

FIN EROSION AMONG FISHES COLLECTED NEAR 

 A SOUTHERN CALIFORNIA MUNICIPAL WASTEWATER OUTFALL 



(1971-82)* 



Jeffrey N. Cross ^ 



ABSTRACT 



In the Southern Cahfornia Bight, fin erosion is most frequently encountered among fishes collected 

 near municipal wastewater outfalls. This paper presents an analysis of the trends in the incidence of fin 

 erosion among fishes collected by otter trawls near Los Angeles from 1971 through 1982. 



About 24% of the 122 species offish and 9% of the more than 170,000 individuals collected had the 

 disease. Flatfish (Pleuronectidae, Bothidae, and Cynoglossidae) and rockfish (Scorpaenidae) accounted 

 for 66% of the affected species and 99% of the affected individuals. Dover sole (Pleuronectidae: 

 Microstomus pacificus ) accounted for 89% of the affected individuals. 



The incidence of fin erosion was highest close to the outfalls and declined with increasing distance. 

 The number of species with the disease declined from 1971 to 1982. The incidence of the disease also 

 declined in two of the three most affected species (Dover sole and rex sole, Glyptocephalus zachirus). 

 The contemporaneous decline in the number of species and the proportion of individuals with the 

 disease and the decline in surface sediment contaminant levels suggest that the magnitude of contami- 

 nation and the incidence of fin erosion are directly related. 



The effect of fin erosion on the Dover sole population was examined. Dover sole recruit to the study 

 area when they are 40-50 mm SL; the incidence of fin erosion was negligible in new recruits but 

 increased rapidly with increasing fish size. No significant differences were detected in the length- 

 weight relationships or size-at-age data between Dover sole with and without the disease. Survival 

 rates of Dover sole with and without fin erosion were similar until age 3; thereafter, the survival rate of 

 diseased fish was significantly lower. 



Fin erosion in the Southern California Bight is 

 most prevalent in fish collected near major munic- 

 ipal wastewater outfalls. Of the major outfalls, the 

 disease is most frequently encountered around the 

 Joint Water Pollution Control Project (JWPCP) 

 outfalls on the Palos Verdes shelf (Mearns and 

 Sherwood 1974, 1977; Sherwood and Mearns 1977). 

 About 20% of the 151 species offish collected in the 

 Southern California Bight between 1969 and 1976 

 were affected by the disease. Flatfish (Pleuronec- 

 tidae, Bothidae, and Cynoglossidae) and rockfish 

 (Scorpaenidae) accounted for 60% of the affected 

 species and 97% of the affected individuals 

 (Mearns and Sherwood 1977; Sherwood 1978). 



Municipal wastewater discharge on the Palos 

 Verdes shelf began in the late 1930's. The mass 

 emission of suspended solids increased steadily 

 from about 17,000 metric tons (t) in the early 

 1940's to a peak of 167,000 t in 1971 (Wilson et al. 

 1980). Awareness of the problem of discharging 

 excessive amounts of solids and associated con- 



'Contribution No. 196, Southern California Coastal Water Re- 

 search Project. 



^Southern California Coastal Water Research Project, 646 W. 

 Pacific Coast Highway, Long Beach, CA 90806. 



taminants by JWPCP in the early 1970's resulted 

 in the installation of new equipment and more 

 effective treatment procedures to reduce solid 

 emissions. By 1981, discharge of suspended solids 

 had declined to 84,000 t. The mass emission of 

 contaminants also declined from 1971 to 1981 

 (Schafer 1982). Otter trawling, as part of a regular 

 monitoring program of the animals on the Palos 

 Verdes shelf, began in 1971. 



The purpose of this paper is to determine trends 

 in the incidence of fin erosion among fish collected 

 by otter trawls near the JWPCP outfalls from 1971 

 through 1982. The prevalence of the disease over 

 the size range of individuals collected and the ef- 

 fect of the disease on growth and survival are 

 examined for the most affected species. 



METHODS 



The data analyzed in this study were collected 

 by the Los Angeles County Sanitation District 

 (LACSD) during regular monitoring cruises on the 

 Palos Verdes shelf; station and transect identifica- 

 tions used herein are LACSD designations. Day- 

 time trawls were made at three depths (23, 61, and 



Manuscript accepted April 1984. 



FISHERY BULLETIN: VOL. 83, NO. 2, 1985. 



195 



