321 
Abstract .-^The reproductive biol- 
ogy and sexual maturity of Atka mack- 
erel ( Pleurogrammus monop terygius) in 
Alaskan waters were examined with 
data collected from commercial fishing 
vessels and National Marine Fisheries 
Service research surveys. The female 
reproductive system and ovarian devel- 
opment over time were described by 
using histological methods. The repro- 
ductive cycle is characterized by a pe- 
riod of slow development from J anuary 
until May, a rapid growth period of vi- 
tellogenesis in June, and a protracted 
spawning period, July until October, 
during which three batches of eggs are 
spawned on average. 
Length and age at maturity were cal- 
culated and compared for different sub- 
areas of the Aleutian Islands and Gulf 
of Alaska region. Size at 50% maturity 
was significantly different among the 
subareas, decreasing from east to west. 
Lengths at 50% maturity were 38.24, 
35.91, 33.55, and 33.64 cm in the Gulf 
of Alaska, eastern Aleutian Islands, 
central Aleutian Islands, and western 
Aleutian Islands, respectively. Age at 
maturity was not significantly differ- 
ent by area; Atka mackerel were found 
to reach 50% maturity at 3.6 years. 
Therefore, it was assumed that differ- 
ent sizes at sexual maturity were re- 
flections of different growth rates in the 
respective geographic subareas. 
Manuscript accepted 24 September 1996. 
Fishery Bulletin 95:321-333 ( 1997). 
The reproductive cycle and sexual 
maturity of Atka mackerel, 
Pleurogrammus monopterygius, 
in Alaska Waters 
Susanne F. McDermott 
University of Washington 
Schooi of Fisheries 
Seattle, Washington 98115 
E-mail address: smcdermo@fish.washington.edu 
Sandra A. Lowe 
National Marine Fisheries Service 
Alaska Fisheries Science Center 
7600 Sand point Way, NE 
Seattle, Washington 981 15-0700 
Atka mackerel, Pleurogrammus 
monopterygius, is a member of the 
greenling family (Hexagrammidae). 
It is distributed in Alaskan and 
Russian waters from the Gulf of 
Alaska to Kamchatka and is most 
abundant in the North Pacific 
Ocean, southern Bering Sea, and 
along the Aleutian Archipelago 
(Rutenberg, 1962). It has been of 
increasing commercial importance 
to the United States, with Alaskan 
catches averaging about 80,000 
metric tons (t) in the last 3 years 
(valued at $14 million [ex-vessel] in 
1993). 
Recent information suggests that 
Atka mackerel play an important 
role in the Aleutian Islands and 
Gulf of Alaska ecosystems as forage 
for other groundfish, seabirds, and 
marine mammals, including the 
Steller sea lion ( Eumetopias jubatus) 
which has been listed as a threat- 
ened species under the U.S. Endan- 
gered Species Act (Kajimura, 1984; 
Livingston et al., 1993; NMFS 1 ). 
Despite the value of the species to 
commercial fisheries and other 
piscivores, many aspects of its life 
history and ecology are poorly un- 
derstood. Furthermore, information 
and data available suggest behav- 
iors and distribution patterns 
unique among Alaska groundfish. 
During much of the year, Atka 
mackerel are pelagic but migrate 
annually from the lower edge of the 
continental shelf to shallow coastal 
waters where they spawn demersally. 
In eastern Kamchatka waters, the 
spawning migration begins at the 
end of May and peaks in the middle 
of June (Zolotov, 1993). Spawning 
peaks June through September, but 
may occur intermittently through- 
out the year (Gorbunova, 1962; 
Zolotov, 1993). Atka mackerel 
spawn their eggs in rock crevices or 
among stones, which are guarded by 
brightly colored males until hatch- 
ing occurs (Gorbunova, 1962; Zolo- 
tov, 1993). Females are reported to 
spawn an average of three batches 
per season with at least a 2-week 
hiatus between subsequent spawn- 
ings (Zolotov, 1993). Batches of eggs 
in different phases of development 
were found inside one nest, suggest- 
ing a promiscuous mating system 
1 NMFS. 1995. Status review of the U.S. 
Steller sea lion ( Eumetopias jubatus) 
population. Natl. Mar. Mamm. Labora- 
tory, Natl. Mar. Fish. Serv., NOAA, 7600 
Sand Point Way NE, Seattle, WA 98115, 
61 p. 
