Marine seismic surveys are under increasing scrutiny because of concern that they may disturb or otherwise harm marine mammals and impede their communications. Most of the energy from seismic surveys is low frequency, so concerns are particularly focused on baleen whales. Extensive mitigation efforts accompany seismic surveys, including visual and acoustic monitoring, but the possibility remains that not all animals in an area can be observed and located. One potential way to improve mitigation efforts is to utilize the seismic hydrophone streamer to detect and locate calling baleen whales. This study describes a method to localize low frequency sound sources with data recoded by a streamer. Beamforming is used to estimate the angle of arriving energy relative to sub-arrays of the streamer which constrains the horizontal propagation velocity to each sub-array for a given trial location. A grid search method is then used to minimize the time residual for relative arrival times along the streamer estimated by cross correlation. Results from both simulation and experiment are shown and data from the marine mammal observers and the passive acoustic monitoring conducted simultaneously with the seismic survey are used to verify the analysis.