Measuring strain in lead-in cables in a marine seismic acquisition system

A seismic acquisition system towed by a vessel 10 includes lead-in cables 16,18, paravanes 14, tow ropes 8, spreader cables 24 and streamers 20. Each lead-in cable 16,18 has at least one strain gauge (e.g. optical fibre with a Bragg grating). The cables may include a plurality of strain gauges at spaced apart locations. The length of the lead-in cables can be adjusted such that the measured strains are substantially equal. The spreader cables may also include strain gauges. Values of peak strain may be recorded. The value of peak strain and/or a parameter related to a product of strain and deployment time is recorded. When this value exceeds a threshold, an indicator is generated to indicate that the cable should be withdrawn from service for safety reasons. Axial and bending strain gauges may be used.