FISHERY BULLETIN: VOL. 78, NO. 3 



larger fish progressively increased through the 

 successive quarterly periods so that in November 

 the catch was made up of primarily large juveniles 

 and secondarily offish in the reported mature size 

 range. Winter spawning was evident even though 

 few adults were collected. The rarity of adults 

 could have been due to at least four factors: 1) net 

 avoidance by adults, 2) postspawning mortality by 

 adults, 3) migration of adults out of the area after 

 spawning, or 4) migration of young individuals 

 into the area after spawning occurred elsewhere. 

 Although the third factor has been discounted by 

 Tasto (1975), all four possible causes deserve 

 further investigation. 



In terms of Haedrich's (1975) model for assess- 

 ing the environmental quality of estuaries and 

 embayments, Morro Bay can be classified as a 

 relatively unspoiled habitat in that relatively high 

 total diversity and a wide range of seasonal 

 similarity values were recorded. It is instructive, 

 however, to compare the Morro Bay data with 

 those available for three southern California 

 bay-estuarine habitats with similar ichthyo- 

 faunas: 1) Mugu Lagoon (lat. 34.1° N), 2) Colo- 

 rado Lagoon (lat. 33.8° N), and 3) upper Newport 

 Bay I lat. 33.6° N). Mugu Lagoon is a rela- 

 tively unaltered habitat with diversity and 

 similarity values comparable to those for Morro 

 Bay whereas Colorado Lagoon and upper Newport 

 Bay, two more highly perturbated sites, have lower 

 diversity values yet wider ranging season-to- 

 season similarity indices than Morro Bay or Mugu 

 Lagoon (Table 5). 



All four habitats are largely marine in charac- 

 ter with salinities usually approaching those of 

 the ocean. Upper Newport Bay is the most fre- 

 quent exception in that during occasional years of 

 heavy winter rainfall salinities are greatly re- 

 duced in the extreme upper portions of the habitat. 

 Although generally considered to be a relatively 

 unaltered estuary in southern California (Frey et 

 al. 1970), upper Newport Bay, unlike Morro Bay, is 

 subject to pollutant inflow from both urban and 

 agricultural runoff and a high rate of sedimenta- 



tion (with accompanying increased turbidity) dur- 

 ing years of increased rainfall (e.g., Horn and 

 Allen in press). Colorado Lagoon, the partially 

 isolated upper arm of Alamitos Bay, receives pol- 

 lutants and nutrients from street runoff and 

 heavy recreational use especially during the 

 summer months when eutrophic conditions 

 usually develop (Allen and Horn 1975). The lower 

 reaches of both Newport Bay and Alamitos Bay 

 have been altered by extensive marina develop- 

 ment and by modification of their openings to the 

 sea. Mugu Lagoon is in a relatively undisturbed 

 condition primarily because it has been for more 

 than 30 yr under ownership of the U.S. Navy 

 which restricts access to the area (MacDonald 

 1976). The fish faunas of these three environments 

 are basically similar to that of Morro Bay with 

 three of the five most abundant species in upper 

 Newport Bay and Mugu Lagoon and four of the five 

 most abundant species in Colorado Lagoon also in 

 the top five in Morro Bay. 



The sampling procedure (bag seine deployed 

 from shore) and substrate conditions (varying 

 mud to sand) were similar for the four habitats. 

 Collections were made monthly in the locations 

 other than Morro Bay; quarterly data were ex- 

 tracted for comparison with the Morro Bay values. 

 The main difference in the collection of data 

 among the four locations was the type of beach 

 seine used. In Colorado Lagoon, as in Morro Bay, a 

 29.2 m seine with 6 mm mesh in the bag was used, 

 whereas in Mugu Lagoon and upper Newport Bay 

 a 15.2 m seine with 3 mm mesh in the bag was 

 employed. The difference in effectiveness of the 

 two types of seines is incompletely known but con- 

 sidered to be slight (M. H. Horn and L. G. Allen 

 unpubl. data); moreover, the discrepancy is judged 

 to be of minor importance since it does not parallel 

 the diversity-similarity differences among the 

 four ichthyofaunas (Table 5). 



Quarterly data (February-November 1977) from 

 bag seine samples of 29 species in Mugu Lagoon 

 (Quammen^) yielded a total H ' value of 1.52 and 

 PS values ranging from 30 to 627f (Table 5). Thus, 



Table 5. — Number of species (S), Shannon- Weiner diversity (W), and season-to-season percentage similarity values (PS) based on 

 quarterly bag seine collections of fishes in four bay-estuarine habitats in California. Environmental status is a qualitative assessment 

 (see discussion section). 



Bay-estuary 



Location (latitude) 



H' 



PS 



Environmental status 



Data source 



Morro Bay 

 Mugu Lagoon 



Colorado Lagoon 

 Upper Newport Bay 



Central California (35.3 N) 

 Southern California (34 1" N) 



Southern California (33.8 N) 

 Southern California (33.6 N) 



768 



