Study tracks 34 years of Bering Sea fish populations

A newly released study from the Alaska Fisheries Science Center tracks distribution shifts of groundfish in the Eastern Bering Sea from 1982 to 2015.

Researchers say the visualizations provided by this 331-page document will help them to understand the life histories of 22 groundfish and skate species over time and space and provide clues to how climate change may potentially impact those species at different life stages.

During the standardized bottom trawl surveys of the Eastern Bering Sea shelf area between 20 and 200 meters from May to August in those years, researchers collected species composition and bottom temperature for all tows, as well as measurements from all fish encountered. That data provides a unique look at the spatial and environmental preferences of many species, as well as ontogenetic shifts in spatial distribution and environmental preferences over 34 years, they said.

Steve Barbeaux, the fisheries biologist who served as lead author of the study, said climate variability has increased in the Bering Sea in recent years and AFSC will use this information to study how ecosystems respond to change.

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Researchers said the data demonstrates the importance of understanding the life history of organisms being studied and effects of the environment on different stages of their life history. The data will allow them to investigate in detail the sensitivity of species to environmental change and the degree to which species are already adapted to natural variation in the environment.

Bottom trawl surveys of the Eastern Bering Sea have been conduced since the 1940s, but 1982 is considered the starting point of the EBS shelf bottom trawl survey time series as trawl gear and methods were inconsistent in previous surveys.

Researchers said that mapping species distributions by size revealed not only ontogentic migration patterns, but environmental preferences and effects of changing conditions over time.

Barbeaux offered several highlights of the study, including that some species prefer relatively cold or warm, shallow or deep waters. Such knowledge could help predict where they will go when conditions change, he said.

Climate had the most impact on middle life stages. For species that shifted distribution between warm and cold years, mid-size fish were most affected. Barbeaux speculated that mature and young fish may be limited to spawning and nursery grounds, while mid-size fish are free to follow food and temperature preferences.

Six species showed distinct shifts in distribution over time in response to climate, and these shifts may affect interactions among species or stages. For example, more overlap in the distributions of Pollock and arrowtooth flounder could mea more predation on Pollock; or more overlap between young and adult Pollock could mean more cannibalism, the study indicated.

Overall, Barbeaux emphasized that these findings represent just some potential knowledge to be gained from this data. The study presents a wealth of data in an accessible form that other scientists can use in their research, he said.

The complete report is online at 

https://www.afsc.noaa.gov/Publications/AFSC-TM/NOAA-TM-AFSC-348.pdf