Capture Production and Stock Assessment of Solea Aegyptiaca Chabanaud, 1927 (Soleidae: Pleuronectiformes) in Bardawil Lagoon, Egypt

Home , Egyptian sole, Lake Bardawil, Solea (fish)

Egyptian Journal of Aquatic Research (2015) 41, 101–110

HOSTED BY National Institute of Oceanography and Fisheries Egyptian Journal of Aquatic Research

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FULL LENGTH ARTICLE Capture production and stock assessment of Solea aegyptiaca Chabanaud, 1927 (Soleidae: Pleuronectiformes) in Bardawil Lagoon, Egypt

Mohamed H. Gabr *,1

Marine Biology Department, Faculty of Marine Sciences, King Abdulaziz University, P.O. Box 80207, Jeddah 21589, Saudi Arabia National Institute of Oceanography and Fisheries, Suez, Egypt

Received 27 November 2014; revised 14 January 2015; accepted 28 January 2015 Available online 24 February 2015

KEYWORDS Abstract Capture production from Bardawil Lagoon was described and analyzed. Fish samples of Solea aegyptiaca; Solea aegyptiaca were collected for growth study. Otoliths were extracted from each specimen and Growth parameters; used for age determination. Back-calculated lengths-at-ages were estimated and used to determine Exploitation; growth rates in length and weight. The von Bertalanffy growth parameters; L1, K and t0, were Relative yield per recruit; determined. Growth in length could be described by the von Bertalanffy growth equation ‘‘VBGE’’: 0.42(t+0.4) Reference points Lt = 37.52 [1 e ]. The total mortality coefficient ‘Z’, the natural mortality coefficient ‘M’ and the fishing mortality coefficient ‘F’ were estimated to be 2.35, 0.63 and 1.72 year1, respec- 1 tively. The current exploitation rate ‘Ecur’ was 0.73 year . Beverton and Holt’s relative yield per recruit Model (1966) was used to estimate the relative yield and biomass per recruit of S. aegyptiaca

in Bardawil Lagoon. The yield-based biological reference points Emax and E0.1 were determined and found to be 0.717 year1 and 0.62 year1, respectively. Results indicated that the stock of S. aegyptiaca in Bardawil Lagoon is currently over-exploited. The current exploitation rate should be 1 decreased to the widely adopted target reference point, E0.1 = 0.62 year for sustainable ﬁshery production of S. aegyptiaca in Bardawil Lagoon. ª 2015 National Institute of Oceanography and Fisheries. Hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

1. Introduction

The Egyptian sole Solea aegyptiaca is one of the flatfish species of the family Soleidae which are of commercial importance in the Mediterranean Sea. It has been recently predicted to be a * Address: Marine Biology Department, Faculty of Marine Sciences, King Abdulaziz University, P.O. Box 80207, Jeddah 21589, Saudi valid species (Vachon et al., 2008; Boukouvala et al., 2012) Arabia. Tel.: +966 562707427; fax: +966 26401747. and is not a synonym of the common sole Solea solea as E-mail addresses: [email protected], [email protected] reported by Ben-Tuvia (1990) and Borsa and Quignard (2001). 1 Permanent address. Soles production represents an important part of the com- Peer review under responsibility of National Institute of Oceanography mercially exploited marine species in Bardawil Lagoon which and Fisheries. http://dx.doi.org/10.1016/j.ejar.2015.01.006 1687-4285 ª 2015 National Institute of Oceanography and Fisheries. Hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 102 M.H. Gabr is situated along the northern coast of Sinai, Southeast Medi- obtained from the general authority for fish resources develop- terranean (Fig. 1). The Lagoon was built for utilizing fish ment (GAFRD) branch at the fish landing site of Eltelool. Fish resources that originate from the adjacent Mediterranean samples of S. aegyptiaca were collected during the fishing sea- Sea. It covers an area of about 650 km2, with depths ranging son from May to December 2010. Measurements of total fish from 0.5 to 1.5 m and rare depths of 3 m. Many authors stud- length and body weight were recorded for 445 specimens. ied the fish production, fishery biology of many fish species The power equation: W = aLb was used to describe the rela- and crustaceans and fisheries management of Bardawil tionship between fish length and body weight. Lagoon (Ben-Tuvia, 1984; El-Gammal et al., 1994; Abdel- For age determination, the sagittal otoliths were removed Hakim et al., 1997; Abd-Alla, 2004; Ameran, 2004; Sabrah, from each specimen and preserved clean in an Eppendorf vial, 2004; Khalifa, 1995; Abdel-Razek et al., 2006). containing water, with reference to the species name, date and Mehanna (2006) mentioned that a dramatic change serial number. The left-side otolith was examined using an occurred in the catch composition of the Lagoon during the optical system consisting of MEIJI Zoom Stereomicroscope last two decades, where the crustacean production increased connected to a computer system through digital video camera. and reached about 60% of the total catch in 2005, while the Pictures were captured and saved by Micrometrics SE Premi- catch of economic fish species like sea bream and sea bass um software for measuring distance from the otolith focus to was reduced. She attributed this change in catch composition the outer margin and the margin of each annulus. to many factors including: change in ecological conditions, Back-calculated lengths-at-ages were estimated according increased salinity, continuous dredging (silting) of the Lagoon to the Lee’s equation (1920): inlets, prohibition of the purse-seining in 1993, and introduction of shrimp trawl (called Kalsa). Ln ¼ c þðL cÞsn=S Despite the economic importance of Soles in Bardawil where, L is the calculated length when the annulus ‘n’ was Lagoon (their maximum catch was about 342.5 ton in 2008); n formed, L is the observed fish length, s is the distance in only El-Gammal et al. (1994) estimated the yield per recruit n ‘mm’ from the otolith focus to the margin of the annulus ‘n’, of S. solea in the Lagoon. Mehanna (2007) described aspects S is the otolith radius (from the focus to the outer margin), c of the population dynamics and stock status of the Egyptian is the intercept of the linear regression analysis between the sole S. aegyptiaca in the Southeastern Mediterranean coast observed fish length (cm) and the otolith radius (mm) accord- off Egypt. Ahmed et al. (2010) studied the reproduction of ing to the linear relation: L ¼ c þ dS. S. aegyptiaca from Port Said in the Southeastern Mediter- The von Bertalanffy Growth Equation (VBGE): ranean coast off Egypt. The present study aimed to describe L ¼ L ½1 eKðtt0Þ was applied to describe growth in length and analyze the capture production of Soles compared to total t 1 of S. aegyptiaca in Bardawil Lagoon. The growth parameters; capture production from the Lagoon during the last decade, L and K were estimated by fitting Ford (1933) and Walford determine age and estimate growth parameters, mortality coef- 1 (1946) plot to the average back-calculated lengths-at-ages. The ficients, relative yield and biomass per recruit of S. aegyptiaca following equation described by Sparre and venema (1998) was in Bardawil Lagoon. The values of E and E were deter- max 0.1 used to estimate the value of t : mined in order to evaluate the current stock status relative 0 to these yield-based reference points. t0 ¼ t þ 1=KLogeð1 Lt=L1Þ: The formula suggested by Pauly and Munro (1984); 2. Materials and methods ø = LogK + 2LogL1, was used to calculate the index of growth performance ø for S. aegyptiaca in Bardawil Lagoon. Total catch statistics (by species or species group) from The instantaneous total mortality coefficient ‘Z’ was esti- Bardawil Lagoon during the period from 1996 to 2012 were mated by the Linearized length-converted catch curve method of Pauly (1983). The natural mortality coefficient ‘M’ was estimated by the Jensen (1996) equation: M = 1.5 K. The difference between the total mortality coefficient ‘Z’ and the natural mortality coefficient ‘M’ was estimated to be the fishing mortality coefficient ‘F’. The exploitation rate ‘E’ was estimated as the ratio E/Z. The length at first capture ‘Lc’ was determined graphically by the cumulative catch curve analysis as described by Pauly (1984). The following model of Beverton and Holt (1966), modified by Pauly and Soriano (1986), was used to estimate the relative yield per recruit Y0/R and biomass per recruit B0/R of S. aegyptiaca in Bardawil Lagoon, applied in FiSAT II software and also in Excel worksheet:

Y0=R ¼ EUM=Kf1 ½3U=ð1 þ mÞ þ ½3U2=ð1 þ 2mÞ ½U3=ð1 þ 3mÞg

where, Figure 1 Map showing Bardawil Lagoon in Northern Sinai coast of the Mediterranean Sea, Egypt. U ¼ 1 ðLc=L1Þ; m ¼ð1 EÞ=ðM=KÞ; and E ¼ F=Z Stock assessment of Solea aegyptiaca in Bardawil Lagoon 103

Moreover, the gradual decrease of the total catch during the Table 1 Specifications of trammel net ‘Dabba’ used in fishing seasons 2010–2012 resulted from the annual decrease Bardawil Lagoon. of crustaceans catch during this period. It is clear from the fig- Gear item Characteristics ure that the annual catch variability of crustaceans determines Unit length 30 m the pattern of the annual total catch from the Lagoon. Net depth 1.8–2 m In Fig. 4, the average annual total catch of Soles from the Number of units per boat 20–30 Lagoon increased from 147 ± 13 ton during the fishing sea- Float line material and diameter Polyethylene, 4 mm sons 1996–2005 to 287 ± 45 ton during the fishing seasons Lead line material and diameter Polyethylene, 4 mm 2006–2009, and then decreased again to an average of Number and material of floats per unit 50 Cork floats, 25 gf 159 ± 35.5 ton during the fishing seasons 2010–2012. Results Distance between two floats 60 cm showed that the increase of soles catch accompanied the Weight of lead (sinkers) per unit (kg) 4–4.5 (50 g each sinker) Distance between two sinkers 35 cm increase in the Crustaceans catch in the fishing seasons 2006– Inner panel mesh size and 35 mm 2008. twine diameter 0.3 mm It seems that there were prevailing environmental condi- Outer panel mesh size and 120 mm tions, preferred for Crustaceans, which lead to the increase twine diameter 0.4 mm in their catch production. Khalil et al. (2013) indicated that Twine material Polyamide, monofilament the population density of total macrobenthos has dramatically declined from year to another and reached its minimum values in 2003 and 2004 then increased sharply during 2006/2007. 3. Results and discussion They concluded that the decline of bottom feeders, which represent the majority of commercial fish species migrating 3.1. Capture production between the Mediterranean Sea and the Lagoon, leads to the increase and flourishing of macrobenthic invertebrates, which The main fishing gear used to catch Soles in Bardawil Lagoon represent the main food items for those bottom feeders. is the trammel net called locally ‘‘Dabba’’. Specifications of However, the fact that the total capture production from this fishing gear are listed in Table 1. Usually two fishermen the Lagoon has decreased to its minimum in 2004 and, at on one boat, of 7 m length and 2 m width provided with an the same time, the population density of total macrobenthos outboard engine of about 10 horse power, spread the net in reached its minimum in 2004, may indicate that both mac- the water just before the sun set and haul it in the morning, robenthos and bottom feeders fishes are affected by the pre- then collect caught fish from the net to baskets (Fig. 2) to sell vailing high water salinity before 2004, and when the salinity it at harbor. decreased to its minimum 38–71.1& (Khalil et al., 2013; Abd As shown in Table 2 and Fig. 3, the average annual total Ellah and Hussein, 2009); a salinity range became suitable catch (fishes and crustaceans) during the fishing seasons for the growth of many species of macrobenthic invertebrates 1996–2004 was 2587 ± 583 ton, with a maximum of 3326 ton (Preston, 1985), the macrobenthic invertebrates started to during 2004 and a minimum of 1536 ton during 1996. During grow again in the Lagoon, and this in turn attracted bottom the fishing seasons 2005–2012, this average annual catch feeders to grow again in the Lagoon during the next years. increased to 4534 ± 677 ton, with a maximum of 5410.1 tons As a result, a sharp increase of the macrobenthos including during 2009 and a minimum of 3534 ton during the fishing sea- craps and shrimps which constitute the major part of the total son 2005. The percentage increment in the total catch was catch increment occurred during the fishing seasons from 2005 75%. Crustaceans and fishes contributed with 79% and to 2012, in addition to soles which feed mainly on polychaetes, 21%, respectively, of the total catch increment during the fish- mollusks, amphipods and Crustacean fragments (Link et al., ing seasons 2005–2012. The fall down of the total catch in 2004 2005; Sharaf et al., 2007). was mainly due to the sharp decrease of the crustaceans catch The decrease in the average catch of soles in 2010–2012 may (79% of the total catch decrease). Crustaceans also contribut- be due to the excessive fishing effort by the trawl net (Kalsa) to ed with 92% of the sharp increase of the total catch in 2005. catch shrimps and craps. Mehanna et al. (2011) reported that

Figure 2 Picture showing ﬁshermen on their boats (left) collecting caught ﬁsh from the net to basket (right) at the main landing site (eltelool) of Bardawil Lagoon. 104 M.H. Gabr

Table 2 Capture production from Bardawil Lagoon during the ﬁshing seasons 1996–2012. Fishing season Total catch Craps and shrimps catch Fishes catch Soles catch 1996 1536 175 1361 149 1997 2128 794 1334 139 1998 2277 823 1454 135 1999 2758 1235 1523 165 2000 3145 1541 1604 149 2001 2801 1116 1686 142 2002 3081 1422 1660 140 2003 3326 1762 1564 159 2004 2227 899 1328 127 2005 3534 2097 1438 168 2006 4142 2448 1694 292 2007 4729 2909 1820 281 2008 5393 3035 2358 343 2009 5410 3408 2002 232 2010 4731 2676 2055 123 2011 4529 2378 2151 194 2012 3844 2027 1817 159 Average catch 1996–2004 2587 1085 1501 145 2005–2012 4534 2622 1917 224 Increment 1952 1537 (79%)* 415 (21%)* 79 (4%)* Standard deviation 1996–2004 583 477 139 12 2005–2012 677 477 286 76 * % of the average catch increment.

6000

5000 Craps & Shrimps Fishes 4000

3000

Total Catch (tons) 2000

1000

Fishing Season

Figure 3 Annual total catch including ﬁshes and crustaceans (shrimps and craps) from Bardawil Lagoon during the ﬁshing seasons from 1996 to 2012.

more than 2 millions of Soles juveniles were caught as bycatch seasons causing fishermen to shift their effort to catch other each year. As a result, we can expect that soles in Bardawil abundant species. Lagoon suffer from recruitment overfishing due to shrimp trawling. 3.2. Age and growth The average monthly catch of Soles during the fishing seasons 2000–2009 is shown in Fig. 5. It is clear that there are two In flatfishes, the use of otoliths as an accurate method of age maximum values; in May (29.89 tons) and in November determination has been early accepted, because the majority (42.67 tons), and two minimum values; in August (8.38 tons) of species examined showed clear increments on their otoliths and in January (7.35 tons). This monthly variation in Soles (Nash and Geffen, 2005). Williams and Bedford (1974) men- catch may be attributed to seasonal migration from the tioned that it is necessary to establish two criteria in order to Lagoon to Mediterranean Sea for spawning and returning use otolith of any species of fish for age determination; the first back to the Lagoon (Gibson, 1997; Dierking et al., 2012), is to see a recognizable pattern in the otolith, and the second is which in turn will affect soles abundance during the different to allocate a time scale to the visible pattern. As shown in Stock assessment of Solea aegyptiaca in Bardawil Lagoon 105

350

300 Average catch of 287 ± 45 ton

250 Average catch of 159 ± 35.5 ton 200 Average catch of 147 ± 13 ton 150

Annual catch (ton 100

0 1997 1999 2000 2004 2006 2007 1996 1998 2001 2002 2003 2008 2009 2010 2011 2012 2005 fishing season

Figure 4 Annual total catch of Soles from Bardawil Lagoon during the ﬁshing seasons from 1996 to 2012.

Average catch (ton) 20

0 April May June July Aug. Sept. Oct. Nov. Dec. Jan.

Month

Figure 5 Average monthly catch of Soles from Bardawil Lagoon during the ﬁshing seasons from 2000 to 2009.

Fig. 6, there is a recognizable pattern of alternative opaque As shown in Fig. 7, the relationship between the observed and hyaline bands in otoliths viewed with transmitted light, total fish length (TL) and total otolith radius (S) is linear increasing in their number with the increase in fish length as (the coefficient of determination r2 = 0.9). The following shown in the otoliths from 0+to III+ age group specimens equation could be written to describe the relationship between (Fig. 6a–d). They also indicated that in most winter or spring the growth in fish length and the growth in otolith radius: spawners of marine teleosts of the Northern hemisphere, the TL ¼ 1:25 þ 10:41S. nucleus is usually composed of opaque materials which contin- The intercept of the last equation was applied in the Lee’s ue to be deposited until the onset of late autumn or early win- equation (1920) to calculate the individual back-calculated ter when the hyaline material starts to be formed until late lengths-at-ages. The average back-calculated lengths at ages winter or early spring. This means that each pair of alternative were estimated and listed in Table 3. It is clear from the results opaque and hyaline zones in the otolith of S. aegyptiaca in that the largest annual growth in length was during the first Bardawil Lagoon represents an annulus. year of life (17.1 cm/year), while the largest growth in weight Ahmed et al. (2010) concluded that the Egyptian sole S. was in the third year of life (97 g/year). aegyptiaca in the East Mediterranean coast off Egypt is a win- Fig. 8 shows the von Bertalanffy growth curve that ter spawner. Mehanna (2007) found that samples of S. aegyp- describes the theoretical growth in length of the Egyptian sole tiaca in the same area collected in January and February have S. aegyptiaca in Bardawil Lagoon, based on the following true annuli on the otolith margin or close to it. However, in the VBGE: Lt ¼ 37:52½1 expf0:42ðt þ 0:4Þg, that could be present study, otoliths from specimens collected in July described after estimating the growth parameters:

(Fig. 6c and d) show the start of opaque zone formation, L1 = 37.52 cm, K = 0.42, and t0 = 0.4 year. The index of whereas otoliths from specimens collected in December growth performance for S. aegyptiaca in Bardawil Lagoon (Fig. 6b) show late stage of opaque zone formation. Accord- was found to be: ingly, each pair of alternative opaque and hyaline zones is con- : : : sidered as an annulus for S. aegyptiaca in Bardawil Lagoon. Ø ¼ Log 0 42 þ 2 Log 37 52 ¼ 2 77 Based on otolith readings of 319 specimens ranging in ﬁsh Compared to results of growth parameters and perfor- length from 10 to 31 cm, four age-groups could be determined mance listed in Table 4, the asymptotic length and growth per- from 0+ to 3+. formance of the S. aegyptiaca in Bardawil Lagoon were higher 106 M.H. Gabr

S 1

(a) (b) F F

TL = 15.6 cm, S = 1.7 mm TL = 19.8 cm, S = 2.0 mm

S S 3 2

2 1

1 (c) (d) F F

TL = 26.3 cm, S = 2.6 mm TL = 31.2 cm, S = 3.1 mm

Figure 6 Otoliths from Solea aegyptiaca showing age groups from 0+ to 3+ where TL is the total ﬁsh length and S is the otolith radius from the focus ‘‘F’’ to the outer margin.

35.0 TL = 1.25 + 10.41 S Pe´rez-Ruzafa et al. (2013) that species shared by euhaline 2 30.0 r = 0.90 Lagoons and marine environments are larger and having large length at ﬁrst maturity and maximum yield. 25.0 3.3. Length-weight relationship and Lc 20.0

15.0 The relationship between total fish length and fish weight of Total length (cm) the S. aegyptiaca in Bardawil Lagoon could be described in 10.0 Fig. 9. The power equation describing this relationship could be written in the form: W = 0.0052 L3.179 (r2 = 0.96). The b 5.0 value (3.179) in the present study is higher than that obtained by Mehanna (2007) for S. aegyptiaca (Table 3), and indicates a 0.0 positive allometric growth for S. aegyptiaca in the Lagoon. 1 1.5 2 2.5 3 3.5 This may reflect high-quality habitats in Bardawil Lagoon, Otolith Radius (mm) where fish growth can be optimized (Brehmer et al., 2013; Figure 7 Total length–otolith radius relationship of Solea Taylor et al., 2007). aegyptiaca in Bardawil Lagoon. The length at first capture ‘Lc’, which is the length at which the probability of capture is 50%, was determined from the accumulated catch curve (Fig. 10) as described in Pauly than those obtained by El-Gammal et al. (1994) for the com- (1984) and found to be 18.75 cm, and the corresponding age mon sole S. solea in the Lagoon. Whereas the growth perfor- ‘Tc’ was estimated to be 1.2 year. Mehanna (2007) obtained mance of S. aegyptiaca in the Lagoon was similar to that smaller values of length (14.15 cm) and age (0.8 year) at first obtained by Mehanna (2007) for the same species in the capture for S. aegyptiaca. Mediterranean coast off Egypt, the asymptotic length was This difference may be attributed to the impacts of the higher for the species in the Lagoon than that in the Mediter- trawl nets used to exploit the Egyptian sole there compared ranean, and this is in agreement with the fact shown by to the trammel net used in the Lagoon. Stock assessment of Solea aegyptiaca in Bardawil Lagoon 107

Table 3 Average back calculated lengths at ages, growth in length and growth in weight of Solea aegyptiaca in Bardawil Lagoon. Age group (year +) Back-calculated length and corresponding weight at the end of each year of life Annual increment cm (g) 12 3 I+ 17.1 17.1 (43.4) (43.4) II+ 17.2 24.1 7.0 (44.3) (128.2) (84.8) III+ 17.2 24.2 28.7 4.7 (43.8) (129.9) (225.3) (97.0) Underlined values refer to the values used to estimate the annual increment.

40.00 L∞= 37.52 cm 300.0

W = 0.0052 L 3.179 32.00 250.0 K = 0.42 r 2 = 0.961

200.0 24.00

150.0 16.00 Total length (cm) Total weight (gm) 100.0

8.00 50.0

0.00 0.0 10.0 15.0 20.0 25.0 30.0 35.0 1 2 3 4 5 6 7 8 9 10 11 Age (year) Total length (cm )

Figure 8 von Bertalanffy growth curve for Solea aegyptiaca in Figure 9 Length–weight relationship of Solea aegyptiaca in Bardawil Lagoon. Bardawil Lagoon.

3.4. Mortalities and exploitation rate 3.5. Relative yield per recruit and reference points

The instantaneous total mortality coefficient ‘Z’ estimated by Fig. 12 shows the plot of the relative yield and biomass per the Linearized length-converted catch curve method, as recruit of S. aegyptiaca in Bardawil Lagoon as obtained described in Pauly (1983), was found to be 2.35 year1 through FiSAT II software. The figure shows the biological (Fig. 11). The natural mortality coefficient ‘M’, as estimated reference points; Emax and E0.1 (analogous to Fmax and F0.1, by the method of Jensen (1996), was 0.63 year1. The differ- respectively), and the corresponding relative yield per recruit. ence between Z and M was accounted for the Fishing mor- The reference point ‘Emax’, which is the exploitation tality coefficient ‘F’, and found to be 1.72 year1. The rate required to get the maximum relative yield per recruit 1 0 1 current exploitation rate ‘Ecur’ was 0.73 year . (Y /Rmax = 0.05139), was determined to be 0.717 year , and

Table 4 Population parameters of Solea aegyptiaca and Solea solea at different localities by different authors. Locality Species Sex Growth parameters Reference

KL1 t0 ø Greece Solea solea Unsexed 0.38 34.9 0.41 2.67 Stergiou et al. (1997) Egypt Bardaweel Lagoon Solea solea Pooled 0.33 30.04 1.51 2.47 El-Gammal et al. (1994) Egypt Southeast Mediterranean Solea aegyptiaca Pooled 0.53 30.9 0.33 2.70 Mehanna (2007) Egypt Bardawil Lagoon Solea aegyptiaca Pooled 0.42 37.52 0.449 2.77 Present study Length–weight parameters ab r2 Portugal Solea solea Unsexed 0.0078 3.080 0.969 Veiga et al. (2009) France Solea solea Unsexed 0.0048 3.175 0.998 Dorel (1986) Egypt Southeast Mediterranean Solea aegyptiaca Pooled 0.0086 3.0054 0.987 Mehanna (2007) Egypt Bardawil Lagoon Solea aegyptiaca Pooled 0.0052 3.179 0.961 Present study 108 M.H. Gabr

8.00 Ln N/(t2-t1)

calc LN 7.00

z = -slope 6.00 = 2.35

5.00 r2 = 0.97

4.00 Ln (N /t2-t1)

3.00

2.00

1.00

0.00 0.00 1.00 2.00 3.00 4.00 5.00

Relative age ( years)

Figure 10 Length-converted catch curve for Solea aegyptiaca from Bardawil Lagoon (Pauly, 1983).

100

40 Accumulated % 30

10 L50=18.75cm

0 10 12 14 16 18 20 22 24 26 28 30 Total length (cm)

Figure 11 Length at ﬁrst capture Lc (or L50)ofSolea aegyptiaca Figure 12 Relative yield and biomass per recruit of Solea in Bardawil Lagoon (accumulated catch curve method). aegyptiaca in Bardawil Lagoon as estimated by FiSAT software

(the yellow line represents the relative yield at Emax, the green line represents the relative yield at E , and the red line represents the the reference point ‘E ’, which is the exploitation rate at 0.1 0.1 relative yield at E ). which the marginal increase of the relative yield per recruit is 0.5 10% of its value at E = 0, was estimated to be 0.62 year1. In Fig. 13, the plot of the relative yield and biomass per in the Lagoon (0.05138) is smaller than that of the same species recruit against the exploitation rate, as estimated and designed in the east Mediterranean Sea (over 0.055), which is a charac- in Microsoft ofﬁce Excel worksheet, shows the current status teristic of species shared by euhaline Lagoons and marine envi- of exploiting S. aegyptiaca ‘Ecur’ compared to the biological ronments (Pe´rez-Ruzafa et al., 2013). reference points Emax, and E0.1. The current exploitation rate However, Emax, and E0.1 are the most commonly used tar- 1 ‘Ecur’ was found to be 0.73 year giving a relative yield per get biological reference points, where the majority of interna- 0 recruit (Y /Rcur) of 0.05138 which is just 0.00001 less than tional ﬁsheries commissions adopted these two points as a 0 Y /Rmax. Compared to the results obtained by Mehanna long-term objective of management, and in some cases Emax (2007), the current relative yield per recruit of S. aegyptiaca have been proposed as a Limit reference point, whereas E0.1 Stock assessment of Solea aegyptiaca in Bardawil Lagoon 109

0.060 1.0

0.056 0.9 Y'/R max = 0.05139 0.052

Y'/R 0.1 = 0.0504 0.048 0.8

0.044 0.7 Y'/R = 0.0382 0.040 0.5 =0.717 (Y'/R)

0.036 =0.73 0.6 =0.62 max cur 0.1 E E 0.032 E Recruit Recruit (B'/R) B'/R 0.5 = 50 % 0.5 0.028

0.024 0.4 Relative Yeild per

0.020 =0.363

0.5 0.3 Relative Biomass per 0.016 E B'/R 0.1 = 23 %

0.012 0.2 B'/Rcur = 14.2 % B'/R max = 15.1% 0.008 0.1 0.004

0.000 0.0 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 Exploitation rate(F/Z)

Figure 13 Relative yield and biomass per recruit of Solea aegyptiaca in Bardawil Lagoon as drawn in Microsoft Excel worksheet. is more applicable as a target reference point because it is more the anonymous referees for their effort and valuable conservative than selecting Emax (Hoggarth et al., 2006; comments. Cadima, 2003). As shown in Fig. 13, by reducing the current 1 1 exploitation from 0.73 year to the level of E0.1 = 0.62 year References 0 (15.1% reduction in the fishing effort), the Y /Rcur will be reduced from 0.05138 to 0.0504 (only 1.9% reduction), at Abd-Alla, S.M., 2004. Biological Studies for the Fishery Regulations the same time the current relative biomass per recruit will be and Management of the Bardawil Lagoon (Ph.D. thesis). Fac. Env. increased from 14.2% to 23% of its value at the unexploited Agri. Sci., Suez Canal Univ., 184pp. 1 Abdel-Hakim, N.F., Azab, A.M., Moustafa, A.T., 1997. Fisheries state. If we considered the reference point E0.5 = 0.36 year (the exploitation rate at which the biomass per recruit is status in Bardawil Lagoon, North Sinai. Egypt J. Aquat. Boil. Fish 50% of its value in the virgin stock biomass ‘Bv’ at E = 0), 1 (2), 309–323. Abd Ellah, R.G., Hussein, M.M., 2009. Physical limnology of as shown in the figure, the current exploitation should be Bardawil Lagoon, Egypt. Am. Eurasian J. Agric. Environ. Sci. 5 reduced by 50% resulting in 25.7% reduction in the relative (3), 331–336. yield per recruit. So, it will be more reasonable and acceptable Abdel-Razek, F.A., Taha, S.M., Ameran, M.A., 2006. Population (by fishermen society) to adopt the obtained value of E0.1 as a biology of the edible crab Portunus pelagicus (Linnaeus) from target reference point for the management of S. aegyptiaca Bardawil Lagoon, northern Sinai, Egypt. Egypt. J. Aquat. Res. 32, fishery in Bardawil Lagoon. 401–418. The exploitation rate can be decreased by reducing the fish- Ahmed, E.A.A., Sharaf, M.M., Laban, H.A., 2010. Reproduction of ing mortality (F) through fishing effort restrictions (Hoggarth the Egyptian sole, Solea aegyptiaca (Actinopterygii: Pleuronecti- et al., 2006). For S. aegyptiaca in Bardawil Lagoon, I recom- formes: Soleidae), from Port Said, Egypt, Mediterranean. Acta mend reducing the number of trammel net units (dabba) used Ichthyol. Piscat. 40 (2), 161–166. Ameran, M.A., 2004. Studies on the Crustacean Fishery in Bardawil to catch soles during each trip, in addition to reducing the Lagoon (Ph.D. thesis). Faculty of Environmental Agricultural number of fishing trips (days) per fishing season. Also I recom- Science, Al-Arish, Suez Canal University. mend the prohibition of shrimp trawl net (Kalsa) as reported Ben-Tuvia, A., 1984. Biological basis for the fishery regulation and by Mehanna et al. (2011) to avoid their negative impacts on management of the Bardawil Lagoon, Mediterranean coast of the Lagoon ecosystem as a whole, and on soles juveniles in Sinai. Papers Presented at the Expert Consultation on the particular. Regulation of Fishing Effort. FAO. Ben-Tuvia, A., 1990. A taxonomic reappraisal of the Atlanto- Mediterranean soles Solea solea, S. senegalensis and S. lascaris.J. Acknowledgments Fish Biol. 36, 947–960. Beverton, R.J.H., Holt, S.J., 1966. Manual of Methods for Fish Stock I would like to thank Dr. Mousa Ameran very much for help- Assessment. Part 2. Tables of Yield Functions. FAO Fish. Tech. ing me to get catch statistics of Bardawil Lagoon. I also thank Pap./FAO Doc. (38) Rev. 1, 67p. 110 M.H. Gabr

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