Probably not thrusters but simply sea water ballast being discharged. When tankers are empty, or only patially loaded, they take on sea water ballast to keep the ship level. This one likely came into port partially loaded and is pumping out the sea water as it takes on oil.
If they were bow thrusters there'd be only one at the bow and it would create a whole lot more disturbance than the little bit we see. Tankers, if they have bow thrusters, typically have only one, contained within a tunnel at the bow. Also, they only push water to one side at a time, not both as we see in the image.
Well, they say you learn more by failing. So I've learned quite a bit it would seem in my erronious guesses. Thanks for the great information once again.
It was a reasonable guess. You recognized that there was something discharging near the bow and, based on your experience, thrusters were a reasonable assumption.
Another clue that they are not bow thrusters is that the thrusters are only used to position the tanker when entering or leaving port. If it was doing either of these evolutions there would have also been several tugs in attendence. The ship in the photo is moored quite solidly to the pier.
No Longer There 
If they were bow thrusters there'd be only one at the bow and it would create a whole lot more disturbance than the little bit we see. Tankers, if they have bow thrusters, typically have only one, contained within a tunnel at the bow. Also, they only push water to one side at a time, not both as we see in the image.
See http://www.boatnerd.com/news/newpictures03/Algobay-bow-thruster-2-Dec-.jpg