Curtis: Validation of a method for estimating annual fecundity for Hippocampus guttu/atus 



335 



corresponded to months with warmer water tempera- 

 tures and higher primary and secondary production 

 (Sprung, 1994a, 1994bl, as observed in other fishes 

 (Bye, 1984; Milton and Blaber, 1990). The duration 

 of the reproductive season in the Ria Formosa lagoon 

 (March-November) was similar to that reported for 

 populations in southern Spain at a similar latitude 

 (March-October, 36.7°N; Reina-Hervas, 1989) but was 

 almost twice as long as in the higher latitude Arcachon 

 Basin population (May-September, 44.7°N; Boisseau, 

 1967). Among-population differences in the duration of 

 the reproductive season may be attributable to differ- 

 ences in temperature regimes (Robert et al., 1993) and 

 photoperiod. Although Boisseau (1967) suggested that 

 peaks in H. guttulatus reproductive activity occurred 

 during full moons in the Arcachon Basin, there was 

 no evidence of a correlation between lunar phase and 

 reproduction in the Ria Formosa. 



Models for estimating realized annual fecundity 



Neither assumption of the CR model (rapid remating 

 and continuous reproduction) was met empirically for H. 

 guttulatus (Table 1, Fig. 3). This means that accurate 

 estimates of realized annual fecundity in other seahorse 

 species of conservation concern (Foster and Vincent 

 2004; lUCN^) may require further biological research. 

 Annual spawning frequency and realized annual fecun- 

 dity may be overestimated by as much as 270*7? when the 

 assumptions of rapid remating or continuous reproduc- 

 tion have not been met (Table 1). Assumptions inherent 

 in the CR model may be more likely to hold for monoga- 

 mous species with short interbrood intervals (e.g., H. 

 ivhitei; Vincent and Sadler, 1995) that breed year round 

 in tropical environments (e.g., H. comes; Perante et al., 

 2002). Incorporating an estimate of interbrood interval 

 into the IR model produced intermediate estimates of 

 annual spawning frequency. However, estimates of inter- 

 brood intervals required considerable effort because of 

 the need to monitor changes in the reproductive activity 

 of individually tagged seahorses. Use of the ISR model 

 circumvented the need to directly estimate interbrood 

 intervals (see "Material and methods" section) and led 

 to unbiased estimates of spawning frequency for both 

 males and females. 



The success of the ISR model in predicting observed 

 estimates of male spawning frequency and the number 

 of days females spent preparing eggs indicates that 

 this model, based on the spawning fraction method 

 developed by Hunter and Leong (1981), may be broadly 

 applicable to all organisms for which batch fecundity 

 and the time to prepare or brood a clutch of eggs are 

 known. This model is suitable for species with broods 

 that can be readily and periodically surveyed by using 

 either fisheries-independent catches or underwater vi- 

 sual census techniques. Although fisheries-independent 

 collections were opportunistically used in this study 

 to estimate brood sizes and the fraction of spawning 

 males and females, reliable estimates of these values 

 were also obtained nondestructively by caging brood- 



ing males to count batch fecundity directly, and by 

 monitoring changes in the fraction of spawning males 

 and females over time with underwater visual cen- 

 suses (Fig. 3). For species at risk that can be surveyed 

 periodically during the reproductive season with non- 

 destructive fisheries-independent sampling (e.g., under- 

 water visual census), the generalized spawning fraction 

 method becomes a potentially effective and appropriate 

 means of estimating spawning frequency and realized 

 annual fecundity. 



Acknowledgments 



This is a contribution from Project Seahorse. I thank 

 K. Erzini and J. Ribeiro for providing their seahorse 

 catches, the Parque Natural da Ria Formosa for logistic 

 support, and R. Adams, H. Balasubramanian, K. Bigney, 

 J. d'Entremont, B. Gunn, S. Lemieux, C.-M. Lesage, 

 E. Murray, J. Nadeau, S. Overington, M. Veillette, K. 

 Wieckowski, and S. V. Santos for excellent assistance. 

 C Hall, D. O'Brien, and A. Vincent provided valuable 

 comments on this manuscript. Funding was provided 

 by Guylian, Natural Science and Engineering Research 

 Council, Fonds Quebecois de la Recherche sur la Nature 

 et les Technologies, and McGill University. 



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