Corresponding author: Dawood Almamari ( almamari9988david@gmail.com ) Academic editor: Adnan Tokaç
© 2021 Dawood Almamari, Said Rabia, Joo Myun Park, Laith A. Jawad.
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:
Almamari D, Rabia S, Park JM, Jawad LA (2021) Age, growth, mortality, and exploitation rate of blueline snapper, Lutjanus coeruleolineatus (Actinopterygii: Perciformes: Lutjanidae), from Dhofar Governorate, Sultanate of Oman. Acta Ichthyologica et Piscatoria 51(2): 159-166. https://doi.org/10.3897/aiep.51.63572
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The blueline snapper, Lutjanus coeruleolineatus (Rüppell, 1838), is a significant commercial fish species harvested from the traditional fishery in the Sultanate of Oman. Deficient data on this species, however, make the management strategies challenging, especially in fisheries ecology. A total of 978 specimens were obtained from Dhofar Governorate off the coast of the Arabian Sea during the period between February 2015 and March 2016. In total, 296 sectioned otoliths were analyzed and growth was estimated from non-seasonal growth by using von Bertalanffy method. The parameters of von Bertalanffy growth function, total mortality (Z), natural mortality (M), fishing mortality (F), and exploitation rate (E) were determined and compared with those for Lutjanidae fishes elsewhere. The age structure of male fishes was between 1 and 14 years for males while the age of females ranged from 1 to 18 years. Growth rate (K) was 0.21 y–1 and 0.16 y–1 for males and females, respectively. The hypothetical length of female (L∞ = 46 cm) was relatively higher than that of male (L∞ = 42 cm). The natural mortality (M) was 0.296, total mortality (Z) was 0.372, fishing mortality was 0.076, and exploitation rate (E) was estimated as 0.2. The presently reported study is conducted to examine this fish in relation to growth parameters by analyzing otolith structure. The results of the presently reported study will contribute towards planning the regional fishery management policies in Oman.
Arabian Sea, blueline snapper, Dhofar, exploitation rate, mortality, otolith
Fishery resources are one of the greatest marine resources in the Sultanate of Oman and have been extensively helping fishermen for their livelihood (
The blueline snapper, Lutjanus coeruleolineatus (Rüppell, 1838) (hereafter blueline snapper), is a member of the family Lutjanidae which contains 17 genera and about 113 species (
The presently reported study was conducted to analyze the stock assessment parameters of blueline snapper, Lutjanus coeruleolineatus, using otolith microstructure. Furthermore, the presently reported study attempted to determine the growth parameters based on males and females of blueline snapper that can reveal signs of exploitation level. Such data clarify the state of the stock which can be then used by decision makers to manage and control the exploitation of the stock of blueline snapper for sustainability over time. Hence, an essential study on the age and growth of this species is required to understand their longevity and growth rate in the Arabian Sea.
In total, 978 specimens of blueline snapper were landed by gillnets and handlines from Salalah Fish Market (SFM) (17°01.2′N, 54°04.58′E) at Dhofar Governorate from March 2015 to February 2016. Among the samples collected, randomly selected 296 fish (158 females and 138 males) were used for age determinations using sagittal otolith. A pair of otoliths (Fig.
The growth parameters of blueline snapper were estimated as a relation between body size and age the non-seasonal von Bertalanffy growth function (
Lt = L∞ × (1 – e K(t – t0))
where Lt is length of fish at age t, L∞ is the hypothetical length, K is the instantaneous growth coefficient and t0 is the hypothetical age at which length is equal to 0. The growth parameters of sex’s pooled, male and female data were fitted using the Vonbitb program (
The longevity (life span) was estimated by (
t max = 3K–1
where tmax is the longevity and K is the instantaneous growth.
In order to validate if the opaque and hyaline zone are laid annually, the marginal increment analysis of the otoliths was investigated following
MIR = (RC – RL) × (RL – RL – 1)–1
where MIR is the marginal increment ratio, RC is the otolith radius from the primordium to the edge, RL is the otolith radius from the primordium to the last annulus, and RL – 1 is the otolith radius from the primordium to the annulus next to the last one.
The mean marginal increment ratio was calculated monthly and plotted to examine if the annuli of the otolith formed annually or not and to estimate the translucent ring growth (slow–fast) during the year.
The annual instantaneous rate of mortality (Z) was estimated using the length converted catch curve method (
F = Z − M
Natural mortality (M) was estimated from the empirical equation using temperature and growth parameter K (
log M = –0.0066 – 0.279 log L∞ + 0.6543 log K + 0.4634 log T
where the T value was taken as 24°C as this value represented the mean bottom water temperature in the Arabian Sea of Oman (
The exploitation rate can be defined as the proportion of harvestable-sized fishes that are removed from a population annually through different fishing activities (
E = F × Z–1
where E is the exploitation rate, F is the fishing mortality, and Z is the annual instantaneous rate of mortality.
Total lengths (TL) of all blueline snapper sampled ranged from 19.4 to 43.7 cm with a mean of 28.4 cm (±0.14). Among them, 529 female and 449 male (sex ratio of F:M = 1.18) specimens were determined, females ranged from 20.4 to 43.7 cm TL with a mean of 29.1 cm (±0.21), which was significantly longer than the mean TL of males (27.5 ± 0.16 cm, t0.05, df = 976 = −5.63, P < 0.05).
Analysis of the length distribution for blueline snapper revealed that the majority of specimens (male and female) were concentrated at length classes between 26 cm TL and 36 cm TL. However, lengths classes less than 26 cm TL and bigger than 36 cm TL were recorded by few specimens (Fig.
The rings were clearly visible with a high level of readability (90%) and the age of the fish could be determined in the majority of them.
The size of blueline snapper to age data were fitted for each sex separately by using the non-seasonal von Bertalanffy growth function (VBGF) in order to estimate the growth pattern of this species (Fig.
Age–length key of Lutjanus coeruleolineatus males from Dhofar Governorate, Sultanate of Oman.
TL [cm] | Age [year] | Total | |||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | ||
18–20 | 0 | ||||||||||||||
20–22 | 1 | 5 | 6 | ||||||||||||
22–24 | 3 | 15 | 2 | 20 | |||||||||||
24–26 | 8 | 9 | 11 | 1 | 29 | ||||||||||
26–28 | 11 | 6 | 4 | 2 | 23 | ||||||||||
28–30 | 2 | 4 | 8 | 6 | 1 | 1 | 22 | ||||||||
30–32 | 1 | 2 | 1 | 8 | 1 | 2 | 1 | 16 | |||||||
32–34 | 1 | 2 | 4 | 4 | 2 | 1 | 1 | 1 | 16 | ||||||
34–36 | 1 | 1 | 1 | 1 | 1 | 5 | |||||||||
36–38 | 1 | 1 | |||||||||||||
38–40 | 0 | ||||||||||||||
40–42 | 0 | ||||||||||||||
42–44 | 0 | ||||||||||||||
Total | 12 | 43 | 26 | 13 | 19 | 7 | 6 | 5 | 0 | 2 | 1 | 1 | 1 | 2 | 138 |
Mean length [cm] | 23 | 24 | 26 | 28 | 29 | 32 | 31 | 32 | 33 | 33 | 34 | 35 | 35 | 27 |
Age–length key of Lutjanus coeruleolineatus females from Dhofar Governorate, Sultanate of Oman.
TL [cm] | Age [year] | Total | |||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | ||
18–20 | 0 | ||||||||||||||||||
20–22 | 3 | 2 | 5 | ||||||||||||||||
22–24 | 3 | 17 | 1 | 21 | |||||||||||||||
24–26 | 3 | 15 | 6 | 24 | |||||||||||||||
26–28 | 1 | 5 | 12 | 4 | 22 | ||||||||||||||
28–30 | 6 | 2 | 13 | 2 | 23 | ||||||||||||||
30–32 | 2 | 3 | 8 | 5 | 1 | 1 | 20 | ||||||||||||
32–34 | 5 | 3 | 2 | 1 | 11 | ||||||||||||||
34–36 | 3 | 2 | 1 | 2 | 1 | 9 | |||||||||||||
36–38 | 1 | 2 | 2 | 1 | 3 | 1 | 2 | 12 | |||||||||||
38–40 | 2 | 1 | 1 | 1 | 5 | ||||||||||||||
40–42 | 1 | 1 | 1 | 1 | 1 | 5 | |||||||||||||
42–44 | 1 | 1 | |||||||||||||||||
Total | 10 | 47 | 24 | 25 | 13 | 8 | 7 | 4 | 7 | 2 | 1 | 2 | 3 | 2 | 0 | 0 | 2 | 1 | 158 |
Mean length [cm] | 23 | 25 | 26 | 29 | 31 | 34 | 34 | 34 | 34 | 36 | 36 | 40 | 39 | 39 | 41 | 43 | 29 |
Age–length key of sex combined Lutjanus coeruleolineatus from Dhofar Governorate, Sultanate of Oman.
TL [cm] | Age [year] | Total | |||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | ||
18–20 | 0 | ||||||||||||||||||
20–22 | 4 | 7 | 11 | ||||||||||||||||
22–24 | 6 | 32 | 3 | 41 | |||||||||||||||
24–26 | 11 | 24 | 17 | 1 | 53 | ||||||||||||||
26–28 | 1 | 16 | 18 | 8 | 2 | 45 | |||||||||||||
28–30 | 8 | 6 | 21 | 8 | 1 | 1 | 45 | ||||||||||||
30–32 | 3 | 5 | 9 | 13 | 1 | 3 | 2 | 36 | |||||||||||
32–34 | 1 | 7 | 7 | 6 | 3 | 1 | 1 | 1 | 27 | ||||||||||
34–36 | 0 | 4 | 2 | 1 | 2 | 2 | 1 | 1 | 1 | 14 | |||||||||
36–38 | 1 | 2 | 2 | 2 | 3 | 1 | 2 | 13 | |||||||||||
38–40 | 2 | 1 | 1 | 1 | 5 | ||||||||||||||
40–42 | 1 | 1 | 1 | 1 | 1 | 5 | |||||||||||||
42–44 | 1 | 1 | |||||||||||||||||
Total | 22 | 90 | 50 | 38 | 32 | 15 | 13 | 9 | 7 | 4 | 2 | 3 | 4 | 4 | 0 | 0 | 2 | 1 | 296 |
Mean length [cm] | 23 | 24 | 26 | 28 | 30 | 33 | 32 | 33 | 36 | 35 | 36 | 36 | 38 | 36 | 41 | 43 | 28 |
The (VBGF) which describes male, female and combined sex of blueline snapper at age can be expressed as:
Male: TL [cm] = 42 [1 – e–0.21(t + 0.22)], (r2 = 0.70)
Female: TL [cm] = 46 [1 – e–0.16(t + 0.15)], (r2 = 0.78)
Combined sex: TL [cm] = 44 [1 – e–0.17(t + 0.18)] (r2 = 0.73)
Mean monthly marginal increment ratios (MIR ± SE) in the otoliths of blueline snapper are shown in Fig.
The coefficient of total mortality (Z) of blueline snapper was estimated by the length converted catch curve method (Z = 0.393) for combined sex (Fig.
The basic biological studies such as morphometric, age and growth parameters, and reproductive characteristics are important in understanding the life history of the fishes. The maximum fish length of the presently reported species was 43.7 cm TL while previous estimation (
In the presently reported study, sectioned otoliths were used to estimate growth parameters. Various methods have been used for estimating growth parameters of Lutjanus species, but reading otolith sections are one of the best application for annuli determination due to its accuracy and reliability (
Age–length frequency distributions for the presently reported blueline snapper revealed that only 1% of the samples were older than age 15. Although the sample size in this study was not enough for validating population-level age structure. Male’s age ranged from 1 to 14 years, while females were between 1 and 18 years showing toward higher age distribution. The age structures were variable between sexes, with the female having the highest longevity at 18.7 years. This estimation of longevity is similar to those attained by Lutjanus carponotatus (Richardson, 1842) sampled within the Great Barrier Reef (
The asymptotic length (L∞) of blueline snapper estimated was 44 cm TL for combined sex. The growth rate of males (K = 0.21) was higher than females (K = 0.16). Such finding is relatively in agreement with other Lutjanidae fishes (
Some Lutjanus snappers have a relatively long life span and larger maximum size (≥50.0 cm TL), often exceed 40 years such as Lutjanus bohar (Forsskål, 1775) nearly close to 56 years (
Estimates of natural mortality (M) for the presently reported species was 0.296 which is similar to those for other Lutjanidae fishes. Generally, many Lutjanus species are long-lived fishes and have a low value of the instantaneous rate of natural mortality; for instance, natural mortality of Lutjanus analis ranged from 0.28 and 0.49 (
The presently reported study estimation of the annual instantaneous rate of mortality (Z) for the blueline snapper in the Dhofar Governorate was 0.372 and the fishing mortality (F) was 0.076. Total mortality calculations based on the length converted catch curve method has been recorded high value (0.393) than the Beverton–Holt method (0.350). Estimates were greatly lower than that found by
The study was competent to investigate age structure, growth rate, and the mortality of blueline snapper, L. coeruleolineatus in Omani waters (Arabian Sea). The length and weight distributions between females and males were comparable to those reported in L. fulviflamma from Southern Arabian Gulf, Mafia Island in Tanzania, and Lutjanus campechanus from the northern Gulf of Mexico suggesting females having bigger and heavier body than males (
My great thank to the Ministry of Agriculture, Fisheries Wealth and Water Resources, Sultanate of Oman for providing me all facilities to make this research. My kind appreciation goes to my colleagues at Marine Science and Fisheries Center for their recommendations.