FISHERY BULLETIN; VOL. 78. NO. 3 



was highest in May and lowest in February, 

 whereas H ' on biomass was greatest in November 

 but also lowest in February. The PS levels for both 

 numbers and biomass were highest between May 

 and August. Lowest PS values were obtained for 

 numbers between August and November and for 

 biomass between February and May. Total diver- 

 sity H' on numbers was similar to that for 

 biomass. 



Of the four common species in the samples, A. 

 affinis was the most abundant species, composing 

 Sl'/r of both total individuals and biomass (Table 

 1). For the total collection, significantly more indi- 

 viduals and biomass of A. affinis were captured at 

 night than during the day; however, for quarterly 

 periods, a significant day-night difference was 

 recorded only for numbers (night >day) in August 

 (Table 4). Although somewhat larger individuals 

 were commonly obtained in night compared with 

 day samples, the differences were not significant 

 for any collecting period (Table 4). In February, A. 

 affinis were bimodal in length frequency (Figure 

 3), intermediate in mean size (Figure 4), and ob- 

 tained in small numbers and the smallest 

 biomass. The contribution of A. affinis to the total 

 February catch was relatively minor for both 

 numbers (16% of total) and biomass (8*^ ). In May, 

 the largest fish of the four periods were captured 

 and in relatively high numbers. The biomass ob- 

 tained was the greatest of the study for the species 

 composing >AY7c of the total May sample. In Au- 

 gust, the fish were strongly bimodal in length fre- 

 quency and smaller in mean size. Numbers 

 reached their lowest level and biomass declined 



but nevertheless made up >AV/( of the total Au- 

 gust sample. In November, the smallest fish of the 

 study were captured, but they occurred in the 

 greatest numbers and composed >65% of the total 

 November sample. The biomass value, because of 

 the smaller fish, was lower than that for August. 



Cymatogaster aggregata, even though absent 

 from February samples, was the second most 

 abundant species composing >26'7f of total num- 

 bers and >2A% of total biomass (Table 1). In all 

 sampling periods that C aggregata was captured, 

 larger numbers and greater biomass of the species 

 were collected at night than during the day; how- 

 ever, the differences were significant only in May 

 (Table 4). Although somewhat larger individuals 

 were, in most cases, captured in night compared 

 with day samples, the difference was significant 

 only during May (Table 4). In May, the largest fish 

 of the study were collected (Figure 4) but a wide 

 size range was also represented (Figure 3). Num- 

 bers were relatively high and the biomass ob- 

 tained was the greatest of the study for the species 

 composing >AV/c of the total May sample. In Au- 

 gust, the smallest fish of the study were collected. 

 Biomass declined but numbers increased relative 

 to the previous period and made up >70% of the 

 total August sample. Slightly larger fish were col- 

 lected in November but numbers and biomass 

 reached low levels, each composing only about 2% 

 of the totals. 



Leptocottus armatus was the third most abun- 

 dant species, composing almost 24% of total num- 

 bers but only 7% of total biomass (Table 1). In all 

 sampling periods, larger numbers and greater 



Table 4. — Number of individuals, biomass, and mean weight of the three most abundant fish species for each sampling period and the 

 total collection in Morro Bay. "Difference" line indicates whether day (D) samples were significantly (S) or not significantly (NS) 

 different from night (N) samples based on four ranked samples from each day and each night period for each species (Mann-Whitney 

 C/-test,P«0.05, two-tailed). 



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