Species 



FISHERY BULLETIN: VOL. 74, NO. 3 



Table 4.-Mysids collected in the water column, day and night. 



Day 



Night 



Middepth 



collections 



{n = 6) 



Near-bottom 



collections 



{n = 6) 



Middepth 



collections 



{n = 6) 



Size 

 (mm) 



% 

 freq. 



Mean 



no. 



indiv. 



% 

 freq. 



Mean 



no. 



indiv. 



% 

 freq. 



Mean 



no. 



indiv. 



Near-bottom 



collections 



{n = 6) 



% 

 freq. 



Mean 



no. 

 indiv. 



An unidentified erythropinid species (Figure 

 5L) behaved much like iS. pacifica, but was seen 

 less often. Although one daytime near-bottom 

 collection took 32 individuals (probably the net 

 sampled a diurnal aggregation close to the sea 

 floor), generally the species was taken in the 

 plankton net only at night. During the day we 

 found it numerous amid the flocculent material 

 that often accumulates in shallow depressions on 

 sandy bottom (Hobson and Chess in prep.) 



The predominant mysid observed and collected 

 in the canopy of the kelp forest was Acanthomysis 

 sculpta (Figure 5K), which aggregated in small 

 openings among the kelp fronds during the day. 

 {Siriella pacifica also was numerous in the kelp 

 canopy, but not the erythropinid.) At night some 

 A. sculpta moved out over the adjacent open 

 regions sampled by our net (Table 4), but most 

 stayed close to the kelp. The stomach contents of 

 20 A. sculpta collected during day and night were 

 examined: DAYTIME-All 10 (8.5-11 mm, x = 

 10.0) collected amid the canopy of giant kelp 

 during midafternoon contained food, with their 

 stomachs averaging 85% full. All 10 contained 

 plant material, apparently Mocrocystis (69% of 

 diet volume), while 7 contained crustacean frag- 

 ments, mostly copepods, (30% of diet volume). 

 NIGHTTIME-All 10 (8-11 mm, .f = 9.6) collected 

 in the kelp canopy 30 min before first morning 

 light contained food, with their stomachs averag- 

 ing 82% full. All 10 contained plant material. 



apparently Mocrocystis (56% of diet volume), and 9 

 contained crustacean fragments, mostly copepods 

 (44% of diet volume). Thus, A. sculpta, which does 

 not join the other two mysid species in their mass 

 movement into open water after dark, seems to 

 feed on plants and animals during both day and 

 night. 



Cumaceans 



Cumaceans were numerous in the water column 

 at night, but absent there during the day. On four 

 evenings we noted the first one to rise as much as 1 

 m above the bottom, and found this level attained 

 26 to 41 (x = 32.3) min after sunset. On four 

 mornings we noted the last individual 1 m above 

 the bottom, and recorded this event 37 to 50 {x = 

 41.3) min before sunrise. Usually we were unable 

 to determine the species of cumaceans seen swim- 

 ming in the water, but our plankton collections 

 (Table 5) took only two species in substantial 

 numbers: Cumella sp. A (Figure 5N) and Cyclaspis 

 nubila (Figure 50). Both of these species were 

 numerous in samples of sand taken from the 

 surface of the sea floor during the day (Hobson and 

 Chess in prep.). 



Tanaids 



Tanaids were absent in the daytime collections, 

 but one species, Leptochelia dubia, was collected at 



Table 5.-Cumaceans collected in the water column, day and night. 



576 



