specimens taken from both the algae-covered 

 tidal flats and sandy intertidal areas. Mean 

 densities as high as 16,500 animals/m 2 were 

 encountered (Dexter, unpubl. data). 



The ability of invertebrates to establish or 

 recover from extreme conditions is largely 

 determined by the availability of larvae (i.e., 

 life history characteristics), but chance also 

 plays a role. Species with large numbers of 

 larvae present at the time when estuarine 

 habitats are accessible and suitable for 

 settling have high probability for 

 recruitment. Within continued hydrologic 

 disturbances (i.e., wastewater inflows 

 through 1991), only the most resilient 

 species (short-lived species with early re- 

 productive age) have persisted (Chapter 5). 

 It is not clear whether there are sufficient 

 sources of larvae of the species that once 

 dominated the estuary. Whether the historic 

 benthic community will ever regain its high 

 species richness, or whether large, old clams 

 will ever be abundant again, remains to be 

 seen. 



3.6.3 Fishes-Adults and Juveniles 



Before the 1978 flood, 29 species of fish 

 were found in Tijuana Estuary (Table 3.7). 

 The community was dominated by goby 

 species, California killifish (Fundulus 

 parvipinnis) , striped mullet (Mugil 

 cephalus) , and longjaw mudsucker 

 (Gillichthys mirabilis; Figure 3.22), all of 

 which are considered resident species. 

 Commercial/recreational species that used the 

 estuary included California halibut 

 (Paralichthys californicus), surfperches, 

 anchovies, pleuronectids, croakers, and sea 

 bass, although none of these occurred in high 

 numbers relative to resident species. 



The distribution and abundance of the 

 fishes were altered by flooding in 1980 and 

 inlet closure and hypersalinity in 1984. 

 Wastewater inflows in the late 1980's had 

 even greater effects on the fish community 

 (Chapter 5). Changes in water salinity affect 

 the fishes directly by physiological stress and 

 indirectly by elimination of food items. 



Nordby (SDSU, unpubl. data) sampled 

 three sites for adult and juvenile fishes from 

 August to November, 1979, and from mid- 

 February through March, 1980, using a 1/4 

 inch mesh seine. Sampling was interrupted 

 from late November to mid-February due to 

 flooding, and the sampling effort was 

 abandoned after mid-March because of flood- 

 induced changes. The data from five sampling 

 dates were dominated by topsmelt and included 

 eight other species. During late January and 

 early February 1980, and again in mid- 

 February through March, major flooding 

 occurred in the estuary, lowering salinities to 

 ppt. Samples collected after the 1980 flood 

 had fewer species, with topsmelt and mullet 

 most abundant. These data support the 

 findings of other investigators in similar 

 habitats which indicate that species diversity 

 decreases after periods of reduced salinity 

 (Allen 1980, Onuf and Quammen 1983). 



The effects on fishes of the 1984 closure 

 to tidal flushing were examined in the fall of 

 1984 (Donohoe, unpubl. data). At this time 

 the mouth had been closed for approximately 

 six months. As previously mentioned, water 

 levels were lower than normal, salinities 

 were as high as 60 ppt, and many areas of 

 former mudflat were sunbaked and cracked. 

 Fish were collected by means of a 1/4 inch 

 mesh bag seine at seven locations. Of the 575 

 individuals measured, 74% were topsmelt, 

 22% were California killifish, and 4% were 

 longjaw mudsucker. All of the species 

 collected during mouth closure have wide 

 salinity tolerances (Zedler et. al. 1984b). It 

 is likely that gobies and mullet were 

 undersampled by this sampling technique. 

 Many gobies can take refuge in burrows or 

 pass through a 1/4 inch mesh seine, while 

 mullet can escape around or over most seines. 

 However, both Nordby and Donohoe used the 

 same sampling gear. Thus, it is clear that 

 diversity of fishes was lower in 1984 than in 

 the 1970's. 



The most abundant species collected in 

 1979-80 and in 1984 was topsmelt. A 

 comparison of the length-frequency 

 distributions of this species demonstrated 

 significantly smaller size during 1984 

 (Figure 3.23). Wastewater inflows in the 



53 



