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Vol. 53 - Alaska Resources Library and Information Services

Vol. 53 - Alaska Resources Library and Information Services

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Since P. tridens occurred less frequently than P. borealis, Figure<br />

6.12 shows abundance <strong>and</strong> distribution for April-July for all year combined<br />

except PROBES 1978.<br />

Highest larval densities were clustered southwest<br />

of the 200 m isobath over the shelf break (1000-4000 larvae/100 m 2 )<br />

<strong>and</strong> from Unimak Pass to Unalaska Isl<strong>and</strong> (5000-6000 larvae/100 m²). The<br />

highest mean larval density by stratum was 1461 larvae/100 m 2 for stratum<br />

12 in the Unimak Pass area during the NOAA 1977 cruise.<br />

In general,<br />

P. tridens larvae were found only rarely shoreward of the 100 m isobath<br />

over the middle shelf domain.<br />

Figures 6.13 <strong>and</strong> 6.14 compare P. tridens larval distribution in<br />

April with May <strong>and</strong> June distribution from PROBES 1978.<br />

April hatch out<br />

occurred south of St. George at the Pribilof Isl<strong>and</strong>s late in April (Fig.<br />

6.13). By May <strong>and</strong> June larvae were most abundant southwest of the shelf<br />

break (1000-4000 larvae/100 m 2 in strata 3 <strong>and</strong> 4) <strong>and</strong> over the southern<br />

part of the St. George Basin (1000-2000 larvae/100 m 2 in stratum 5).<br />

By<br />

May <strong>and</strong> June, P. tridens overlapped P. borealis larval distribution over<br />

the St. George Basin <strong>and</strong> west of the shelf break (compare Figs. 6.9 <strong>and</strong><br />

6.13).<br />

Figure 6.15 contrasts May <strong>and</strong> June mean larval densities in stratum<br />

2 with stratum 3 for the years 1978, 1980, <strong>and</strong> 1981. (Since this<br />

species was less common than P. borealis, <strong>and</strong> since the extent <strong>and</strong><br />

degree of sampling varied within strata interannually, zero stations -<br />

no larvae found - were omitted from calculations of mean density.)<br />

There was a three- to five-fold increase in larval density of P. tridens<br />

in stratum 3 beyond the shelf break as compared to stratum 2 of the<br />

732

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