Growth, mortality and spawning stock biomass of the striped red mullet Mullus surmuletus, in the Egyptian Mediterranean waters

Population parameters such as age, growth, mortality and maturity-at-age are crucial parameters for accurate stock assessment and management plans to ensure the sustainable development of fisheries. Also, they are essential for the calculation of spawning stock biomass (SSB) and equilibrium yield as well as biological reference points including Fmax, F0.1 and F30%SSB. Age and growth parameters were estimated for the striped red mullet, Mullus surmuletus, sampled from commercial landings of the trawl fishery in the Egyptian Mediterranean waters, using the otolith reading technique. M. surmuletus has a longevity of 5 years, but over 70% of fish were less than 2 years old. The growth parameter estimates were K= 0.47 yrs-1, L∞= 31.74 cm, and to= -0.3 yrs. Natural mortality (M) was 0.43 yrs-1, fishing mortality (F) was 0.73 yrs-1, survival rate (S) was 0.31 and exploitation ratio was 0.63 yr-1. Length-at-50% maturity was estimated at 15.1 cm TL, while the length at first capture was estimated at 11.6 cm TL. SSB analysis showed that effort reduction is strongly recommended such that F be reduced by 40% to rebuild spawner biomass to acceptable levels. Per-recruit analysis revealed that F should be reduced by about 27% to achieve the maximum Y/R. All approaches point to the need for drastic reduction in fishing pressure by about 30-40% in the Egyptian Mediterranean fisheries

Growth, mortality and yield per recruit of the king soldier bream Argyrops spinifer (Sparidae) from the Oman coast of the Arabian Sea

The King soldier bream Argyrops spinifer at Arabian Sea (Omani waters) was assessed using Beverton and Holt yield per recruit model. A total of 5520 specimens were collected during five trawl surveys between September 2007 and August 2008. The maximum life span was 11 years for length range of 11.0 – 62.1 cm TL. The von Bertalanffy growth parameters were K = 0.22 year^-1, L∞ = 65.51 cm, to = -0.75 year and W∞ = 5430g. The rates of total mortality Z, natural mortality M and fishing mortality F were 0.85, 0.26 and 0.59 year^-1 respectively. The exploitation ratio E was 0.69 indicating the high level of exploitation. The estimated total length at 50% maturity was 31.8 cm. Yield per recruit analysis revealed over-fished stock conditions particularly because small fish are effectively unprotected by current minimum size regulations. Therefore measures such as closed seasons or changes in fishing patterns would be desirable to safeguard the spawning stock and recruits. Also, the commercial fishery of Arabian Sea, Oman should be subjected to a total allowable catch and a maximum size limit be implemented

Population Dynamics of Two Cichlids, Oreochromis aureus and Tilapia zilIi, from Wadi EI-Raiyan Lakes, Egypt

Age, growth, mortality, relative yield-per-recruit and relative biomass-per-recruit of Oreochromis aureus and Tilapia zilli collected from Wadi EI-Raiyan lakes during the period from August 2000 until July 2001 have been estimated. Age was determined from scale readings and the results showed that the maximum life spans of O. aureus and T. zilli were three and four years, respectively. The von Bertalanffy growth equations were L1= 27.15 (l-e'0.56(t+0.32) for 0. aureus and L1= 33.5 (l-e -0.49(t+0.15) for T. zilli. The instantaneous annual rates of total, natural and fishing mortality were calculated as 1.69, 0.25 and 1.44, respectively for 0. aureus and 1.1, 0.2 and 0.9, respectively for T. zilli. Exploitation rate was estimated as 0.85 and 0.82 for 0. aureus and T. zilli, respectively. Relative yield-per- recruit and relative biomass-per-recruit analysis indicated that the stocks of O. aureus and T. zilli were overexploited and that the current exploitation rate should be reduced by about 53% for 0. aureus and 55% for T. zilli to ensure that at least 50% of the individuals could be maintained for spawning and recruitment

Morphology study of the otoliths of the parrotfish, <i>Chlorurus sordidus</i> (Forsskal, 1775) and <i>Hipposcarus harid</i> (Forsskal, 1775) from the Red Sea coast of Egypt (Family: Scaridae)

In the present study a comparison of the otolith morphology of two species of parrotfish, family Scaridae, collected from the Red Sea coast of Egypt, is conducted to identify the most appropriate taxonomic characters that separate these species. Ontogenetic changes in the otoliths of the two scarid fishes become evident. In the otoliths of Chlorurus sordidus, the following characters are comparable in small-sized adult fishes: otolith width, otolith depth, mesial surface shape, lateral surface shape, shape of sulcus acusticus, column, rostrum and size of rostrum. The otoliths of young adults (GI) C. sordidus differ from the adult ones in 14 out of the 22 characteristics studied. In the otoliths of Hipposcarus harid, the following characters are comparable in small and large fish: otolith width, otolith depth, mesial and lateral surface shapes, shape of sulcus acusticus, rostrum and size of rostrum