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Fishery Bulletin 101(4) 



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B 



4ab "' 



-1 1 — 



II i: 



Ni n: si s: 



<» A 



Nl 



N2 N3 



Fishing area 



Figure 4 



Standard length ±standard error as a function of fishing area in (A) 1998 and 

 (B)1999. Letters indicate where significant differences lie at P<0.05. 



Population structure 



We assessed population structure in terms of size cohorts, 

 life history stages, sex ratio (males/total) and reproductive 

 status. Standard-length frequency histograms suggested 

 that the 1998 bycatch was composed of three year classes 

 but the largest of these was not evident in 1999 (Fig. 5). 

 Of 530 seahorses measured, 87.7% were considered to be 

 adults. The ratio of juveniles to adults did not differ by year 

 (P>0.10) or tidal phase (P>0.90). However, significantly 

 more juveniles were caught during the first quarter than 

 during other lunar phases (Table 3). Fishing area had a 

 significant effect on size class, with the highest numbers 

 of juveniles caught in N2 and N3 (Table 3). 



The sex ratio (males as fraction of total) of 0.42 differed 

 significantly from a 1:1 ratio (;t:;-^= 19.56, df=l. P<0.001). 

 The sex ratio did not vary temporally or spatially (Table 

 3), but it did vary as a function of size class. There were 

 proportionally more males in the larger size class (>150 

 mm, 0.61) than in the smaller size class (<150 mm, 0.30) 

 (X,^=14.95, df=l,P<0.005). 



About 25% of the male seahorses captured in 1998 were 

 considered to be reproductively active, whereas fewer 

 than 1% were reproductively active in 1999. Indeed, male 

 reproductive activity was higher in 1998 than 1999 even 

 after controUing for smaller male size in 1999 (Table 3). The 

 proportion of reproductively active males did not vary with 

 lunar or tidal phase but did vary significantly with area 



