Field work

Another crazy road trip for genetic silverside research

15 May 2022. A full, blood red moon rises over Pine Island this Sunday evening. The sight makes not just humans swoon – its pull extents underwater to all kinds of critters that take it as cue for reproduction. Critters just like the Atlantic Silverside, which once again we pursue this season to extract more of its genomic 'secrets'.

Specifically, it is this weekend that we embark on yet another ambitious road trip to find and sample spawning-ripe silversides from two very far apart places: Morehead City, North Carolina and Beverly, Massachusetts. The goal: transport spawners live from each population to UConn's Rankin Seawater lab and produce calculated crosses that will allow studying the role of genomic inversions in local adaptation.

The crew this time are Maria Akopyan and Jessica Rick from Cornell University, along with Lucas Jones and Hannes Baumann from UConn. Big shout-out to Tara Duffy for her help with beach seining at Beverly, MA. During the spawning event on May 15th, Nina Therkildsen also joined the efforts. The design and experiment are part of Jessi's successful NSF post-doctoral fellowship proposal, which the whole UConn-Cornell silverside team supports.

Click through the pictures below to retrace the steps of an exhausting but so far successful effort. Fingers crossed that all goes well during the next weeks, when the fish need to hatch, survive and grow, so they can be assessed for their traits.

Map-trip
The US east coast map illustrates our ambitious sampling plan.

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On 12th May, fog envelopes the Chesapeake Bridge on our drive south to Morehead City, NC.

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Maria, Hannes, Lucas, and Jessi getting ready to beach seine the Morehead City site

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Our 100ft beach seine is being laid out on the Morehead City site.

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On May 13th, Atlantic silversides caught in Morehead City swim in a bucket.

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Lucas checking whether the fish are properly prepared for transport.

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Ripe adult silversides are being transported in large coolers, with proper aeration and water changes underway.

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Maria driving through the night. The long trip back up north is especially taxing.

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On May 14th, Jessi and Tara pull our seine net up the beach on Obear Park, Beverly, MA.

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Maria bringing a new sampling bucket to Jessi and Tara (background) seining.

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Seining at low tide in Obear Park is made more difficult by ankle deep mud.

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Nina and Jessi strategizing about designing crosses.

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On May 15th, Hannes, Jessi, and Nina spawn individual silversides.

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Jessi squeezing a silverside female for eggs in UConn's Rankin Lab.

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A 24 hours old silverside embryo developing at 26C.

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On May 15th, Jessi lays out individual crosses to be reared in the circle tanks in UConn's Rankin Lab.

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Nina and Maria extract DNA from male and female spawners to determine a specific regions homo- vs. heterozygosity.

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Screens with attached embryos are being suspended in buckets for development under two different temperatures.

Unveiling a new sturgeon outreach sign at Hammonassett State Park

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On May 7th, project members, CTDEEP, and CT SeaGrant representatives unveil the new outreach sign about Atlantic sturgeon at Hammonassett State Park (f.l.t.r. Mason Trumble, CTDEEP deputy commissioner; Tom Savoy, CTDEEP scientist; Kelli Mosca, CTDEEP; Joe Cunningham, CTDEEP; Hannes Baumann, UConn; Sylvain Deguise, CT SeaGrant Director; Jacque Benway, CTDEEP

May 7th, 2022. Despite the chilly, rainy weather on Hammonassett Park's Meigs Point and the resultant lack of a beach crowd, the mood among the group was elated and proud. For over two years, our lab together with researchers from the Connecticut Department of Energy and Environmental Protection (CTDEEP, Tom Savoy, Jacque Benway) have worked tirelessly to better understand the growth and seasonal movement patterns of Atlantic Sturgeon (Acipenser oxyrhynchus) in Long Island Sound and the Connecticut River. The research project was funded by Connecticut SeaGrant (NOAA Award NA18OAR4170081, Project R/LR-29).

Kelli Mosca did her M.S. thesis research using fin spine sections for growth analyses and telemetry data for movement patterns. After defending in March 2022, she immediately accepted an offer by CTDEEP to become a full time staff scientist. Congrats again, Kelli!

The sign was designed by Joe Cunningham with pictures from Jacob Snyder (RedSkiesPhotography.com). It combines several outreach goals. 1) Convey to people that these ancient, iconic fish actually occur in our waters, 2) teach the interested readers that sturgeon spawn in freshwater and then grow up in saltwater, 3) give readers a sense of the ongoing research on Atlantic sturgeon, 4) tell the public that sturgeon may come back to Long Island Sound and River, but need protection. Particularly, they rely on any accidental catches to be released and reported. The sign is also available in Spanish language to broaden its reach.

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The sturgeon outreach sign at Hammonassett State Park

Kelli Mosca presents Master thesis research on Atlantic Sturgeon

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21 March 2022. Today, Baumann lab graduate student Kelli Mosca presented her Masters thesis entitled "Atlantic sturgeon (Acipenser oxyrinchus) Growth and Habitat Use in the Connecticut River and Long Island Sound". She did a marvelous job summarizing the multifaceted findings on age and growth of Atlantic sturgeon in the eastern Long Island Sound and the Connecticut River, their movement patterns based on analyses of acoustic telemetry data, while evaluating the evidence for indications that Atlantic sturgeon may utilize the Connecticut River again for spawning.

Kelli was an inspirational and cherished member of the Baumann lab, who literally mastered the challenges of being a 'whole-pandemic' Master student. Her dedication and continued work for CTDEEP were awarded by an offer for a CTDEEP Fishery Biologist I position, which she has wholeheartedly accepted. Congratulations Kelli, and all the best for the next steps in your career!

The UConn Department of Marine Sciences
Presents a Master’s Thesis Presentation by

Kelli Mosca
B.S., University of New Haven, 2017

12:00 p.m., Monday, March 21, 2022
Lowell Weicker Building, Seminar Room 103 or Via WebEx

Atlantic sturgeon (Acipenser oxyrinchus) Growth and Habitat Use in the Connecticut River and Long Island Sound

Atlantic sturgeon (ATS, Acipenser oxyrinchus) are long-lived, anadromous, and endangered fish with a wide geographical distribution along the east coast of North America. Historically known to spawn in numerous rivers, many spawning runs ended due to intense fishing pressure and habitat obstruction in the 19th and 20th centuries. This was thought to be true for the longest river in the US Northeast, the Connecticut River, until pre-migratory ATS juveniles appeared in the river in 2014. Here, I use a long-term archive of fin spine samples and three years of acoustically tagged ATS to generally expand knowledge about the ATS using the CT River and LIS, and specifically examine these empirical data for potential evidence of re-emergent spawning behavior. I analyzed 301 sections of ATS fins spines collected from 1988-2021 to determine age, annuli widths, and thus population- and individual-based growth patterns. I found that the vast majority of ATS in my study area were juveniles and sub-adults with an average (± SD) age of 7.5 ± 3.1 years and an average (± SD) length of 101 ± 26 cm. The weighed, population-based Von Bertalanffy growth model estimated a K of 0.08 (95% CL, 0.01/0.17) and a L∞ of 171.2 cm (95% CI, 129/547 cm), the latter likely showing signs of missing large adults. K and L∞ distributions showed no sign of sex-specific multi-modality. Longitudinal length back-calculations revealed the selective disappearance of faster growing phenotypes (at ages 2-6) with increasing age at capture, which is clear evidence for Lee’s phenomenon. Acoustic detections of telemetered Atlantic sturgeon (2019-2021) revealed that most sturgeon in 2019 and 2020 utilized the Lower CT River (brackish water), whereas in 2021 detections were highest in LIS (salt water). Detections in the Upper CT River (freshwater) were common but much less dense across years, with 53%, 69% and 45% of ATS detected in the Upper CT River at some point in each season (2019-2021 respectively). I found a positive relationship of fish proportion in the CT River with temperature, but an inverse relationship of fish proportion in the CT River with river discharge. On average, the arrival of fish in the CT River occurred in June, when water temperatures were 17.5 - 24.9 ºC, while the departure from the CT River generally occurred in October, coinciding with river temperatures of 15.2 - 20.4 ºC. Some of the fish utilizing the Upper CT River made directed movements to a potential spawning ground at Portland, CT (river km 47). However, these movements occurred in mid- to late August (12th -23rd), which is inconsistent with the typical spring timing of ATS spawning runs in northern populations. Fall spawning runs are only known for southern ATS populations. In addition to timing, ATS sizes in the Upper CT River also do not support spawning behavior, because fish of all sizes (72 – 154 cm TL) and ages (3-15) visited the Portland area for 0.25 – 63.25 days. I conclude that neither age nor telemetry data support the re-emergence of the CT River as an ATS spawning ground. Future work will benefit from a more even sampling of gear sizes and should examine possible explanations for ATS freshwater utilization including feeding and individual preferences.

Major Advisor: Hannes Baumann
Associate Advisor: Eric Schultz
Associate Advisor: Tom Savoy
Associate Advisor: Jacque Benway
Associate Advisor: Catherine Matassa

A day on the water with CTDEEPs sturgeon researchers!

28 September 2021. The day started nice enough but soon turned into dark threatening clouds, which the sturgeon researchers that day eyed with concern. Tom Savoy, Deb Pacileo, and Jacque Benway from CTDEEP, along with Kelli Mosca, Steve, Jake, and Hannes started to cast off late morning and slowly motored up the Connecticut River. "We're trying to catch the slack tide to set our sturgeon gill nets" explained Tom, the veteran sturgeon researcher, who has accompanied and steered most monitoring and protection efforts of these iconic fish over the past decades. It was Tom and his colleagues, who in 2014 caught the first baby Atlantic sturgeon in Connecticut River - a potential sign for a long hoped for recovery and the starting point of our project funded by CT SeaGrant.

The day trip was almost over, before it began. The downpour short but relentless and Jacque eyeing the lightening coming from the west with unease. But just before we could decide to fully head back, the radio call from the other boat that several sturgeon had indeed been caught in the gill nets! We therefore proceeded going through the routine measurement protocol that has been implemented for many years and is part of a federal permit to study this endangered species (No. 19641). Even a photograph is considered a sample, which is why we were glad to have our photographer Jacob Snyder (RedSkiesPhotography.com) fully accredited for the trip today. We saw with our own eyes, how a caught sturgeon was first being carefully pried loose from the gill-netting and placed in an aerated observation sump to prevent stress. All individuals are then checked for previously inserted tags using a specialized scanner (1) and if none is found, a new PIT-tag is inserted under the skin with the help of a syringe (3). All sturgeon are also measured for length (2), gape (5) and head width, and weighed (6) before being released back into the water. Tissue samples and in a limited number of fish also fin spine samples are taken for genetic information and growth data, the latter Kelli analyzed for her Masters Thesis.

The potential re-emergence of Atlantic sturgeon spawning in the Connecticut River is a success story of research and conservation, however, these efforts need to be sustained and widely communicated for the success to endure.

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1. On 28 September 2021, a juvenile Atlantic sturgeon caught in the Connecticut River is being checked for any previously implemented tags 2. Juvenile or sub-adult sturgeon are being measured for fork and total length using a measuring board 3. CTDEEP researcher Jacque Benway inserts a PIT tag into an sub-adult Atlantic sturgeon 4. Subadult sturgeon on a wet tarp before being released into wild again 5. All sturgeon are measured for mouth gape and head width 6. All sturgeon are being weighed with a gentle contraption 7. Master student Kelli Mosca with an adult sturgeon (all images by Jacob Snyder, RedSkiesPhotography)

Our sandlance work featured in the CapeCodFishermen

Reposted from TheCapeCodFishermen, April 28th 2021

By David N. Wiley

Bluefin tuna and striped bass crash through the waves. Seabirds wheel overhead and plunge into the water. Gape-mouthed whales rise from below. Schools of cod and dogfish hide below the surface.

While the convergence of such diverse sea life might seem accidental, those in the know thank a small, slender fish called a sand eel for the bonanza.

Also known as sand lance, these three-to-six inch forage fish are a main food source for many of the top predators in the Gulf of Maine and on Georges Bank, including some of the most commercially important species.

As their name implies, sand lance are tied to sand habitat, but not just any sand will do. To avoid predators, sand lance spend most of the night and parts of the day buried. When disturbed, they rocket out of the bottom, then dive head first and at full speed back into the sand.

As a result, their sand of choice has to be coarse enough to hold oxygen for the fish to “breathe” while buried, but soft enough to allow high-speed body penetration. One of the reasons Cape Cod is their Mecca is a band of perfect sand stretching from Stellwagen Bank along the backside of Cape Cod, past Chatham and up through Georges Bank. Whether you are a fisherman, whale watcher or seabird enthusiast, it’s this band of sand, and the sand lance that inhabit it, that makes the Cape special.

Sand and sand lance are the backbone of Stellwagen Bank National Marine Sanctuary, responsible for it being one of the top places in the United States for viewing marine life, and a centuries old, highly productive fishing ground. Yet while fishermen appreciate the importance of sand lance, little is known about their biology and most of the world does not know they exist.

To remedy the situation, a team of researchers led by scientists from Stellwagen Bank National Marine Sanctuary with partners from Boston University, Center for Coastal Studies, University of Connecticut, U.S. Geological Survey and Woods Hole Oceanographic Institution have been studying the forage fish to determine its importance and unlock some of its secrets.

One of the project’s first goals was to identify the sand lance spawning season. Using a specially designed and permitted small-mesh trawl, fished from Steve Welch’s F/V Mystic or NOAA’s R/V Auk, the team captured and examined sand lance. Thought to spawn from late fall through winter, several years of work demonstrated that sand lance on Stellwagen Bank spawn in a very narrow window at the end of November. Eggs are deposited on the seafloor and hatch after approximately six weeks.

Then things get interesting. Once hatched, sand lance are tiny, free-floating larvae for two to three months. Given this long free-floating period and the currents flowing over Stellwagen Bank, many sand lance born on the bank cannot stay there. So where do they come from and where do their offspring go?

To answer this question, the team used hydrographic modeling to backtrack to where free floating particles (like larval sand lance) would have originated prior to their sand settlement in March or April, and where drifting particles would end up two or three months after hatching.

It appears that larval sand lance settling on Stellwagen originate off the coast of Maine; years of highest sand lance abundance correspond to conditions that would have transported additional larval sand lance from as far north as Nova Scotia. The same modeling indicated that larval sand lance originating on Stellwagen Bank transport south to the Great South Channel and Nantucket Shoals (but not Georges Bank). In some years, currents moved them as far as New Jersey.

This is just another example of the interconnected world that creates a productive marine environment. Since few sand lance in the study lived past three years, the dependence on shifting currents to populate the bank could be one thing responsible for boom and bust years typical of sand lance abundance. The team is currently examining genetics of sand lance taken from throughout the Gulf of Maine, the mid-Atlantic, and eastern Canada, to gain additional insight into population structure.

Do boom-bust years influence the distribution and abundance of predators? The team investigated the association of sand lance with humpback whales and great shearwater seabirds by placing satellite tags on both species to track their movements.

Throughout the Gulf of Maine, tracking revealed that both species spend the vast majority of their time over sand lance habitat, and DNA from fecal shearwater samples showed sand lance to be the bird’s main prey. Surveys in Stellwagen also demonstrated a high co-occurrence of sand lance, humpback whales and great shearwaters.

Sand lance feed primarily from February to July, mostly on Calanus finmarchicus copepods. They stop feeding from August through October, with low levels of feeding from the end of November to January. Body growth and fat content show similar trends, with length and fat stores increasing from February to July. After July, the fish retreat to bury in the sandy bottom, conserving energy for spawning.

The team then turned its attention to the future of the valuable fish, something of extreme importance to fishermen. Ripe fish captured in November were strip-spawned on board the boats and transported to Connecticut, where eggs and larvae were raised in special tanks that allowed temperature and acidity to be manipulated to mimic future ocean conditions under climate change. Increased temperature and acidity had a dramatic negative impact on larval survival. According to Dr. Hannes Baumann, whose lab led the work, sand lance may be unusually sensitive to ocean acidification.

The future of sand lance was also a focus of team members Joel Llopiz and Justin Suca from Woods Hole Oceanographic Institution. They came to some worrisome conclusions.

The abundance of tiny C. finmarchicus copepods directly influences sand lance health: Abundant C. finmarchicus led to good parental condition and high reproductive success, while low numbers resulted in poor parental condition and poor reproductive success. Scientists have suggested climate change scenarios in the Gulf of Maine will lead to reduced abundance of this critical copepod resource. Adding to the problem was their finding that warm slope water coming through the Northeast Channel north of Georges Bank led to the death of overwintering reproductive adults.

With the Gulf of Maine warming faster than 99 percent of the world’s oceans, there is concern about the future of sand lance and its potential impact to the productivity of the Gulf of Maine, Georges Bank and other areas. While states with fisheries and other marine resources supported by sand lance cannot solve climate change issues, they can work to make sand lance more resilient to climate change. One way is to eliminate as many non-climate stressors as possible.

For example, in 2020 Massachusetts promulgated a rule limiting daily sand lance landings to 200 pounds. Rhode Island followed suit in 2021. These rules were designed to discourage the development of a commercial fishery for the species, such as the huge industrial fishery in Europe’s North Sea.

Since a commercial sand lance fishery does not currently exist here, adopting this rule by other states would be an easy, proactive way to make our waters, and the people who depend on them, more resistant to climate change disruption.

(Dr. David N. Wiley is the Research Ecologist for Stellwagen Bank National Marine Santuary. Funding for the project was provided by the Bureau of Ocean Energy Management, The Volgenau Foundation, Northeast and Woods Hole Sea Grant, International Fund for Animal Welfare, Stellwagen Bank National Marine Sanctuary and the National Marine Sanctuary Foundation. Dan Blackwood, Dr. Gavin Fay, Peter Hong, Dr. Les Kaufmann, Kevin Powers, Dr. Jooke Robbins, Dr. Tammy Silva, Mike Thompson, and Dr. Page Valentine contributed to the study)

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Baby sturgeon in the Connecticut River!

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Juvenile Atlantic sturgeon caught in June 2020 in the Connecticut River (photo: Jacque Benway, CTDEEP)

By Kelli Mosca.
3 July 2020. Atlantic sturgeon (Acipenser oxyrinchus) is an endangered, long-lived, anadromous fish that is found along the North American coast from the St. Lawrence River (Canada) to the St. John’s River (Florida). Historically, Atlantic sturgeon spawned in the Connecticut River, but until recently spawning populations were thought to be extirpated. In June 2020, a small, very young and therefore likely pre-migratory specimen (253mm) was captured by CTDEEP in the Connecticut River (above). This discovery is only the second after the first occurrence of small sturgeon in 2014! Together, this may be the beginning of a small Atlantic Sturgeon population rediscovering their long-lost spawning ground in the Connecticut River. CTDEEP and the Baumann Lab are working to find more fish of this size- and year class, and answer related questions about surgeon age and size and migration patterns. (CT SeaGrant project)

[New Publication] Fish and Fisheries publishes review of sand lance!

20 March 2020. We are happy to announce that the prestigious journal Fish & Fisheries just published a comprehensive review about the role of sand lance in the Northwest Atlantic Shelf ecosystem. The article, which came out of a workshop on this topic three years ago, reviews the the current state of knowledge about these enigmatic and important forage fish and urges continued efforts to better understand their role in the ecosystem and sensitivity to climate stressors.


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Sand lance caught on Stellwagen Bank in November 2014

The publication of this article was featured by UConn Today on 24 March 2020.


This work represents the first comprehensive assessment of this important forage fish in the Northwest Atlantic, though similar efforts have been carried out in the Pacific Northwest and Europe. In the Atlantic, sand lance are observed to be a significant food source for the federally endangered Roseate tern, Atlantic sturgeon and cod, Harbor and Grey seals and Minke and Humpback whales. “This paper is a call to our peers and colleagues that there is a big gap in knowledge, and to bring more attention to these species as unmanaged forage fish,” says Staudinger.


Staudinger, M., Goyert, H., Suca, J., Coleman, K., Welch, L., Llopiz, J., Wiley, D., Altman, I., Applegate, A., Auster, P., Baumann, H., Beaty, J., Boelke, D., Kaufman, L., Loring, P., Moxley, J., Paton, S., Powers, K., Richardson, D.E., Robbins, J., Runge, J., Smith, B.E., Spiegel, C., and Steinmetz, H. (2020)
The role of sand lances (Ammodytes sp.) in the Northwest Atlantic Ecosystem: a synthesis of current knowledge with implications for conservation and management
Fish and Fisheries (published online 20 March 2020)

[New Project] CTDEEP is funding our Atlantic sturgeon proposal!

1 Feb 2020. We are elated to announce that Connecticut Sea Grant has decided to fund our latest research proposal to study Atlantic sturgeon in Long Island Sound and the Connecticut River! The project is funded for two years under the most recent Omnibus Funding call and will examine the growth and seasonal movement of these magnificent, ancient fish.
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Kelli Mosca
The project will fund the Master thesis research of Kelli Mosca, the most recent addition to our lab! After receiving her Bachelors degree from the University of New Haven, Kelli became a dedicated seasonal worker at the Connecticut Department of Energy and Environmental Protection (CTDEEP), where she assisted particularly with the sturgeon monitoring program. This has made her the best possible graduate candidate to work this project. Welcome, Kelli!

To learn more, head over to the project page.


Baumann, H., Savoy, T., Benway, J., and Pacileo, D. 2020. A re-emergent spawning population of Atlantic Sturgeon in the Connecticut River? Combined age analyses and telemetry data will provide new insights. Connecticut Sea Grant Program (NOAA) #R/LR-29, Feb 2020 - Feb 2022 ($150,000)

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[Lab news] Hannes and Lucas on a ‘genetic’ road trip

18 December 2019. Hannes and Lucas just returned from a spontaneous road trip to visit our good friends and collaborators at the University of Quebec in Rimouski (UQAR), Canada. We drove for over 10 hours (one-way) through snowstorms and icy voids to meet with Prof. Dominique Robert, who had collected sand lance samples from the Gulf of St. Lawrence and from Nova Scotia to be included in our new genomic study on the population connectivity of this species. Hannes gave a talk about our sand lance work and we saw a new institute in a new place, while frantically trying to stay warm amidst the brutal cold. Seeing the St. Lawrence in its icy, majestic beauty was a truly amazing experience.
Afterwards, we drove back through Maine and then repeated the fin-clipping of samples in Scituate at the Stellwagen Bank National Marine Sanctuary office, so we now have almost all samples in hand to start the DNA extraction and sequencing.
We are excited for the next steps!
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Sand lance samples to be included in the genomic study

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Rimouski on the south shore of the mighty and icy St. Lawrence River on 12/13/19

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Lucas and Hannes listened to Corinne Burns talking about her PhD research at UQAR on 16 Dec 2019

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Hannes gave a talk about sand lance research at UConn

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The icy beauty of the St. Lawrence River

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Sun glistening on the ice on the banks of the St. Lawrence River on 16 Dec 2019

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Snow storm on the I91 in Vermont on 15 Dec 2019

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Driving back through Maine on 17 Dec 2019 ... 6h of snowstorm

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Sand lance sample thawing to be fin-clipped

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Hannes and Lucas fin-clipping specimens in the Stellwagen Bank NMS office in Scituate on 18 Dec 2019

[New Publication] MEPS publishes Julie’s Ms research on silverside otoliths

12 December 2019. We are happy to announce that Marine Ecology Progress Series just published our latest paper on Atlantic silversides, but this time not an experimental but a field study! During her time in our lab, Julie Pringle investigated the otolith microstructure of young-of-year silversides, finding intriguing patterns about differential growth in males and females that likely result in sex-selective survival during their growing season. Congratulations, Julie, well done!


Pringle, J.W. and Baumann, H. (2019) Otolith-based growth reconstructions in young-of-year Atlantic silversides (Menidia menidia) and their implications for sex-selective survival. Marine Ecology Progress Series 632:193-204


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This graph shows reconstructed hatch distributions of male and female Atlantic silversides sampled in fall 2015. Counting daily otolith increments, young-of-year fish caught in October could be reliably aged, whereas those from November and December where likely underaged because water temperatures had already decreased below their growth threshold. This graph compbines previous knowledge, environmental monitoring and results of otolith microstructure analysis.

From the abstract:

“We examined the utility of otolith microstructure analysis in young-of-year (YoY) Atlantic silversides Menidia menidia, an important annual forage fish species along the North American Atlantic coast. We first compared the known hatch window of a local population (Long Island Sound, USA) to otolith-derived hatch distributions, finding that YoY collected in October were reliably aged whereas survivors from November and December were progressively under- aged, likely due to the onset of winter ring formation. In all collections, males outnumbered fe- males, and both sexes had bimodal size distributions. However, while small and large females were almost evenly represented (~60 and ~40%, respectively), over 94% of all males belonged to the small size group. We then examined increment widths as proxies for somatic growth, which suggested that bimodal size distributions resulted from 2 distinct slow- and fast-growing YoY phe- notypes. Length back-calculations of October YoY confirmed this, because fast- and slow-growing phenotypes arose within common bi-weekly hatch intervals. We concluded that the partial sexual size dimorphism in this population resulted largely from sex-specific growth differences and not primarily from earlier female than male hatch dates, as predicted by the well-studied phenome- non of temperature-dependent sex determination (TSD) in this species. Furthermore, observed sex ratios were considerably less male-biased than reconstructed thermal histories and published laboratory TSD values predicted. Assuming that selective mortality is generally biased against slower growing individuals, this process would predominantly remove male silversides from the population and explain the more balanced sex ratios at the end of the growing season.”