Individual Growth in the Patagonian Gastropod Buccinanops cochlidium (Nassariidae): A Field Tagging-Recapture Experiment

This study describes the growth of individuals in a population of Buccinanops cochlidium (Nassariidae) through the identification of the best-fitting growth model based on field tag-recaptured experimental data. A total of 48 individuals (8.6% of total tagged snails) were recaptured after 2 to 25 months, representing a remarkable proportion for a field experiment with infaunal organisms. The sex ratio was not different from 1:1. Males measured between 63.4 and 89.0 mm (n = 25), while females measured between 50.9 and 103.2 mm (n = 23) in shell length. The maximum annual length increment obtained was 35.74 mm, mean annual length increment was 4.51 and 8.43 mm for females and males, respectively. Because no statistically significant differences were found between male and female growth increments, a single growth model was fitted to the entire data set. Regarding individual growth modeling, the inverse Logistic (iLog) model adequately described the pattern in the data, but showed heteroscedasticity. A refitting of iLog using weighted least squares, weighted inverse Logistic (iLog*), better fit the data (and agrees with biological knowledge of B. cochlidium) than the inverse Logistic (iLog), exponential (Exp), von Bertalanffy (vB) and Gompertz (Gz) models. Estimated parameters for the iLog* model were MaxΔL: 27.83, L50: 69.89, L95: 93.36. The results of this study are valuable for assessment of snail fisheries in Patagonia and suggest fisheries management policies for a sustainable future of this potential stock prior to extensive exploitation.Fil: Averbuj, Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biología de Organismos Marinos; ArgentinaFil: Escati Peñaloza, Gabriela. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Penchaszadeh, Pablo Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales ; Argentin

Analysis of longitudinal growth increment data using mixed-effects models: Individual and spatial variability in a clam

Modeling growth is required in many ecological studies and stock assessment applications, but most fish and shellfish growth analyses focus on the estimation of average parameters, which do not provide a complete description of the growth of members of a population. We investigated individual and spatial variation of growth in striped clams (Ameghinomya antiqua) from San Jose Gulf (Argentine Patagonia) using series of growth ring measurements obtained from individual clams from seven populations (" longitudinal data" ). Data showed a clear geographical pattern, with two clusters of locations corresponding to domains separated by a thermal front. In the West Domain circulation is dominated by strong tidal-driven eddy flushing, temperature is lower during the growth season, and nutrient concentration and primary productivity are generally higher; circulation is sluggish in the East Domain. West of the front (i) growth rate of small clams and maximum growth rate are highest, and (ii) individual growth rate tends to peak at a smaller size and at a younger age. Evidence of an inflection point in growth rate prompted use of the Richards model, which has been frequently applied to benthic invertebrates for that reason. The model, however, had structural limitations and failed to fit the sharp inflection point. Differences in average parameter values, on the other hand, captured the variability between populations. While all individuals followed the same general growth pattern, there was high variability in individual growth profiles. Accounting for this variability through random effects in all growth parameters affected the estimated average parameters: predicted growth increments at size were larger initially, and the trend reversed after a certain size. Within-individual autocorrelation was not significant, a benefit of using growth increments instead of size-at-age data. We discuss between populations variation in relation to mesoscale environmental gradients, the use of mixed-effects models to analyze longitudinal data, and the implications of our results for stock assessment and management.Fil: Escati Peñaloza, Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Parma, Ana María. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Orensanz, Jose Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentin

Conflicting objectives in trophy trout recreational fisheries: evaluating trade-offs using an individual-based model

Standard fisheries models, based on average populations metrics are inadequate for analyzing recreational fisheries where fishing is size-selective and management objectives are related to preserving population size structure. Using data from the steelhead (Oncorhynchus mykiss) fishery in the Santa Cruz River (Patagonia, Argentina) we developed an individual-based harvest model to characterize the relationship between growth, mortality and size structure under different size-based harvest strategies. We evaluated fishery performance with indicators associated to catch-related components of anglers? satisfaction: yield (kg), population size, and availability of trophy-size fish. Large declines in trophy-size fish are to be expected at fishing mortalities much too light to cause a sizeable decline in recruitment from virgin values. When somatic growth is density independent, fish harvest occurs at the expense of other indicators associated to the quality of fishing experienced by individual anglers. Our results clearly expose such trade-offs, providing the kind of quantitative information managers need to decide where to operate. Size limits provide some tools to better accommodate harvest without compromising fishing quality. When preserving population size is favored over preserving trophy-size fish, minimum size limits constitute the best policies overall, whereas maximum size limits are best when the emphasis is on preserving trophy-size fish.Fil: Garcia Asorey, Martin Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Escati Peñaloza, Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Parma, Ana María. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Pascual, Miguel Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentin