512 
Fishery Bulletin 96(3), 1998 
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CO O H 
the western Gulf of Alaska 
portion of the population 
may be the result of juve- 
nile or adult migration (or 
both) or habitat expan- 
sion. Kimura and Ronholt 
(1988) postulated that 
Gulf of Alaska Atka mack- 
erel are at the extreme 
limit of their geographic 
range (the extreme limit of 
which is populated only 
during periods of favorable 
environmental conditions). 
Zolotov ( 1984) found that 
Atka mackerel spawning 
habitat in Russian waters 
extended from the Kam- 
chatka Peninisula through 
the Kurile Islands almost 
without breaks. Continuous 
distribution of Atka mack- 
erel spawning habitat and 
dispersal of larvae into the 
open ocean pointed to an 
absence of mechanisms 
that would result in repro- 
ductively isolated stocks in 
Russian waters. Zolotov 
(1984) thus concluded that 
Atka mackerel did not 
form ecological groupings 
along the Kamchatka Pen- 
insula and Kurile Islands 
but made up a single popu- 
lation. Although we cannot 
rule out that there are un- 
known mechanisms or 
processes which might re- 
sult in reproductive isola- 
tion of groupings of Aleu- 
tian Island Atka mackerel, 
life history information 
suggests that a process for 
extensive mixing occurs 
during the early life stages. 
We currently do not have 
any observations to sup- 
port the necessary pro- 
cesses (e.g. larval reten- 
tion, natal homing, genetic 
imprinting), that would 
result in reproductive iso- 
lated populations in the 
Aleutian Islands. 
