Growth and mortality rates for management of the common smooth-hound shark, Mustelus mustelus in the Egyptian Mediterranean waters

The present study aimed to provide information on growth and mortality rates for the management of the common smooth-hound shark, Mustelus mustelus in the Egyptian Mediterranean waters at Alexandria. The study was based on a total of 311 specimens of M. mustellus which were monthly collected from the commercial catch at Alexandria coast of the Mediterranean Sea, during the period from June 2020 to May 2021. Results showed that the total length of male M. mustellus ranged from 38.6 to 106.8 cm for males and from 38.6 to 117.5 cm for females. The total weight varied from 155.9 to 3611.7 g for males and from 157.3 to 2828 g for females. The b value (2.88, 2.74, and 2.8 for male, female and whole population, respectively) is slightly lower than the ideal, indicating a tendency towards slightly negative allometric growth. Results showed that the present levels of exploitation represented 0.407, 0.417 and 0.42 for males, females, and the whole population, respectively which were higher than that of E_0.5= as 0.30, 0.295, and 0.297 for males, females, and the whole population, respectively. It gives the maximum (Y/R), which means that the stock of M. mustellus is highly overexploited, which is needed to maintain 50% of the stock biomass. For management purposes, the exploitation rate of M. mustellus should be reduced to be < E_0.5 i.e., the fishing mortality should be reduced to lower than the current fishing mortality (F=0.39, 0.42 and 0.45 y^-1 for male, female, and the whole population respectively) to maintain sufficient spawning biomass for sustainability. Finally, this study concluded that the length of the first capture of M. mustellus was calculated at 33.8 cm, while M. mustellus doesn’t reach maturity unless reaches 83 cm at least. These indicated that M. mustellus in Egyptian Mediterranean waters was captured way before it reached its maturity stage.