ROSENBERG: GROWTH OF JUVENILE ENGLISH SOLE 



YAQUINA BAY 



rfUm 



OCT NOV OEC ; JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC'JAN FEB MAR APR MAT JUN JUL AUG SEP 



1977 ! 1978 '• 1979 



Month of Recruitment 



Figure 9.— Distribution of Parophrys vetulus recruitment to 

 the sampled population in the Yaquina Bay estuary during 

 1978-79. Full recruitment to the sampling gear was estimated 

 to occur at 120 d of age. 



The other two studies (Westrheim 1955; Ken- 

 dall 1966) utilize the technique of following 

 modal progressions through time in length- 

 frequency distributions. These estimates are 

 strongly influenced by the efficiency of the sam- 

 pling gear. If the smaller fish are sampled less 

 efficiently than the larger, growth will be over- 

 estimated. Emigration of small individuals, 

 immigration of larger fish, and differential mor- 

 tality of small fish would all produce overesti- 

 mates of growth using this method. Also, length- 

 frequency modal progression may give variable 

 results dependent on the method of choosing the 

 modes. 



Variability in the size-at-age data was much 

 higher for fish sampled in the estuary compared 

 with those sampled in the open coastal area, but 

 the mean growth rates for fish from the two areas 

 were similar. Physical factors may affect growth 

 variability. Yaquina Bay has highly variable 

 temperature and salinity. Frey 4 found differ- 

 ences of up to 57.. salinity and 2°C between high 



and low tides in the lower bay. Bottom tempera- 

 ture in the estuary ranges between 5° and 15°C 

 through the year, and salinity from virtually to 

 347... At Moolach Beach in contrast, a more con- 

 stant environment may be expected. The open 

 coastal region does not have a large source of 

 freshwater to influence salinity and tempera- 

 ture. Huyer (1977) and Huyer and Smith (1978) 

 reported that bottom water salinity off the Ore- 

 gon coast fluctuates about 17.. from winter to 

 summer. Temperature varies from 6.5°C in sum- 

 mer, due to seasonal upwelling, to about 10°C in 

 winter. 



There are two ways in which growth variabil- 

 ity can be reduced. Either outlying individuals 

 have their growth rates altered towards the 

 mean or they are removed from the population. 

 Particularly good or bad growth conditions in an 

 area would affect the growth of all individuals, 

 and alter the mean. Emigration and mortality 

 are the two possible removal processes. The size- 

 at-age plot for Moolach Beach (Fig. 3) and other 

 data (Laroche and Holton 1979) indicate that 

 most P. vetulus juveniles move out of the near- 

 shore area at between 70 and 80 mm SL. Emi- 

 gration from the estuary appears to be at a larger 

 size, approximately 100 mm SL (Westrheim 

 1955; Olson and Pratt 1973). 



Predation in the estuary is probably low com- 

 pared with the open coast. Few large fishes are 

 regularly found in the bay, although birds may 

 be significant predators. Kuipers (1977), in a 

 study of an estuarine nursery for plaice in the 

 Wadden Sea, reported predation mortality to be 

 low in contrast to a coastal nursery area studied 

 by Steele and Edwards (1970). 



Finally, intraspecific competition may affect 

 growth. The estimated densities of juvenile Eng- 

 lish sole in the estuary are a consistent order of 

 magnitude greater than at Moolach Beach (Kry- 

 gier and Pearcy 5 ). Competition may potentially 



4 B. Frey, School of Oceanography, Oregon State University, 

 Corvallis, OR 97331, pers. commun. March 1980. 



5 E. E. Krygier and W. G. Pearcy, School of Oceanography, 

 Oregon State University, Corvallis, OR 97331, pers. commun. 

 March 1980. 



Table 2.— Summary of growth estimates from previous studies: the data has been recal- 

 culated so that direct comparisons can be made (see text). 



Location 



Size at 



1 yr of age 



(mm SL) 



Yaquina Bay, Oreg 

 Monterey Bay. Calif 

 Puget Sound, Wash 

 Puget Sound. Wash 



Daily growth rate 

 (mm/d) 



117 0.40 



108-126 0.36-0 43 



128 44 



— winter 48 



summer 0.73 



Source 



Westrheim 1956 

 Smith and Nttsos 1969 

 Van Cleve and El-Sayed 1969 

 Kendall 1966 



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