Meet Jonas Hentati Sundberg – scientific leader for the SPRAS-expedition

"Each expedition becomes a bit of a workshop. There are always problems to solve and things we want to improve. We have a fully equipped workshop on board, skilled repair technicians, knowledgeable IT staff, and a dedicated crew. That means we can build, test, and refine things as we go. We solve problems together," says Jonas Hentati Sundberg.

From herring and sprat…

Jonas is a researcher at SLU and scientific lead for SPRAS – an annually recurring, internationally coordinated expedition that monitors herring, sprat, and now also stickleback stocks in the Baltic Sea. Since 2020, the expedition has been carried out on board Svea, SLU’s research vessel.

The goal: to get as accurate a picture as possible of how much fish is out there. The results are submitted to ICES, where they become part of the scientific advice that forms the basis for the EU’s fishing quotas.

"What we’re doing is basically a hydroacoustic fish survey. We use Svea’s scientific echosounders to estimate total fish biomass, and combine that with trawling to collect biological samples – to determine things like species composition, length, weight, age, and sexual maturity."

…to a bigger picture

But SPRAS has evolved. While the main purpose is still to monitor commercially important fish stocks, the scope has broadened.

“We know we have to broaden the scope of the survey if we want to understand the whole ecosystem. In recent years, for example, we’ve started looking at seabirds, since they’re important top predators. And we analyse fish stomach contents and sample plankton with nets to understand what the herring and sprat are eating. SPRAS isn’t an ecosystem survey yet – but that’s the ambition.”

“And the ferrybox is always running. It takes in surface water while we’re underway and automatically measures temperature, salinity, oxygen levels, and plankton presence. It’s data we might not analyse ourselves right now, but it could become invaluable in the future. It’s a smart way to make use of Svea’s capacity.”

The tools that make it all happen

That Svea is the platform for SPRAS is no coincidence. The vessel is purpose-built for this kind of survey.

“Svea is equipped with advanced acoustic systems – scientific echosounders operating at multiple frequencies, plus several multibeam echosounders that let us see both the seafloor and out to the sides. And she’s very quiet. That gives us really clean echosounder data.”

Svea is ICES-certified for low underwater noise, and the echosounders are mounted in drop keels that can be lowered below the hull. This reduces interference from engine noise and air bubbles.

“Svea is also truly designed to handle fish – not just to catch it, but to process it efficiently. From the deck to the freezer, the workflow is super smooth. And the fish lab... it’s nothing like a dark storage hold. It’s a modern, well-equipped working environment.”

Welcoming more collegues on board

So what does Jonas say to other researchers considering booking time on Svea?

“Do it! Svea is incredibly versatile. On board, you’ll find all the equipment you could ask for, a strong team, and a culture that gets things done. And you don’t always have to book a full expedition yourself. We’re at sea for many weeks each year, and there’s often room for other researchers to join. It usually leads to really great collaborations.”

From data to insights

And the future?

“My vision for Svea is that we connect all the sensor systems on board – not just collect data, but continuously interpret it. We’d have a live snapshot of the ecosystem, in real time.”

By comparing expectations with the actual data collected, models could be tested against reality straight away.

“If the model doesn’t match, then we know either the model is wrong or there’s something we don’t yet understand. In that way, we’d be working in a knowledge loop – or an action loop – constantly improving the models, the questions, and the research. In the long run, that means improving our understanding of the sea we’re trying to manage,” says Jonas Hentati Sundberg.