Research Article |
Corresponding author: André M. Vaz-dos-Santos ( andrevaz@ufpr.br ) Academic editor: Cassiano Monteiro-Neto
© 2017 Lygia C. Ruas, André M. Vaz-dos-Santos.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Ruas C, Vaz-dos-Santos AM (2017) Age structure and growth of the rough scad, Trachurus lathami (Teleostei: Carangidae), in the Southeastern Brazilian Bight. Zoologia 34: 1-11. https://doi.org/10.3897/zoologia.34.e20475
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The rough scad, Trachurus lathami Nichols, 1920, is a small pelagic species distributed along the West Atlantic coast. It is most abundant in the Southern Brazil (28°30’–34°S) and in the Southeastern Brazilian Bight (SEBB, 22°–28°30’S). The rough scad is fished by purse seines, which main target is the Brazilian sardine, Sardinella brasiliensis (Steindachner, 1879). Age and growth are vital to understand the life cycle of a species, to fishery management and ecosystem modeling. This study aimed to assess the age and growth of T. lathami, to identify its age structure in the SEBB, and to evaluate what causes the wide differences among Trachurus species in terms of body size and growth parameters. Data available on T. lathami was attained between 2008 and 2010 from surveys at SEBB. A total of 278 whole otoliths of T. lathami, total length between 27 mm and 208 mm, were analyzed and compared with the only other source of otolith data, from 1975. Three blind readings were performed and assessed using traditional methods to study fish age and growth. Zero up to eight rings were found, each ring corresponding to one year in the life of an individual of this species. The von Bertalanffy growth model parameters were L∞ = 211.90 mm and K = 0.319 year-1. The results of the analyses have shown similarities between 1975 and 2008-2010, indicating that the otolith development, the growth pattern and the age structure remained stable. T. lathami is the smallest species of Trachurus and it has the highest growth rates among them. This is probably related to the different temperatures where larvae/juvenile and adult grow, to the absence of a strong fishing pressure and to decadal population variability.
ECOSAR, otolith, sclerochronology, von Bertalanffy
In the Atlantic Ocean, the rough scad, Trachurus lathami Nichols, 1920, is a pelagic species distributed between the United States and North of Argentina, mainly on the continental shelf. It occurs between 50 and 100 m in depth, where it forms schools (
In the SEBB, rough scad landings varied a lot until the end of the 1990’s (
Commercial landings of Trachurus lathami and Sardinella brasiliensis in the Southeastern Brazilian Bight (SEBB). Data of 2008, 2009 and 2010 are restricted to states of Paraná and São Paulo that representing 95% of the total landings. Data source:
There is a single stock of the rough scad at the SEBB (
Studies on age and growth provide an essential tool to understand the biology and ecology of fish, providing a foundation for population dynamics assessments (
The significance of the small pelagic fisheries at SEBB led the Brazilian government to promote evaluation and monitoring programs of these resources. Although they were not continuous, the most recent initiative was the ECOSAR Program (Prospection and assessment of the sardine stock biomass in the Southeastern coast by the use of hydro-acoustic methods) carried out between 2008 and 2010 (
Four survey cruises were carried out between 20 and 100 m deep with the OV Atlântico Sul by FURG during January-February 2008 (Summer), November 2008 (Spring), September-October 2009 (Spring) and February-March 2010 (Summer) in the Southeastern Brazilian Bight (22°–28°30’S). Transects in perpendicular profiles, oblique to the coast, were followed. The echo sounder (Simrad EK500) was employed and when shoals were detected, both pelagic trawling and purse seine were carried out. Details on the methodology are available in
Whenever possible, ten otoliths of T. lathami were selected from each survey by total length class (10 mm) (
In order to study age and growth, the annual growth zones of the otoliths (macrostructural analysis) were analyzed (
The von Bertalanffy growth model parameters (VBGM) (L∞, K, t0) were estimated from observed lengths per age and by the average lengths per age using the least-squares iterative method (
The total length of 1,312 T. lathami individuals sampled varied between 27 mm and 208 mm, resulting in bimodal distributions in each period surveyed, one of juveniles (20 to 60 mm) and a second mode composed of adults (>115 mm TL), which predominated in the seasons analyzed (Fig.
Following the selection criteria, 282 otoliths of T. lathami were analyzed (it was not always possible to attain ten otoliths from each survey by TL class). The regressions among the otolith measurements (Table
Trachurus lathami: coefficients of potential regressions between total length (TL, mm) and otolith length (OL, mm), height (OH, mm) and weight (OW, g). (r2) Coefficient of determination, n = 282.
Regression | a ± IC95% | b ± IC95% | r2 |
---|---|---|---|
TL vs. OL | 0.041 ± 0.003 | 0.991 ± 0.017 | 0.979 |
TL vs. OH | 0.050 ± 0.004 | 0.825 ± 0.017 | 0.970 |
TL vs. OW | 3.96. 10-8 ± 8.84. 10-9 | 2.524 ± 0.052 | 0.971 |
After three readings, 278 otoliths were considered legible (98.6%) and four non legible (1.4%), which were not considered in the following analysis. The average percentage error among the three readings was 4.1%, and the coefficient of variation was 5.4%. Otoliths with up to eight rings were observed with high precision and consistency, revealed by the box plot and constancy analysis (Figs
The von Bertalanffy growth model parameters were L∞ = 211.90 mm, K = 0.319 year-1 and t0 = -0.576 years for observed lengths per age, and L∞ = 206.31 mm, K = 0.336 year-1 and t0 = -0.578 years for average lengths per age. When considering the maximum length obtained in the sampling (208 mm), the parameters estimated through the average lengths were disregarded, and the parameters fitted from observed lengths per age were adopted to estimate fish age (Fig.
Trachurus lathami: age-length key in the Southeastern Brazilian Bight during 2008–2010: percentage (from the total) of individuals by length class and age; number of ages estimated through otolith readings and with the inverse von Bertalanffy Growth Model (VBGM).
Total length class (mm) | Age (years) | Otolith readings | Inverse VBGM | Total | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8+ | ||||
20–30 | 100% | – | 2 | 2 | ||||||||
30–40 | 100% | 11 | 13 | 24 | ||||||||
40–50 | 100% | 15 | – | 15 | ||||||||
50–60 | 100% | – | 1 | 1 | ||||||||
60–70 | 100% | 16 | – | 16 | ||||||||
70–80 | 100% | 10 | 5 | 15 | ||||||||
80–90 | 100% | 10 | 13 | 23 | ||||||||
90–100 | 100% | 10 | 52 | 62 | ||||||||
100–110 | 100% | 1 | 1 | 2 | ||||||||
110–120 | 100% | – | 1 | 1 | ||||||||
120–130 | 100% | 3 | 1 | 4 | ||||||||
130–140 | 7% | 93% | 18 | 27 | 45 | |||||||
140–150 | 100% | 38 | 160 | 198 | ||||||||
150–160 | 28% | 72% | 40 | 276 | 316 | |||||||
160–170 | 94% | 6% | 33 | 212 | 245 | |||||||
170–180 | 100% | 30 | 171 | 201 | ||||||||
180–190 | 25% | 75% | 27 | 84 | 111 | |||||||
190–200 | 80% | 20% | 16 | 14 | 30 | |||||||
200–210 | 100% | – | 1 | 1 | ||||||||
Total | 42 | 116 | 10 | 328 | 458 | 244 | 83 | 24 | 7 | 278 | 1034 | 1312 |
In relation to the space-time distributions, in the summer of 2008, the rough scad schools were concentrated closer to the coast at 27°–28°S (89%), with all ages represented, and a predominance of one-year old fish (Fig.
The growth parameters estimated for T. lathami in this study are the most recent after 1975 (
The development of the otoliths of T. lathami had only been analyzed by
The quantitative elements (APE, CV, box plot, constancy analysis) used to evaluate otolith readings indicated that the ring radius presented high precision and does not vary much (
The use of whole otoliths, sectioned otoliths or both, to count rings and to estimate age has been broadly discussed (
The lack of self-validation, which was not possible in view of our sample design, does not compromise our results. The previously adopted validation was correctly performed, based on 399 otoliths (21% of the total) with coincident ring analysis by
The growth parameters (L∞, K) estimated with observed lengths per age were most suitable to describe the growth of T. lathami, since that obtained from the average lengths per age underestimated the maximum length values. The estimated theoretical age at zero length, is inconsistent in biological terms, since the rough scad hatches around 1.5 mm long (
Comparison of the growth parameters obtained here with previous estimates in Brazil (Table
Comparison with the nine congeneric species, considering the parameters of VBGM for sex pooled and based on the total length available at the FishBase (
Worldwide, environmental conditions play an important role in the growth of Trachurus species (
Another factor that may explain the differences in body size and growth parameters (between 1975 and 2008-2010, and in relation to the congeneric species) is fishing. In Brazil, during the 1970s, the fishing pressure on T. lathami was quite strong (
Decadal shifts in the populations of pelagic fish (
Trachurus lathami: growth parameters estimated and average total length at age for the species in the Southeastern Brazilian Bight.
Method | Growth parameters | Average length at age (mm) | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
L | K | t0 | TL0 | TL1 | TL2 | TL3 | TL4 | TL5 | TL6 | TL7 | TL8 | |
Otoliths (1975)a | 258.97 | 0.160 | -1.85 | 66 | 94 | 118 | 139 | 157 | 172 | 184 | 195 | 205 |
Back-calculation (1975)a | 228.46 | 0.250 | -0.56 | 30 | 74 | 108 | 135 | 155 | 172 | 184 | 194 | 202 |
Otoliths (1975)b | 252.00 | 0.170 | -1.73 | 64 | 94 | 118 | 139 | 157 | 172 | 184 | 195 | 204 |
ELEFAN (1997–1998)b | 270.00 | 0.250 | – | 0 | 60 | 106 | 142 | 171 | 193 | 210 | 223 | 233 |
Otoliths (2008–2010)c | 211.90 | 0.319 | – | 40 | 79 | – | 145 | 164 | 179 | 184 | 190 | 191 |
All sample (2008–2010)c | 211.90 | 0.319 | – | 39 | 86 | 121 | 145 | 160 | 175 | 184 | 191 | 198 |
General average lengthd | – | – | – | 48 | 81 | 114 | 141 | 161 | 177 | 188 | 198 | 205 |
We thank IBAMA/ICMBio for funding ECOSAR surveys, Lauro S.P. Madureira (FURG) and their staff during surveys and all students who processed the biological samples. We express our gratitude to Maria Cristina Cergole, Suzana Anita Saccardo, Carmen Lúcia Del Bianco Rossi Wongtschowski, Antônio Olinto Ávila da Silva, Marcus Rodrigues da Costa and Teodoro Vaske Júnior. To CAPES for the scholarship granted to the first author. For referees and their valuable recommendations. The first author expresses his gratitude to CNPq due to the research grant 305403/2015-0.