MURPHY and CLUTTER: PLANKTON PURSE SEINE 



Table 1. — Results of paired purse seine and 1-m plankton 

 net samples expressed as numbers per 300 m^. Lengths 

 are preserved lengths. There were 44 paired samples. 



Standard 

 length 

 (mm) 



1.5 

 2.5 

 3.5 

 4.5 

 5.5 

 6.5 

 7.5 

 8.5 

 9.5 

 10.5 

 11.5 

 12.5 

 13.5 

 14.5 

 I5.a 

 16.5 

 17.5 

 18.3 

 19.3 

 20.3 

 21.5 

 22.5 

 23.5 

 24.5 

 25.5 

 26.5 

 27.3 

 28.5 

 29.5 

 30.5 

 31.5 

 3C.5 

 33.5 

 34.5 

 35.5 

 36.5 

 37.5 

 38.5 

 39.5 

 40.5 

 41.5 

 45.5 



Total 



Day 



Purse 

 seine 



0.3 

 39.3 



3QJl 



20.4 



23.6 



20.8 



19.5 



16.6 



13.5 



10.9 



6.9 



7.4 



5il 



4.3 



3.8 



3.3 



3.2 



2.7 



2.2 



2.7 



1.7 



1.0 



0.7 



0.5 



0.2 



0.2 



0.02 



0X13 



0.02 



244.47 



Meter 

 net 



1.5 

 30.7 

 53.9 



13.0 

 4.6 

 5.0 

 1.2 

 2.0 

 1.0 

 0.2 

 0.02 

 0.05 

 0.08 

 0.05 



113.30 



Night 



Purse 

 seine 



219.9 



Meter 

 net 



121.0 



be accompanied by behavioral changes, e.g., on- 

 set of schooling, as well as more efficient swim- 

 ming — all of which might increase their ability 

 to escape the purse seine. The low numbers in 

 the 1.0 to 2.0 mm (preserved lengths) are, at 

 least in part, a function of the newly hatched 

 larvae being able to pass through the 333 /x Nitex. 

 The seeming differences in the next two larger 

 intervals are not statistically significant (P = 

 0.216 and 0.141, respectively). The remainder, 

 involving larvae greater than 4.0 mm, are all 

 significant at the 0.01 level or greater. 



NIGHT SAMPLES 



The night samples (Table 1, Figure 4) were 

 fewer in number (10) and, therefore, exhibit 

 greater variance. They also suffer from poor 

 stratification as evidenced by the near lack of a 

 negative slope below 12 mm in length, in spite 

 of what must be a very high mortality rate (see 

 Figure 3) . These data clearly indicate that the 

 purse seine is superior at night too, even with 

 respect to the smaller sizes, supporting Ahl- 

 strom's (1954) contention that larvae probably 

 dodge nets at night as well as day. For example, 

 over the interval 3.5 to 11.5 mm, inclusive, the 

 purse seine took 127.9 per 300 m^, and the meter 

 net took only 69.8. Over a larger interval (3.5- 

 19.5 mm), the purse seine took 163.2 larvae and 

 the meter net 99.6. For this interval the F ra- 

 tio is 6.19 with 1 and 32 df (P < 0.025) . Never- 



100 

 90 

 80 

 70 

 60 

 SO 

 40 



30 - 



£ 



I [ I I I I I I I I I I I I I 1 I I I I I I I I I I I I I I I I I I 



Purse Seine 

 Plankton Net 



I I I I I I I I I I I I I I i I I I I I I I I I I I I I I I I I I 



5 10 15 20 25 30 35 



Standard Length (mm) 



Figure 4. — Night catches of the purse seine and plankton 



net. 



793 



