system and method for providing an anti - fouling function to a streamer to be towed under water for seismic survey data collection . the method includes mixing a thermoplastic material with a biocide material to form an external sheath material ; and forming an external sheath over a main sheath of the streamer to provide the anti - fouling function . the external sheath is formed from the external sheath material such that the biocide material is distributed throughout the external sheath .