Tropentag, October 6 - 8, 2009 in Hamburg "Biophysical and Socio-economic Frame Conditions for the Sustainable Management of Natural Resources"

Growth, Mortality and Spawning Stock Biomass of Red Mullet Mullus barbatus in the Egyptian Mediterranean Waters

National Institute of Oceanography and Fisheries, Fish Population Dynamics, Egypt

Abstract

In Egypt, Mediterranean sea supports a large fishery that harvests about 50 thousand tonnes per annum. Red mullet is one of the most important demersal target species of the commercial fisheries in the Egyptian Mediterranean and contributes a mean annual catch of 2000 tonnes. This paper presents the first assessment of the Mullus barbatus resource using per-recruit analysis as a suitable stock assessment tool for data-limited Egyptian fisheries. Age-based growth, mortality and sexual maturity parameters necessary for the per-recruit models were determined. Age and growth parameters were estimated for red mullet, M. barbatus, sampled from commercial landings of the trawl fishery using otolith's reading technique. M. barbatus has longevity of 3 years, but about 75% of fish were less than 2 years old. The growth parameters estimates were K= 0.66 yr^-1 and L= 27.1 cm. Natural mortality (M) was 0.46 yr^-1, fishing mortality (F) was 0.85 yr^-1 and exploitation ratio was 0.65. Length-at-50% maturity was estimated at 13.3 cm TL, while the length at first capture was estimated at 10.4 cm TL. The length (L) -weight (W) relationship was estimated as W = 0.0077 L^3.1095. It is shown that the red mullet resource in the Egyptian Mediterranean waters is over-exploited with spawner biomass - per - recruit at 26% of pristine levels. SSB analysis showed that effort reduction and/or establishing temporal closures for trawlers, trammel nets and gill-nets during the period of maximum spawning are strongly recommended. Also, a minimum legal landing size of 15 cm should be enforced to avoid the risk of recruitment overfishing. Per-recruit analysis revealed that F should be reduced by about 30% to achieve the maximum Y/R. All approaches point to the need of drastic reduction in fishing pressure of about 30-50% in the Egyptian Mediterranean fisheries.

Keywords: Age composition, Egypt, Mullus barbatus, reference points, spawning stock biomass

Contact Address: Sahar Mehanna, National Institute of Oceanography and Fisheries, Fish Population Dynamics, P.O. Box 182, Suez, Egypt, e-mail: sahar_mehannayahoo.com