ELSEVIER Fisheries Research 22 (1995) 265-277

Estimation of age and growth of sardine, Sardina pilchardus ( Walbaum, 1792 ), larvae by reading daily

otolith increments

Jakov DulEiC Institute of Oceanography and Fisheries, set. I, MeftroviCa 63, Split, Croatia

Accepted 15 June 1994

Abstract

Surdina pilchardus (Walbaum, 1792) were sampled during the period February-Ma) 199 1 and in April 199 1 in the eastern part of the Adriatic and in the Bay of Biscay, respec- tively. Specimens were aged by means of growth rings in the sagittal otoliths. The Gom- pertz and Laird-Gompertz growth equations, commonly used in larval growth analysis, described the growth of this species in the length range sampled. The initial length of sar- dine larvae at time r=O for the Adriatic was 4.138 mm at a mean temperature, 7’, of 13.1O”C. The daily growth rate was found to be slightly higher in sardine larvae from the Bay of Biscay than in those from the Adriatic, but the difference was not statisticallq significant.

Keywords: !iardinapilchardus; Growth, fish; Age determination; Otoliths

1. Introduction

The sardine, Sardina pilchardus ( Walbaum, 1792 ), represents the main pelagic species of the purse-seine catch in the Croatian Adriatic.

Larval fish growth is of particular importance to population dynamics, espe- cially to recruitment and biological models incorporating environmental param- eters (Methot, 198 1 a; Houde, 1986, 1987 ).

Microscopic markings in thin sections of otoliths of fishes, with evidence that these marks present a record of daily growth (Pannella, 197 1, 1974)) provide an alternative means of ageing tropical species for which seasonal and annual growth rings are often hard to interpret. These marks are produced in many fishes

0165-7836,‘95/$09.50 0 1995 Elsevier Science B.V. All rights reserved XSDIOl65-7836(94)00316-O

266 J. DulM /Fisheries Research 22 (I 995) 265-277

(Struhsaker and Uchiyama, 1976; Brothers et al., 1976; Neilson et al., 1985; Jones and Brothers, 1987; Palomera et al., 1988; Karakiri and Westernhagen, 1989; Moksness and Wespestad, 1989). Counting otolith microincrements has been useful in estimating the growth of juvenile and larval fishes (Barkman, 1978; Methot, 1981b; Geffen, 1986; Jones, 1986).

Age and growth information on larval sardine, especially in the natural envi- ronment, is limited. Gamulin and Hure ( 1955 ) first observed sardine egg devel- opment at 13 “C and 18’ C in a natural environment. Blaxter ( 1969) reared sar- dine larvae from La Manche, at 10, 15, 16, 17 and 17.3”C, but did not provide any numerical data or mathematical estimates. From Blaxter’s growth graphs, Regner et al. ( 1987) mathematically determined the relationship between the length and age of larvae. RC ( 1983a) suggested the existence of daily growth in- crements in the otoliths of pilchard larvae and that these might be used to age field-capture specimens. More recently (RC, 1983b) the growth rates of sardine larvae and the thickness of daily units were found to vary in relation to the time of year. The daily nature of these microincrements in the otoliths of Sardina pil- chardus has been demonstrated by RC ( 1983a,b, 1984).

The objective of this study was to analyse and estimate the growth character- istics of sardine larvae from the Adriatic and the Bay of Biscay, from otolith rings. The significance of the difference in growth rate between sardine larvae from the Adriatic and those from the Bay of Biscay was tested as well as that of the differ- ence in the regression coefficients of linear growth equations. This should pro- vide the basis for future studies of sardine growth parameters and of the condi- tions that affect the renewal of this population in the Adriatic.

2. Materials and methods

2. I. Sampling

Sardine yolk-sac larvae and larvae were collected from the middle of the Ad- riatic and the Bay of Biscay, by the research vessels ‘Bios’ and ‘Cornide de Saa- vedra’, respectively. Between February and May 199 1, specimens were collected from the following locations in the middle of the Adriatic: ( 1) Kagtela Bay, (2) BraT: Channel, (3) Pelegrin and Pakleni otoci archipelago and (4) StonEica and B%evo Island (Fig. 1). These four locations are permanent stations where the Institute of Oceanography and Fisheries has performed hydrographic and plank- ton community investigations for more than 40 years.

Four methods of collection were used: ( 1) oblique tows from a maximum depth of 200 m to the surface using a 40 and 72 cm Bongo net with 0.260 and 0.333 mm mesh, (2) nektonic larvae were caught using gear specially made for this purpose with frame sides of 1 m and 1 mm mesh size, (3) by plankton net, mesh size 0.250 mm, with a circular aperture of 98 cm diameter and aperture surface 0.75 cm , and (4) by Hensen plankton net, mesh size 0.250 mm, bottom to surface hauls. Nektonic larvae were collected under artificial light of 250 and 400 W,

J. D&it /Fisheries Research 22 (1995) 265-277 261

Fig. 1. Area of investigation, Adriatic. A, KaStela Bay; B, BraE Channel; C, Pelegrin and Pakleni otoci archipelago; D, StonEica and Bikvo Island.

11. IO * 9. 8’ 7’ 6’ 5’

Fig. 2. Area of investigation, the Bay of Biscay.

fishing for about half an hour at Pantan in Kagtela Bay. Four gear types were used to obtain a wide length range of larvae (from the end of yolk-sac absorption to metamorphosis).

The total material from the Bay of Biscay was collected at Station 12, Transect 4, area Gijon-Ortega& during a SARP pilot study for sardine off north and north- west Spain in April/May 199 1 (Fig. 2 ). Specimen sampling was carried out by

268 J. DulcW /Fisheries Research 22 (1995) 265-277

double oblique Bongo net, mesh size 280 p and 200 pm in either a 40 cm or 72 cm diameter frame, respectively.

Hydrographic sampling was carried out by CTD casts at selected stations in both areas. The mean surface temperature over the surveyed areas was 13.1 ‘C in the Adriatic and 11.8 ‘C in the Bay of Biscay.

Planktonic material from the middle of the Adriatic was preserved for a 0.5 h in 2% buffered formalin (pH 7.8-8.6). Thereafter larvae were transferred to 90% ethanol (after first having established that formaldehyde destroys otoliths, in agreement with findings of Radtke and Dean ( 1989) ). The material from the Bay of Biscay was preserved in 4% form01 of pH 8.6.

2.2. Length determination

A total of 160 sardine larvae from the Adriatic and 120 from the Bay of Biscay were examined. Specimens from the Adriatic contained some sardines at the end of metamorphosis, as shown by the furrows on the operculum characteristic of juvenile and adult fish.

Standard length was measured from the top of the mouth to the base of the notochord using a micrometer with loupe ocular at 10 x magnification. Shrink- ing of larvae in the formaldehyde was neglected in the length measurement. Re- duction in larval length caused by preservation depends on the initial lengths of the specimens and duration of storage. Preservation in formalin causes an aver- age 5% loss in standard length of larvae but preservation in ethanol does not af- fect length (McGurk, 1984).

2.3. Otoliths

Before removal of otoliths, larvae were rinsed in distilled water. Otoliths were removed from the otocysts using dissecting needles and placed in a drop of water. The distilled water was removed using line paper, and the otoliths were then moistened with immersion oil. In some cases, otoliths were polished using aliza- rin dissolved in alcohol to improve clarity. Otoliths were left in the immersion oil for 24 h since it has been found that otoliths are more easily read after storage in the oil. Rings were read at 450 x ,600 x and 1000 x magnification with a Reich- ert light microscope. Two workers read the otoliths to achieve higher precision; the percentage reading difference was negligible. The sagittae as viewed by light microscope revealed a pattern of alternating light and dark concentric rings sur- rounding a nucleus deposited in the earliest stages of development. One light and one dark ring visible all round the otolith were counted as one complete growth increment. Dark rings on the otolith edge were regarded as increments that were still forming and hence were counted as half a growth increment.

Data from the Adriatic and the Bay of Biscay were mathematically and statis- tically analysed. Age at length of larvae was estimated by common non-linear growth equations (Kramer and Zweifel, 1970; Regner, 1980).

J. DulEic /Fisheries Research 22 (1995) 265-277 269

3. Results

Sagittae in small sardine larvae were round, and in older larvae ellipsoidal. The nucleus was easily discernible in all sagittae. Two rings were visible in yolk-sac larvae at the initiation of yolk-sac absorption, and up to five rings in yolk-sac larvae at the end of yolk-sac absorption. These latter were taken as indicating larvae of zero age for the analysis of growth curves. Larval rings were counted from the ‘check ring’. Results of ring counts in the sagittae larvae from the Ad- riatic and the Bay of Biscay are presented in Tables 1 and 2, respectively.

3.1. Length at age in larvae

Two equations were used to describe length at age of sardine larvae. The first equation is after Gompertz ( 1825 ):

&=aexp( -h-‘*) (1)

where I, is the length of larvae at time t, a is the asymptote, and b and c are con- stants. The second equation is after Laird et al. ( 1965 ) :

&=Zoexp[ (A,/c) (1 -e-C’)] (2)

where 1, is the length of larvae at time t = 0, A0 is the instantaneous growth rate at time t=O, and c is the same constant as in Eq. ( 1). Function parameters were calculated from the data on age obtained from otolith readings and on length of larvae, by an iterative procedure using the FIT program (S. Regner, unpublished data, 1987).

Values for the parameters in Eqs. ( 1) and (2) are given in Table 3 for the Adriatic and in Tables 4 and 5 for the Bay of Biscay. For the latter location, Table 4 depicts the values of both functions for all the data, and Table 5 only the data for 7-day-old larvae, since up to that day larvae were more numerous per unit age.

Both functions show high coefficients of correlation at the 99% significance level with the data obtained from otolith counts and length measurements in lar- vae from the Adriatic and the Bay of Biscay. The initial length of larvae at time t = 0 was 4.138 mm at a mean temperature T of 13.10” C in the Adriatic. The mean length of captured yolk-sac larvae at the transition to larvae was 4.87 mm. In terms of statistical significance, this means that the measured value of initial length is quite close to the actual initial length. The values of initial length of larvae at time t = 0 obtained for the Bay of Biscay were useless because no zero or 1 -day-old larvae were collected. Graphical representation of the data fitted by the Gompertz function is given in Fig. 3 for the Adriatic and in Fig. 4 for the Bay of Biscay.

The differentiation of values obtained by the Gompertz function by means of the expression

270 J. DulEic /Fisheries Research 22 (I 995) 265-277

Table 1 Number of daily rings and the length range of sardine larva-Adriatic

Number of rings

(days)

No. of larvae Length range

(mm)

Mean length

(mm)

0 7 4.06-5.67 4.87 2 2 5.39-5.42 5.41 2.5 3 5.42-5.84 5.61 3 17 4.58-7.22 5.86 3.5 6 5.62-6.55 5.89 4 32 5.56-8.33 6.60 4.5 9 6.1 l-9.72 7.19 5 26 6.81-10.83 8.43 5.5 2 8.33-10.14 9.24 6 8 6.67-12.92 9.46 6.5 2 9.31-10.56 9.94 7 5 9.31-14.17 12.17 8 2 12.50-14.45 13.48 9 1 13.61 13.61

10 1 15.97 15.97 11 1 15.64 15.64 12 1 17.50 17.50 14.5 1 17.64 17.64 18 1 19.45 19.45 20 1 21.25 21.25 24 1 21.11 21.11 29 1 23.34 23.34 30 1 24.17 24.17 32 1 21.09 27.09 33 1 26.81 26.81 35 3 22.36-24.59 23.61 36 3 24.31-27.22 24.31 38 2 26.67-29.17 21.92 39 2 23.89-24.86 24.86 41 2 27.09-28.47 27.87 42 2 25.84-27.92 26.88 45 1 27.09 27.09 46.5 1 27.43 21.43 53 1 29.86 29.86 55 3 26.1 l-28.75 21.82 56 2 30.56-31.39 30.98 57 2 28.56-35.89 32.39 59 1 31.25 31.25 61 1 32.36 32.36 64 1 34.03 34.03

J. DuW /Fisheries Research 22 (1995) 265-2 77 271

Table 2 Number of daily rings and the length range of sardine larvae-Bay of Biscay

Number of rings

(days)

No. of larvae Length range

(mm)

Mean length

(mm)

2 3 3.61-3.89 3.80 3 6 3.61-4.86 4.40 3.5 2 4.45-4.86 4.70 4 8 4.17-6.39 5.23 4.5 2 5.56-6.39 5.98 5 8 6.53-8.75 7.34 5.5 5 7.08-8.75 7.89 6 27 7.22-l 1.81 9.79 6.5 4 9.72-l 1.81 10.84 7 18 9.03- 14.03 10.97 7.5 3 9.72-11.53 10.41 8 5 9.85-l 3.61 12.17 8.5 4 10.97-12.92 11.74 9 6 10.83-15.97 12.99 9.5 1 15.97 15.97

10 3 12.78-13.89 14.31 10.5 1 13.89 13.89 11 2 11.81-14.17 12.99 12 2 14.17-16.39 15.28 15 2 14.03-17.36 15.70 17.5 1 17.22 17.22 18 2 15.28-18.06 16.67 20 2 15.28-17.78 16.53 20.5 1 20.00 20.00 22 1 19.42 19.42 26.5 1 23.06 23.06

Table 3 Estimated values of Gompertz and Laird-Gompertz functions-Adriatic

Gompertz i9.58856

b 1.967218

P kO8410072 b.982 i 0.00 1

Laird-Gompertz 10 Ao P 4.138228 0.1654595 kO8411218 b.982 <O.OOl

Table 4 Estimated values of Gompertz and Laird-Gompertz functions-Bay of Biscay (all the data)

Gompertz a 18.19694

b 2.934296

P k.2449932 L.939 <O.OOl

Laid-Gompertz 10 Ao C P 0.9660789 0.7194761 0.24508 11 L.939 10.001

272 J. D&W /Fisheries Research 22 (1995) 265-277

Table 5 Estimated values of Gompertz and Laird-Gompertz functions-Bay of Biscay (data on 7-day-old sardine larvae)

Gompertz f9.6175

b 3.304057 :. 1759623 i.923

P io.001

Laird-Gompertz Ll Ao P 1.086755 0.582053 :.I761917 L.923 CO.001

0.00 1”“,““,““,““,,,,,~,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,~ 0 5 IO 15 20 25 30 35 LO I.5 50 55 60 65

DAYS

Fig. 3. Growth of sardine larvae in the Adriatic observed (asterisks) and estimated, by Gompertz and Laird-Gompertz functions (solid line). Age was estimated from the number of daily growth rings in otoliths.

d_6y_Yi-Yi-1 -6X-Xi -Xi_ 1 (3)

where yi and Xi are ith values, and yi_, and Xi_, are the preceding values, allowed estimation of the growth rate of larvae, i.e. their daily growth increment. The daily growth rate was found to be higher in larvae from the Bay of Biscay than in those from the Adriatic. The greatest increments were recorded for 7-day-old ( 1.9 1 mm) larvae from the Bay of Biscay, and for 9-day-old (0.92 mm) larvae from the Adriatic. This is shown in Fig. 5.

The linear form of the Gompertz function was used to establish statistically significant differences in the growth rate of larvae by the method of linear regres- sion for higher y values per x value (Solcal and Rohlf, 1969). Only data for larvae up to 12 days old were considered, since the data for that period were relatively most homogeneous both for the Adriatic and for the Bay of Biscay. An F-test was performed to determine the difference between two regression coefficients. The

J. DulEiC /Fisheries Research 22 (1995) 265-2 77 273

. 7 g 2000

E .

a r,c_______________---__-____-------

5 2

Fig. 4. Growth of sardine larvae in the Bay of Biscay observed (triangles) and estimated, by Gom- pertz and Land-Gompertz functions (solid line, values of both functions for all the data; dashed line, values of both functions only for data by the seventh day of age of sardine larvae). Age was estimated from the number of daily growth rings in otoliths.

2500

7 E 2900 _

z

5 i 1500

z

2 z 1000

5 00

7

Fig. 5. Daily growth increments of sardine larvae from the Adriatic (- - - ) and the Bay of Biscay (- . -).

274 J. Dulfic /Fisheries Research 22 (1995) 265-277

value of F, was 0.0902, and the values of I;11( 1,226j for PC 0.001 and P< 0.05 were 10.8 and 3.84, respectively. Since both values of F,(,,226j exceeded the value of F, there is no statistically significant difference between the regression coefficients.

The age of larvae, from fertilization, was obtained by adding egg development time and age obtained from otolith reading in yolk-sac larvae to the age obtained from otolith rings in larvae, i.e. to the relative age. Age could be calculated for larvae from the Adriatic. Yolk-sac larval age obtained by otolith reading was 4.5 days and egg development time was 3.5 days at temperature T of 13.lO”C, ob- tained by the equation of the relationship between egg development and temper- ature (Regner et al., 198 1). Therefore, 8 days should be added to the age deter- mined by otolith examination. This was not possible for the larvae from the Bay of Biscay because the material contained no yolk-sac larvae at the end of yolk-sac absorption.

4. Discussion

Sardine growth and development rates can be determined by analysis of otolith increments, which can be counted and measured with a light microscope or scan- ning electron microscope (SEM) . The light microscope is relatively simple and can be used routinely for large numbers of samples. In this study the technique was used successfully for all routine counts. Under light microscopy transmitted light is refracted at obtuse angles at the otolith edge because of its curved surface. As a result, microincrements may be difficult to distinguish when faint bounda- ries occur. When using SEM, visual artifacts do not occur, and increments that are not easily discerned with a light microscope can be seen clearly (Campana and Neilson, 1985). Otolith increment width measurements are more precise when digitized from SEM photographs or video-taped images than when mea- sured with a light microscope (Campana and Moksness, 199 1). However, exten- sive use of SEM for field surveys is impractical because of the cost and prepara- tion time required. Confirmation of light microscope counts by SEM is highly desirable.

All published studies indicate that otolith increments are formed at different developmental stages but are characteristic of the species being studied. Some species hatch with increments already formed, while others do not form incre- ments until yolk-sac absorption. For several clupeiform species, it has been shown that the first daily increment is normally deposited at the end of the yolk-sac absorption period (Brothers et al., 1976; Methot and Kramer, 1979; Alshuth, 1988). Otoliths form early in sardine larvae, but in the present study no rings were found before hatching. The rings observed (2-5) between the beginning and end of yolk-sac absorption, around the central core of sagittae of sardine yolk-sac larvae, suggest a daily growth rhythm during the yolk-sac larval stage. Such rings are frequent in the sagittae of yolk-sac larvae of anchovy, Engruulis encrusicolus L. (Palomera et al., 1988), and may have been deposited either in the embryo, as suggested by Brothers and McFarland ( 198 1) for Haemulon j&z-

J. DulEii /Fisheries Research 22 (1995) 265-277 275

volineatus and by Radtke and Dean ( 1982) for Fundulus heteroclitus, or in the stage preceding yolk-sac absorption as suggested by McGurk ( 1984) for CZupea harengw palfasi. RC ( 1984) suggested that otolith ring formation was probably initiated at a sardine larval length of about 5.5-6 mm, the size of sardine larvae at the time of yolk-sac absorption (3-5 days after hatching).

As to the statistically significant high correlation coefficients (r=0.982, r=0.923 ), the Gompertz and Laird-Gompertz functions describe the growth of sardine very well. The growth of larvae may be well described only at constant temperatures and food concentrations. The relationship between instantaneous growth rate and temperature being known, the growth of larvae at different tem- peratures may be calculated if the parameter c in these equations is replaced by the equations of their relationship to temperature. Temperature affects not only the variations in instantaneous growth rate but also the values of the asymptote and of initial length. The mean temperature was 13.10” C for the entire Adriatic study area; the standard deviation was 0.3268 and variability coefficient 2.48. This suggests that this marine environment was constantly homogeneous during that period. The mean temperature obtained fits the range of optimum sardine spawning temperature, 12.1-13.9”C (Regner et al., 1987). Accordingly, an even- tual temperature effect on the variations in growth rate could not be neglected in this instance. As shown by the F-test results, the regressions in themselves are statistically significant, whereas the differences between them are not. The data for the Bay of Biscay are far less reliable, even though the non-significance of the difference supplies at least some information on the actual situation. The growth of the larvae from the Bay of Biscay was slowed down earlier because they reached metamorphosis sooner than those from the Adriatic. Even though this difference is not statistically significant, it may be assumed to be an indicator of the possible influence of temperature and food availability differences in the areas investi- gated. The estimated values, in this study, of the asymptote were 4.138 mm at 13.10” C at transition of yolk-sac larvae to larvae for the Adriatic sardine, and 29.59 mm at the transition to the juvenile stage. Characteristics of sardine yolk- sac and larval growth were calculated using graphical presentations of growth as proposed by Blaxter, the value of the asymptote for yolk-sac larvae at 14’ C was 5.17 mm and for larvae 47.00 mm (Regner et al., 1987). These calculated param- eters ( ZO= 5.17 mm, a = 47.00 mm) were used in estimating larval mortality of sardine in the Adriatic by calculating the coefficient of regression between the mean age of individual embryonic stage or length group of larval stages and the natural logarithm of the number of individuals under a square metre per day (Regner et al., 1987). Differences in the parameters of asymptotes calculated in this study and by Regner et al. ( 1987) (for reared sardine larvae from La Manche) suggest that the larval mortality in the Adriatic had been underestimated. Regner at al. ( 1987) simply used the data presented in the paper by Blaxter ( 1969) for calculating the parameters of the Gompertz equations for larval stage growth rate in the Adriatic and no separate experiments or field investigations in the Adriatic were performed to obtain these data. The equations obtained by Regner et al. ( 1987) may be used only for a rough age estimate of a length group on the basis

276 J. DulEic /Fisheries Research 22 (199s) 265-277

of which instantaneous mortality rate was calculated. As distinct from the results of this study, Re ( 1983a, 1984) obtained a linear relationship between total length of sardine larvae and daily rings (r=0.973, n=37; r=0.936, n= 110). The linear relationship may reflect a statistically insufficient sample. In fact, the specimens of the length ranges (total length 7- 18 mm and 8-26 mm) whose growth could be shown by only linear equations, were taken into consideration.

References

Alshuth, S., 1988. Daily growth increments on otoliths of laboratory-reared sprat, Sprattus sprattus L., larvae. Meeresforsch. Rep. Mar. Res., 32: 23-29.

Barkman, R.C., 1978. The use of otolith growth rings to age young Atlantic silversides, Menidia men- idia. Trans. Am. Fish. Sot., 107: 790-792.

Blaxter, J.H.S., 1969. Experimental rearing of pilchard larvae, Sardinapilchardus. J. Mar. Biol. Assoc. UK, 46: 2 19-234.

Brothers, E.B. and McFarland, W.N., 198 1. Correlations between otolith microstructure, growth and life history transitions in newly recruited French grunts (Haemulonflavolineatum). Rapp. P.-V. Reun. Cons. Int. Explor. Mer, 78: 369-374.

Brothers, E.B., Mathews, C.P. and Lasker, R., 1976. Daily growth increments in otoliths from larval and adult fishes. Fish. Bull., 74: l-8.

Campana, S.E. and Moksness, E., 199 1. Accuracy and precision of age and hatch date estimates from otolith microstructure examination. ICES J. Mar. Sci., 48: 303-316.

Campana, S.E. and Neilson, J.D., 1985. Microstructure of fish otoliths. Can. J. Fish. Aquat. Sci., 42: 1014-1032.

Gamulin, T. and Hure, J., 1955. Contribution a la connaissance de l’ecologie de la ponte de la sardine (Sardina pilchardus Walb. ) dans l’Adriatique. Acta Adriat., 7: l-23.

Geffen, A J., 1986. The growth of herring larvae, C’fupea harengus L., in the Clyde: an assessment of the suitability of otolith ageing methods. J. Fish Biol., 28: 279-288.

Gompertz, B., 1825. On the nature of the function expressive of the low of human mortality, and on the mode of determining the value of live contingencies. Phil. Trans. R. Sot. Land., 115: 53 l-585.

Houde, E.D., 1986. Potential for growth, duration of early life stages and regulation of recruitment in marine fish. Int. Coun. Explor. Sea ICES CM 1986/L, 28 pp.

Houde, E.D., 1987. Fish early life dynamics and recruitment variability. Am. Fish. Sot. Symp., 2: 17- 29.

Jones, C., 1986. Determining age of larval fish with the otolith increment technique. Fish. Bull., 84: 91-103.

Jones, C. and Brothers, E.B., 1987. Validation of the otolith increment ageing technique for striped bass, Morone saxatilis, larvae reared under suboptimal feeding conditions. Fish. Bull., 85: 171- 178.

Karakiri, M. and von Westemhagen, H., 1989. Daily growth patterns in otoliths of larval and juvenile plaice (Pleuronectesplatessa L.): influence of temperature, salinity and light conditions. Rapp. P.- V. Reun. Cons. Int. Explor. Mer, 191: 376-382.

Kramer, D. and Zweifel, J.R., 1970. Growth of anchovy larvae (Engraulis mordax Girard) in the laboratory as influenced by temperature. Calif. Coop. Oceanic Fish. Invest. Rep., 14: 84-87.

Laird, A., Tyler, S.A. and Barton, A.D., 1965. Dynamics of normal growth. Growth, 29: 233-248. McGurk, M.D., 1984. Ring deposition in the otoliths of larval Pacific herring, Ciupea harengus pal-

lassi. Fish. Bull., 82: 113-120. Methot, R.E., 1981a. Growth rates and age distributions of larval and juvenile northern anchovy

Engraufis mordax, with inferences on larval survival. Thesis, University of California, San Diego, CA.

Methot, R.D., Jr., 1981b. Spatial covariation of daily growth rates of larval northern anchovy, En-

J. D&k /Fisheries Research 22 (1995) 265-277 277

graulis mordax, and the northern lampfish, Stenobrachius leucopsaurus. Rapp. P.-V. Reun. Cons. Penn. Int. Explor. Mer, 178: 424-431.

Methot, R.E. and Kramer, D., 1979. Growth of northern anchovy Engraulis encrasicholus larvae in the sea. Fish. Bull., 77: 413-423.

Moksness, E. and Wespestad, V., 1989. Ageing and back-calculating growth rates of Pacific herring, Clupea pallasii, larvae by reading daily otolith increments. Fish. Bull., 87: 509-5 15.

Neilson, J.D., Geen, G.H. and Bottom, D., 1985. Estuarine growth of juvenile chinook salmon (On- corynchus tshawytscha) as inferred from otolith microstructure. Can. J. Fish. Aquat. Sci., 42: 899- 908.

Palomera, l., Morales-Nin, B.M. and Lleonart, J., 1988. Larval growth of anchovy, Engraulis encras- icolus, in the Western Mediterranean Sea. Mar. Biol., 94: 283-29 1.

Pannella, Ci., 1971. Fish otoliths: daily growth layers and periodical patterns. Science, 173: 1124- 1127.

PannelIa, G., 1974. Otolith growth patterns: an aid in age determination in temperate and tropical fishes. In: T.B. Bagenal (Editor), The Ageing of Fish, D. Unwin, London, pp. 28-39.

Radtke, R. and Dean, J.M., 1982. Increment formation in the embryos, larvae and juveniles of mummchog, Fundulus heteroclitus. Fish. Bull., 50: 201-2 14.

Radtke, R. and Dean, J.M., 1989. Larval fish age, growth, and body shrinkage: information available from otoliths. Can. J. Fish. Aquat. Sci., 46: 1884-l 894.

Rt, P., 1983a. Daily growth increments in the sagitta of pilchard larvae Sardina pilchardus (Wal- baum, 1792) (Pisces: Clupeidae). Cybium, 7: 9- 15.

Rt, P., 1983b. Growth of pilchard larvae Sardina pilchardus (Walbaum, 1792) in relation to some environmental factors. Inv. Pesq., 47: 277-283.

RC, P., 1984. Evidence of daily and hourly growth in pilchard larvae based on otolith growth incre- ments, Sardinapilchardus (Walbaum, 1792). Cybium, 8: 33-38.

Regner, S., 1980. On semigraphic estimation of Gompertz function and its application on fish growth. Acta Adriat., 21: 227-236.

Regner, S., Piccinetti, C., Specchi, M. and SinovEiC, G., 198 1. Preliminary statistical analysis of sar- dine stock estimation from data obtained by egg surveys. FAO Fish. Rep., 253: 143-l 54.

Regner, S., KrSiniC, F., Marasovic I. and Regner, D., 1987. Spawning of sardine, Sardina pifchardus (Walbaum, 1792 ), in the Adriatic under upwelling conditions. Acta Adriat., 28: 16 l-l 99.

Sokal, R.R. and Rohlf, F.J., 1969. Biometry. W.H. Freeman, London, pp. l-776. Struhsaker, P. and Uchiyama, J.H., 1976. Age and growth of the nehu, Stolephoruspurpureus (Pisces:

Engraulidae), from the Hawaiian Islands as indicated by daily growth increments of sagittae. Fish. Bull., 74 9-17.