| Summary: | This research has a purpose to elucidate basic informations of the
Rhinoclavis sinensis population dynamics at Krakal Beach, Yogyakarta, such as:
(1) Studying the characteristics of population such as density, biomass,
reproductive pattern, age, age structure, sex ratio, life span of R. sinensis
temporarily from 2005 to 2008. (2) Studying the processes within population such
as growth rate, reproductive pattern recruitment pattern, mortality (natural
mortality and catch mortality) of R. sinensis. (3) Studying the respons of catching
to the population of R. sinensis. The field research was basically collecting snails
from residents every month, for the duration of four years from 2005 to 2008.
Further the laboratory researches were including characterization of reproductive
system such as the size of maturation, reproductive pattern based on gonad
index, and age determination using operculum. Length frequency data were
analized yearly and total four years using stock analysis such as: growth
parameter (K, t0, L00) natural mortality (M), fishing mortality (F), recruitment
pattern, age structure, yield per recruit (Y�/R) and biomass per recruit (B�/R)
prediction using FiSAT II. The relationship among research variables (density,
biomass, and Gonad Index) to physics and chemics of beach environment were
analyzed using ordination (Redundancy Analysis (RDA) and Canonical
Correspondence Analysis (CCA)) using Canoco. The research showed that the
population�s character of R. sinensis apparently increase year by year, with the
density of 28-55 individual per month with a range of 248-1627 individual per year
with an average 661 ± 647,24 individual per year. This was equal to yield�s range
of 519.89g � 5762.43g with an average of 2203,3 ± 2399,23 g per year. The ages
of first maturity snails were three years with the size of shell length about 28mm.
The lives span which are refrected by the operculum and age structure with an
average of 5+ years and maximum of 7+ years. This means that there are at
least two-four years for the snails to reproduce. Reproductive pattern of the
species was all year round, bimodal, with the gonad index reached its peak on
April and November with April as the highest. The sex ratio of female: male was
about 100: 150. Population processes elucidated were include the growth rate,
which was increased year by year with VBGF�s curvature, K, 0.41-0.49 with K
0.47 for four years. Recruit pattern had its peak on May and September. The
natural mortality, M, about 0.917-1.016 catch mortality, F, about 0.093-1.064, and
total mortality, Z, about 1.01-2.08, which means more snails can be yielded, with
exploitation ratio 0.2-0.89 or low, however since the K value was low, it is risky to
yield more. The survivorship rate, S, was about 0.125-0.364 or 12.5%-36.4% for
invertebrate with survivalship type III, this is categorized low. The effect of
catching of R. sinensis during four years of research was increased in number or
density of population, as a consequence, the value of MSY has predicted using
analisis holistic (Cadima formula).
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