Historically at the Alaska Fisheries Science Center, stock assessment science and habitat science have been considered separately, but that practice needs to change, according to a scientist with the center’s Habitat and Ecological Processes Research.
“We need to develop new approaches to better integrate these two disciplines,” senior scientist James Thorson said, adding that habitat science needs to move beyond just describing habita-specific distribution, fish density, demography and benthic community recovery.
Stock assessment science primarily focuses on catch removals, and this affects how many fish are left to reproduce and the number of young fish born in the future, otherwise known as stock productivity. However, Thorson said that the scope of stock assessment science needs to broaden to also consider the role of habitat and how changes in habitat may impact fish productivity.
Researchers at AFSC are working hard to link their habitat research of stock assessments, Thorson remarked, and have already had some successes using information about how cod and Pollock respond to cold versus warm temperatures to create better indices of abundance for use in their stock assessments.
“These new modelling approaches and new tools being developed allow us to extend the capabilities of our data collection, processing and analysis research,” the science center’s director, Bob Foy, explained to Fishermen’s News. “In turn, the strength of these models lies in continuing to have good data from fisheries surveys, research projects and process and analysis studies to support them.”
“Integrating data on habitat and stock assessment will require combining laboratory, field and modeling work and obviously require buy-in from scientists and partners doing a lot of different types of science, and this effort is somewhat challenged by diminishing budgets,” Foy said.
That said, “we believe it would allow fisheries managers to have a better sense for how future habitat impacts could affect fisheries productivity,” he remarked.
Also part of the challenge is the need for more sophisticated habitat data. Specifically, researchers have mentioned the need to identify prevailing biological and environmental conditions for habitats at specific locations.
Researchers have identified three challenges to overcome to learn more about the role of habitat in supporting fish stock productivity. The first is the stage-structure responses to habitat impacts, during which scientists would better account for variability in growth rates as a fish develops from egg to larvae to juvenile to adult.
Fish metabolism and growth rate are typically higher when fish are young, and slow down as they reach maturity. Currently, scientists and resource managers typically account for habitat impacts at each stage of life of a fish separately.
Also, according to researchers, scientists need to account for non-local responses to recognize that habitat changes in one location can affect productivity in distant locations. An example is when bowhead whales in the Chukchi sea prey on euphausiids (krill) that grow in the Bering Sea and are transferred north due to advection, the horizontal movement of an ocean current.
Bowhead distribution is impacted by environmental conditions that affect their food, and they are found where the current and wind transport krill.
Scientists also need to understand relationships between environmental variables and how these relationships affect fish development and growth, from water temperatures to salinity, researchers say.
Predicting the likely consequences of changing temperatures due to climate change or light levels due to increased suspended sediment associated with coastal development requires understanding of the impact of each of these variables on population productivity, as well as the impact of each habitat variable on other habitat variables.
Thorson said that advancing stock assessment and predictive capabilities are particularly critical in the face of climate change, which is causing many fish and marine mammals to shift their distributions.
“We need this information to ensure continued fisheries sustainability,” he said, “and to protect marine mammal populations.”