in abundance, particularly at IN. Because trawl 

 sampling effort was about the same each year, 

 total catch was also used as an index of relative 

 abundance for comparison among the six stations 

 (Table 29). Decreases of juveniles and adults were 



TABLE 19. Total number of cunner caught by trawl for each 

 station during each report period (June-May). 



apparent at the four stations closest to MNPS 

 (IN, NB, JC, and TT), but at BR numbers re- 

 mained stable over the period and they fluctuated 

 at NR. Most (57%) cunner were taken at IN, 

 where numbers began to decrease in the 1980-81 

 report period and decreased further in 1983-84. 

 Simultaneous decreases occurred at JC, TT, and 

 NB, 2 years after the decline at IN began. Al- 

 though causes for these declines may never be 

 known with certainty, physical alterations of the 

 habitat in the MNPS intake area near IN occurred 

 just before the decreases at that station and could 

 have accounted for the observed change. In 

 March 1975, a bottom fish boom was installed 

 at Unit 1 intake to reduce impingement. It was 

 unsuccessful and was removed in the spring of 

 1981 just before the initial decline at IN. The 

 Unit 3 cofferdam was constructed in March of 

 1976 and was removed in the summer of 1983 

 just before the second decline. Both of these 

 structures provided ideal habitats for cunner. Un- 

 fortunately, trawl monitoring was not done at IN 

 prior to the installation of these structures and it 

 could not be determined if these structures actually 

 caused an increase in the cunner population 

 around the MNPS intake. 



During the latest report period of 1986-87, the 

 mean length of cunner caught by trawl decreased 

 markedly at all stations, except at BR (Fig. 14), 

 indicating a reduction in the abundance of older 

 fish. To determine the age structure of the local 

 population at the three trawl stations where they 

 were most abundant (JC, NB, and IN), cunner 

 were assigned to age-classes using an age-length 

 key (Serchuk 1972). From 1976-77 through 

 1980-81, ages I, II, and III were dominant (Table 

 30). The low percentage of age (young- 

 of-the-year) during this time period indicated that 

 the trawl may not have sampled smaller individ- 

 uals as effectively as larger ones. In 1981-82, age 

 became the dominant age-class. The estimated 

 number of age fish was significantly correlated 

 to the 5-mean density of larvae at EN during the 

 same time period (Spearman rank correlation, 

 r = 0.71, p = 0.015). Although sample size was 

 small, over 80% of the cunner taken in 1986-87 

 at the three stations near MNPS were age 0. 

 These findings showed that older cunner were less 

 abundant near MNPS. This predominance of 

 younger fish and low abundance during the 

 1986-87 report period probably accounted for the 

 decease in eggs collected at EN during the same 

 period. 



TABLE 30. Percentage of cunner by estimated age-class 

 caught by trawl at JC, NB and IN combined during each 

 report period (June-May). 



Length-age key from Serchuck (1972) 



Data collected at SNPS were examined to de- 

 termine if trends in cunner abundance were similar 



286 



