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Fishery Bulletin 95(2), 1997 
Reproductive timing and parameters can vary from 
year to year; this might be reflected in increased vari- 
ance and range of the results in this study. 
The spawning period during late summer and fall 
for Atka mackerel is earlier than that observed for 
the masked greenling (September through October; 
Munehara and Shimazaki, 1989), but later in the 
year than most other Alaska groundfish of commer- 
cial importance. Sablefish (Anoplopoma fimbria), 
Pacific halibut ( Hippoglossus stenolepis), arrowtooth 
flounder ( Atheresthes stomias), and flathead sole 
(Hippoglossoides elassodon) are reported to spawn 
in winter and early spring in the Gulf of Alaska, 
whereas walleye pollock ( Theragra chalcogramma). 
Pacific cod ( Gadus macrocephalus), Pacific ocean 
perch (Sebastes alutus), and rock sole ( Pleuronectes 
bilineatus) were reported to have their spawning 
peak from spring to early summer in the Gulf of 
Alaska (NPFMC 4 ). The life history feature of sum- 
mer and fall spawning for Atka mackerel and other 
greenling species might be an adaptation to spawn- 
ing large demersal eggs, the larvae of which enter 
the plankton at a larger size than larvae from pe- 
lagic eggs (Kendall and Dunn, 1985). 
The differences by subarea for length at 50% ma- 
turity can be attributed to different growth rates by 
subarea, given that no age-at-maturity differences 
among geographical areas were found. Length-at-age 
curves in each management area revealed an increas- 
ing size at age from west to east (Lowe and Fritz 3 ). 
The reasons for these different growth rates are un- 
known. It is not clear whether more favorable condi- 
tions such as food availability, or a more favorable 
temperature regime are contributing to a higher 
growth rate in the Gulf of Alaska and eastern Aleu- 
tian Islands subarea, or whether there are genetic 
differences in the populations. However, initial ge- 
netic studies suggest that there is little or no stock 
differentiation in Alaska (Winans 5 ). 
Analysis of fisheries data (Fritz 2 ) indicated that 
in late summer and fall commercial hauls in many 
locations had a larger proportion of females than 
males. Sex segregation coincided with the spawning 
season (July through October) and supported the 
hypothesis that males were unavailable to the fish- 
ery, presumably guarding nests close to shore. Seg- 
regation of the Atka mackerel population by sex dur- 
ing the spawning season could also affect the results 
of summer trawl surveys used to assess population 
4 NPFMC. 1994. Fishery Management plan for the Alaskan 
Gulf of Alaska groundfish fishery. North Pacific Fishery Man- 
agement Council, P.O. Box 103136, Anchorage, AK 99510. 
5 Winans, G. Northwest Fish. Sci. Center, Natl. Mar. Fish. Serv., 
NOAA, Seattle, WA 98112. Personal commun. 
size if only a portion of the population is surveyed. 
More information on the location of nesting sites, 
behavior, and spawning distribution is necessary to 
understand the implications of population segrega- 
tion on resource assessments. 
Future research should be conducted on a more 
long-term basis for collection of maturity informa- 
tion, and larval and juvenile biology and distribu- 
tion. Time and area gaps should be filled to under- 
stand the spatial and seasonal distribution patterns 
linked to spawning, crucial for assessing and man- 
aging this species appropriately. 
Acknowledgments 
The authors would like to thank the following scien- 
tists from the Alaska Fisheries Science Center: F. 
Morado for the generous use of his laboratory space 
and his helpful advice in histological matters, L. W. 
Fritz and J. N. lanelli for their helpful suggestions 
and comments, D. Nichol and A. R. Hollowed for re- 
viewing the manuscript, and D. Anderl (Age and 
Growth Unit) for the ageing of Atka mackerel 
otoliths. This study would not have been possible 
without the help from the Observer Program and the 
research scientists of the Resource Assessment and 
Conservation Engineering division in obtaining 
samples in the field. We greatly appreciated the sup- 
port and advice of R. D. Gunderson (University of 
Washington) through all phases of this work. 
Literature Cited 
Chilton, D. E., and R. J. Beamish. 
1982 . Age determination methods for fishes studied by the 
groundfish program at the Pacific Biological station. Can. 
Spec. Pub. Fish. Aquat. Sci. 60, 102 p. 
Galigher, A. E., and E. N. Kozloff. 
1971 . Essentials of practical microtechnique. Lea and 
Febiger, Philadelphia, PA, 531 p. 
Gorbunova, N. N. 
1962 . Spawning and development of greenlings (family 
Hexagrammidae). Tr. Inst. Okeanol., Akad. Nauk SSSR 
59:118-182. In Russian. (Trans, by Isr. Program Sci. Trans., 
1970, p. 1-103. In T. S. Rass ( ed. ), Greenlings: taxonomy, 
biology, interoceanic transplantation. Available from U.S. 
Dep. Commer., Natl. Tech. Inf. Serv., Springfield, VA, as 
TT 69-55097. 
Gunderson, D. R., and P. H. Dygert. 
1988 . Reproductive effort as a predictor of natural mortal- 
ity rate. J. Cons. Cons. Int. Explor. Mer. 44:200-209. 
Hunter, J. R., and B. J. Macewicz. 
1985. Rates of atresia in the ovary of captive and wild north- 
ern anchovy, Engraulis mordax. Fish. Bull. 83( 2 ): 119 — 
136. 
Kajimura, H. 
1984 . Opportunistic feeding of the northern fur seal, 
