Lagocephalus guentheri, Miranda Ribeiro, 1915

Mutlu, Erhan, Meo, Ilaria de & Miglietta, Claudia, 2020, Spatio-temporal distribution of pufferfish (Tetraodontidae) along the Turkish coast of the Mediterranean Sea Abstract, Mediterranean Marine Science 22 (1), pp. 1-19 : 6-8

Lagocephalus guentheri

The species L. guentheri was found between 10 and 75 m seafloor depth. The maximum biomass was 25 kg / km 2 and maximum abundance was 690 ind/km 2 ( Fig. 4 ). With the exception of R 2 which only had one occurrence, the species was frequently found in the other regions and seemed to decrease from west to east across the study area.

Regional differences were observed for the biomass of L. guentheri ( ANOVA, p = 0.002). The mean biomass was significantly higher in R 4 (7.94 ± 1.79 kg /km 2), seaward of the river mouths. R 2 had the least biomass (0.02 ± 0.83 kg /km 2), and the other regions varied between 0.73 ± 0.80 kg /km 2 in R 3 and 1.61 ± 0.78 kg /km 2 in R 1. The biomass did not differ significantly with season (p = 0.27); however, the biomass increased from May (0.17 ± 0.92 kg /km 2) through August–to-October (0.68 ± 1.04 to 1.59 ± 0.94 kg /km 2) to February (2.72 ± 0.99 kg /km 2). The species was found at depths of bottom of 10–25 m and 75 m during the year ( Fig. 4 ) and showed no significant differences in biomass as a function of bottom depth (p = 0.135). The biomass decreased with bottom depth and was only significantly higher at 10 m (4.28 ± 1.09 kg /km 2) than at 75 m (0.76 ± 1.13 kg /km 2).

Unlike biomass, abundances were not statistically different among regions ( ANOVA, p = 0.221). The minimum abundance was 0.91 ± 20.66 ind/km 2 in R 2 and the maximum abundance 101.80 ± 44.32 ind/km 2 in R 4. Region R 3 had an abundance of 23.32 ± 19.82 ind/km 2 and R 1 had 32.23 ± 19.44 ind/km 2. There was no significant difference in the abundance among seasons (p = 0.404). Minimum abundance was estimated in May at 0.86 ± 21.34 ind/km 2, while maximum abundance occurred in February (54.05 ± 22.96 ind/km 2). Abundance was 28.71 ± 24.27 ind/km 2 in August and 19.86 ± 21.84 ind/km 2 in October. Differences in abundance as a function of bottom depth was not statistically significant (p = 0.250); however, abundance in shallow waters was significantly higher (80.87 ± 25.46 ind/km 2) than in deep waters (0.93 ± 26.36 ind/km 2), and the abundance at 25 m was 55.77 ± 27.35 ind/km 2.

Sex ratios did not change significantly among regions, seasons, and bottom depths (p = 0.875, 0.865, and 0.188, respectively). Regions 1 and 4 had higher ratios (0.66 ± 0.39 each) than R3 (0.34 ± 0.54). The ratios increased linearly from August (0.18 ± 0.80) to May (1.00 ± 0.80) with a difference of 0.25 between seasons. With respect to bottom depth, the ratios varied between 1.00 ± 0.29 at 10 m and 0.28 ± 0.29 at 25 m.

The total length of L. guentheri varied between 7 and 25.2 cm during the year. The COST function estimated an optimum size class interval of 0.43 cm. Five cohorts were fixed using the KDF to estimate the density of each cohort corresponding to minimum densities, ranging from <8.5, 8.5–14, 14–17, 17–19, and> 19 cm. Cohort 2 dominated the population, followed by cohort 3. The lengths were significantly different among regions, seasons, bottom depths, and sex (p = 1.0 × 10 -8, 6.8 × 10 -6, 0.0006, and 0.0031, respectively). The minimum length (12.69 ± 0.33 cm) was found in R 2 and the maximum length (15.88 ± 0.59 cm) was found in R 4. The length was not significantly different between R 1 (9.26 ± 0.86 cm) and R 3 (11.92 ± 0.49 cm). The lengths were significantly longer (24.10 ± 2.73 cm) in May than in other seasons and were not significantly different between October (13.72 ± 0.52 cm) and February (12.78 ± 0.34 cm) whereas the minimum lengths were significantly different in August (11.00 ± 0.58 cm). The length decreased from bottom depths of 10–25 m (13–12± 0.43 cm) to 50 m (8.98 ± 1.01 cm), and the longest individuals were observed at bottom depths of 75 m (15.30 ± 2.84 cm). Length (10.81 ± 0.68 cm) was significantly different by sex. Post-hoc tests showed no significant differences between the total length of females (13.55 ± 0.42 cm) and males (12.79 ± 0.42 cm).

Individual weight differed significantly among regions, seasons, and sex including pooled sexes (p = 2.9 × 10 -6, 5.0 × 10 -8, and 0.0203, respectively). Individuals were significantly heavier in R 4 (83.37 ± 8.19 g) than in the other regions, ranging from 21.97 ± 11.90 g in R 2 to 37.91 ± 4.53 g in R 1; the latter two did not differ significantly from each other. Similar to length, weight was highest (220.91 ± 34.42 g) in May and lowest (21.19 ± 7.34 g) in August. October and February did not differ significantly in weight (60.06 ± 6.50 g and 38.98 ± 4.24 g, respectively), and weight was not significantly different between bottom depths of 50 m (21.89 ± 14.01 g) and 75 m (65.84 ± 39.62 g). Shallow waters had fish of moderate weight (~ 40 g /ind.). The difference in weight did not differ significantly between males (40.42 ± 5.58 g) and females (52.22 ± 5.64 g).

The length-weight relationship was significantly different for females, males, and pooled individuals ( Fig. 5 ). The slopes of the regression lines were significantly different from the isometric growth value of 3 (n = 112, t = -2.455) for all individuals but not for the males and females (n = 49, t = -1.474 and n = 48, t = -1.991) at p <0.05, resulting in negative allometric growth for the individuals. Overall, there was a significant difference in length-weight regression constants among regions, bottom depths, and sex owing to the contribution from individuals of undefined sex (p = 0.041, 0.044, and 0.038, respectively).

Estimates of slopes and intercepts among regions were statistically similar between R1 (2.724 and 0.0355, respectively) and R2 (3.065 and 0.0471, respectively), and between R3 (3.085 and 0.0125, respectively) and R4 (2.916 and 0.0218, respectively). The slope was significantly higher in R3 than in R2 whereas the intercept was significantly lower in R3 than R2 . There were no significant differences in L-W regressions among seasons. Only the intercepts differed significantly between bottom depths of 25 m (0.0124) and 50 m (0.0420), and one individual was found in regions with bottom depths of 75 m. The L-W relationships were not significantly different between females and males ( Fig. 5 ) .

Figures

Fig. 4: Distribution of (A) biomass, (B) abundance (circles square-rooted), and (C) percent sex composition of Lagocephalus guentheri in time (months) and space (regions and depths). Seasonal colors on figures are: blue = May 2014, green = August 2014, red = October 2014, and magenta = February 2015. Colors for sex ratio: females follow seasonal color scheme, males are black, and juveniles are white in seasons.

Fig. 5: Length-weight relationships of males (blue), females (pink), and pooled data (red) of Lagocephalus guentheri.