Tagging and length-frequency analysis (LFA) are common methods to study body growth and mortality in populations of fish and invertebrates, but little has been done to assess and compare the inherent uncertainty of these methods. This study applies a new bootstrap-based approach, within the fishboot R package, to a case study of semi-terrestrial crabs (Cardisoma guanhumi) . Crabs were sampled at upper mangrove fringes of Itamaraca Island over 12 months, from April 2015. A total of 1,078 individuals were captured and measured. Among these, 291 individuals were marked with PIT tags. 130 size increments were obtained. Carapace widths varied from 20.9 to 70.0 mm (mean: 43.4 mm). Tagging and LFA produced similar median parameter estimates, but tagging produced significantly (p < 0.0001) narrower 95\% CIs. Estimates for K from tagging were 3 times more precise than from LFA, estimates for Linf were 2.2 times more precise. Both methods indicate very slow growth and Linf far above Lmax. Tagging-based estimates were K = 0.12 y-1 (95\% CI: 0.024 to 0.26 y-1), Linf = 118 mm (95\% CI: 81 to 363 mm), Phi' = 1.23 log10(cm y-1) (95\% CI: 0.86 to 1.36 log10(cm y-1)). Seasonality in growth was significant (p = 0.006, 95\% CI for C: 0.15 to 0.93, median: C = 0.56). Estimates for K and Linf were imprecise, but they formed well-structured pairs along a narrow Phi' isopleth, leading to a high precision for Phi'. A two-step non-parametric bootstrap was used to assess Z and to investigate the log-linear relationship (slope = 1) between Z and input growth parameters, with implications for previous meta-analyses. Total mortality was Z = 2.18 y-1 (95\% CI = 1.7 to 4.5 y-1). Slow growth and a very high Z/K ratio for this population confirm the need for protective measures. Implications for length-based studies of growth and mortality are discussed .
The land crab Cardisoma guanhumi Latreille, 1828 is harvested in several countries in Latin America, and a critically endangered species. This is the first study to conduct bootstrapped tagging analysis (BTA) together with bootstrapped length-frequency analyses (BLFA) . Crabs were sampled monthly in a mangrove patch at Itamaraca Island (Brazil), over 12 months, and marked with PIT tags. Both methods (BTA and BLFA) indicate very slow growth and Linf far above Lmax. BTA estimates were K = 0.12 y-1 (95\% CI: 0.024 to 0.26 y-1), Linf = 118 mm (95\% CI: 81 to 363 mm), Phi' = 1.23 log10(cm y-1) (95\% CI: 0.86 to 1.36 log10(cm y-1)). Seasonality in growth was significant (p = 0.006, 95\% CI for C: 0.15 to 0.93, median: C = 0.56). Pairs of K and Linf always followed narrow Phi' isopleths. Total mortality was Z = 2.18 y-1 (95\% CI = 1.7 to 4.5 y-1). Slow growth and a very high Z/K ratio highlight the need for protective measures. BTA results were 2.2 to 3 times more precise than BLFA. Traditional length-based methods produced grossly biased results, indicating the urgent need for new, robust approaches and a critical reevaluation of long-standing methods and paradigms .
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The land crab Cardisoma guanhumi Latreille, 1828 is harvested in several countries in Latin America, and a critically endangered species. This is the first study to conduct bootstrapped tagging analysis (BTA) together with bootstrapped
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analysis (LFA) are common methods to study body growth and mortality in populations of fish and invertebrates, but little has been done to assess and compare the inherent uncertainty of these methods. This study applies a new bootstrap-based approach, within the fishboot R package, to a case study of semi-terrestrial crabs (Cardisoma guanhumi)
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at upper mangrove fringes of Itamaraca Island
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from April 2015. A total of 1,078 individuals were captured and measured. Among these, 291 individuals were
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130 size increments were obtained. Carapace widths varied from 20.9 to 70.0 mm (mean: 43.4 mm). Tagging and LFA produced similar median parameter estimates, but tagging produced significantly (p < 0.0001) narrower 95\% CIs. Estimates for K from tagging were 3 times more precise than from LFA, estimates for Linf were 2.2 times more precise. Both methods
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BTA results were 2.2 to 3 times more precise than BLFA. Traditional
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