GLASS TUBE {] 

 CONNECTOR f 



'3 RUBBER STOPPER 



■-i 



Vs ALIQUOT MARK^ 



GLASS TUBE'^>;6 I D." 



*3 RUBBER STOPPER- 



GLASS TUBING % I D- 



-1 



RUBBER SURGICAL 

 TUBING li" I.D 

 ILENGTH AS REQUIRED ) 



^GLASS TUBE CONNECTOR 



4 RUBBER SYRINGE BULB 



Figure 3. 

 ton. 



-Syringe device used for subsampling plank- 



The amount of each sample examined de- 

 pended on the settled volume of plankton. Hauls 

 in which the settled volume was less than 25 ml. 

 were examined in their entirety ; when sample 

 volume exceeded 25 ml., only one-fifth of the 

 total sample was examined. Aliquots were ex- 

 tracted directly from the samples with a 

 syringe device (fig. 3). Subsampling accuracy 

 was checked by applying chi-square tests to 

 pooled counts from aliquot sizes ranging from 

 one-fifth to four-fifths of the total sample 

 (table 3). These tests indicated that the sub- 

 sampling technique provided adequate esti- 

 mates of total counts. 



TRENDS IN SEASONAL ABUNDANCE AND 

 THEIR IMPLICATIONS 



Seasonal trends in abundance for all plank- 

 tonic stages of Penacus spp. were determined 

 for 14-, 27-, 46-, and 82-m. stations (table 4). 

 Cumulative yearly totals showed that the 

 greatest catch per unit of effort for each stage 

 was made at the 46-m. stations. 



Distinct trends in abundance for all plank- 

 tonic stages combined were evident at each of 



SAMPLING DEPTHS IN METERS 



ALL PLANKTONIC STAGES 



NAUPLI I 



rPW^ fW^ 



PROTOZOEAE 

 N-ZZ N=5TI 



MYSES 



N = 76 



.^ 



POSTLARVAE 



fl-R-, 



^*S 



JMMJSN JMMJSN JMMJSN JMMJSN 

 AVERAGE BOTTOM TEMPERATURE 



' I I II M I I I I I I 1 I I I I I I • I I I 1 I I ' I I I I I I I I I T I I 



JMMJSN JMMJSN JMMJSN JMMJSN 



Figure 4. — Seasonal abundance trends of planktonic- 

 stage Penaeus spp. and average bottom temperature 

 by station depths in 1961. 



the four depths (fig. 4). Two peaks of abun- 

 dance were evident at each depth, but abun- 

 dance was always much greater during the 

 second peak. The time of greatest abundance 

 was during May to August in 14 m. of water, 

 August to November in 27 m., and September 

 to November in 46 and 82 m. In general, peak 

 abundance was attained at a progressively later 

 time in the year with an increase in water 

 depth. In addition, observed increases in abun- 

 dance and increases in temperature of bottom 

 waters at each depth were closely parallel, sug- 

 gesting a possible direct relation. 



At the 27-. 46-, and 82-m. stations, larval 

 stages, excluding postlarvae, were taken in 



U.S. FISH AND WILDLIFE SERVICE 



327 



