slope-shelf water transport and is one 
of the most productive regions in the eastern Bering 
Sea (Stabeno et ah, 1999); it has supported walleye 
pollock and Pacific cod bottom trawl fisheries for more 
than 25 years. Walleye pollock, the main food source 
of adult Alaska skates (Lang et ah, 2005), co-exist in 
the outer-shelf region during summertime (Kotwicki 
et ah, 2005). Results from the nursery seasonal diet 
analysis indicated that reproductively active skates feed 
throughout the year, almost exclusively on walleye pol- 
lock. A ready supply of food may allow skates to remain 
near the nursery site and minimize foraging excursions 
during protracted reproductive cycles. 
Adequate current flows and stable temperatures 
such as those encountered in the upper slope area of 
the eastern Bering Sea may be critical for successful 
hatching and embryo development. From early stages 
of development, the embryo is dependent on a constant 
current of fresh seawater to supply tissues with oxygen, 
remove metabolic waste (Hamlett and Koob, 1999), and 
prevent the egg case from being buried in sediment. 
Although strong currents pose a hazard to egg cases 
by transporting them out of the nursery site, this does 
not appear to happen frequently because egg cases are 
rarely found widely scattered outside the nursery, and 
within nurseries egg cases often cover a small area 
and are highly concentrated. The upper slope environ- 
ment provides a nearly constant bottom temperature 
through upwelled waters that inundate the outer shelf 
