FISHERY BULLETIN: VOL. 74, NO. 3 



Fish Eggs 



Fish eggs were a regular component of both 

 middepth and near-bottom plankton collections 

 during both day and night (Tables 1, 2). Owing to 

 their small size and transparency, however, they 

 went unseen by us in the water. 



Fish Larvae 



Fish larvae were consistently seen and collected 

 at middepths and near the bottom both day and 

 night (Tables 1, 2). 



Activity Patterns of 

 Planktivorous Fishes, Day and Night 



Having described the zooplankters that occur in 

 the water column during both day and night, we 

 now consider the feeding activities of the fishes 

 that find prey there. 



Sebastes serrayioides—oWve rockfish 



Small juveniles of this species first appeared 

 inshore during midsummer when about 30 mm 

 long. They remained here throughout the ensuing 

 year, growing to about 100 to 110 mm long. Al- 

 though their numbers declined sharply during the 

 following summer, when the next crop of small 

 juveniles arrived, many remained in the area well 

 into a second winter, and some stayed longer. 

 Nevertheless, few olive rockfish exceeding about 

 120 mm occurred in the study area. Larger in- 

 dividuals (to well over 200 mm) were numerous in 

 deeper water, but were not considered in this 

 study. Limbaugh (1955) noted: "The young appear 

 in large schools, from May through September. 

 The schools form behind protective reefs, in bay 

 entrances, and in the lee of islands." Other data on 

 this species presented by Limbaugh, and also by 

 Quast (1968), pertain generally to individuals 

 larger than those discussed here. The species is 

 reported to reach 610 mm (Miller and Lea 1972). 



The activity pattern of this fish changes mark- 

 edly during its first year inshore. Most of the 

 smaller juveniles are active by day and relatively 

 inactive at night. Beginning among those about 55 

 mm long, however, there is a general shift toward 

 feeding after dark. Nocturnal habits are charac- 

 teristic among individuals larger than about 65 

 mm (to at least 120 mm— the largest considered 



here). This report, therefore, recognizes three size 

 categories, and treats each separately: 



1) small juveniles, which are predominantly diur- 

 nal, are those shorter than 55 mm; 2) intermediate 

 juveniles, which represent a transition to the 

 nocturnal mode, are those between 55 and 64 mm; 

 and 3) large juveniles, most of which are nocturnal, 

 are those 65 mm and longer. 



SMALL JUVENILES.-During daylight, the 

 small juveniles generally hovered in small ag- 

 gregations at middepths in less than 5 m of water. 

 In the study area they were most numerous along 

 the shoreward margin of the kelp forest, close to 

 rising stands of Macrocystis and other large algae. 



The small juveniles appeared in the water 

 column each morning, beginning about 40 min 

 before sunrise, after a night spent sheltered under 

 cover of algae or rocks. They occurred first as 

 solitary individuals, but soon assembled in ag- 

 gregations that were well-formed by 30 min 

 before sunrise. Only after sunrise, however, did 

 they feed appreciably. Then, sporatically at first, 

 but with steadily increasing frequency, they 

 began to snap at objects in the water indistin- 

 guishable to a human observer a few meters away. 



The onset of feeding in the morning is illus- 

 trated by the decreasing incidence of empty guts 

 in specimens collected during this period from the 

 mid-water aggregations. Empty guts occurred in 

 84% of those sampled during the 40 min before 

 sunrise (52 of 62 specimens; 42-54 mm, x = 49), in 

 58% of those collected during the 15 min following 

 sunrise (7 of 12 specimens; 41-53 mm, .f = 48), in 

 25% of those taken 15 to 30 min after sunrise (2 of 8 

 specimens; 45-53 mm, .f = 50), and in none of those 

 collected 30 to 60 min after sunrise (10 specimens; 

 41-54 mm, .f = 50). 



Intermittent observations throughout the day 

 showed consistent feeding activity. The guts were 

 full in all 11 specimens (40-51 mm, x = 45) sampled 

 from aggregations during midafternoon. Items 

 they had taken, combined with items taken by the 

 31 specimens containing food that were collected 

 during early morning (a total sample of 42 fish), 

 document the food habits of these small juveniles. 



Prey of the 44 small juveniles that had iden- 

 tifiable material in their guts are listed below in 

 order of their rank as prey. (The same format is 

 used in presenting the gut contents of the other 

 fish species, below.) In this list, the major num- 



580 



