An estimation of growth parameter, mortality rates and yield-per-recruit for beluga (Huso huso) living in Caspian Sea

This paper presents the results of study on age, growth, mortality rates and yield-per-recruit of Beluga (Huso huso) living in Caspian Sea. The mean length of successive years, mortality rates and yield-per-recruit studies indicated that at present the resource is under heavy fishing pressure. For the female Beluga growth was regarded as comprising of three stages, and the von Bertalanffy parameters were calculated for juveniles, for middle stanza (<8 to 24 years), and third stanza (>24 years). The value of K was the highest (0.065) for the first stanza, lower for the middle (0.029) and the lowest for the third one (0.023). Total mortality of female and male Beluga estimated from the descending limb of the catch curve using the combined data (1990-1994) were: for females, Z=0.48 per year, r=0.982, p<0.01 and for males, Z=0.38 per year, r=0.992, p<0.01. Natural mortality for female and male Beluga was estimated using Richter and Efanovs formula as 0.03 for females and 0.05 for males. Values of fishing mortality (F) were estimated from Z and M, using values of Z from catch curves and M estimated from Richter and Efanovs formula as 0.045 and 0.33 for female and male, respectively. Yield-per-recruit curve was produced for female and male Beluga. It was found that the maximum Y/R (Maximum sustainable yield-per-recruit) were produced at Fs =0.07, for female and Fs=0.16 for male. Inspection of the yield-per-recruit model for the Beluga in the Caspian Sea showed that the fishing mortality should be stopped for this species in the Caspian Sea. This result confirms the over-fishing of the sturgeon in Caspian Sea. Several other authors such as Smith (1990), Birstein (1993), Bemis and Findeis (1994), Dumount (1995) and current catch data, have confirmed the overfishing of the Beluga in the Caspian Sea.