Research News

Could Endangered Sturgeon Make a Comeback in the Connecticut River?

reposted from UConn Today 30 April 2025

Fish that swam next to the dinosaurs are once again appearing in CT waters

 

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After sightings of young sturgeon were reported, CT DEEP researcher Kelli Mosca ’22 MS and Professor Hannes Baumann began researching whether these ancient fish are making a comeback in the Connecticut River. (Credit Jacob Snyder)

By Elaina Hancock

For 160 million years, long-lived and highly migratory Atlantic sturgeons have made their way from the ocean to freshwater spawning grounds inland. The Connecticut River was one of the waterways sturgeon sought out – that is, until they were fished nearly to extinction in the early 20th century.

In 2014, however, researchers from the CT Department of Energy and Environmental Protection (CT DEEP) caught a few juvenile sturgeons in the Connecticut River, implying that sturgeons were spawning there again. More little sturgeon appeared in 2020 and again in 2022, leading some to wonder if this iconic fish that swam next to the dinosaurs was indeed making a comeback in our regional waters.

A new study from UConn professors Hannes Baumann from the Department of Marine Sciences and Eric Schultz from the Department of Ecology and Evolutionary Biology, in collaboration with researchers from CT DEEP including Kelli Mosca ’22 MS, Jacque Roberts, Thomas Savoy and Evan Ingram from Stony Brook University, shows that we have much to learn about sturgeons and that it may not be too late to give them a chance for recovery. Their findings are published in the National Oceanic and Atmospheric Administration’s open access journal, Fishery Bulletin.

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CT Deep researchers including Jacque Roberts, pictured here, used acoustic telemetry to track the movements of sturgeons. For telemetry, the fish were equipped with a small transponder and CT DEEP responders mounted throughout the Connecticut River recorded signals whenever fish swam near. (Credit Jacob Snyder)

Baumann says the project started at a conference in 2019, when he connected with researchers at CT DEEP who pitched a potential collaboration with Mosca, who was a CT DEEP seasonal resource assistant at the time and was hoping to pursue a graduate degree and focus her research on sturgeon. Despite these sightings, Baumann says he was skeptical that the fish were having a comeback, but he was interested in the project.

“These fish spawn in freshwater and then they develop until they are about 50 centimeters in size, then they travel to the ocean so if you find a little sturgeon in the Connecticut River, it must have been born there,” says Baumann. “We know there are sturgeon entering the Connecticut River; then the question is, how far do they go?”

For the project, Baumann secured funding from Connecticut Sea Grant, Mosca joined Baumann’s lab, and they started analyzing data to study sturgeon movement in the Connecticut River.

In 1998, sturgeons became a protected species but only after their situation had become dire. They are now heavily regulated, and even getting permits for research is not an easy task, says Baumann.

The researchers took samples of their pectoral fins that indicate the fish’s approximate age. Mosca looked at samples taken from the fish to determine the age,

“Ageing fish is often compared to ageing trees, in the sense that just as trees gain a ring in their trunk for each year they’re alive, a fish adds what we call an annulus (ring) to various hard parts in their body each year they are alive. In sturgeon’s case, they are not fully calcified, meaning there are not many hard bones to choose from to age. However, a small piece of their pectoral fin is hard enough to create those rings and can thankfully regrow so there is no deleterious effect on the fish. I am thankful to have access to such a large archive of these samples, which are rare given the endangered status of this species,” says Mosca.

People have also tagged these fish with acoustic transmitters, a specialized tag that send out a signal which is then picked up by listening equipment called receivers. CT DEEP deploys receivers anchored along the Connecticut River and within Long Island Sound that record the tag data as tagged sturgeon swim by.

The researchers used data on tracked sturgeons over the course of the three-year study, and over that period, sturgeons were detected as far upriver as Wilcox Island (Middletown, at river kilometer 52).

density-plot-and-abacus
Abacus plots (left) allows following the seasonal movement of individual fish along the Connecticut River receiver array, from the mouth of LIS, to the brackish estuary and into the fresh, upper river. A Kernel density plot (right) is used to visualize the habitat occupancy of many telemetered individuals.

“In theory, it’s all very easy, you just have to download the data and look where the sturgeon are,” says Baumann. “In practice, there are lots of statistics and analytical steps to properly assess these data. There were something like 1.5 million detections, over the three years in total, so 1.5 million rows of data, where every ping was a sturgeon somewhere. This corresponded to 85 individuals tracked over three years.”

Tracking animals in this way is called acoustic telemetry, and Baumann says the technology has profoundly changed our understanding of animal movements in the wild. There were some surprises in this one, he notes.

“Instead of just episodic accounts of single individuals, this study stands out for the large number of tracked fish,” says Baumann. “It showed that sturgeons generally arrive in the estuary in spring and leave in fall and that most stay in the brackish estuary. But intriguingly, a lot of the fish are indeed making these long upstream excursions into the freshwater. Why would they do this?”

Baumann says that the initial, most intuitive explanation of the fish displaying spawning migrations appeared unlikely after closer inspection. This is because most of the fish were not of adult size and age and, therefore, too young to spawn.

“We always thought Atlantic sturgeon are only in the estuary when they are young, and it is only when they want to spawn that they go into the freshwater. But that appears to be false. Our study shows that almost every size of sturgeon travelled into the freshwater portion of the Connecticut River. We had two individuals in our data set who were 18 years old. Most of the fish that we caught were younger than 12 years, and the average was about eight years, so they’re youngsters,” says Baumann.

The data therefore revealed that Atlantic sturgeons are using the entire Connecticut River, not just the estuary. Baumann says their working theory is that the fish are exploring other areas to find food, since the estuary can become crowded in the summer.

“In the paper, we advanced a theory that some of these Atlantic sturgeons move further up the river due to competition because it’s getting too crowded. The gist is we now know that we need to protect sturgeons at least during these important summer months, when they are in the entire Connecticut River.”

These findings are promising and important for ensuring measures are in place to help give the sturgeons the best chance possible at making a recovery. Though Baumann cannot say with certainty that the population is growing, a hopeful indication is that sightings of juveniles likely born in the River are happening more frequently.

“The sightings are still very sporadic and sort of ephemeral, but perhaps it’s a start.”

Protecting a highly mobile species like sturgeons can be tricky because they recognize no borders. Therefore, it takes national, federal, and international cooperation, but other measures are also important to ensure people are aware of their presence to help reduce accidental boat strikes or bycatch in commercial fisheries.

“From a logical perspective, they have been fished to quasi extinction in the beginning of the 20th century. Indeed, it would be a small miracle if these fish came back,” says Baumann. “At the end of the day, they made it 160 million years, and we need to just give them a chance to make it another 100. It doesn’t take much. It does take time, but if we allow it, I’m convinced that nature will find a way.”

Length-distr-background
Length (upper panel) and age distributions (lower panel) of Atlantic sturgeon in Long Island Sound and the Connecticut River (modified after Mosca et al. 2025)

Fishery Bulletin publishes black sea bass diet metabarcoding study

22 November 2024. We are happy to share that our paper on black sea bass stomach content metabarcoding has been published today in the traditional NOAA journal Fishery Bulletin. Our study used black sea bass juveniles caught in Mumford Cove to study their diet via a molecular approach known as metabarcoding. This method often detects rare or soft-bodied prey better than traditional morphological content analyses. We found that small, newly settled black sea bass eat mostly shrimp, but also many softbodied polychaetes. And weirdly, they seem to like one particular kind of (invasive) amphipod. Only larger juveniles seem to add fish to their diet.

Our study is a great first collaboration between our departments genomic experts (Ann Bucklin, Paola Batta-Lona) and the Evolutionary Fish Ecology Lab. The first product of our collaborative efforts has seen the light!

Fishery Bulletin is the 143 years old peer-reviewed journal managed and published by the National Marine Fisheries Service (NMFS) of the National Ocean and Atmospheric Administration (NOAA). It publishes Open Access at no costs to authors. Click the link below to download the paper.



BSB-COI-summary-web
Composition of prey detected in samples from stomachs of juvenile black sea bass (Centropristis striata), collected in Mumford Cove off Connecticut in August 2020, through metabarcoding with (A) the mitochondrial cytochrome c oxidase subunit I (COI) gene region and (B) the V9 hypervariable region of 18S rRNA. Bars represent the total number of COI and V9 gene sequences identified for each of 6 and 10 major prey taxa in DNA samples from 35 and 99 stomachs, respectively. In panel A, lists / pictures of the major prey species and their relative proportions for each prey taxon are provided (modified after Figure 1 in Batta-Lona et al. 2025)

Trawling for sand lance at the Revolution offshore wind field

6 September 2024. During the first research cruise of the CIEROW group on board the R/V Connecticut, our lab deployed a box trawl in- and outside the Revolution Wind field for a total of 7 times and 5 different locations. The box trawl had a 6 mm cod-end and tickler chains to catch small benthic fish – specifically sand lance of the genus Ammodytes.

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Research crew on CRW09-24 (fltr: Xavier Warren, Hannes Baumann, Evan Ward, Jessica Vorse, Michael Whitney, Bridget Holohan, Michael Cappola, Paola Batta-Lona)

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On 4 September, the sun sets at the Revolution wind field, still under construction

The box trawl was deployed from the main deck winch of the R/V Connecticut, with approximately 200m of wire let out in stations with water depths ranging from 34 – 38m, trawl speeds of 2 – 2.5kn for 13-15 upon reaching full wire-out lengths. Total trawl time (trawl in water – out of water) was about 25 minutes. During light hours, the trawl was equipped with a GoPro (Hero 4) to obtain footage of the trawled seafloor and potential organisms.

Overall, the trawl worked well with the ship and deployed as intended over the bottom. The GoPro footage revealed mostly sandy/muddy substrates with surprisingly little benthic fish life. Sand lance were neither caught in the trawl nor seen on the videos. Most trawls caught only few organisms, with the exception of Trawl 3 at station R6, which collected a number of common benthic fishes such as two hake species, one skate, sea robin and scup.

Box-trawl
The box trawl stands on the deck of the R/V Connecticut

Compilation-specimen-pics
Fish species caught at Trawl 03 at station R6 on 4th September 2024 (9:30 PM): Northern (1) red hake (Urophycis chuss), (2) thorny skate (Leucoraja erinacea), (3) silver hake (Merluccius bilinearis), (4) red hake juvenile, (5) butterfish (Peprilus triacanthus), (6) scup (Stenotomus chrysops), (7) Northern sea robin (Prionotus carolinus). Gridded background has 5 mm squares.

For this first deployment, we were cautious operating the gear in safe areas, but probably ended up trawling over sandy/muddy sediments that are not good habitat for sand lance. For the next cruise, we will therefore aim to alter trawl locations to include stations with known gravel or coarser sediment types.

A special thanks to Joel Llopiz and Lyndsey Lefebvre from Woods Hole Oceanographic Institution, who kindly lent us the box trawl to fish for sand lance, and to Justin Suca for facilitating this. We are also grateful to Marco, Sam, John and Luke from the R/V Connecticut crew for helping to deploy this new gear, even in somewhat rougher seas.

Fishing for inshore sand lance in Maine

20 August 2024. Emma and Hannes went on a road trip through New England to again visit our good friends and colleagues at the National Estuarine Research Reserve (NERR) in Wells, ME, Jeremy Miller and Jason Goldstein. Our mission this time was to try - for the first time - to find and collect American sand lance (Ammodytes americanus), the congener species to the Northern sand lance (A. dubius), which our lab has been investigating for now more than 7 years.

While the Northern sand lance can be reliably found on Stellwagen Bank in the southern Gulf of Maine, the specific whereabouts and promising collection sites for A. americanus are new, uncharted territory for us. They are often referred to as the inshore sand lance species, but where exactly would be a good spot to collect them?

On this late August week, we followed a tip from Jeremy from the Wells NERR to look at the harbor, where he had seen large schools near the docks all through summer.

After a good amount of scouting and trial (and error!) we ultimately got lucky at dead low tide, where we were able to use the beach seine to catch more than a thousand  sand lance adults and eventually succeeded in transporting ~ 300 of them back to the Rankin Lab for further learning how to rear and keep them.

This was the first of a handful of upcoming trips, where we plan to catch sand lance closer and closer to the begin of their spawning season at the end of November.

We hope that the luck stays with us during the next trips.

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The harbor of Wells, ME, on the afternoon of August 19th 2024

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American sand lance swimming in our tank at Rankin Lab on 21 August 2024

High CO2 tolerance of Black Sea Bass embryos / larvae – just out!

12 June 2024. We are excited to share that Environmental Biology of Fishes just published our study on the CO2 sensitivity of Black Sea Bass early life stages! The experimental work was part of Max Zavell's PhD-research and required the development of new approaches for obtaining spawning adults, new rearing methods, and new techniques for quantifying hatchlings and feeding larvae.

In the end, our research extends earlier experimental work to show that Black Sea Bass embryos and larvae are surprisingly tolerant to even extreme pCO2 conditions - which means that this species is likely resistant to the direct (!) effects of ocean acidification. Scientifically, this is intriguing because it points to some form of pre-adaptation that adults confer to their offspring in a manner we just don't understand yet.

Congrats, Max, to another chapter of your thesis published!


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Black Sea Bass early life stages, developing rapidly at 20C

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Hatching success of black sea bass embryo exposed to different pCO2 conditions (modified after Zavell & Baumann 2024)

The new cod – WrackLines article on our Black Sea Bass research

28 May 2024. The latest issue of Wrack Lines, the in house magazine of Connecticut Sea Grant, just published a nice feature article about our recent and ongoing research on Black Sea Bass in Long Island Sound. Written by Paul Choiniere, the article explains the background and the research in an easy, accessible way, while introducing our lab and its main actors.

Have a read!
(downloads pdf)


Thenewcod-WrackLines2024

Hannes returns from Chile!

 

16 April 2024. After a 9-month sabbatical stay at the University of Concepcion in Chile, Hannes returned to US soil today, full of experiences, data, and a chest full of samples of larval, juvenile, and adult Chilean silversides. Grateful to the many helpful colleagues and friends, a first year of experiments are in the bag, resulting in a number of interesting findings that await further analysis and - crucially - a second, replicate experiment in the year to follow. In other words, while the sabbatical is now over - the project of revealing co- and countergradient variation in the Chilean silverside is still very much underway. On to the next chapter!

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The cove of Puda near Dichato to the north of Concepcion, Chile

TAFS publishes our first Black Sea Bass experiment paper!

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Black Sea Bass have rapidly increased in abundance particularly in Long Island Sound (LIS Trawl survey data).

 

27 December 2023. We are excited to announce that Transactions of the American Fisheries Society just published our first large experimental study on Black Sea Bass overwintering! The work is part of Max Zavell's PhD research and reports on temperature- and food-ration dependent overwinter growth in Black Sea Bass juveniles from Long Island Sound. We reared juveniles individually in two separate experiments, one applying three static temperature treatments (6, 12, 19°C) and another using a seasonal temperature profile to mimic the thermal experience of juveniles emigrating to their offshore overwintering grounds coupled with various food treatments.

We found that Black Sea Bass juveniles showed positive overwinter growth even at temperatures as low as 6°C. However, the best temperature for growth, survival, and lipid accumulation was 12°C, which is close to the presumed conditions at offshore overwintering habitats of this species.

Congratulations, Max, to this great paper! Also, congrats to undergraduate student Matthew Mouland, who helped tirelessly with the rearing and has now deservedly become a co-author.



Fig03---Exp1-GRTL-SGR-Cons
(A) total length (TL) growth (mm/day), (B) weight-specific growth (%/day), and (C) growth efficiency (%) of juvenile Black Sea Bass reared at 6°C (blue circles), 12°C (green circles), and 19°C (orange circles) for 42–78 days. Each symbol represents an individual fish.

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Juvenile Black Sea Bass rearing setup in March 2022 in the Rankin Lab. Each white bucket contained an individual fish.

New 2023 sand lance experiment under way!

 

By Lucas Jones.

November 26, 2023. Members of the Sand lance Mafia assembled onboard the F/V Miss Emily in hopes of finding spawning ripe fish for our 2023 experiment. After loading our gear, Captain Kevin navigated us towards the southwest corner of Stellwagen Bank and deployed our beam trawl for our first 10-minute tow.

Boom! From the first tow, fish in spawning condition were brought on board, counted and separated by sex. Now, we just needed to repeat this for 13 more trawls until we had a sufficient amount of fish to start the experiment. After collecting 40+ spawning ripe males and females, we headed back to port wile starting to strip-spawn. This is an all hands on deck process, where we need to work together to evaluate the fish in real time and use the most ripe fish available.

The successful strip-spawn event now marks the start of our most ambitious experiment to date, where DNA and RNA samples will help us further investigate potential mechanisms behind the sand lances high CO2 sensitivity.

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Blastula stage sand lance embryos ~ 24h post fertilization

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The sandlance 2023 team after the first trip to Stellwagen Bank this year (left to right: Sam, Emma Siegfried, Chris Murray, Lucas Jones, Zosia Baumann, David Wiley)

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On 26 November, Lucas is back at the Rankin Lab with the goods!

UConn Today reports on Hannes’ Chile research

This article has been reposted from UConn Today. Read the original here

October 12, 2023 | Elaina Hancock - UConn Communications

Snap Shot: How Will Organisms Adapt to Climate Change?

A UConn Marine Sciences researcher is spending time in Chile studying an important forage fish, and how this vital part of the food chain will adapt to a changing climate

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The rocky and picturesque shores of the Pacific near Dichato

The world’s oceans have experienced record heat in 2023. With rising temperatures and increasing acidification, we don’t yet know the full extent these changes will have on marine ecosystems.

UConn Department of Marine Sciences Associate Professor Hannes Baumann studies fish, including important forage fishes such as sand lance and silverside, to see how they adapt to changes in environmental conditions. Many species are already adapted to temperature gradients that exist across latitudes on Earth, and Baumann believes that from these patterns, we can learn how fish may adapt to climate change – in time. This so-called “Space-for-Time” approach is one tool scientists use to predict the long-term consequences of climate change.

As part of his post-doctoral work, Baumann experimentally found similar climate adaptation patterns in Atlantic and Pacific silversides. He suspects that a higher-order relationship exists between the strength of adaptation and the strength of the underlying climate gradient.

Now, with a grant from the National Science Foundation, Baumann has the opportunity to return to and expand his study of silversides to a South Pacific species and study how they are adapted to their coastal latitudinal temperature gradient.

“We are hoping the prove the validity of a principle of evolutionary adaptation for the Southern Hemisphere. It will then allow us to compare and integrate the patterns with the silverside species from the Northern Hemisphere, which evolutionary ecologists have been studying for decades already,” says Baumann.

After a two-week proof-of-concept trip to Chile in the Fall of 2022, Baumann established connections with local fishermen and colleagues at the Universidad de Concepcion in Dichato, Chile.

“To get spawning fish, we visit fish markets – called here caletas de pescadores – and first establish a connection to those who make a living catching silversides (“pejerrey del mar”). We’re making friends to explain our unusual request to accompany a fisherman during the night. This is the best method to make sure that the eggs get fully fertilized," he says.

In the Summer of 2023, Baumann began his yearlong sabbatical and has now moved to Chile for five months to begin the main experimental work on Chilean silversides, their adaptations, and the strength of those adaptations to underlying climate change.

01 - HB-Tongoy
Hannes in Tongoy near Coquimbo/Chile