overwintering

A grouper on its way north – MEPS publishes Black Sea Bass synthesis paper

16 April 2026. We are excited to share that Marine Ecology Progress Series today published our synthesis paper on Black Sea Bass in Long Island Sound!

The publication combines laboratory research on juvenile and adult black sea bass with ocean and climate modeling to make the case that these fish are already or at some point soon likely to change their habit of moving offshore in winter. This is because inshore waters are warming, so the fish can stay longer in fall and return earlier in spring, but also because the whole Northwest Atlantic shelf is warming, which reduces the distance the fish need to swim to reach overwinter habitat.

Picture of a juvenile black sea bass
A juvenile black sea bass during the 2022 overwinter experiment

In the laboratory, PhD student Max Zavell with the help of his dedicated undergraduate assistants Matt Mouland and David Barnum conducted 2 overwinter experiments on juveniles to simulate their thermal experience of migrating offshore or remaining within Long Island Sound (LIS). Surprisingly, this showed that overwintering inshore caused only minor reductions in survival (100→84%), led to no loss in lipid reserves, but incurred a growth cost in both length and weight.

Thanks to the involvement of two inhouse physical oceanography groups (James O'Donnell, Samantha Siedlecki), we were able to project how mean LIS winter temperatures will increase from 3.2°C to 4.8°C by mid-century, which reduces the average time black sea bass cannot live in LIS by 30%, from 95 to 68d per year. A separate shelf model projected the rapid northward movement of the 10°C isotherm in February bottom temperatures on the Northwest Atlantic shelf - this reduces the overwinter migration distance from  ~600 to ~120 km by mid-century!

Inshore overwintering will become increasingly feasible for black sea bass, perhaps lead to partial migration that furthers the poleward range expansion of this species.

The publication results from a particularly strong interdisciplinary collaboration of no less than 5 research labs: The Baumann and Schultz lab dedicated to fisheries and evolutionary fish ecology, the Matassa Lab with expertise in benthic ecology, the O'Donnell and Siedlecki groups dealing with modeling projections for nearshore and offshore waters in the North-Atlantic. The publication is an example of inclusiveness, given that the list of authors not only includes the graduate student as the lead, but also two particularly engaged undergraduate students, in addition to two post-doctoral researchers and the 5 more senior faculty. 

Plot of black sea bass occurrence in Long Island Sound
A detailed look at how temperature (green line) and black sea bass abundance (circles) have changed over the past 40 years in Long Island Sound (LIS). The circles are scaled to the total number of individuals caught per year and length class (1 cm) during the spring LIS trawl survey (April to June). Blue circles: juveniles (≤14 cm TL); orange circles: adults (≥15 cm TL); green solid line: average annual winter temperature 1991–
2023 (LISICOS ELIS buoy) (modified after Zavell et al. 2026)


Can adult black sea bass overwinter in Long Island Sound?

18 July 2025. We are thrilled to share that Marine & Coastal Fisheries (an AFS Journal) published today the 3rd chapter of Max Zavell's PhD research! The paper asks the simple but pertinent question

Can adult Black Sea Bass overwinter in Long Island Sound, USA?

The research followed the fate of 2 x 25 adult black sea bass that were angled in Long Island Sound (LIS) in fall 2022 and then kept at realistic winter inshore temperatures in two large flow-through tanks at the Rankin Seawater Laboratory of the University of Connecticut at Avery Point. The authors repeatedly measured survival, length- and weight growth, gonad investment and lipid contents of experimental and wild fish. They cautiously conclude that

"At present, overwintering in LIS appears possible but likely disadvantageous for Black Sea Bass, because offshore winter migration results in greater energy reserves and subsequent reproductive investment. In the future, however, warming coastal waters will continue to shorten the duration of unsuitable winter temperatures, which could become conducive to year-round inshore residency or partial migration patterns in the northern stock of Black Sea Bass."

The article was published Open Access. Congratulations, Max et al.!

Fig1-Survival-Temp-Figure
Dynamic overwinter temperature profile and survival for two black sea bass tanks in 2022/23

Male Black Sea Bass - April2021
Male Black Sea Bass (H.Baumann April 2021)


TAFS publishes our first Black Sea Bass experiment paper!

Fig01---BSB-CTDEEP-trawl-survey-count_new-copy
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.

BlackSeaBass_Mar2022_01
Juvenile Black Sea Bass rearing setup in March 2022 in the Rankin Lab. Each white bucket contained an individual fish.