Table 2
Estimated parameters and their 95% confidence intervals (CI) of models assessing standard length increment (ΔL) of stocked common carp and pikeperch in Lake Balaton according to the GROTAG method of Francis (1988a) and using number of days (d) and degree-day sum at 8 °C threshold water temperature (D8 °C) as predictors. Estimated values (mean and CI) of von Bertalanffy growth parameters, growth rate (K) and asymptotic length (L∞) are also shown. Since some stocking season and recapture area (I − Keszthely, II − Szemes, III − Siófok basin) related variability was found in the ΔL when related to d in both species and in pikeperch, respectively (Table 1), thus growth models based on d were composed both for the total samples and each relevant subsample as well. Only the best model according to the likelihood ratio test is shown for each model type.
| Model type predictor − season | gα (mm year1) (CI) | gβ (mm year−1) (CI) | v (CI) | s (CI) | m (mm) (CI) | P (CI) | Likelihood | R2adj. | n | K (year−1) (CI) | L∞ (mm) (CI) |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Common carp | |||||||||||
| d − spring | 221.6 | 153.2 | 0.34 | 0.0 | – | – | −1085.3 | 0.576 | 226 | 1.153 | 524 |
| (211.7–230.3) | (136.0–168.4) | (0.28–0.37) | (0.0–12.8) | – | – | (0.899–1.473) | (476–581) | ||||
| d − summer | 225.7 | 133.7 | 0.36 | 11.7 | 5.0 | – | −1588.0 | 0.621 | 332 | 2.536 | 445 |
| (215.4–235.9) | (122.7–144.8) | (0.31–0.40) | (9.2–14.0) | (1.3–8.8) | – | (2.165–2.973) | (431–460) | ||||
| d − autumn | 143.0 | 113.4 | 0.21 | 34.9 | – | – | −654.5 | 0.731 | 126 | 0.351 | 683 |
| (132.1–154.2) | (105.0–121.3) | (0.05–0.30) | (23.7–43.6) | – | – | (0.233–0.504) | (578–856) | ||||
| d − all | 144.3 | 99.7 | 0.40 | 26.4 | 32.4 | – | −3430.6 | 0.643 | 684 | 0.590 | 524 |
| (132.9–156.8) | (90.9–107.6) | (0.34–0.45) | (24.0–28.8) | (27.4–37.2) | – | (0.445–0.768) | (481–579) | ||||
| D8 °C − all | 173.6 | 128.0 | 0.30 | 12.6 | 3.7 | – | −3277.5 | 0.739 | 684 | 0.609 | 581 |
| (166.4–181.6) | (121.8–134.2) | (0.27–0.32) | (10.5–14.6) | (0.2–6.9) | – | (0.512–0.723) | (542–624) | ||||
| Pikeperch | |||||||||||
| d − spring | 94.7 | 82.0 | 0.00 | 29.6 | 25.3 | – | −961.2 | 0.795 | 211 | 0.291 | 574 |
| (78.3–114.1) | (71.0–96.0) | (0.00–0.12) | (24.9–32.1) | (12.7–36.2) | – | (0.145–0.463) | (497–780) | ||||
| d − autumn | 101.3 | 89.8 | 0.18 | 22.4 | – | – | −1450.3 | 0.752 | 302 | 0.262 | 640 |
| (94.4–109.1) | (85.6–94.6) | (0.14–0.22) | (18.3–26.3) | – | – | (0.188–0.352) | (564–755) | ||||
| d − basin III | 106.6 | 89.5 | 0.10 | 28.6 | – | – | −429.8 | 0.709 | 89 | 0.419 | 512 |
| (91.3–120.3) | (81.0–97.6) | (0.00–0.19) | (21.6–33.4) | – | – | (0.216–0.660) | (445–669) | ||||
| d − basins I and II | 103.4 | 89.0 | 0.18 | 29.2 | 15.1 | – | −2131.5 | 0.698 | 424 | 0.338 | 560 |
| (87.4–119.5) | (77.8–101.3) | (0.13–0.22) | (24.9–33.0) | (3.6–25.3) | – | (0.217–0.464) | (51–652) | ||||
| d − all | 93.6 | 82.7 | 0.14 | 27.8 | 14.5 | – | −3430.6 | 0.643 | 513 | 0.590 | 524 |
| (81.8–104.9) | (74.1–90.8) | (0.09–0.18) | (24.6–30.7) | (6.5–22.5) | – | (0.156–0.341) | (560–783) | ||||
| D8 °C − all | 98.5 | 85.0 | 0.20 | 17.0 | 12.7 | – | −2334.2 | 0.780 | 513 | 0.315 | 565 |
| (89.7–107.8) | (78.5–91.8) | (0.17–0.22) | (14.1–19.6) | (6.6–18.2) | – | (0.239–0.402) | (521–630) | ||||
gα and gβ are the estimated growth rates at preselected standard lengths α and β (α = 200 mm and β = 300 mm for common carp and α = 200 mm and β = 250 mm for pikeperch in this study); v, s, m and p are additional model parameters to be estimated; likelihood is a function to be maximized during the model optimization and is calculated according to equation (3); R2adj is the adjusted coefficient of determination, while n is the sample size. “–” indicates that the concerning parameter was not retained in that model.
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