Bob #6

The alewife Bob is named after Dr. Robert Muth of the University of Massachusetts, and a member of my graduate committee. Dr. Muth has been instrumental in helping us understand and further examine the cultural importance of river herring and the role they play in many social issues, such as dam removal, watershed and river restoration, and management policies. The river herring Bob was captured in the Ipswich Mills Dam box trap on April 23 and released there after tagging. He was last seen by the stationary receiver at Site 1 on May 17, and was found in this downstream area using manual tracking as well.

April 23, 7:00 pm: Bob is captured in the box trap near Site 2 (Ipswich Mills Dam). After being tagged, he was released at the trap.

April 23, 8:38 pm: Bob remains near Site 2 throughout the night. He descends the dam and heads out of range of the Site 2 receiver the following morning, April 24, at 4:30 am.

April 24, 4:55 am: Bob quickly heads downstream, reaching the receiver at Site 1 soon after leaving Site 2. He remains in the range of this receiver for about half an hour, then is not heard from again for two full weeks.

May 8, 4:47 am: Bob makes a surprising return to the Site 1 receiver, but is only in range for three minutes. We don't hear from him again until...

May 10, 5:06 am: It seems as though Bob is following the tidal influence of the area. He arrives in the morning to Site 1 and his last hit on the receiver is at 9:27 am.

May 11, 5:19 am: Bob shows up the next morning at Site 1 but has a shorter stay, leaving the range at 7:44 am.

May 12, 5:04 am: Bob arrives early in the morning again to Site 1, staying until 9:33 am.

May 13, 7:27 pm: Switching things up a little, Bob arrives to Site 1 in the early evening, and stays for just over an hour.

May 15, 9:26 am: Bob arrives a little later this morning after spending a day out of range of the receivers. His last hit on the receiver at Site 1 is at 1;07 pm. Later on in the evening, we use the manual receiver to locate Bob during the low tide. We find he is in the area near the town wharf called the Turnbuckle or Ring Bolt Rock, and there are 10 other tagged fish in the same area. We observe splashing at the surface as the sun begins to set.

May 16, 9:31 am: Bob follows the same pattern of movement as the previous day, arriving to Site 1 in the morning and moving out of range at 1:53 pm. During manual tracking from a kayak, we locate Bob moving upstream just before noon.

May 17, 1:53 am: Bob is heard by the receiver at Site 1 again, then moves out of range and is not heard again by the receiver just after 4:00 pm.

What do you think Bob was doing when he was swimming back and forth in the area near Site 1? The area is tidally influenced freshwater (so water levels fluctuate, but it's always fresh in the springtime), and he could have continued upstream if he wanted (he already passed the dam once, why did he go downstream afterwards?). Bob has an interesting path, what do you think it means??