Some Targeted Reference Points for Thin Lip Grey Mullet Liza ramada Management in Bardawil Lagoon, North Sinai, Egypt
Received Date: Oct 16, 2018 / Accepted Date: Jan 08, 2018 / Published Date: Jan 18, 2018
The evaluation and management of fisheries resources require knowledge of spatial and temporal changes in the habitat-associations of fishes as well as studying the biology and dynamics of commercial fishes of that fishery. The thin lip mullet, L. ramada is one of the most important and high valued species in Bardawil lagoon, Egypt. Long term commercial catch statistics show a significant decrease in the commercial landings of grey mullet in Bardawil lagoon since 1995. By learning more about this species and protecting the habitat upon which it depends, we can ensure that this important valuable fish remains abundant. Age was determined based on scale’s readings of fish collected in May 2017 to December 2017 and in May 2018 to October 2018. Growth parameters, mortality rates, exploitation level as well as the critical lengths and ages were estimated. Based on yield per recruit analysis, the mullet fishery in Bardawil lagoon was found to be heavily exploited. The study suggested some applicable reference points for sustaining and optimizing the thin lip grey mullet yield in Bardawil lagoon.
Keywords: Egypt; Bardawil lagoon; Mugilidae; Population dynamics; Management
Grey mullets (Family: Mugilidae) are extremely important fish, which are cultured in many countries due to their high quality flesh, superior growth and wide salinity and temperature tolerance. The grey mullets are the most important fish species inhabiting Bardawil lagoon. Their catches fluctuated between 733 and 1590 ton during the last 15 years  forming about 38% of the total lagoon production and 60% from fish production of the lagoon. In 2016, 1548 ton of grey mullets were landed forming a net profit of about 80 million Egyptian pounds. Mullet's catch is composed mainly from Mugil cephalus , L. ramada and L. aurata , while both Chelon labrosus and L. saliens are found in very small amounts and recorded under the “others” group. Although the mullets in Bardawil lagoon contribute greatly to the economy of Egypt, very limited studies concerning their dynamics and management are available [2-5]. On the other hand, the biology and dynamics of mugilid species were studied in the different water bodies in Egypt [5-13].
Effective management decision making requires knowledge of the state of the fishery relative to management targets or limits, and of the likely responses of the fishery to alternative management options. Providing such knowledge typically in a quantitative form is the aim of fisheries stock assessment [14-16]. To assess fish stock, many detailed information such as age and growth, mortality and exploitation rates should be available. The present paper provides an up to date data about the biology and dynamics of L. ramada in Bardawil lagoon required for proposing some targeted reference points for its management.
Materials And Methods
Bardawil lagoon (Figure 1) is one of the northern lakes in Egypt and it is a part of the Mediterranean coastal lands of Sinai. It is an important source of local and economic fishes in North Sinai, and it plays an essential role in the fish production in Egypt, where it produces very economically important species of fishes such as seabass, seabream, sole, grey mullet, eel, meager and white grouper. Bardawil lagoon is a shallow hypersaline lagoon. Its area is about 685 km2 extends for a distance of about 95 km, from a point 45 km east of Port Said and extending to a point 18 km west of El-Arish. Its maximum width is 22 km and The average depth is 135 cm with a maximum depth next to inlets 1 and 2, whereas, reach to (2-5) m, while in the main opening reach to (4-7) m. A long sand-bar, (200-1000) m wide maximum, separates the lagoon from the adjacent Mediterranean.
Sampling and measurements
Monthly random samples of L. ramada were collected from the Bardawil lagoon during the period from May 2017 to December 2017 and from May 2018 to October 2018 (almost two fishing seasons). The length frequency for about 3000 L. ramada , 1080 males (12 cm to 42 cm TL) and 1920 females (11 cm to 47 cm TL), were grouped in 1 cm length groups.
For each fish data on total length (measured to the nearest millimeter), total weight (weighed to the nearest gram), and scale samples were collected. Age determination from scale readings was performed and only 2650 scale (88.3%) were accepted for age determination, the rest (11.7%) were regenerated scales and were rejected.
The general power equation (W=a Lb) was applied to estimate the length-weight relationship, where a and b are constants whose values were estimated by the least square method. Confidence intervals of 95% were calculated for the slope (b) to see if these were statistically different from 3.
Age composition was constructed based on scales’ readings and the resulting mean lengths at age were used in the construction of growth models. The von Bertalanffy  growth parameters were estimated using the Ford et al.  version as described by FAO . Total mortality rate Z was computed using three different methods; the semi-logarithmic regression method of Ricker  as Ln Nt=Ln No −Zt, this is a straight line with a slop equal to −Z, Jones et al.  as Ln(CN)=a+(Z/K)*Ln(L∞−L) where CN is the cumulative frequency, K is the growth coefficient and a and b are constants and Hoenig formula  as Z=1/(c1·(tmax−tc)) and SE(Z)=(c2·Z2)½ where the SE is the standard error of the estimated Z, c1 and c2 are table values and a function of N . Natural mortality coefficient was calculated as the geometric mean of three different methods; Ursin  as M=W−1/3, Rikhter et al.  as M=((1.52/tmass)0.72)−0.16 and Pauly  as LogM=−0.0066−0.179 Log L∞+0.e43 Log K+0.4634 Log T. where T is the mean annual water temperature of the lagoon.
Critical lengths and ages
The length at first capture (Lc) was estimated by the analysis of catch curve using the method of Pauly . The length at first sexual maturity Lm was estimated by the empirical formula of Froese et al.  as Log Lm=0.8979 Log L∞−0.0782. While the corresponding age at first sexual maturity (Tm) was computed using the von Bertalanffy growth equation as Tm=t0−(1/k*ln[1−(Lm/L∞)]). Besides, the smallest individual in the catch was considered as the length at recruitment Lr.
Relative yield per recruit (Y’/R)
Where: M=1−E/(M/K)=K/Z and U=1–(Lc/L∞).
Resource status was evaluated by comparing estimates of the fishing mortality rate with target (Fopt) and limit (Flimit) biological reference points (BRP) which were defined as: Fopt=0.5M and Flimit=2/3M .
Results And Discussion
The present study has established some target reference points for management the L. ramada stock which are exploited in Bardawil lagoon, Egypt. These regulations are suggested based on the study of population parameters and biological characteristics of this species including age and growth, length-weight relationship, mortality and exploitation rates and yield per recruit.
Age and growth
Scales were used for age determination of L. ramada collected from Bardawil lagoon. Scales have been proven as a reliable and valid method for ageing grey mullets [3,12,33-39]. The results showed that the maximum life span of L. ramada is five years for males and seven years for females and age group one was the most frequent group in the catch. The back-calculated lengths were (19.25, 28.08, 33.92, 38.71 and 40.94) cm for males for 1st, 2nd, 3rd, 4th and 5th year of life respectively and (20.15, 29.04, 35.19, 39.2, 42.39, 44.89 and 46.31) cm for 1st, 2nd, 3rd, 4th, 5th, 6th and 7th year of life respectively for females. The greatest incremental growth in length occurred during the first year of life and declined gradually thereafter (Figure 2). The same finding was recorded in the previous studies in different localities (Table 1) [3,12,13,33,34,36,37,39-41].
Table 1: Length at age (cm) of L. ramada given by different authors in the Egyptian water bodies.
A total of 3000 individuals of L. ramada have been collected from the commercial landings in Bardawil lagoon. The total lengths of males varied from 12 cm to 42 cm, while their weights ranged between 20 g and 670 g. The total lengths of females varied between 11 cm and 47 cm TL and between 15.8 g and 790 g in weight. The length-weight relationship equations were: W=0.0173 L2.7695 for males and W=0.0173 L2.7687 for females (Figure 3). The allometry coefficient of the length-weight relationship indicates negative allometric growth. Also, there is no significant difference between sexes in length-weight relationship. The b-value is more or less similar to that obtained by the previous workers (Table 2).
|Wadi El-Raiyan Lakes||3.0719|
The difference between estimated b-value between localities and in the same area in different periods is may be due to the fact that b-value could be an indicator of the physiological condition of the fish and vary seasonally in response to seasonal variations in environmental condition and changes in the fish wellbeing . The length-weight relationship and the b value can also be influenced by fishing pressure that excessively catches the adults. This is can explain the difference in growth type in Bardawil lagoon in 2006 and in the present study.
Parameters of the Von Bertalanffy growth function were calculated for L. ramada population in Bardawil lagoon, the parameters of growth were L∞=45.79 cm TL, K=0.40 per year and t0=−0.36 year for male, L∞=49.92 cm TL, K=0.35 per year and t0=−0.41 year for female and for pooled data were L∞=50.25 cm, K=0.34 per year and t0=−0.42 year. Thomsonet et al.  mentioned that the average K value for this species is 0.15 per year and varies between 0.11 and 0.45 per year, which is in accordance to the findings of our study. The K-value indicates that this species undergoes a rapid growth. Also, the negative t0 value worked out in the present study indicated faster growth rate at the juvenile stage [19,44-46].
As there is no sex specific fishing gear in Bardawil lagoon, the growth parameters for sexes combined were used for the subsequent calculations. Total mortality (Z) was estimated at 1.38 per year, natural mortality was estimated at 0.42 per year, while the fishing mortality was estimated at 0.96 per year. The exploitation ratio was computed at 69.6%. Based on the mortality data, the percentages of non-survivors were: From natural causes =1−e-M=34.3% and from fishing =1−e- F=61.7%.
Length at first sexual maturity Lm is of great importance when determining the optimum mesh size and SSB. The Lm of L. ramada in Bardawil lagoon fishery was found to be 28.2 cm TL for sexes combined. The corresponding age was 1.9 yrs, which means that the exploited L. ramada must be protected till their second year of life in order to be able to spawn at least once. The estimated length at first capture Lc in the present study was 22.9 cm TL. Both the estimated Lc and the observed lengths of fish captured indicated growth and recruitment overfishing. In the light of these results, a minimum size limit should be implemented for L. ramada in Bardawil lagoon.
Reference points and management
The relative Y/R analysis (Figure 4) showed that the EMSY was 0.65 which is lower than the current one (0.696), so the current E should be reduced from 0.696 to 0.65. For the sustainability of this fishery resource, it should be work at E value that conserves 50% of the spawning stock. In the present study the E0.5, the target reference point, was 0.32 and the current E should decrease from 0.696 to 0.32.
In conclusion, the obtained F (0.96) and E (0.696) values revealed that the thinlip grey mullet in Bardawil lagoon is overexploited. It is worth mentioning that the excessive fishing effort is not the only reason responsible for the declining of fishery resources in the lagoon, the illegal harvesting of fish fry and spawners, using destructive fishing methods as well as gazzering the sea grasses which represent the shelter and nursing areas for grey mullets are other important reasons. There are many efforts now to maintain the different fish stocks in the lagoon such as prohibition of destructive gears, dredging the boughazes (the connections with the sea) and monitoring the illegal fishing practices in the lagoon but more detailed study about the interaction between species and between species and the ecosystem as well as the multiple objectives of all stakeholders should be done.
- GAFRD, General Authority for Fish Resources Development (2016) Annual statistical report for fisheries. Egyptian Ministry of Agriculture, Cairo, Egypt.
- Mehanna SF (2006) Lake Bardawil fisheries: current status and future sight. J Egyp Ger Soc Zool 51: 91-105.
- Mehanna SF (2006) Fisheries management of the thinlip grey mullet Liza ramada and Golden Grey Mullet Liza aurata from lake Bardawil, Egypt. Egypt J Aquat Biol & Fish 10: 33-53.
- Mehanna SF, Hegazi MM (2013) Population dynamics of grey mullet Mugil cephalus associated with seagrass community in Bardawil lagoon, Northern Sinai, Egypt. INOC-XIII International Symposium 2013, Malaysia.
- Ismail MZ (1973) A biological study of the mullet fisheries in Nozha Hydrodrome. M.Sc. Thesis, Alexandria University, Egypt.
- Youssef SF (1973) Studies of the biology of family Mugilidae in Lake Manzala. M.Sc. Thesis, Faculty of Science, Cairo, University.
- Boraey FA (1974) Biological study in the family Mugilidae in Lake Quarun. Ph.D. Thesis, Ain-Shams University, Cairo.
- Shafik MM (1991) Biological studies on Mugil cephalus and Liza ramada of Lake Quarun, Egypt, with special emphasis on the fisheries of the lake and principle of inducing breeding of M. cephalus. M.Sc Thesis, Faculty of Science, Cairo University.
- El-Serafy SS (1993) Biology of Liza ramada (Risso, 1826) in two different habitats. Journal of the Egyptian German Society of Zoology 11: 17-36.
- Abdel-Baky TE, Bahnasawy MH (1993) Age and growth of grey mullet, Liza ramada in Lake Manzallah, Egypt. Journal of the Egyptian German Society of Zoology 13: 169-189.
- Khalil MT (1996) Changes in the mullet fishery of Lake Manzala, Egypt. International Journal of Salt Lake Research 5: 241-251.
- El-Gammal FI, Mehanna SF (2004) The dynamics and exploitation of the population of Liza ramada (Risso, 1810) in Wadi EI-Raiyan lakes. Egypt. Egypt J Aquat Biol Fish 8: 35-51.
- Mehanna SF, El-Gammal FI (2007) Population characteristics and reproductive dynamics of the thinlip mullet Liza ramada (Risso, 1810) at Suez Canal Lakes, Egypt. Egyp J Aquat Biol & Fish 11: 307-324.
- Hilborn R, Walters CJ (1992) Quantitative Fisheries Stock Assessment: Choice, Dynamics and Uncertainty. Springer, New York.
- Cowx IG (1996) Stock assessment in inland ﬁsheries. Fishing News Books, Oxford.
- Walters CJ, Martell SJ (2004) Fisheries ecology and management. Princeton University Press, Princeton.
- Bertalanffy L von (1938) A quantitative theory of organic growth (Inquiries on growth Laws. 2 ). Hum Biol 10: 181-213.
- Ford E (1933) An account of the herring investigations conducted at Plymouth during the years from 1924 to 1933. J Mar Biol Assoc UK 19: 305-384.
- Walford LA (1946) A new graphic method of describing the growth of animals. Biol Bull Mar Biol 90: 141-147.
- FAO (1981) Fishery and aquaculture country profile: the Arabic Republic of Egypt. Food and Agriculture Organization of the United Nations (FAO), Rome.
- Ricker WE (1975) Computation and interpretation of biological statistics of fish populations. Bulletin of the Fisheries Research Board of Canada 191: 1-382
- Jones R, Van Zalinge NP (1981) Estimates of mortality rate and population size for shrimp in Kuwait waters. Kuwait Bull Mar Sci 2: 273-288.
- Hoenig JM (1982) Estimating mortality rate from the maximum observed age. ICES. C.M./1982/D:5 10p.
- Hoenig JM, Lawing WD (1982) Estimating the total mortality rate using the maximum order statistic for age. Int Coun Explore Sea C.M./D: 7, 13p.
- Ursin E (1967) A mathematical model of some aspects of fish growth, respiration and mortality. J Fish Res Bd Can 24: 2355-2453.
- Rikhter VA, Efanov VN (1976) On one the approaches to estimation of natural mortality of fish population. ICNAF Res Doc 76/VI/8: pp: 12.
- Pauly D (1980) On the interrelationships between natural mortality, growth parameters and mean environmental temperature in 175 fish stocks. J Cons CIEM 39: 175-192.
- Pauly D (1984) Length-converted catch curves. A powerful tool for fisheries research in the tropics. (part II) . ICLARM Fishbyte 2: 17-19.
- Froese R, Binohlan C (2000) Empirical relationships to estimate asymptotic length, length at first maturity and length at maximum yield per-recruit in fishes, with a simple method to evaluate length frequency data. J Fish Biol 56: 758-773.
- Beverton RJH, Holt SJ (1966) Manual of methods for fish stock assessment. Part 2. Tables of yield functions. FAO Fish Tech Pap/FAO Doc 1: 67.
- Pauly D, Soriano ML (1986) Some practical extensions to Beverton and Holt's relative yield-per-recruit model. In: Maclean JL; Dizon LB, Hosillo LV (editors.). The First Asian Fisheries Forum 491-496.
- Patterson K (1992) Fisheries for small pelagic species: an empirical approach to management targets. Rev Fish Biol Fish 2: 321-338.
- Hashem MT, El-Maghraby AM, Ezzat A (1977) Age and growth of Mugil capito C. & V. in Nozha Hydrodrome, Alexandria. Bull Inst Oceanog Fish ARE 7: 191-206.
- Salem SA, Mohammed SZ (1982) Studies on Mugil seheli and Mugil capito in Lake Temsah. I. Age and growth. Bull Inst Oceanog Fish ARE 8: 29-48.
- Campana SE, Annand MC, McMillan JI (1995) Graphical and statistical methods for determining the consistency of age determination. Trans Am Fish Soc 124: 131-138.
- Glamuzina B, Dulcic J, Conides A, Bartulovic V, Matic-Skoko S, et al. (2007) Some biological parameters of the thin-lipped mullet, Liza ramada (Pisces, Mugilidae) in the Neretva River delta (Eastern Adriatic, Croatian coast). Vie et Millieu 3: 131-136.
- Kasimoglu C, Yilmaz F, Torcu Koc H (2011) Growth and Reproductive Characteristics of the Thinlipped Grey Mullet, Liza ramada (Risso, 1826) Inhabiting in Gökova Bay (Muğla), the Southern Aegean Sea, Turkey. BAU Fen Bil Enst Dergisi Cilt 13: 35-49.
- Hotos GN, Katselis GN (2011) Age and growth of the golden grey mullet Liza aurata (Actinopterygii: Mugiliformes: Mugilidae), in the Messolonghi-Etoliko Lagoon and the adjacent Gulf of Patraikos,Western Greece. Acta Ichthyol Piscat 41: 147-157.
- Khalifa MM, Ramadan AS, Elawad AN, El-Mor M (2016) Age and growth pattern of the thin-lipped mullet Liza Ramada in the Eastern coast of Libya. International Journal of Bioassays 56: 4620-4624.
- Rafail SZ (1968) Investigation of the mullet fishery by the beach seine of the U.A.R Mediterranean Coast. Gen Fish Coun Medit 35: 1-19.
- Hosny CFH, Hashem MT (1995) Biology of growth of Liza ramada in Lake Borollus, Egypt. Bull Nat Inst Oceanog Fish ARE 21: 469-475.
- Biswas SP (1993) Manual of methods in fish biology. South Asia, New Delhi, India.
- Thomson JM (1990) Mugilidae. In Quero JC, Hureau JC, Post CA, Saldanha L (editors), Check-list of the fishes of the eastern tropical (CLOFETA). UNESCO, Paris 2: 857-858.
- El-Maghraby AM, Hashem MT, El-Sedafy HM (1973) Some biological characters of Mugil capito (Cuv.) in Lake Borollus. Bull Inst Oceanog Fish ARE 3: 55-82.
- El-Maghraby AM, Bishara NF (1971) Length-weight relationship in two species of grey mullet. Bull Fac Sci Alex Univ 10: 95-108.
- Fayek S (1973) Biological studies on Mugilidae in Lake Manzalah. Thesis, Faculty of Science, Cairo University.
Citation: Mehanna SF, Desouky MG, Makkey AF (2019) Some Targeted Reference Points for Thin Lip Grey Mullet Liza Ramada Management in Bardawil Lagoon, North Sinai, Egypt. Fish Aqua J 10: 263. DOI: 10.4172/2150-3508.1000263
Copyright: © 2019 Mehanna SF, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Select your language of interest to view the total content in your interested language
Share This Article
- Total views: 187
- [From(publication date): 0-0 - Jun 27, 2019]
- Breakdown by view type
- HTML page views: 156
- PDF downloads: 31