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Fishery Bulletin 98(3) 



Some evidence for the annual nature 

 of the increments seen in the otohths 

 of L. mahsena was found in the pattern 

 of the marginal increment through the 

 year (Fig. 7). This evidence was confirmed 

 by the unimodal distribution resulting 

 from edge analysis (Fig. 8 ), indicating that 

 opaque band formation was initiated once 

 a year, from May to August. 



For A. virescens, identification of the 

 pattern in marginal increments (Fig. 9) 

 was confused by the poor resolution of 

 the unstained sections and the relatively 

 small samples sizes, rendering the results 

 inconclusive. However, the unimodal plot 

 resulting from edge analysis on stained 

 specimens from this species indicated that 

 the transition between the translucent 

 and opaque bands occurred once a year 

 (Fig. 10), between October and March. 



From this evidence, we considered the 

 increments seen in the otoliths of both L. 

 mahsena from Mauritius and A. virescens 

 from Seychelles validated as annual deposits. 



Opaque zone deposition is thought to occur during peri- 

 ods of increased growth, whereas the corresponding "trans- 

 lucent zone" is formed during periods of low metabolic 

 activity (Beckman and Wilson, 1995). The period of opaque 

 zone initiation in L. mahsena from the Mauritian bank, 

 from May to August, corresponded to the season of the 

 southeast trade winds, a period of rough weather The 

 period of opaque zone deposition in A. virescens from Sey- 

 chelles, from October to March, coincided with the north- 

 west monsoon season from mid-November to mid-March. 



In reviews of otolith studies in tropical latitudes, Beck- 

 man and Wilson (1995) and Fowler (1995) found that, for 

 the majority of tropical species studied, the period of opaque 

 growth coincided with spring and summer months, as seen 

 in L. mahsena from the Mauritian bank. Aprion virescens 

 from Seychelles appears to contradict this general pattern 

 its opaque zone formation begins during winter months. 

 The authors also performed edge analysis studies for 1090 

 L. mahsena individuals from Seychelles (not presented). 

 These studies indicated that in this area, L. mahsena also 

 exhibits opaque zone initiation during winter Of the twenty- 

 nine tropical species reviewed by Fowler (1995), only four 

 showed opaque zone formation in the winter period. Timing 

 of opaque zone formation in these two species may be driven 

 by local phenomena. If opaque zone formation is linked with 

 increased food availability, the monsoon periods experienced 

 in Seychelles at this time, combined with local upwelling, may 

 improve local productivity and feeding conditions. Although 

 little empirical data exist to support this theory, algal blooms 

 have been identified around Seychelles at this time of year ' 



Although edge analysis indicated differences in the 

 timing of opaque zone deposition at Nazareth bank (Mau- 



700., 



600 



500 



"S 400. 



1-5 n 6+ 



May Jun Jul 

 Month 



Figure 7 



Marginal increment plot by month for L. mahsena. Mar- 

 ginal increment measured in VID units (pixels). Data segre- 

 gated as in Table 1. Error bars denote one standard error 



•* Tarbit, J. 1980. Demersal trawling in Seychelles waters. 

 Fisheries Bulletin 5, Fisheries Division, Seychelles. Seychelles 

 Fishing Authority, P.O. Box 449, Victoria, Mahe, Seychelles. 



ritius), and Seychelles (Figs. 8 and 10), patterns in the 

 marginal increment analysis for these locations were simi- 

 lar (Figs. 7 and 9). This similarity may result from the rel- 

 atively small data sets available for marginal increment 

 analysis, requiring ages to be grouped into age classes, 

 and the difficulty experienced in measuring the marginal 

 increment in A. virescens otoliths from Seychelles. Simi- 

 larities may therefore result from inadequacies in the data 

 that obscure the true pattern. 



The results of marginal increment analysis for P. fila- 

 mentosus were inconclusive because problems were expe- 

 rienced in identifying and measuring the outer zone in the 

 otolith. Staining did not improve the clarity of the zones 

 owing to the frequent appearance of "indeterminate incre- 

 ments." Validation was therefore considered to be unsuc- 

 cessful for P. filamentosus in Seychelles and contrasts with 

 that achieved in Hawaii where microincrements were used 

 (Ralston and Miyamoto. 1981, 1983). During our study, ini- 



