SCRS/2019/116 Collect. Vol. Sci. Pap. ICCAT, 76(7): 169-173 (2019)

LIFE HISTORY PARAMETERS FOR FRIGATE TUNA AUXIS THAZARD IN THE NORTHEAST ATLANTIC

Petukhova N. G.1

SUMMARY

This study presents the estimates of life history parameters for Frigate tuna Auxis thazard calculated with data from Russian research in the Northeast Atlantic (Morocco, Mauritania, Senegal and Guinea-Bissau waters). New estimates of length-weight relationship (WL_a, WL_b) and length values for 50% and 95% fish maturation (Lm50 и Lm95) were assessed.

RÉSUMÉ

La présente étude fait état des estimations des paramètres de cycle vital d’auxide, Auxis thazard, calculés avec des données provenant de recherches russes menées dans l'Atlantique Nord-Est (eaux du Maroc, de la Mauritanie, du Sénégal et de la Guinée-Bissau). De nouvelles estimations de la relation taille-poids (WL_a, WL_b) et des valeurs de la taille à laquelle 50% et 95% des poissons sont matures (Lm50, Lm95) ont été évaluées.

RESUMEN

En este estudio se presentan estimaciones de los parámetros del ciclo vital de melva (Auxis thazard) calculadas con datos de la investigación rusa en el Atlántico nororiental (aguas de Marruecos, Mauritania, Senegal y Guinea-Bissau). Se evaluaron nuevas estimaciones de la relación talla- peso (WL_a, WL_b) y de los valores de tallas en las que el 50% y 95% de los peces son maduros (Lm50 y Lm95).

KEYWORDS

Frigate tuna Auxis thazard, length-weight relationship, maturity

1 FSBSI «Russian Federal Research Institute of Fisheries and Oceanography» (FSBSI «VNIRO»), 17, V. Krasnoselskaya, Moscow, Russia. E-mail: [email protected]. 169 1. Introduction

Frigate tuna Auxis thazard (Lacepède, 1800) is a small pelagic tuna of the family Scombridae. However, despite a wide distribution of this species in the Atlantic and its value for regional commercial fisheries in many coastal communities Frigate tuna life history has not been studied properly. The reason of it is a deficit of a primary information. Nevertheless, some assessments of Frigate tuna life history parameters were performed for Frigate tuna stocks in Southeast Atlantic (Grudtsev and Korolevich, 1986) and Southwest Atlantic (Frota et al., 2004). Besides, the above-mentioned results were used by Pons at al. (Pons at al., 2019) for the preliminary stock status assessment of Auxis thazard in the Northeast Atlantic.

The aim of this study was to estimate life history parameters (Lmax, Lm50, Lm95, WL_a, WL_b) for Frigate tuna in the Northeast Atlantic on the bases of Russian primary data and to investigate differences between the estimated results and those obtained before.

2. Material and methods

The research is based on Russian data collected between 2010 and 2018 by AtlantNIRO observers in the Northeast Atlantic (Morocco, Mauritania, Senegal and Guinea-Bissau waters). Frigate tunas occurred in research trawls as a by-catch from a few individuals or up to several hundred at depths, ranging from 23 to 1350 meters. Number of caught individuals is presented in Table 1. Caught individuals were weighted (g) and measured (mm) for their total length. Besides, sex and maturity stage were defined for every individual. The difficulty of this research was the age data missing. Overall the input data included the following parameters: catch date, total length, weight, maturity statement «mature» or «immature» and maturity stage of fish.

The length-weight relationship was described by the following equation of linear regression (Ricker, 1975): log W = log a + b log L, where W is body weight (g), L is total length (mm), a is a coefficient related to body form and b is the fish relative growth rate.

The result was expressed in the well-known form:

W = a Lb.

Length in which 50% and 95 % of the fish are mature was assessed with package FSA v0.8.24 (Ogle et al., 2018) in R, which allows to use general linear model for further curve fitting of logistic regression. The paper published by Dr. Derek Ogle (Ogle, 2013) was the pattern for the corresponding script in R. The input data for this analysis included catch date, total length, maturity statement («mature» or «immature») and maturity stage of every individual for period from 2011 to 2018.

3. Results

The length of Auxis thazard ranged from 210 mm to 430 mm and the weight ranged from 140 g to 1200 g for all survey years. Individuals of low sizes were not caught due to fishing gear selectivity. The results obtained from the length-weight relationship analyses for Auxis thazard are summarized in Table 2. Data from this table include year, sample size, length and weight range, estimates parameter of a and b, determination coefficients (r²), standard error for b from non-linear regressions. These results are significant at the p < 0.01 level. As shown on the Table 2 there are many values of parameters a and b. Maximum and minimum values for a and b were excluded for calculation a final value. The rest of the values were averaged. As a result, final parameters of length-weight relationship were a = 1.5×10-5, b = 3.240.

Analysis of input data showed that size at first maturity Auxis thazard is 26 cm. This value was registered in February 2011 in waters of Senegal. The Figure 1 shows the maturity ogive for Auxis thazard. The results obtained from estimation of length in which 50% and 95% of the fish was mature are following: Lm50 = 31.7 cm, Lm95 = 42.2 (Figure 1).

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4. Discussion

Now the question concerning the maхimum length of Auxis thazard in by-catches remains open whereas it is important both for assessment of stocks and for management of them. FishBase contains information about the maximum length of this species of the Eastern Central Atlantic equal to 65 cm (Cayré et al, 1993). If one takes this size for the truth, then the maximum length of the tuna observed in Russian by-catches (43 cm) can demonstrate that not all senior size groups are caught. The reasons there can be two: 1) larger individuals of the Auxis thazard are capable to avoid hit in trawls, or 2) they are missing in this area of the Atlantic. The second assumption is spoken well by the fact that individuals of other species of small tunas more than 43 cm long were caught regularly by the same fishing gears. For example, other small tuna species Atlantic bonito Sarda sarda and Little tunny Euthynnus alletteratus over 65 cm were registered in the by-catches almost in each discussed year.

The majority of 8 length-weight relationship parameters b has revealed a positive allometries in growth of Auxis thazard. Besides, the final value of b (3.240) not so different from estimates by Frota et al. (Frota et al., 2004). The final length-weight relationship parameter a (1.5×10-5) differs from obtained by Frota et al. (6×10-6) (Frota et al., 2004). This difference can be explained the sizes of samples and different research areas. Previous study was based on the data from central Brazilian coast.

The results of estimates for Auxis thazard maturity (Lm50 = 31.7 cm and Lm95 = 42.2 cm) did not show any significant changes in comparison with values, published by Cayré et al. in 1993 (Lm50 = 30 cm and Lm95 = 40 cm) (Cayré et al., 1993). The type for research fish length, most likely is reason in difference between values. This research was based on total length data and the previous one was based on fork length data.

Small Tunas Species Group in 2018 selected most reliable life history parameters by region and species for running the Data Poor Models (Linf, Lmax, k, t0, Tmax, Lm50, Tm50, WL_a, WL_b, Fmeanbatch) (ICCAT, 2018) for each of the five Atlantic areas. This study contains the part of parameters set that can be used for Frigate tuna Auxis thazard stock assessment by length-based models. The summary results of the study present in Table 3.

The author expresses profound gratitude to AtlantNIRO scientists for the basic data of Frigate tuna Auxis thazard for this study.

5. References

Cayre, P., Amon Kothias, J. B., Diouf, T., and Stretta, J. M. 1993. Biology of tuna. In Resources, Fishing and Biology of the Tropical Tunas of the Eastern Central Atlantic. Ed. By A. Fonteneau and J. Marcille. FAO Fisheries Technical Paper, 292. FAO, Rome, Italy. pp. 354. Frota, L. O., Costa, P. A. S., and Braga, A. C. 2004. Length-weight relationships of marine fishes from the central Brazilian coast. Naga, WorldFish Center Quarterly, 27: 20–26. Grudtsev, M. E., and Korolevich, L. I. 1986. Studies of frigate tuna Auxis thazard (Lacepede) age and growth in the eastern part of the Equatorial Atlantic. Collective Volume of Scientific Papers of ICCAT, 25: 269–274. ICCAT. 2018. Report of the 2018 ICCAT Small tuna species group intersessional meeting, Madrid, Spain 2–6 April, 2018. Collective Volume of Scientific Papers of ICCAT, 75: 1–67. Ogle, D.H., 2013. fishR Vignette – Maturity Schedules. 10. http://derekogle.com/fishR/examples/oldFishRVignettes/Maturity.pdf. Ogle D.H, Wheeler P, Dinno A. 2018. FSA: Fisheries Stock Analysis. R package version 0.8.22.9000, https://github.com/droglenc/FSA. Pons, M., Kell, L., Rudd, M. B., Cope, J. M., and Frédou F. L. 2019. Performance of length-based data-limited methods in a multi- fleet context: application to small tunas, mackerels and bonitos in the Atlantic Ocean. Canadian Journal of Fisheries and Aquatic Sciences. 13 p. Ricker, W.E., 1975. Computation and interpretation of biological statistics of fish populations. Bull. Fish. Res. Bd. Can. 191, 382.

171 Table 1. Number of caught Frigate tunas Auxis thazard in Russian by-catches in the Northeast Atlantic (in Morocco (MAR), Mauritania (MRT), Senegal (SEN), Guinea-Bissau (GNB) waters). Year 2010 2011 2012 2013 2014 2015 2016 2017 2018 Auxis 150 391 280 29 138 128 245 83 56 thazard MAR MAR+ MRT MAR+ MAR+ MAR+ MAR+ MAR+ MAR+ SEN GNB MRT MRT MRT MRT MRT

Table 2. Descriptive statistics and length-weight relationship parameters for Frigate tuna Auxis thazard caught in the Northeast Atlantic waters (N – sample size; L – length (mm); W – weight (g); mean, min, max – mean; minimum; maximum; SD – standard deviation; SE – standard error for b (regression coefficient); C.I. – confidence interval).

Year N Lmean ± SD Wmean ± SD Equation Determination SE of b 2 (Lmin–Lmax) (Wmin-Wmax) coefficient (r ) (95% C.I. of b) 320 ± 31 525 ± 211 0.074 2010 150 W=3.7×10-7 L3.642 0.94 (280 - 390) (300 - 1145) (3.495-3.790) 2011 391 310 ± 34 440 ± 190 W=2.5×10-7 L3.697 0.90 0.060 (240 - 410) (160 - 1060) (3.578-3.816) 2012 307 330 ± 31 559 ± 168 W=2.3×10-7 L3.717 0.97 0.032 (210 - 380) (140 - 890) (3.653-3.780) 2013 29 Insufficient sample 2014 148 340 ± 22 666 ± 137 W=1.8×10-5 L2.979 0.91 0.076 (280 - 390) (360 - 1045) (2.827-3.131) 2015 123 340 ± 25 582 ± 136 W=6.2×10-5 L2.749 0.88 0.091 (300 - 405) (380 - 1000) (2.569-2.930) 2016 245 350 ± 26 649 ± 171 W=4.7×10-6 L3.192 0.95 0.046 (300 - 430) (360 - 1200) (3.102-3.283) 2017 82 330 ± 21 583 ± 86 W=1.6×10-2 L1.803 0.53 0.189 (287 - 374) (330 - 775) (1.425-2.180) 2018 52 370 ± 17 753 ± 121 W=5.0×10-6 L3.181 0.87 0.173 (330 - 411) (448 - 1014) (2.832-3.530)

Table 3. Analogy between obtained and previous results (Lmax – maximum registered length (cm); WL_a, WL_b (g) – parameters of length-weight relationship; Lm50, Lm95 – length in which 50% and 95% of the fish are mature, (cm)).

Parameters Obtained results Previous studies results Lmax 43 44 AT-SE (Grudtsev and Korolevich, 1986) WL_a 1.5×10-5 6×10-6 AT-SW (Frota et al., 2004) WL_b 3.240 3.19 AT-SW (Frota et al., 2004) Lm50 31.7 30 (Cayré et al., 1993) for fork length Lm95 42.2 40 (Cayré et al., 1993) for fork length

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Figure 1. Maturity curve for Frigate Tuna Auxis Thazard.

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