NOAA Teacher at Sea
Stacey Morris
Aboard NOAA Ship Reuben Lasker
July 26-August 10, 2026
Mission: Integrated West Coast Pelagics Survey
Geographic Area of Cruise: West Coast Pacific Ocean
Date: August 3 , 2026
Weather Data from the Bridge
Latitude: 43ยฐ 06.4 ‘N
Longitude: 124ยฐ52.3 ‘W
Wind Speed: 25 kts
Air Temperature: 14.9 ยฐC
Science and Technology Log
To understand more about the acoustic study component of our fish survey, I sat down with Kevin Stierhoff, Chief Scientist and Primary Investigator, and Brad Erisman, marine biologist, to see how our sonar mapping efforts integrate with the nightly trawling operations.
Interview Discussion with Kevin Stierhoff, Chief Scientist:
The Acoustic Trawl Methodology
Kevin: The acoustic trawl method is a globally recognized technique for surveying coastal pelagic species. By utilizing sonar, the ship can efficiently map expansive stretches of the seafloor and record precise echoes from fish populations. These instruments are highly calibrated and sensitive, providing us with accurate data on the biomass below. However, acoustics alone cannot identify the specific species creating the signal. To solve this, we conduct sonar surveys during the day when fish are schooling at depth, and then perform net trawls at night as they rise toward the surface. This nocturnal sampling allows us to determine the species and size composition without the fish avoiding the net as easily. By combining these datasets, we can apply the ratios found in our catches to the sonar echoes gathered during the day. This robust method is the primary tool for managing sardine and anchovy stocks along the West Coast.
Historical Context
While simpler sonar and net surveys were conducted as early as the mid-1970s, the modern integrated approach used by the NOAA Southwest Fisheries Science Center in San Diego began in 2008. Since 2012, we have maintained a consistent schedule, performing these surveys at least once annually.
Observing Ecosystem Shifts
The marine environment has changed significantly since the surveys began. In 2012, sardines were the dominant species, but their numbers plummeted leading to the fishery’s closure in 2015. Conversely, northern anchovy and jack mackerel populations have surged, with anchovies remaining the most prevalent species we encounter today. Sardines have yet to show signs of a rebound following their crash a decade ago.
Environmental Drivers
There is much discussion regarding why these shifts occur. While fishing pressure reduced stocks in the past, current low levels are likely driven by environmental and biological factors, rather than active overfishing.
Leadership Roles at Sea
The structure of the scientific team ensures the integrity of the data collected. The Principal Investigators (PIs) are responsible for the overall coordination and quality of the long-term survey. On the ship, the Chief Scientist manages daily operations and leads the scientific party, coordinating with the PIs to ensure the survey’s objectives are met successfully.
Advanced Sonar Systems
The shipโs acoustic “eyes” are located on a retractable centerboard, or keel, beneath the hull. While in port, this keel is flush with the ship, but it is lowered once we reach deep water. The Reuben Lasker is equipped with an impressive array of six different sonar frequencies. Low frequencies, like the 18 kilohertz signal, penetrate deep into the ocean to map the seabed, while higher frequencies are better for detecting smaller organisms like krill in the upper water column. We primarily use the 38 kilohertz frequency to measure fish echoes. Anything in the water column with a different density than the surrounding seawaterโwhether it be a fish, squid, or the ocean floorโreflects sound waves that our instruments carefully measure.
Omnidirectional and Multi-beam Sonars
Beyond the downward-looking sonar, we utilize an omnidirectional sonar mounted forward that scans in a radius around the ship. This helps us see fish near the surface that might be missed by the keel-mounted sensors. We also have multi-beam echo sounders, like the ME70 and MS70, which provide detailed three-dimensional views of fish schools and behavior. While these are invaluable for observing marine life, they are more difficult to calibrate for the precise biomass estimates provided by our primary systems.
Survey Transects and Navigation
The survey follows a series of transects that span the U.S. continental shelf from Mexico to Canada. These lines generally extend at least 35 miles offshore to ensure we capture the full range of the species we are monitoring. Each transect provides a localized estimate of biomass, and by repeating these measurements across the entire coast, we can calculate a mean population estimate with statistical confidence. The spacing between these linesโcurrently 12.5 nautical milesโis a careful balance between our available time at sea and the need for scientific precision. While navigating perpendicular to the coast can sometimes lead to a rougher ride in the troughs of the waves, it remains the most efficient and scientifically sound way to sample across the varying densities of marine life.
Image Credit: NOAA
Did you Know?
The sonar system on the Reuben Lasker is so sensitive it can detect individual organisms based on their density relative to the water.
Interview with Brad Erisman, marine biologist about the use of the MVP
Brad: The precision of our acoustic survey relies heavily on the physical properties of the water we traverse. Factors such as temperature and density significantly influence the strength and travel speed of sonar echoes. While we calibrate our instruments in San Diego, the conditions change as we move north along the coast. To maintain the accuracy of our biomass estimates, we must continuously adjust our parameters to account for variations in sound absorption and velocity within the water column.
The Moving Vessel Profiler (MVP)
This is where the MVP, or Moving Vessel Profiler, becomes indispensable. We deploy this specialized probe to capture a comprehensive temperature profile of the water column. These real-time measurements allow us to calculate essential coefficients for our acoustic data. Along every transect, we perform multiple deployments to ensure we have representative environmental data. This constant fine-tuning allows us to produce the most reliable estimates of fish populations possible.
Environmental Sensors
The MVP is a sophisticated tool, far more capable than a simple surface drifter. It is equipped with an array of sensors that measure salinity, chlorophyll levels, oxygen concentration, and sound speed. While a drifter only provides a surface snapshot, the MVP reveals the three-dimensional structure of the sea, highlighting fascinating features like thermoclines where warm, shallow water meets the colder, deeper ocean water.
Correlating Fish Patterns with Ocean Data
These environmental datasets help us explain the spatial and vertical distribution of the species we monitor. By collecting in situ data at the same fine scale as our sonar and trawl operations, we can identify correlations between habitat conditions and fish behavior. While satellite data provides a broad overview, the MVP gives us the high-resolution evidence needed to understand why schools appear in certain areas or why species patterns shift across different oceanographic breaks.
Efficiency at Sea
The beauty of the Moving Vessel Profiler is in its nameโit allows us to sample while the ship is in motion. A traditional Conductivity, Temperature, and Depth (CTD) cast involves a large cage lowered from a stationary ship, which would force us to halt our acoustic sampling. The MVP allows us to gather the necessary data without sacrificing valuable time. Although it doesn’t collect water samples or reach the extreme depths of a stationary cast, it provides exactly what we need to keep the survey on schedule.
A Three-Dimensional View of the Habitat
Oceanographers use these data points to build complex 3D models of the marine environment. These models are vital for understanding fish preferences; for instance, if sardines migrate further north, we can often trace that movement to a specific temperature preference, such as 15-20 Cยฐ-degree water, shifting with the currents. This helps us distinguish between a population decline and a simple change in habitat location.
Climate Signals and Regional Patterns
While large-scale climate signals like El Niรฑo or La Niรฑa are often monitored via satellite, our shipboard data helps define how these patterns manifest regionally. By looking at the data across the entire coast, we see the localized reflections of these massive basin-wide shifts, providing a clear picture of how the changing climate impacts our West Coast ecosystems.
Personal Log
Weโve run into windy conditions after we crossed over the border into Oregon. We only were able to do one trawl last night before we had to call it a night due to rough waters. Tonight, we were on watch until midnight to see if things would calm down but itโs still too rocky. To fill the time, we are discovering the delightful world of Dungeons and Dragons, led by the artful storytelling of the Operations Officer, Mike Fuller.
Itโs challenging walking down the hallways, and a large wave can scatter anything that isnโt well secured. Luckily the Dramamine is doing its trick and I havenโt felt queasy at all this week.
