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Vol. 53 - Alaska Resources Library and Information Services

Vol. 53 - Alaska Resources Library and Information Services

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were found in the upper 40 m. Eighty-six percent of SI <strong>and</strong> 82% of SII<br />

zoeae were found in the upper 20 m.<br />

The depth distribution of megalops larvae, analyzed with both species<br />

combined, also showed a tendency for distribution higher in the<br />

water column.<br />

However, greater variability was found at all depths for<br />

this stage than for the zoeal stages <strong>and</strong> a greater proportion of megalops<br />

occurred at 40-60 m depth compared to zoeae (Fig. 4.9). At 16<br />

stations (18 tows) during June <strong>and</strong> July 1981, only one megalops larva<br />

was found below 60 m depth.<br />

4.6.2 Vertical Migrations<br />

Although the data indicated that only a small proportion of all<br />

Tanner crab larvae were found below 40 m, the data were further analyzed<br />

for possible diurnal patterns masked by the overall analysis.<br />

This was<br />

done by examining the proportion of larvae found below 40 m at various<br />

times of the day.<br />

Forty meters was selected because on the average few<br />

larvae were found below this depth, so any diurnal pattern should be<br />

readily seen. The day was divided into six periods (0000-0300, 0300-0600,<br />

0600-0900, 0900-1800, 1800-2100 <strong>and</strong> 2100-0000), roughly corresponding to<br />

various light intensities <strong>and</strong> periods of increasing or decreasing light.<br />

The data (proportion of larvae below 40 m) for each station were entered<br />

according to the time of day the sample was taken.<br />

Data from twelve<br />

diel (24-hr) stations were analyzed <strong>and</strong> then the data from all 79<br />

stations were analyzed. The data were re-examined using the proportion<br />

below 20 m as the migration criterion.<br />

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