NOTE Stark: Age- and length-at-maturity of female Atheresthes stomias in the Gulf of Alaska 
331 
Table 1 
Female arrowtooth flounder (Atheresthes stomias) age- 
at-maturity results based on ovary histological samples 
( n ) collected between the spawning and late spawning 
periods in the Gulf of Alaska by date of collection. The 
parameters of the logistic equation that were used to fit 
the data were the following: B (slope of the line) and A 
(y intercept), variance (the square of the standard devia- 
tion of B and A), covariance (the product of the standard 
deviations of B and A and the coefficient of correlation 
between them), age (years) at which 50% of females were 
expected to reach sexual maturity (A 50 ), and variance 
° fA 50. 
Date of collection 
February 2002 
July 2003 
n 
301 
226 
B 
1.3817 
0.6835 
A 
-9.6183 
-4.4945 
Variance (B) 
0.0077 
0.0016 
Variance (A) 
1.7381 
1.3528 
Covariance (B, A) 
0.0070 
0.0007 
^50 
6.9614 
6.5754 
Variance (A 50) 
0.0326 
0.1448 
Table 2 
Female arrowtooth flounder (Atheresthes stomias ) 
length-at-maturity results based on ovary histology 
samples (n) collected between the spawning and late 
spawning periods in the Gulf of Alaska by date of col- 
lection. The parameters of the logistic equation that 
were used to fit the data were the following: B (slope of 
the line) and A (y intercept), variance (the square of the 
standard deviation of B and A), covariance (the product 
of the standard deviations of B and A and the coefficient 
of correlation between them), length (mm) at which 50% 
of females were expected to reach sexual maturity (L 50 ), 
and variance of L 50 . 
Date of collection 
February 2002 
July 2003 
n 
303 
251 
B 
0.0455 
0.0215 
A 
-20.9220 
-9.9786 
Variance (B) 
1.1171 
2.9534 
Variance (A) 
6.9072 
6.3385 
Covariance (B, A) 
0.0002 
-0.0002 
^50 (mm) 
459.6917 
464.1629 
Variance (L 50 ) 
27.5705 
75.9320 
and the 1993 maturity study results by Zimmermann 
(1997). For this present study, the estimated female L 50 
was 460 mm, which did not differ significantly (P=0.08) 
from the September 1993 L 50 estimate of 469 mm. Cur- 
rently, that length-at-maturity estimate is used to man- 
age the arrowtooth flounder stocks of both the GOA 
and Bering Sea, because the A 50 has not been known. 
Consequently, with the use of the age-at-maturity esti- 
mates determined in the present study, the estimates 
of arrowtooth flounder abundance would be expected 
to improve significantly within the stock management 
model. 
Stock management would also benefit from a deter- 
mination of the arrowtooth flounder annual spawning 
period. The arrowtooth flounder spawning period prob- 
ably begins in December, based on results from the 
AFSC ichthyoplankton surveys in the Gulf of Alaska, 
during which developing embryos and larvae were found 
at the end of January (Blood et al., 2007). The rate of 
spawning declined from February 2002 (50%) to July 
2003 (<5%), according to this study. Spawning may 
conclude at the end of summer because Zimmermann 
(1997) found no spawning females during September. 
Therefore, the overall spawning period of arrowtooth 
flounder appears to extend for over 8 months or more 
in the GOA. This is a longer spawning period than 
has been found for other principal groundfish species 
in Alaska, which have spawning periods of 6 months 
or less (Matarese et al., 2003; Stark, 2004, 2007). A 
protracted spawning period could promote stock re- 
cruitment by increasing the dispersion of progeny and 
thereby increasing the probability of placing progeny in 
a favorable rearing environment. Turnock et al. (2005) 
estimated that the spawning biomass of female ar- 
rowtooth flounder has increased annually since 1961 
(1.98xl0 5 t) and remains above 1.24 x 10 6 t in the GOA. 
Similarly, the spawning biomass was estimated to be at 
its highest level ever recorded in the Bering Sea and 
Aleutian Islands, at more than 8.24 x 10 5 t (Wilderbuer 
and Nichol, 2006). However, the size of the spawning 
biomass may be overestimated for the Bering Sea and 
Aleutian Islands because of the reliance on the Gulf of 
Alaska L 50 estimate for the Bering Sea and Aleutian 
Islands management model. This overestimate could 
occur if the rate of female arrowtooth flounder growth 
was significantly higher for the Bering Sea and Aleutian 
Islands population than it was for the Gulf of Alaska 
population. A significantly higher rate of growth could 
result in a significantly larger L 50 , which could lower 
the spawning biomass estimate by excluding smaller 
females that may have been mature. Therefore, the 
estimates of the arrowtooth flounder spawning biomass 
that are determined by stock managers should be more 
reliable after the current length-based maturity models 
are replaced with age-based maturity models using the 
A 50 estimate from this study. 
Conclusions 
Arrowtooth flounder has consistently been the most 
abundant groundfish species in the Gulf of Alaska 
because of its high levels of recruitment and low fish- 
ing-induced mortality. Age was found to be a significant 
