Twenty years of Ranger: supporting fisheries science in Alaska

When Sonardyne's Ranger USBL system was launched in 2006, one of the first users was the Alaska Fisheries Science Center. Today, the need to understand seabed habitats off Alaska – and beyond – is still as crucial as it was then. Incredibly, as we celebrate 20 years of Ranger, the center's Ranger system – and our first-generation digital transceiver, the GDT – is still going strong. Dr Bob McConnaughey, who took on that first system, reflects on the centre’s need for positioning and how it’s evolved.

Dr Bob McConnaughey:

At the Alaska Fisheries Science Center (AFSC) (part of NOAA’s National Marine Fisheries Service (NMFS)) the journey into underwater positioning really began with a problem we couldn’t ignore. Back in the late 1990s, when Essential Fish Habitat requirements were added to the Magnuson–Stevens Fishery Conservation and Management Act (of 1976), it fundamentally changed how we approached fisheries science.

It was about answering a simple scientific question: where are fish, what do they live on, and how does fishing change those places? This is important to Alaska. Our fisheries are among the most productive in the world, supporting livelihoods and communities across the state.

We had decades of solid fish abundance data in the eastern Bering Sea—but almost nothing on the seabed characteristics—bedforms, sediment texture—those fish depended on. And if you’re trying to understand ecosystems, that’s a pretty big gap.

That realisation raised a practical problem: how to characterise seabed habitats across, specifically, a trawl survey area of roughly 500,000 square kilometres in the eastern Bering Sea.

Clearly, taking small grab samples would be hopelessly inefficient. We needed ways to scale up, and that pointed us toward acoustics—and toward accurate positioning. That set me off on what I’d call a long and sometimes humbling search for workable subsea positioning.

My first real attempt, in 1997, was a dismal failure. We partnered with another agency using an early USBL system on a commercial fishing vessel, and it just didn’t perform. At the time, the explanation was vessel noise—but in reality, it came down to implementation issues. The deployment simply wasn’t suited to the platform. It was a hard lesson, but an important one.

Not long after, we ran comparative trials in a Navy torpedo tracking range, putting USBL systems up against a fixed acoustic array. That was the turning point. We could see clearly that USBL could work on fishing vessels—if it was done right.

Back to Bob…

So, I went looking for a system we could rely on. I first came across Sonardyne’s technology at an Oceans conference in the early 2000s. We were planning a multi-year study on trawling impacts, and we needed precise, real-time positioning of the gear.

With some fortunate Congressional funding support, we purchased two of Sonardyne’s first-generation digital transceivers—the yellow GDTs—in 2004 and 2005. At the time, we were using their Fusion USBL software, but when Ranger was launched in 2006, we transitioned over. It was a much simpler system to use!

Those early systems quickly became central to how we worked—particularly when we started pushing the boundaries of what we could do with seabed mapping.

One of the more ambitious efforts involved testing a prototype side-scan sonar that we came to call “the big fish.” It was a multi-million-dollar system designed for high-speed, very broad-swath mapping of the seabed. The goal was to generate bathymetry-corrected backscatter data that we could use quantitatively—something that’s becoming more commonplace, but at the time was truly cutting edge for fisheries applications.

To make that work, precise positioning wasn’t just helpful—it was essential. We were trying to tie acoustic returns to real features on the seabed and then link those to the distribution and abundance of groundfish and crab species. Without confidence in position, the whole exercise gets murky and starts to fall apart.

Because of that, we pushed the systems a bit further than standard configurations. One of the things we specified early on was a “receiver mode” capability, allowing improved two-way communication with the transponders. The idea was to minimise errors through the water column and tighten up the positional accuracy as much as we could. At the time, that wasn’t a typical setup, but it reflected how focused we were on getting the best possible data and, in the process, made us realise the crucial value of dedicated support.

Back to Bob…

We spent a number of seasons working through sea trials aboard the NOAA Ship Fairweather, figuring out not just system performance, but also the practicalities of deployment. Even something as simple as where to mount the transceiver—on a pole or on the skeg—made a difference.

In the end, we leaned toward the skeg mounting. It was more stable and, just as importantly, avoided some of the negative… feedback and errors you tend to get from over-the-side pole operations, especially when it starts flexing the hull and thumping loudly during transit. While we experienced this in those trials, we have refined the pole design over the years and it has performed well since!

But, by that point, we had a system we trusted. We were able to map seafloor habitats at scale and start building more robust models of how fish and crab distributions relate to those environments.

At the same time, we used Ranger for real-time positioning of other sampling tools—an instrumented grab sampler and a towed video system. Having that consistent positional reference across different data types made a big difference in how we could interpret the results.

All of that work fed into the 2012 FISHPAC study in the eastern Bering Sea. FISHPAC used acoustic seafloor surveys to map fish habitat in the Bering Sea, especially to see whether sonar backscatter could help define habitat associated with groundfish abundance.

For this, Ranger was used in a comparison of five different sonar systems. The idea was to understand not just what tools were available, but which ones could give us the kind of consistent, usable habitat data we needed to define and manage Essential Fish Habitat (EFH).

Over time, Ranger has been part of a number of projects, including mapping work in 2016 across the eastern Bering Sea shelf, where we carry out annual bottom-trawl surveys that ultimately feed into catch quota decisions. The objective was to understand how seabed characteristics affected performance of our survey trawls and adjust our population estimates for red king crab.

For both surveys, we ran tracklines over our established trawl stations using a range of sonar systems, including multiple sidescans, all tracked using Ranger.

More recently, we’ve been preparing for a large, multi-year study looking at the potential effects of bottom trawling in the Arctic. As fish populations shift northwards in response to warming waters, there’s increasing interest in those areas—but also a clear need to understand the environmental impacts before any fishing activity takes place.

From my perspective, that really brings things full circle. The questions we’re asking now are bigger, but they still come back to the same fundamental need: knowing what’s on the seafloor, how it’s being used, and being able to position our observations accurately enough to make sense of it all.

USBL capability is an invaluable tool for our EFH work and the excellent performance of Ranger over more than 20 years’ service life is quite remarkable. Combining science and engineering, and working with colleagues across disciplines, has shown how the right tools and the right partners make complex research possible.

Like many of my generation, I was inspired by Jacques Cousteau—his work sparked a curiosity that has stayed with me. There’s nothing quite like knowing the richness of life in the sea and having a role balancing use of the ocean as a resource and protecting it for the future.