Vol. 53 - Alaska Resources Library and Information Services

Wigley 1969; Rasmussen 1953 from Butler 1971).
No fecundity data are
available for the southeastern Bering Sea. Stickney and Perkins (1980)
are currently studying the fluctuating fecundity of Maine stocks of P.
borealis which, after declining in the early 1970's, seem to be
rebuilding.
Horsted and Smidt (1956 from Butler 1980) report that a
parasite Hemiarthrus abdominalis can cause as much as 50% reduction in
the number of eggs carried by P. borealis females in the North Atlantic
Ocean.
Larval Development:
P. borealis has 5 planktonic zoeal stages and
one megalops stage (often referred to as a "mysid" stage) before molting
to a juvenile (Haynes 1979).
Larvae grow from 6.7 mm mean total length
at Stage I to 18.5 mm at the megalops stage.
The average mean growth
increment per molt is 2.36 + 1.04 mm total length.
Duration of planktonic
life is approximately 3 months according to Berkeley (1930).
In the
North Sea, Allen (1959) found P. borealis molts as many as 14 times from
larval metamorphosis to the male phase (from 21 to 93 mm total body
length).
At age 1.5 years, the Pribilof stocks are all immature males
with a carpace length (CL) of 12-13 mm (Ivanov 1969).
At age 2.5 years
(CL = 18-19 mm) some shrimps become sexually mature males and participate
in autumn breeding for the first time. Allen (1959) found that 5
molts are necessary before males exhibit mature sex characteristics.
Most shrimp in the 3+ and 4+ age classes (CL = 22 mm and 25 mm, respectively)
are breeding males with a small proportion as females. By 5.5
years of age (max CL = 27-32 mm) all shrimp are females.
Few shrimp
survive to 6.5 years and according to Ivanov (from NPFMC 1978), all at
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