288 
Fishery Bulletin 109(3) 
Table 2 
Results of the general linear model (GLM) on the effects 
of temperature and hatch rank on standard length (SL), 
yolk area (YA, mm 2 ) and eye diameter (ED, mm) in newly 
hatched northern rock sole ( Lepidopsetta polyxystra ). 
Analysis was performed on tank means (n=3-4 tanks per 
temperature) of 15-20 larvae for each tank during each 
sampling period (n=4-10 sampling periods). 
Source 
df 
F 
P 
Standard length (SL mm) 
Temperature 
1 
76.26 
<0.001 
Hatch rank 
15 
25.87 
<0.001 
Temperaturexhatch rank 
1 
4.08 
0.048 
Error 
63 
Yolk area (YA mm 2 ) 
Temperature 
1 
4.49 
0.038 
Hatch rank 
15 
23.81 
<0.001 
Temperaturexhatch rank 
1 
2.67 
0.108 
Error 
63 
Eye diameter (ED mm) 
Temperature 
1 
0.14 
0.710 
Hatch rank 
15 
1.74 
0.066 
Temperaturexhatch rank 
1 
0.56 
0.457 
Error 
63 
54 
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4.2 
0 2 4 6 8 10 12 14 
Temperature (°C) 
Figure 6 
Maximum size-at-hatch achieved by northern rock sole ( Lepi - 
dopsetta polyxystra ) larvae as a function of temperature 
(2°, 5°, 9°, and 12°C). Size data are based on means (±1 
standard error) of maximum size observed among replicate 
tanks (n = 3) for each temperature of early and late-hatching 
larvae. Data for each hatch period were fitted with a peak, 
Gaussian, 4-parameter nonlinear regression shown in the 
figure panel. 
days longer than late-hatching larvae depending on the 
incubation temperature (Laurel et al., 2008). 
In Pacific cod, early-hatching eggs survived longer 
as free-swimming larvae in the absence of food than 
did late hatching eggs, but hatch rank had no overall 
effect on time-to-starvation from the point of fertiliza- 
tion (Laurel et al., 2008). In other words, early hatching 
larvae survived longer as larvae, whereas late-hatching 
larvae survived longer as eggs. Early hatching larvae 
may gain more experience handling and ingesting prey 
before they need to feed, or may experience higher 
growth potential than late-hatching larvae (Porter and 
Bailey, 2007). 
The upper range of thermal tolerance of northern 
rock sole larvae appears to be around 12°C as evidenced 
by the precipitous decline in hatch quality at this tem- 
perature. In the wild, northern rock sole larvae seldom 
experience temperatures >6°C because spawning oc- 
curs in mid-winter and early spring in Alaskan waters 
(Stark and Somerton, 2002). Northern rock sole adults 
are also generally restricted to higher latitudes, from 
the northern coast of Hokkaido to the Okhotsk Sea in 
the western North Pacific Ocean, the Bering Sea near 
St. Lawrence Island and south to the shelf areas of the 
Gulf of Alaska (Mecklenburg et al., 2002). Collections of 
larvae have extended as far north as the Chukchi Sea 
and outer shelf areas of the Bering Sea where water 
temperatures can be below 0°C (Matarese 1 ). In con- 
trast, southern rock sole adults are distributed further 
south (southeastern Bering Sea along the Alaska 
Peninsula and throughout the shelf areas of the 
Gulf of Alaska to Baja California), with the most 
northernmost extent (rare) being documented 
at around 59°N (just south of Nunivak Island). 
Where northern and southern rock sole overlap 
in Alaska, southern rock sole spawning gener- 
ally occurs later in the warmer summer months 
(Stark and Somerton, 2002). The poor hatching 
performance of northern rock sole at 12°C, along 
with the contrasting spatial and temporal distri- 
bution of northern and southern rock sole in the 
field, suggest temperature tolerance may be an 
important environmental variable reducing gene 
flow between these closely related pleuronectids. 
It was interesting to note that despite having 
larger yolks, larvae in the warm water treat- 
ments starved more quickly and were not able to 
mobilize yolk reserves as efficiently into growth 
as larvae in cold temperature treatments. The 
growth performance in poikilotherms is gener- 
ally optimized at the lower range of the organ- 
ism’s thermal tolerance under low-food situations 
(Jobling, 1997), but there is a lack of such studies 
at life stages when organisms are dependent on 
endogenous resources. In a review of more than 
100 marine fish species, Pepin (1991) found that 
time to starvation decreases with temperature, 
1 Matarese, A. 2010. Unpubl. data. 
Science Center, Seattle, WA 98115 
Alaska Fisheries 
