Growth, movement and recovery of tagged topshell, Trochus niloticus, juveniles in Imondayon, Anda, Pangasinan, Northern Philippines

Abstract

In the present study, the growth, movement and recovery rates of tagged wild Trochus niloticus juveniles were assessed after deployment in Imondayon, Anda, Pangasinan, in Northern Philippines. Two batches composed of 51 (35.88 mm shell diameter ± 3.60) and 35 (36.56 mm ± 3.73) juveniles were tagged and released into an intertidal flat with coral rubble near a sand bar in Imondayon reef on November 27, 2014 and December 18, 2014, respectively. In the first batch, only 5 live specimens were retrieved after 89 days (9.80% recovery rate). On the other hand, in the second batch a low recovery rate of 5.88% was observed after 68 days. Observed growth rates in both batches ranged from 0.052 to 0.096 mm/day, which is similar to that observed in other previous studies on same-sized juveniles. Some shells were also recovered dead but whole and with observed growth, which suggests predation by non-crushing predatory gastropods and/or hermit crabs. Wild trochus are cryptic and highly mobile, moving into deeper areas as they grow in size, which also explains the low recovery rates observed in the present study.