Método para determinar la separación entre barras y la curva de selección teórica de sistemas de grilla selectiva en redes de arrastre para peces

Abstract

This paper proposes a numeric procedure, based on bootstrap simulations, in order to determine the theoretical size-selection curve of grid sorting systems (GSS) in trawlnets to fish. Also, based on the size structure of the captures gotten without the device, it proposes a method in order to determine the inter-bar distance of this device. The procedure considers that the maximal width (A) of the fish determine if this escapes or not. Also, any particular distribution for the maximal width of a l-length fish is not assumed. The probability that l-length fish do not pass through the grid with separation (d) is described by: Pl,d=1/Nl*???i=1Nl ??i,l,d with ??l,d=1 if(Al >d) (retained)??l,d=0 if(Al ???d) (escaped) where Al is obtained at random, of a set of values of A for a particular l, and Nl is the amount of fish of length l that enters to the net. To manner of example, this procedure is apply to Chilean hake (Merluccius gayi gayi) industrial fishery data and an inter-bar distance of 47 mm is determined. With this would be obtained a length of capture (l50) of 390 mm, a length of recruitment to the net (l25) of 381 mm with a short selection range (SR= 18.25 mm). Finally, the technical and biological implication of the implementation of this system, in the industrial fishery of Chilean hake, is discussed.