~ 305 ~ International Journal of Fisheries and Aquatic Studies 2018; 6(2): 305-313 E-ISSN: 2347-5129 P-ISSN: 2394-0506 (ICV-Poland) Impact Value: 5.62 (GIF) Impact Factor: 0.549 IJFAS 2018; 6(2): 305-313 © 2018 IJFAS www.fisheriesjournal.com Received: 27-01-2018 Accepted: 28-02-2018 Mohamed Hosny Gabr (A). Marine Biology Department, Faculty of Marine Science, King Abdulaziz University, P.O. Box: 80207, Jeddah 21589 Saudi Arabia (B). National Institute of Oceanography and Fisheries, Suez, Egypt Ahmad Osman Mal Marine Biology Department, Faculty of Marine Science, King Abdulaziz University, P.O. Box: 80207, Jeddah 21589 Saudi Arabia Correspondence Mohamed Hosny Gabr Marine Biology Department, Faculty of Marine Science, King Abdulaziz University, P.O. Box: 80207, Jeddah 21589 Saudi Arabia Trammel net fishing in Jeddah: species composition, relative importance, length-weight and length-girth relationships of major species Mohamed Hosny Gabr and Ahmad Osman Mal Abstract Efficiency and selectivity of trammel nets used in Jeddah fisheries were assessed in terms of species composition and catch per unit effort. The index of relative importance was estimated for each species. Trammel nets of three inner-panel mesh sizes were used in the fishing operations. Moreover, the length- weight and length-girth relationships for ten fish species were described. Results indicated that the catch of trammel nets was composed of 99 species belonging to 36 families. The overall catch per unit effort was estimated to be 244 individuals (34.6 kg)/1000 m net length. Members of four families: Siganidae, Lethrinidae, Scaridae and Acanthuridae represented collectively 75.05% of the total number of fish caught, and 74.6% of the total biomass of fish caught. In these major fish families, four species: Siganus rivulatus, Acanthurus sohal, Hipposcarus harid, and Lethrinus harak were the most abundant and important species representing collectively 45.2% of the total catch, and having the highest index of relative importance: 29.2%, 15.4%, 12.7%, and 12.4%, respectively. The length-weight and length-girth relationships were described for the most abundant 10 coral reef species, two species of them: Rhinocanthus assassi and Plectorhinchus gaterinus have no previous data on length-weight relationships in the Literature. Keywords: Trammel net Species composition, Index of Relative Importance, Length-Weight relationship, Length-Girth relationship Introduction Trammel nets are included as sub-group of gillnets category which are of the oldest types of passive fishing gears that are widely used to harvest diverse marine species [1, 2] . They are consisting of three rectangular walls of netting panels positioned vertical, by means of floats and sinkers, at the surface, at the bottom, or in the midwater [3] . Due to their structure, a fourth catching method; trammeling (forming pocket) is characteristic to trammel nets beside wedging, gilling and entangling characteristic to gillnets [4, 5] . Consequently, trammel nets have low species and size selectivity compared to gillnets [6-11] . Thus, trammel nets are of the most suitable sampling gears used to investigate the species composition in coral reef areas because they catch more species and numbers in less time having the highest coefficient of variation than other sampling gears [7, 12] . Gillnets and trammel nets having different mesh sizes are recommended by Hovgård and Lassen [5] to be used in fishing operations to catch as many species as possible and getting fishes having large size ranges in stock surveys. For describing the biodiversity and thence its importance in given areas, the first and most often used metrics are the species composition (species richness) and endemism [13] . However, the steep declines in fish stocks and loss of marine habitats due to overfishing reflected an increased pressure on marine biodiversity [14] . Information about the species composition and relative abundance of the different species caught by trammel net fishing in the Red Sea fisheries of Saudi Arabia are not available. The aim of the present study is to determine the percentage composition, estimate the relative abundance (expressed in catch per unit effort) and relative importance 'IRI', and to describe the length-weight and length-girth relationships of the major species caught by monofilament trammel nets in Jeddah coral reef fisheries.