My primary research interest is in using acoustic data to describe ecological variability in response to changes in the physical environment. Current projects also include developing methods to better utilize these observations for understanding organism behavior, and the implications on the structure of the population.
Quantifying population movement from autonomous echosounder platforms
Building off of my previous work with moored echosounder systems, we deployed instrumentation in the eastern Bering Sea to assess the seasonal population dynamics of the walleye pollock along the northwestern portion of the shelf. Using target tracking, we estimating the movement of the pollock stock between U.S. and Russian sectors of the Bering Sea shelf over extended time periods. This work is being used to help define a mechanistic relationship between the migration of pollock between sectors and the environmental changes on the shelf, both seasonally and interannually.
Applications of broadband echosounders for fisheries acoustics
The development of commercially available broadband (frequency-modulated) echosounders in recent years has led to the integration of these systems into many survey and observational platforms. For fisheries acoustics, the adoption of new technologies is highly dependent on the ability to maintain and continue long-standing time series collected using previous generations of instrumentation. My work is focused on addressing the outstanding questions needed to take the next step in the adoption of broadband echosounders for fisheries acoustics surveys such as intercomparison of integration with narrowband data and developing the necessary processing infrastructure for adding this new data type into survey processing pipelines.
Distribution of age-0 Arctic cod in the Chukchi Sea
The Pacific Arctic is experiencing significant warming, and ice conditions in the Chukchi Sea are changing rapidly, but the impact of declining sea ice on the ecosystem is not entirely understood, especially when we can't survey year round because of sea ice. Arctic cod are a particularly important species to the food web dynamics of the region, being the dominant lipid-rich fish species. Past surveys have seen large numbers of juvenile cod, but did not have the ability to see if they leave the area and mature elsewhere or do not survive the arctic winter. The focus of my dissertation is a multi-platform approach to understand the pelagic fish community of the Chukchi Sea and the role of this region as a nursery area for the large population of age-0 Arctic cod observed in previous years.
Using Saildrone unmanned surface vehicles, we conducted repeat surveys of the NE Chukchi Sea in summer in order to observe intraseasonal changes in the backscatter and distribution of the pelagic fish community. Using repeat surveys, we aim to further constrain the potential source and fate of the age-0 Arctic cod population observed on the Chukchi shelf in summer. To investigate the mechanisms responsible for the movement of this population, we used particle tracking simulations to explore the role of currents in advection and retention of this fish population.
A series of survey updates and preliminary science findings were featured on the NOAA Science Blog, and this work has since been published in our article, Autonomous vehicle surveys indicate that flow reversals retain juvenile fishes in a highly advective high-latitude ecosystem.
We conducted two field campaigns in 2017 and 2019 as part of the NPRB Arctic Integrated Ecosystem Research Program in order to expand our interannual observations of this pelagic ecosystem. We used acoustic estimates of abundance and biomass for the dominant pelagic species, derived from acoustic transects and targeted midwater trawls, to understand the implications of changing climate conditions on the Chukchi shelf ecosystem.
The results of this project can be read in Climate-driven shifts in pelagic fish distributions in a rapidly changing Pacific Arctic.
Using autonomous echosounders moored to the seafloor, we monitored fish populations in the Northern Chukchi Sea over a period of two years to see how their behavior changes as a function of their environment and ice cover. Using fish tracks and co-located in situ observations of transport, we identified transport as the primary mechanism driving the movement of the pelagic age-0 gadid population and observed the direction and timing of migration in the northeastern Chukchi Sea.
The results of this work can be found in our article Transport-driven seasonal abundance of pelagic fishes in the Chukchi Sea observed with seafloor-mounted echosounders.
The instruments being used to investigate the fate of Arctic cod were first used in the field at NOAA/AFSC, where I was involved in determining if moored echosounders be used to obtain a comparable abundance of walleye pollock in Shelikof Strait, Alaska. A prototype 70 kHz split-beam echosounder with a newly developed depth-rated transducer was used to study spawning aggregations and timing of the aggregations as they move in and out of the strait. Prior to the deployment, a method was developed using a retrospective analysis of 20 years of annual survey data of pollock biomass in the Gulf of Alaska to determine the number of moorings needed to produce survey-comparable results. Our findings were published in the article Can a bottom-moored echo sounder array provide a survey-comparable index of abundance?
Since the first deployment of mooring in Shelikof Strait, two additional 6-month multi-mooring deployments have occurred in Resurrection Bay, AK and Sanak Trough, AK. Data from these deployments has been used to inform the timing of ship surveys to best observe the spawning aggregations. See the NOAA Fisheries press release for our project – “For Pollock Surveys in Alaska, Things Are Looking Up”, May 2015.
