864 



Fishery Bulletin 97(4), 1999 



(1964) was also employed. Gulland recommends us- 

 ing just the age groups that are best represented and 

 thus avoids errors due to a low representation of some 

 poorly sampled age groups. Some calculations were 

 repeated and the following tg values were obtained 

 for the 3-5 years age groups: -2.74 (females), -3.07 

 (males), -2.89 (both species, sexes combined); and 

 for the 3-6 age groups: -2.67 (females), -2.98 (males), 

 -2.85 (both species, sexes combined). 



The best fit was found with the t^ result calculated 

 for 3-6 years age groups. Thus, these values were 

 used to obtain the average ^q (Table 2). Use of the 

 Beverton^ equation improved the calculated values 

 in comparison with the values observed by Ford 

 (1933) Walford (1946), Tomlinson and Abramson 

 ( 1961 ), Allen ( 1966 ), Bayley ( 1977 ), and Prager ( 1987 ) 

 methods. 



The calculated curve that best fitted values ob- 

 served through otoliths corresponded to the para- 

 meters that were calculated with the Prager (1987) 

 method and fitted with the Beverton^ equation (Table 

 2). The calculated values of the lengths for different 

 ages as well as their standard deviation (SD) were 

 obtained by using these parameters for the two spe- 

 cies (Table 1) which are consistent and, in general, 

 show improved calculated values. Figure 2 presents 

 the theoretical growth curve for M. cephalus ages 

 0-6 years. 



During the first two years of life, striped mullet 

 grew rapidly in length, with average increases of 45.8 

 mm during the first year and 41.4 mm during the 

 second. From the third year on, growth decreased to 

 annual increases in total length of 37.5 mm. Increases 



between the third and fifth years varied from 34.0 to 

 30.8 mm. Between the fifth and sixth years the in- 

 crease was even smaller, with an average increase 

 of 27.8 mm. In general, growth was high during the 

 first two years of life and then decreased. This de- 

 crease is probably related to the time of first sexual 

 maturity, which for this species occurs from 280 to 

 299 mm TL (males and females, respectively), which 

 corresponds to an age of 3 years in both cases (Ibahez- 

 Aguirre and Gallardo-Cabello, 1996b). L^and k have 

 a negative correlation, whereas L,., is high, the growth 

 rate is low (Table 2). 



Mugil curema As can be seen in Table 3, L„ and k 

 values obtained with the Ford (1933) and Walford 

 ( 1946) method show the greatest difference with re- 

 spect to the values calculated by the Tomlinson and 

 Abramson (1961), Allen (1966), Prager (1987), 

 Beverton,' and Bayley (1977) methods. 



As with M. cephalus , new calculations for the t^ 

 value were made by using the Gulland ( 1964 ) method 

 for the 1-4, 3-5, and 2-4 years age groups; the fol- 

 lowing t^ values were obtained: for the 1-4 years age 

 groups -3.94 (females), -3.03 (males), -3.62 (both 

 species, sexes combined), for the 3-5 years age 

 groups: -3.73 (females), -2.77 (males), -3.41 (both 

 species, sexes combined) and for the 2-4 years age 

 groups -3.72 (females), -2.75 (males), -3.39 (both 

 species, sexes combined). 



The von Bertalanffy curves showed the best fit for 

 the calculated values of the 1-4 yr age groups. These 

 values were used to obtain average Iq. The Beverton' 

 equation with the above methods improved calcu- 

 lated values only in the case of the Ford (1933) and 

 Walford (1946) method. The calculated curve that 

 best fitted observed values through otoliths corre- 

 sponded to the parameters calculated with the Prager 

 ( 1987 ) method, as can be seen in Table 3. 



Using these parameters, we calculated values for 

 lengths at different ages, as well as their SD, which, 

 as in the case of M. cephalus, are consistent and, in 

 general, show improved calculated values (Table 1). 

 Figure 2 presents the theoretical curve for growth in 

 length of M. curema , for the ages of 0-5 years. 



A high increase in length was recorded during the 

 first year, after which growth decreased markedly. 

 Size increased by 27.5 mm TL between the second 

 and third years, 23.8 mm between the third and 

 fourth years, and 20.7 mm between the fourth and 

 fifth years. The decrease in growth from the first year 

 on is related to the first sexual maturity, which in 

 this species occurs in small sizes from 181 to 208 

 mm TL for males and females, respectively, at ages 

 "0" and "1" (Ibaiiez-Aguirre and Gallardo-Cabello, 

 1996b). 



