Vol. 53 - Alaska Resources Library and Information Services

them. Contrasts can be made to highlight seasonal, regional and annual
differences in densities (Figs. 5.10-5.12).
These mean larval densities
were only calculated when the number of stations sampled in each stratum
during the time period indicated was >= 5; consequently, densities for
some strata are not given.
Some seasonal changes in regional densities were found when April
was compared to May/June (Fig. 5.10 a & b) in 1978.
There was apparently
an earlier hatch over the middle shelf than over the outer shelf.
Strata 1 and 9 had mean densities of about 1500-2500 larvae/100 m 2 while
strata 2 and 8 had virtually none (Fig. 5.10a).
In May/June larvae were
widely distributed over the shelf but more abundant over the outer
(1142-2222 larvae/100 m 2 ) than the middle shelf (922-1845/100 m²). It
is not known to what extent this shift in regional density represents
differences in timing of species hatch across the shelf (Hyas spp. vs.
Oregonia spp.) and/or intraspecific variability between regions (i.e.
strata).
For interannual comparison of larval densities, May/June samples
were available from strata 1, 2, and 6 in 1978, 1980 and 1981 (Figs.
5.10b, 5.11, 5.12a).
Although standard deviations about mean densities
of each stratum are large, larval density was higher in 1978 than in
either 1980 or 1981.
The latter two years showed very low abundance of
larvae in the plankton; densities were 2-18 times less than those found
in 1978.
The nature of spawner-recruit relationships for this taxon are
unknown, and so the extent to which more or less pelagic larvae indicate
good or poor year-classes cannot be assessed.
Still low larval abundance
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