Preliminary Demography of the Whale Shark Rhincodon typus Smith, 1828
Pauly (2001) suggested k (VBGF)=0.031 yr-1 and a longevity of > 100 years which he considered to be rather high. The corresponding first year growth would be 0.39 m. The observed growth rate in captivity at the National Museum fo Marine Biology-Aquarium, Taiwan ROC was 0.81 cm in 120 days (Fang et al. 1996, AES New Orleans Abstract). The corresponding annual growth would be over 2m which I consider to be to high for growth in the wild. I guesstimated that first year growth of a a whale shark in the wild is 0.80 m, This would be about twice as high as what the Pauly (2001) VBGF suggests and roughly about 1/3 of what growth in captivity might have been in one year with feeding to satiation with a good soup of krill. This yields k (VBGF) = 0.0637 yr-1, in combination with TLo = 0.58 m (Joung et al. 1996) and TLoo= 13.7 m (Compagno, 1984). I further assume that maturity is reached at 70% of TL_{oo}, which would be 9.6 m with corresponding age-at-maturtiy of about 18 years. Age at first reproduction: 18 years. The litter size was 300 in a 10 m TL, 16000 kg female (Joung et
al. 1996, AES meeting New Orleans abstract). I assumed that the reproductive
cycle is 2 years which gives an effective annual female fecundity of 300/2x2)
= 75. The total litter mass was estimated to
be 300 kg, which is a mere 2% of the reported mass of 16000 kg of the
mother. A litter every year is a good possibility and the potential population growth
rate would be even higher. |
Solution using life history table or 55x55 Leslie matrix: |
Elasticities from life history table or 55x55 Leslie matrix E(fertility) = E(m) = E1 = 1/Abar = 0.0448; E(juvenile survival) = E(JS) = E2 = alpha * E1 = 0.8072 (ratio ER2 = alpha = 18.0); E(adult survival) = E(AS) = E3 = 1 - E2 = 0.1928 (ratio ER3 = Abar - alpha = 4.3); (E1 + E2 + E3 = 1.0448; ER2 + ER3 = Abar = 22.30); Normalized elasticities: E1 = 4.29%, E2 = 77.3%, E3 = 18.5%, E3/E2 = 0.239 |
April 2014. Finally updating with the following publication which includes elasticites for the whale shark: |