Researchers looking to estimate biomass of multiple Alaska fish species say it is now possible to estimate fish biomass for more than one species at the same time using environmental DNA found in sea water.
In a report released by NOAA Fisheries on Oct. 31, Kimberly Ledger – a research biologist with the Auke Bay Laboratories of the Alaska Fisheries Science Center and lead author of the study – said researchers had learned they could accurately quantify species composition and estimate biomass for different species of cod and pollock at the same time using eDNA.
“It is possible to apply these methods to other species to improve the quantitative utility of eDNA,” Ledger said.
NAA Fisheries scientists, in partnership with the University of Alaska Fairbanks, collaborated on the research project.
DNA essentially acts as a blueprint for an organism’s traits, and is passed from one generation to the next through reproduction. On the other hand, eDNA is genetic material shed by organisms into the surrounding environment. As a fish swims through the ocean, for example, its DNA is shed and accumulates in the water around it. Some sources of eDNA include scales, skin cells, mucus, feces, and gametes. This genetic material can be recovered from environmental samples.
To successfully manage species, scientists need to understand where they live and how many of them exist – and estimating this information accurately can be difficult. It relies on making inferences about an entire community based on observations of a subset of individuals.
NOAA Fisheries gets this information from fish collected in nets during research surveys and from data collected by fishery observers on commercial fishing boats and in processing plants.
Using eDNA collected in water samples, scientists are able to detect and quantify fish DNA from the environment to help estimate species abundance and biomass from just a sample of water.
This method doesn’t replace standard trawl surveys or actual sampling by fisheries observers, however. Scientists still need to collect biological data – including size, age, sex, sexual maturity and diet information – which is important for stock assessments.
People researching eDNA, meanwhile, are still working to identify ways to use this information to support management decisions with the help of stock assessment authors and quantitative ecologists.
In this study, researchers identified a new genetic marker, a specific segment of DNA, to detect and differentiate eDNA from six closely-related cod species in the North Pacific and the Arctic. Each genetic marker is a gene or a short segment of DNA that has a distinctive location on a specific chromosome that can be used to identify a species or an organism.
In the course of this study scientists showed that they could detect different species of cod and pollock – accurately determining their biomass proportion– and detect not just the most abundant species in the samples, but also species at low relative abundances.
As part of the study, fishery biologist and co-author Mary Beth Hicks kept live Pacific cod, walleye pollock and Arctic cod in various combinations and abundances in holding tanks at the center’s Newport Laboratory. She collected water samples from the tanks with known biomass, based on numbers and weights of each species of fish. The experimental design enabled comparison of eDNA-derived species compositions with true compositions within a group of related species with overlapping habitats and distributions.
As the Arctic warms, fish are moving to find ideal conditions to survive, including moving to find food sources and comfortable temperatures to spawn. Such dynamic shifts pose new challenges for resource management officials and scientists conducting long-term research surveys in traditional areas where these fish are found.
