CHRISTENSEN: TROPHIC RELATIONSHIPS OF SPARID FISHES 



population and so growth rates were not esti- 

 mated. The age of three immature specimens was 

 determined as being 1+ years old (107 and 108 

 mm SL) and 2+ years old (164 mm SL). 



Diplodus cervinus 



The length-frequency distribution is given in 

 Figure 4. The total pooled sample shows that this 

 species first appears in the littoral zone when 

 about 8 mm long and leaves again when about 140 

 mm long. Large fish were observed to move into 

 the intertidal area after low tide, as was the case 

 with D. Sargus, but no specimens were obtained. 



Monthly modes were observed, which are age- 

 classes 0-^, 1 + , and 2+ (Figure 4). Recruitment of 

 juveniles into the tide pools is discontinuous, oc- 

 curring between August and November, with a 

 peak in October. Two fish sampled in August ( 132 

 and 129 mm SL) had just formed the second ring, 

 giving the approximate time of scale-ring forma- 

 tion. The estimated average growth rate as deter- 

 mined for mode 1+ is 45 mm from February to 

 December, which is about 54 mm/yr. 



10 

 5 





 3 



5 



3 



Total 

 n=67 



2* ^n fi 



y^^ 



Mar- .n 

 n=17 



A^ 



Apr. 

 n = 5 



May 



n=1 



^'*»^'''^^^^ 



Jun. 

 n = 3 



Jul. 



Jl=ji 



.-^ iTs^A A 



Aug 

 n = 8 



Sep 

 n=0 



Oct. „ 

 n=7 



Oh 



^/ilA 



Nov. 

 n=12 



, ^> <^^ . 





Dec. 

 n = 5 



50 100 



Standard Length (mm) 



150 



Sarpa salpa 



The length-frequency distribution shows that 

 the majority of the population is from 9 to 45 mm 

 SL (Figure 5). The juveniles appear in the intertid- 

 al when 2=9 mm, and fish >100 mm were never 

 observed in the littoral at low tide; two specimens 

 of age-class 2 -I- were collected 4 h after low tide. 



Three age-classes were observed, labelled as + , 

 1 + , and 2 + . Recruitment of juveniles into the tide 

 pools is discontinuous, occurring between June 

 and September. Age-classes H- and 2+ were ap- 

 proximately % and iy2 yr old, respectively, when 

 sampled. The time of scale-ring formation is then 

 likely to have been about June. The average 

 growth rate is estimated to be 45 mm in 5 mo, or 

 108 mm/yr for the age-class 0-I-. Two fish were 

 obtained in April 1976 with lengths of 68 and 76 

 mm, which indicates that the estimate may be 

 slightly high, the predicted length being 81 mm. 



DIETARY COMPOSITION 



The composition of the diet is illustrated by oc- 

 currence and CFI values scaled down to percent- 

 ages. 



30" 

 20 

 10 

 0' 

 3 



3 



■Si 3 

 IT 



•b 3 



10 



10 

 5 



^^^^ i> 



Total 

 2* n=116 



Feb. 



Mar. 



n=2 



Apr 

 May 



j}=L 



JiJi 



n=1 



Z^ 



Jul. 



J1=S 



^>N. 



Aug 



il=33 



Sep. 



^A. 



ii=i 



Oct. 



_Q=]a 



^\r^ 



Nov. 



n=11 



Dec 



n=A 



50 100 



Standard Length (mm) 



150 



Figure 4. — Monthly and total length -frequency distribution of 

 Diplodus cervinus , showing three age-classes ( -(- , 1 -f , and 2 + ). 



FIGURE 5. — Monthly and total length-frequency distribution of 

 Sarpa salpa, showing three age-classes (0-I-, l-i-, and 2 + ). 



393 



