Marine seismic streamer and method for manufacture thereof

A seismic streamer 10 includes a jacket 30 covering an exterior of the streamer. At least one strength member 42 (eg fibre rope) extends inside the jacket along its length. Seismic sensors 34 (eg hydrophones) are disposed at spaced apart locations within the interior of the jacket. A flexible acoustically transparent material 46 fills the space inside the jacket. The material is introduced into the inside of the jacket in liquid form and undergoes a change of state to become substantially solid. The strength member 42, prior to and during the change of state, is maintained in the same position (eg by applying tension to the strength member) with respect to the jacket as would occur during ordinary operation of the streamer. In particular the strength member is maintained in the desired position where a device (eg compass bird) is to be attached to the outside of the cable. Buoyancy spacers 32 may be provided in the streamer.