HORN: ABUNDANCE AND DIVERSITY OF MORRO BAY FISHES 



Table 3. — Day and night fish samples in termsof numbers of individuals and biomass for each sampling period and 

 the total collection in Morro Bay. Percentage similarity iPS) is explained in the text. "Difference" column indicates 

 whether day samples were significantly (S) or not significantly (NS) different from night samples based on paired 

 percentage values for each species (Table 2) (Wilcoxon signed-ranks test for paired values, P'SO. 05, two-tailed). 



Greater numbers and biomass were obtained at 

 night but the difference was not significant in 

 either case. The PS value between day and night 

 samples was much higher for numbers (78.8%) 

 than for oiomass (43.0%). In November, more 

 species were collected at night ( 15) than during the 

 day (12). Even though the total number of indi- 

 viduals and total biomass obtained during the day 

 were greater than the totals at night, the night 

 samples in both cases were more frequently and 

 significantly larger based on paired day-night 

 abundances of each species using the Wilcoxon 

 signed-ranks test (Table 3). The discrepancy for 

 individuals was primarily due to a relatively large 

 daytime contribution (394 individuals) of £■. mor- 

 dax compared with its much smaller number (3 

 individuals) in the night samples. The inconsis- 

 tency for biomass was mainly due to the large 

 daytime contribution (4,560 g) of M. californicus 

 compared with its smaller contribution (1,368 g) to 

 the night totals. 



Seven species, A. affinis, C. aggregata, L. ar- 

 matus, E. mordax, Fundulus parvipinnis, 

 Syngnathus leptorhynchus, andQuietula y-cauda, 

 were captured at least once in each of the 3-h 

 sampling intervals of the four periods. No common 

 species was collected either only during the day or 

 only at night. Among the uncommon species, 

 Myliobatis californica and Citharichthys stig- 

 maeus were captured only during the day whereas 

 Clupea harengus, Hyperprosopon argenteum, 

 Hypsopsetta guttulata, Platichthys stellatus, and 

 Sebastes sp. were obtained only at night (Table 2). 



Marked changes in numbers, biomass, and di- 

 versity occurred between sampling periods al- 

 though only four species, A. affinis, Cymatogaster 

 aggregata, L. armatus, and Mustelus californicus, 

 were, in different combinations, the most abun- 

 dant (numbers or biomass) fishes in the samples 

 (Table 1; Figure 2). Numbers of individuals and 

 biomass both reached highest levels in May and 

 lowest levels in August. Diversity //' on numbers 



]:■:•'.■'.■] A^. offinis 



I 1 C. aggregata 



I I Other species 



"1 L. armotus 



FIGURE 2. — Quarterly data on fish numbers (upper) and 

 biomass (lower) in the Bay wood Park section of Morro Bay Total 

 diversity is given by // ' in the center of each cycle. The area of 

 each circle is proportional to the sample size, the number to the 

 lower left of each circle is the quarterly diversity H ', and the 

 number on the connecting arrow is the percentage similarity 

 between months. Sampling dates are February 1976, May and 

 August 1975, and November 1974. 



763 



