Comparing the accuracy and precision of novel bootstrapped length-frequency and length-at-age (otolith) analyses, with a case study of lane snapper (Lutjanus synagris) in the SW Atlantic

Length-at-age (LAA) and length-frequency analyses (LFA) are widely used to assess body growth in fish. The main objective of this study was to quantify and compare the uncertainty in growth parameter estimates obtained from novel bootstrapped length-at-age analysis (bootLAA) and bootstrapped length-frequency analysis (bootLFA), based on a case study of lane snapper (Lutjanus synagris) caught at the Abrolhos and Royal Charlotte banks (Brazil). Growth parameter estimates for bootLFA were based on 2564 total lengths. Data for bootLAA were obtained by reading 295 otoliths (sagittae). Otolith readings (bootLAA) were 3.6, 2.4 and 6.1 times more precise (for L∞, K and Φ’, respectively) than bootLFA. The median “optimum fit” growth model from bootLFA (n = 2564 total lengths) had the following soVBGF parameters: L∞ = 70.46 cm (95% CI: 56.37–96.84 cm), K = 0.153 y−1 (95% CI: 0.060–0.266 y−1), Φ' = 2.90 log10 (cm y−1) (95% CI: 2.60–2.99), t_anchor = 0.47 (95% CI: 0.12–0.82), C = 0.52 (95% CI: 0.17–0.89), and ts = 0.50 (95% CI: 0.13–0.85). Growth models obtained with different moving average widths (MA) showed significant differences in precision. BootLFA with MA = 5 was much more precise than estimates with wider MA spans. Median values of K and L∞ were not significantly different between bootLAA and bootLFA, indicating a good consistency and reliability of both methods. The median VBGF growth model from bootLAA (n = 295 otoliths) was: L∞ = 59.68 cm (95% CI: 55.94–67.26 cm), K = 0.199 y−1 (95% CI: 0.154–0.239 y−1), Φ' = 2.85 log10 (cm y−1) (95% CI: 2.82–2.89). Despite the higher precision of bootLAA based on otolith readings, its application is often hampered due to constraints in costs, available personnel and time. Our results and analyses indicate that when certain recommendations and criteria are met, bootLFA can be a reliable tool for assessing growth parameters, which are key inputs for fisheries stock assessment and management.