328 
Age- and length-at-maturity 
of female arrowtooth flounder 
( Atheresthes stomias ) in the Gulf of Alaska 
James W. Stark 
Resource Assessment and Conservation Engineering Division 
Alaska Fisheries Science Center 
National Oceanic and Atmospheric Administration/National Marine Fisheries Service 
7600 Sand Point Way NE 
Seattle, Washington 981 15 
Email address: Jim.Stark@noaa.gov 
Arrowtooth flounder ( Atheresthes sto- 
mias) has had the highest abundance 
of any groundfish species in the Gulf 
of Alaska since the 1970s (Matarese 
et al., 2003; Turnock et al., 2005; 
Blood et al., 2007); however, com- 
mercial catches have been restricted 
because Pacific halibut (Hippoglossus 
stenolepis) are caught as bycatch in 
the fishery. Arrowtooth flounder plays 
a key role in the ecosystem because 
it is a dominant organism within the 
food web, both as an apex predator 
of fish and invertebrates, as well as 
an important prey for walleye pol- 
lock ( Theragra chalcogramma\ Aydin 
et al., 2002). Walleye pollock is the 
dominant groundfish in the Bering 
Sea, a principal groundfish in the 
Gulf of Alaska, and the primary prey 
for marine mammals. The distribu- 
tion of arrowtooth flounder extends 
from Cape Navarin and the eastern 
Sea of Okhotsk in Russia, across the 
Bering Sea, Aleutian Islands, Gulf 
of Alaska, and south to the coast of 
central California (Shuntov, 1964; 
Britt and Martin, 2001; Chetvergov, 
2001; Weinberg et al., 2002; Zenger, 
2004). Because of the importance of 
arrowtooth flounder in the marine 
ecosystem of Alaska, a maturity 
study of this species was undertaken 
to determine age-at-maturity, which 
is essential for age-based stock man- 
agement models. Before these results, 
management has had to rely upon 
a length-at-maturity-based estimate 
(Zimmermann, 1997) to manage 
stocks in the Gulf of Alaska (GOA), 
Bering Sea, and Aleutian Islands. 
The central GOA was selected as 
the location for this maturity study 
because it contains approximately 
70% of the total Gulf of Alaska arrow- 
tooth flounder biomass (1.9xl0 6 t, age 
3 and older) — the highest percentage 
in the world (Shuntov, 1964; Britt and 
Martin, 2001; Weinberg et al., 2002; 
Wilderbuer and Nichol, 2006). 
Materials and methods 
All female arrowtooth flounder used 
in this study were collected with 
bottom trawls. The central GOA was 
initially sampled during February 
2002 (Fig. 1) from the National Oce- 
anic and Atmospheric Administration 
(NOAA) ship Miller Freeman during 
an Alaska Fisheries Science Center 
(AFSC) Recruitment Processes Pro- 
gram cruise (Blood et al., 2007). The 
area selected for trawling was sampled 
the prior year by the AFSC and had 
produced a high abundance of arrow- 
tooth flounder eggs and larvae. 
A second collection was made in 
July 2003 during the AFSC biennial 
GOA groundfish assessment survey. 
In both years, whole ovaries and oto- 
liths were collected. All specimens 
were selected by using length-strati- 
fied sampling method so that three 
to seven females were collected for 
each cm interval of total body length 
larger than 18 cm.. The sampling 
protocol, histological methods, ovary 
maturity classifications, and aging 
methods followed those described in 
Stark (2007). Mature females were 
those specimens classified with ovary 
stages ranging from cortical alveoli 
to postovulatory follicles, which were 
the same criteria used by Zimmer- 
mann (1997) for a September 1993 
GOA arrowtooth flounder maturity 
assessment. To investigate the consis- 
tency of oocyte maturation within the 
ovary, two additional sections were 
taken from the anterior and medial 
regions of both ovaries from 10 speci- 
mens collected during February 2002 
and 10 specimens from July 2003. 
These sections were compared with 
the standard sample section taken 
from the posterior area of one ovary. 
For all the following procedures, S- 
Plus software was used (vers. 2000 
Professional release 3, MathSoft Inc., 
Cambridge, MA). Maturity was es- 
timated as a function of length and 
age by fitting a logistic function to 
the maturity data with generalized 
linear modeling (Venables, 1997). The 
significance of temporal differences 
was tested by fitting the model of 
maturity as a function of total body 
length (L) and age (A), including the 
date of sampling, and by recalculat- 
ing without the date term. Signifi- 
cance of the date term was deter- 
mined by using analysis of deviance 
(Venables, 1997). The variance of 
age (A 50 ) and total body length (L 50 ) 
at 50% maturity were estimated for 
February 2002 and July 2003 by us- 
ing bootstrapping (Efron and Tibshi- 
rani, 1993) based on 200 resamplings 
with replacement of the maturity, 
age, and length data. February 2002 
and July 2003 differences in the A 50 
and L 50 were tested with a Z-test (So- 
kal, 1969). The February 2002 L 50 
result was also tested against the 
September 1993-based estimate by 
Zimmermann (1997) with a Z-test. 
To assess the temporal progression 
of ovary maturity between February 
2002 and July 2003, ovary maturity 
classifications were summarized for 
females that had reached A 50 as de- 
termined by this study. 
Manuscript submitted 21 March 2008. 
Manuscript accepted 6 May 2008. 
Fish. Bull. 106:328-333 (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. 
