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Fishery Bulletin 95(2), 1997 
with polygyny in the males and polyandry in the fe- 
males (Zolotov, 1993). The adhesive eggs hatch in 40- 
45 days, releasing planktonic larvae that have been 
found up to 800 km from shore (Gorbunova,. 1962). 
Preliminary analyses of fishery and survey data sug- 
gest evidence of sex segregation during the spawn- 
ing period. Males presumably remained on the 
spawning grounds guarding the nests, whereas fe- 
males were found in exploitable concentrations far- 
ther offshore in high current areas such as island 
passes. 2 
The Atka mackerel resource in the Aleutian Islands 
appears to be in excess of 0.5 million t. 3 Owing to a 
lack of a strong market for the product, and insuffi- 
cient biological information that prompted conser- 
vative catch recommendations, it was lightly ex- 
ploited through the 1980’s. Catch recommendations 
depend on an accurate knowledge of abundance 
which is based on the biology, distribution, and popu- 
lation dynamics of the species. The expansion of the 
fishery has greatly intensified the need for accurate 
estimates of life history parameters. However, to date 
most of the life history information available on Atka 
mackerel has been obtained in Russian waters 
(Gorbunova, 1962; Rutenberg, 1962; Zolotov, 1993); 
there is little or no information on the reproductive 
cycle, behavior, and ecology of Atka mackerel in U.S. 
waters. Because its distribution appears to be closely 
related to its reproductive life history, information 
on the reproductive cycle and spawning behavior of 
Atka mackerel off Alaska could lead to a better un- 
derstanding of its localized movement patterns. This 
information is necessary to improve surveys for bio- 
mass estimates which will result in more accurate 
stock assessments and provide better long-term man- 
agement of the fisheries. Of particular importance 
are parameters governing the reproductive potential 
of the stock, i.e. maturity at age, which is a direct 
input into the stock assessment model and is required 
to estimate female spawner biomass. 
This paper presents the results of a study that was 
undertaken to examine the reproductive biology of 
Atka mackerel. Female gonads and otoliths were 
collected, gonads examined histologically, egg stages 
and maturity stages defined, and the reproductive 
cycle was described. Ages were estimated from 
otoliths. The gonad somatic index (GSI) and the mean 
2 Fritz, L. W. 1995. Alaska Fish. Sci. Center, Natl. Mar. Fish. 
Serv., Seattle, WA 98115. Personal commun. 
3 Lowe, S. A., and L. W. Fritz. 1995. Atka Mackerel. In Stock 
Assessment and Fishery Evaluation Report for the Groundfish 
Resources of the Bering Sea/ Aleutian Island Regions as Pro- 
jected for 1996. North Pacific Management Council, P.O. Box 
103136, Anchorage, AK 99510. 
egg stage per month were used as indicators of ova- 
rian development over time. Population parameters 
such as length and age at 50 % maturity were deter- 
mined and compared between different geographi- 
cal areas. 
Methods 
Few opportunities existed for the collection of bio- 
logical samples of Atka mackerel other than aboard 
commercial fishing boats or National Marine Fish- 
eries Service (NMFS) research surveys. Conse- 
quently, sample collection was restricted to periods 
when the fishery was open and when the NMFS sur- 
veys were conducted. 
Data and sample collection 
The data and samples analyzed in this study were 
collected from 1992 through 1994 in 1) the Gulf of 
Alaska and 2) the Aleutian Island Region by observ- 
ers and research scientists aboard commercial fish- 
ing vessels and NMFS research boats, respectively 
(Fig. 1). For purposes of collection and analysis, the 
study region was subdivided into four geographical 
subareas: western Aleutians, central Aleutians, east- 
ern Aleutians, and the Gulf of Alaska. 
The total number of gonad samples collected was 
978. Monthly sample sizes ranged from a low of 30 
in August to a high of 196 in June (Table 1 ). Otoliths 
were also collected from 537 of the sampled fish. 
Overall sampling effort by area was fairly even. How- 
ever, sampling effort in each area by month was 
strongly dependent on the location of the seasonal 
fishing effort in winter, spring, and fall. Winter 
samples were available only from the eastern Aleu- 
tians, whereas spring and summer sampling took 
place in all areas. The only fall samples taken were 
in October from the Gulf of Alaska. Samples collected 
on research cruises were taken from June through 
August throughout most of the areas. Since the sam- 
pling scheme for samples on commercial vessels did 
not differ from the sampling scheme on research 
boats, all data were combined. However, commercial 
catches were obtained by directly targeting certain 
locations or schools, whereas the survey catches were 
obtained by sampling at randomly stratified stations. 
Therefore the age and size composition of the com- 
mercial catch may reflect a more uniform popula- 
tion structure because most commercial boats tar- 
get schools of adult fish. 
There were insufficient samples to distinguish 
annual differences, therefore all samples were pooled 
by month and subarea for the determination of length 
