CROSS: FIN EROSION AMONG FISHES 



Table lO. — Copper, cadmium, and chromium concentrations (ppm 

 dry weight) in surface sediments at the sampUng transects from 1975 

 to 1980. Note that the deeper samples were taken at 152 m while the 

 trawls were made at 137 m. Depth of sediments analyzed at bottom of 

 table. (SCCWRP, unpubl. data.) 



Table ll. — Mean organic content (percent) 

 of surface sediments at 61 m from 1972 to 

 1981 and correlation between organic content 

 and years, x = mean, SD = one standard 

 deviation, n = sample size, r = correlation 

 coefficient, P = probability that the calcu- 

 lated r came from a population with p = 0. 



coarser and lower in volatile solids in shallow 

 water, and become finer and higher in volatile 

 solids with increasing depth. Contaminants are 

 generally attached to the finer particles and thus 

 increase in concentration with increasing depth 

 (Hershelman et al. 1982). 



The incidence of fin erosion in Dover sole fol- 

 lowed the spatial pattern of sediment contaminant 

 distribution. The incidence was highest near the 

 outfalls (44.0% of all Dover sole collected at T4 and 

 37.3% at T5) and decreased with increasing dis- 

 tance upcoast (20.3% at Tl and 2.0% at TO). The 

 relationship between disease incidence and sedi- 

 ment contaminant levels suggests that fin erosion 

 is the result of contamination and that the inci- 

 dence of the disease is directly related to the mag- 

 nitude of contamination. Because preimpact data 

 do not exist, gradients of contamination and dis- 

 ease are assumed not to have existed before sew- 

 age discharge began. It is generally accepted that 

 the presence of fin erosion in the environment is 

 the result of contamination (Murchelano and Zis- 

 kowski 1976; Sindermann 1979). Controlled 

 laboratory experiments demonstrated that Dover 

 sole exposed to sediments from the Palos Verdes 

 shelf developed fin erosion (Sherwood 1976; 

 Mearns and Sherwood 1977). 



Temporal Disease Patterns 



The number of species affected by fin erosion 

 declined significantly from 1971 to 1982 and was 

 most rapid from 1971 to 1974 following the waste- 

 water treatment modifications made in the early 

 1970's. This pattern suggests that the decline was 

 related to reduced surface sediment contamina- 

 tion. 



The incidence of fin erosion also declined in two 

 of the three most affected species (Dover and rex 

 soles). The declines were greater at Tl than at T4 

 or T5; the incidence of the disease at TO, the sta- 

 tion farthest from the outfalls, was always low. 

 There was a significant correlation between the 

 sediment concentration of DDT (Table 9) and the 

 proportion of Dover sole with fin erosion (deter- 

 mined by dividing the total number of Dover sole 

 with the disease by the total number of Dover sole 

 collected within a year) at T4-61 m (Spearman 

 r = 0.821, n = 1, 0.02 <P < 0.05). 



s 



The seasonal trends in the catch of Dover sole 

 and the number of Dover sole with fin erosion are 

 the result of recruitment and depth-related mi- 

 grations. Recruitment occurs at 61 and 137 m, but 

 more fish settle out at 137 m. The magnitude of the 

 seasonal swing appears greater at 61 m where few 

 Dover sole were captured in the first and fourth 

 quarters. Large numbers of Dover sole were col- 

 lected at 137 m in the fourth quarter but, by the 

 first quarter, the catches had declined substan- 

 tially. Dover sole apparently move off the shelf into 

 deeper water in the winter and back onto the shelf 

 in the summer. Hagerfnan (1952) reported an an- 

 nual depth-related migration of Dover sole into 

 deeper water in the winter related to reproduction 

 and a return migration into shallower water in the 

 summer related to feeding. 



Examination of the deseasonalized data re- 

 vealed that fin erosion declined over the last 4 yr 



203 



