الفهرس 
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Abstract
Recently, the European eel Anguilla anguilla has become an important part of the production in Bardawil lagoon as a migratory fish. It also forms a food base for the residents of the North Sinai region due to its high nutritional value and reasonable price.
Aim of work:
this work aimed to investigate the biology and population dynamic of A. anguilla and determine the biological data for assessing the status of this species in Bardawil lagoon to provide fishery managers with current and validated life history information on A. anguilla, which may be useful for the maintenance of this valuable fish resource and improvement of its fishery in the Bardawil lagoon.
Steps of the study
1- Study of certain biological characteristics such as age, growth, mortality and exploitation to assess the current stock status and develop a viable strategy for fisheries management of this species.
2- Analyze the fluctuation of fish production and productivity as well as the catch per unit effort, this may contribute to the management of fisheries in Bardawil lagoon.
3- Study the environmental parameters that affect the production of Eels in the lagoon.
Fisheries of European eel in Egypt:
The European eel, Anguilla anguilla (L.), has been reported to be declining throughout its natural distribution range over the last decades. Several factors, both fisheries- and non-fisheries-related, are considered responsible for the high mortality rate among the fish species. The eel has a very complex life cycle covering several metamorphoses as well as long-distance migration, and many details of the species’ life are still unknown.
The European eel Anguilla anguilla in Egypt is distributed mainly in the Nile Delta and along the Mediterranean coast, inhabiting a variety of freshwater and brackish environments. It is primarily found in the northern regions, particularly in the Nile Delta and along the Mediterranean coast.
Productivity
The average productivity during the last ten years from the different eel’s fisheries resources showed that Burullus lagoon was the most productive habitat (24.24 kg ha-1) followed by Edko (5.02 kg ha-1). Nile River came in the third grade by 1.4 kg ha-1 followed by Manzala lagoon (0.37 kg ha-1) and the least productive habitat during the last ten years was Bardawil lagoon (0.20 kg ha-1).
Biological studies
Length-weight relationship
The relationship between length and weight of the males, females and combined sexes were found that the total length for males ranges from 33.5 to 62.2 cm, and weight of 37.7 to 388g. While the total length for female ranges from 23.5 to 64.3 cm, and weight of 56 to 350 grams.
The equations for the relationship between length and weight are as follows:
Combined sexes W = 0.0037L2.805
Females W = 0.0073 L2.625
Males W = 0.0017L2.997
6.4.2. Condition Factor:
The results showed that the condition factor (Kc) undergoes minor changes in specimens belonging to different size classes, it varied between 0.16 (for total length 62.2 cm) and 0.43 (for total length 23.5 cm) for females. In case of males the condition factor (Kc) varied between 0.13 (total length 38.9 cm) to 0.21 (total length 40.5 cm). The relative condition factor (Kn) varied from 0.81 (for average total length of 40.5 cm) to 1.28 (for average total length of 38.5 cm) for males with an average of 1.04 + 0.002. For females the relative condition factor (Kn) varied between 0.52 (for an average total length of 23.5cm) to 1.24 (for an average total length of 38.0 cm) with an average of 1.02 + 0.001. The monthly variations of the Fulton’s or absolute condition factor (Kc) varied from 0.166 in November to 0.194 in March and for males with an average of 0.180 + 0.003. For females the absolute condition factor (Kc) varied from 0.169 in November to 0.193 in March with an average of 0.178 + 0.002 .The monthly variations of the relative condition factor (Kn) varied from 0.94 in March to 1.14 in November for males. For females the relative condition factor (Kn) varied from 0.94 in March to 1.10 in November.
Age determination of the European eel Anguilla anguilla:
According to the otolith examination of 109 specimens, the maximum life span for males was four years with the absence of age group 2 from the samples. The mean lengths of 34.1, 45.57, 50.93 and 54.74 cm, giving increment of 34.1 (62.3%), 11.47 (21.0%), 5.36 (9.8%) and 3.81 cm (7.0%) for age group II, III, IV and V respectively were observed in the otoliths of males. For females, lengths of 23.5, 38.6, 47.85, 55.1 and 59 cm corresponding to an increment of 23.5 (39.8 %), 15.1 (25.6 %), 9.25 (15.7%), 7.25 (12.3%) and 3.9 cm (6.6 %) for age groups I, II, III, IV and V respectively. For pooled data the estimated length at end of each year of life were 23.5, 38.6, 47.9, 53.3 and 56.6 cm with increment of 23.5 (41.5 %), 15 (26.6 %), 9.4 (16.6%), 5.4 (9.6%) and 3.3 cm (5.8 %) for age groups I, II, III, IV and V respectively.
The von Bertalanffy growth model was used to describe the mathematical growth of A. anguilla Values of L∞, K and to were 58.25cm, 0.63 year-1and -1.420 year for males, 67.15 cm, 0.42 year-1 and -1.969 year for females and 64.39 cm, 0.40 year-1 and -2.407 year for combined sexes respectively.
The values of the growth performance indices according to L∞ (Ф) were 3.33, 3.28, and 3.22 for males, females and combined sex respectively. On the other hand, when they were calculated according to W∞, growth performance indices (Ф) values were 1.49, 1.40 and 1.36 for males, females and combined sex respectively.
Ecological studies:
The present study recorded the environments parameters of Bardawill lagoon during fishing seasons 2020.
Results can be summarized in the following points:
Water temperature:
The minimum temperature was recorded in January (14.33ºc), whereas the maximum was in April (22.39ºc) during season 2020.
Salinity:
The least recorded salinities in February (43.66 ppt) and the maximum value was recorded in October (53.59 ppt) during season 2020.
Water pH:
The maximum value was recorded at (8.18) in April, whereas the minimum value at (7.89) in Distemper during 2020.
Dissolved oxygen:
Lowest average was recorded in April (5.06 mg/l) while the highest in February (7.17 mg/l) at season 2020.
Food and feeding:
There was diversity in species included in stomach contents of the European eel A. Anguilla from Bardawil lagoon. Four fish species plus fish remains and two crustacean species, two mollusks species were recorded. Two species of worms were also found. This diversity fluctuated around seasons as some species represented in season and another species not represented.
Population structure:
Age composition analysis showed that the bulk of the commercial catch of A. anguilla collected from Bardawill lagoon during the period from October 2019 to April 2020 composed of age group III which contributed with about 43.4 % and 33.9 % for males and Females respectively.
Age – Length key: Five age groups, from 1+ years to 5+ year’s age, were determined for A. anguilla in Bardawil lagoon by otolith reading. The age-length key for all specimens revealed a considerable range in length for each age group and some overlap between adjacent age groups. Generally, the wider length ranges were those covered with age group II and age group III. Age group II was varied from 31.0 to 52.9 cm for all samples. While age group III was varied from 37.0 to 56.9 cm. Age group V ranged in length from 45.0 to 64.9 cm.
The sex ratio M/F was 1: 0.9. As for the total 318 specimens 169 individuals of them were males and 149 individuals were females.
In the present study total mortality (Z) was estimated by using linearized catch curve (Pauly, 1983) incorporated into FISAT II program, where the length compositions and the relevant data of A.anguilla from Bardawill lagoon were used for the construction of the linearized catch curve. The mean relative age values (t) were plotted against the natural logarithms of N / Δt .The average obtained (Z) of Anguilla anguilla was (1.29 y-1).The natural mortality coefficient (M) was calculated by two methods, the results are:
M = 0.670 Y-1 Pauly (1980) method
M = 0.629 Y-1Then et al., (2015) method
Mean M = 0.649
The fishing mortality (F) was obtained by subtracting M from Z and the resulted (F) of A.anguilla during 2020 was (0.641y-1) and exploitation rate (0.497y-1)