FISHERY BULLETIN: VOL. 83, NO. 2 



at the deeper (137 m) stations near the outfalls but 

 not at the depth of the outfalls (61 m). The total 

 catch of Dover sole also declined at 137 m but not at 

 61 m. The declines in Dover sole abundance in the 

 long-term (1971-82) and deseasonalized quarterly 

 (1979-82) data coincide with declines in surface 

 sediment contamination and therefore are some- 

 what surprising. 



In southern California, Dover sole are an order 

 of magnitude more abundant around the outfalls 

 than in distant control areas. This probably is a 

 function of the distribution of their preferred prey 

 (polychaetes) which are more abundant around 

 the outfalls (Cross et al. in press). Pearcy and 

 Hancock (1978) found a positive correlation be- 

 tween the standing crop of Dover sole and the 

 standing crop of their preferred prey off Oregon. A 

 decrease in the quantity of sewage particles set- 

 tling at stations distant from the outfalls might 

 cause a reduction in the preferred prey popula- 

 tions accounting for the reduced abundance of 

 Dover sole. The decrease in organic content of sur- 

 face sediments at Tl, and the low value at TO, 

 which was within the ^5% confidence interval 

 (2.12-2.84% ) for reference areas in northern Santa 

 Monica Bay (Cross, unpubl. data), support this 

 hypothesis. 



The trends in fin erosion among calico rockfish 

 were different from those of the two soles. The 

 general increase in disease incidence may result 

 from differential susceptibility. 



Effect of Fin Erosion on 

 the Dover Sole Population 



Although fin erosion has been reported in fishes 

 from a number of areas around the world [south- 

 ern California, Puget Sound, and the New York 

 Bight (Sherwood 1982); Japan (Nakai et al. 1973); 

 and northern Europe (Perkins et al. 1972)], no one 

 has yet shown that the disease is harmful to the 

 affected individuals (Murchelano and Ziskowski 

 1982). 



Dover sole recruit to the study area between 

 February and May when they are 40-50 mm SL 

 (Allen and Mearns 1976; Sherwood 1980; Cross 

 unpubl. data). Fin erosion is negligible in new 

 recruits. By the time the fish are 80-100 mm BSL 

 [about 100 d after settlement, based on growth 

 curves presented in Sherwood (1980)], 18% have 

 the disease. The size distributions of Dover sole 

 with fin erosion are narrower than the size dis- 

 tributions offish without the disease (Fig. 3). Un- 

 derrepresentation in the lower tail of the size dis- 



tribution of Dover sole with the disease occurs 

 because the fish do not contract fin erosion until 

 sometime after settlement. Underrepresentation 

 in the upper tail suggests increased mortality 

 among fish with the disease. 



A size difference between Dover sole with and 

 without fin erosion was not detected in the data. 

 The x^ values increased with successive ages 

 suggesting a significant difference in the size- 

 frequency distributions may occur at an older age. 

 Dover sole older than 7 yr were rarely encountered 

 on the Palos Verdes shelf. 



No significant differences were found in the 

 weight-length relationships between males with 

 and without the disease and between females with 

 and without the disease. The significant difference 

 observed between males and females without the 

 disease is characteristic of Dover sole (Hagerman 

 1952). The lack of significant difference between 

 males and females with fin erosion is difficult to 

 interpret at this time. 



Fin erosion appears to have a detrimental effect 

 on the survival rate of Dover sole. Survival rates 

 for Dover sole with and without the disease were 

 similar up to 3 yr of age; thereafter, the survival 

 rate of diseased fish was significantly lower. 



CONCLUSIONS 



The data presented in this study suggest that 

 1) fin erosion is the result of exposure to contam- 

 inants discharged from the outfalls and 2) the 

 magnitude of disease incidence is directly related 

 to the magnitude of sediment contamination. Dis- 

 ease incidence and sediment contaminant con- 

 centrations decrease with increasing distance 

 from the outfalls. Disease incidence is negligible 

 in Dover sole recruits but increases rapidly with 

 increasing body size, and presumably contam- 

 inant exposure, after settlement. The number of 

 species affected by the disease, the disease inci- 

 dence in Dover sole, and the contaminant concen- 

 trations of surface sediments have declined over 

 time. 



While the prevalence of fin erosion has declined, 

 the disease remains a problem. Fin erosion was 

 observed in 5.99c of the fishes collected at 61 m and 

 137 m at T4 and T5 in 1982 and appears to affect at 

 least one population causing increased mor- 

 talities. 



Sindermann (1979) described fin erosion as 

 "Probably the best known but least understood 

 disease of fish from polluted waters... "(p. 719) and 

 concluded ". . .that generalized disease signs, such 



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