Distributed across the Bering Sea, Aleutian Islands and the Gulf of Alaska, Pacific cod are a fast-growing species and a key part of the Alaskan ecosystem.
But little is known about their movements and habitats off the Aleutian Islands, according to Susanne McDermott, David Bryan and Julie Nielsen, Research Fisheries Biologists at the Alaska Fisheries Science Center in Seattle and Kingfisher Marine Research in Juneau.
‘Like Atlantic cod, Pacific cod migrate from feeding grounds in the summer to spawning grounds in winter,’ Susanne McDermott said.
‘They’re known to migrate long distances seasonally, but we don’t know about their migration patterns in the Aleutian Islands so we’re working to understand this. The Aleutian Islands are a chain of volcanic islands that are very remote and very stormy in winter. Any research there is difficult and we have limited information on all the components of this complex ecosystem. It’s a challenging environment but gaining information on seasonal migration patterns is key to the sustainable management of any fish stock.’
Given the importance of Pacific cod as one of the primary species supporting the Aleutian Islands economy, the local fishing industry also wanted to know more about their migration patterns.
McDermott and her team partnered with the industry, bringing together cutting edge technology and fishermen’s expertise. With financial support from the fishing industry, they drew up a proposal to buy pop-up satellite tags and launched a pilot study to develop methods for tagging and releasing cod on working commercial fishing vessels.
The study was a cooperative effort between the Alaska Fisheries Science Center, Adak Community Development Corporation, B&N Fisheries, the Pacific States Marine Fisheries Commission and other members of the Pacific cod fishing fleet. The main goal was to understand the seasonal movement patterns of Pacific cod between summer feeding and winter spawning in the Aleutians and how the summer distribution of the species differs from the winter distribution.
‘We needed to make sure that the tags worked and that we could release them from commercial fishing boats during fishing operations,” she said.
‘It was important to find out whether this kind of research would be possible on commercial vessels without having to charter our own research vessel. We had to figure stuff out on the fly. How would we cope without interfering with fishing activities? Could we do it in the weather that the crew were fishing in? Could we work on deck while they were fishing? Would the fish that come on the boat be in a good enough condition for tagging?
In winter 2019, the team worked off Adak Island and Nazan Bay, which is twelve hours from Adak and located off Atka Island in the central Aleutian Islands. Nazan Bay is home to a known spawning aggregation and an important region for the commercial fishing of Pacific cod. A total of 36 fish were tagged off two different commercial fishing vessels; 185ft trawler Ocean Explorer and 60ft pot boat Deliverance. All were captured during spawning season and came from depths between 90 and 120 metres.
‘We tagged and released 21 fish in Nazan Bay,’ Susanne McDermott said.
‘We then tagged and released 15 near Adak. Deliverance is smaller than Ocean Explorer, a shoreside trawl vessel. We could tag fish during the regular trawl fishing operations on the Ocean Explorer but needed a special trip just for tagging on the Deliverance, since tagging requires slow and careful handling of the fish, which wasn’t possible during fast-paced commercial pot fishing. We were able to tag cod close to shore on the Deliverance and went further offshore with the Ocean Explorer. Both vessels provided time, access and expert personnel at no cost.’