Abstract
Growth is one of the key processes in the dynamic of exploited resources, since it provides part of the information required for structured population models. Growth of mangrove cockle, Anadara tuberculosa was estimated through length-based methods (ELEFAN I y NSLCA) and using diverse shell length intervals (SLI). The variability of L(infinity), k and phi prime (phi') estimates and the effect of each sample were quantified by jackknife techniques. Results showed the same L(infinity) estimates from ELEFAN I and NSLCA across each SLI used, and all L(infinity) were within the expected range. On the contrary, k estimates differed between methods. Jackknife estimations uncovered the tendency of ELEFAN I to overestimate k with increases in SLI, and allowed the identification of differences in uncertainty (PE and CV) between both methods. The average values of phi' derived from NSCLA1.5 and length-age sources were similar and corresponded to ranges reported by other authors. Estimates of L(infinity), k and (phi' from NSCLA1.5 were 85.97 mm, 0.124/year and 2.953 with jackknife and 86.36mm de L(infinity), 0.110/year de k and 2.914 de phi' without jackknife, respectively. Based on the observed evidence and according to the biology of the species, NSCLA is suggested to be used with jackknife and a SLI of 1.5 mm as an ad hoc approach to estimate the growth parameters of mangrove cockle.
Highlights
Growth is one of the key processes in the dynamic of exploited resources, since it provides part of the information required for structured population models
This was observed in all the shell length intervals (SLI) used, except when the month of November was omitted from the estimation, which showed the maximum cockle sizes in the samples
In ELEFAN I there was a positive correlation between the growth rate and increases in the SLI, while for NSCLA the tendency was irregular (Fig. 1 a, c)
Summary
Growth is one of the key processes in the dynamic of exploited resources, since it provides part of the information required for structured population models (e.g. size or age). One of the approximations widely used during the past two decades to estimate the VBGM parameters (L∞ and k) are the so called length-based methods (LBM’s) or indirect methods (IM). IM represent a useful tool for growth studies in tropical species because tropical systems have less variable climatic conditions and age interpretation or model progression analysis based on length frequency distributions (LFD’s) is more difficult (LoweMcConell 1987, Leonce-Valencia & Defeo 1997). Félix-Pico et al 2007, Félix-Pico et al 2009) These studies have used direct methods (DM), IM, culture systems and mark-recapture methods. The length data necessary to create LFD’s are easy to obtain, facilitating the estimation of growth parameters. The application of the last method has been formalized by Galindo (2005), while ELEFAN I and NSCLA are part of the FISAT I and II software’s (Gayanilo et al 1995, 2004)
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