Where herring go after spawning in Prince William Sound (PWS) remains a mystery. Do they remain in PWS or migrate out into the Gulf of Alaska? A pilot project that started in 2012 demonstrated it was possible to implant acoustic tags in Pacific herring and then detect them on acoustic arrays as they traveled to the entrances of PWS. Over the last 7 years, we have put together a network of acoustic arrays at key areas around PWS in order to better understand the movement of these critical forage fish.
With the help of historical knowledge and aerial surveys, we set out into PWS in search of herring to tag. Adult herring are captured on the spawning grounds using jigs and transferred to a seawater holding tank aboard a research vessel. Individually, the herring are sedated, measured, and a small acoustic tag is surgically implanted. The tags then transmit pings that can be “heard” by portable hydrophones and groups of acoustic receivers installed in PWS which “listen” for tagged fish. These receivers are placed on the spawning grounds and at the major entrances to PWS including Hinchinbrook Entrance, southern Montague Strait, and the four southwest passages. Receiver data are uploaded once or twice a year. Data collected from the receivers are then pooled into a Multistate Cormack-Jolly-Seber (CJS) Model. Click here for a full report on the 2018 locations of PWS acoustic arrays.
We have already learned that after spawning, the majority of adult herring move to the entrances to PWS. They can travel approximately 115 kilometers over three days. In 2019 we found two new trends in movement. It was observed that some of the herring migrate seasonally from Hinchinbrook and Montague into the Gulf of Alaska. When the herring migrate out of PWS there is a much higher probability they will leave using Hinchinbrook entrance and then return through Montague straight. We are trying to learn what other routes and areas in PWS the herring are using. To aid in this effort additional receivers were deployed in 2018 near southern Knight Island Passage, Red Head (near Port Gravina), along the west side of Hawkins Island, and across the north end of Montague Strait. Following the spawning events in spring 2019, a total of 165 herring were tagged. Data will be uploaded from the receivers in February of 2020 with the hope of better illuminating the paths these herring take. In April 2020 the team plans to tag an additional 210 herring. By knowing where the fish are, we can improve the design of studies that examine factors such as predation, food availability, and stock genetics that affect herring populations.