The short version
Bay scallops usually spawn at about a year old, and most die before they can spawn again. Scallops born in a fall spawn enter their first winter tiny, and some may live to spawn a second year, which could cushion the big swings in scallop numbers. The authors collected adult scallops from the Peconic Bays of eastern Long Island, New York, in fall seasons between 1990 and 2019 and read each shell's winter growth ring to spot the fall-spawned ones. Averaged across 52 samples, 21.4% of adults were fall-spawned (the median sample was 11.2%), but the share in single samples ran from 0% to 100%. Warmer water did not explain it, while a higher share of ripe scallops one fall went with more fall-spawned scallops the next. The paper also covers meat weight, shell size and parasitic pea crabs. It matters because harvest rules seldom account for scallops that have not yet spawned when the season opens.
What the researchers did
The team collected scallops during the first two months of each fall harvest season, measured shells and meats, and compared the results with estimated water temperatures.
- They collected legal-size adult scallops, mostly by SCUBA diving, whenever sites and conditions allowed. The collections came from 18 areas on 87 different days between 1990 and 2019 (15,701 scallops in all).
- Scallop shells stop growing in winter and leave a raised ring. A ring of 20 mm or less marks a scallop that entered its first winter very small, which the authors treat as the sign of a fall spawn.
- They also recorded total shell height, meat weight, the share of scallops with ripe (bright orange) ovaries, and the share carrying large female squatter pea crabs, a parasite known to slow scallop growth.
- They compared the share of fall-spawned scallops with the ripeness of scallops the year before, and with estimated water temperature (NOAA satellite-based data corrected against a USGS station in Orient Harbor, used as a stand-in for all the bays).
- Because New York moved the season opening from early October to early November in 2005, they analyzed meat weight separately for 1990 to 2004 and 2005 to 2019.
What they found
- About one adult in five was fall-spawned, but it varied enormously. Of the 8,515 scallops with ring measurements, 21.4% (the average across samples) had a ring of 20 mm or less, and individual samples ran from 0% to 100% (Tettelbach et al., 2026). In one 1992 sample every scallop had a ring of 2 to 7 mm. The authors say these apparently came from a fall 1991 spawn after a brown tide (a harmful algal bloom) that summer.
- Very few scallops reached a second year. Scallops 2 years or older made up under 1% of those examined. The authors say this can likely be attributed to heavy fishing, since a 1910 Massachusetts report found up to 20% in some unfished populations. The highest shares they ever saw were after a brown tide or in a closed area, such as an estimated 40% in Napeague Bay in 1996, a year after a brown tide hit adult scallops.
- Ripe scallops one fall went with fall-spawned scallops the next. The share of fall-spawned adults in a year was related to the share of ripe adults the previous fall (R² = 0.51, P = 0.0003). The authors read this to mean that those ripe scallops do spawn and that enough of their young survive to show up a year later. Ripe scallops were a small share of any sample (0% to 18.8%).
- Temperature did not explain it. Average water temperature and the largest one-day temperature change in September to November showed no relationship with the next year's fall-spawned share. Of nine temperature measures tested, one was related: the number of November days with larger-than-average daily swings (R² = 0.20). The authors suggest their temperature data may not have been fine enough, and that food supply may matter.
- Late-born scallops catch up. The smaller a scallop's ring, the more it grew after winter (shell growth fell by about 0.9 mm for each extra millimeter of ring; R² = 0.912). By harvest, fall-spawned scallops reach about the same size as the rest, so they are legal to take even though, in Massachusetts studies the authors cite, half or more had not yet spawned.
- Meat weights rose. Average meat weight rose by about 0.04 g a year from 1990 to 2004 and 0.10 g a year from 2005 to 2019. Many of those samples came from one site (Hog Neck Bay), and the authors say that if the trend is real, warmer water may be a cause where food is plentiful. Meats also gained about 0.07 g a day through the fall.
- No clear trend in pea crabs. Large female pea crabs were found in 0% to 29% of scallops in individual samples, with no clear pattern over 30 years despite warming. The authors made no formal trend test.
- Management rarely counts these scallops. Massachusetts allows harvest only of scallops with a ring of at least 10 mm, or those taller than 63.5 mm if the ring is smaller. The authors say Bay Scallop management elsewhere, including New York, rarely considers fall-spawned scallops, partly because few knew how important they are and partly because checking rings is slow work.
What it means for Waquoit Bay today
Waquoit Bay once supported scallop harvests. All the data in this paper come from the Peconic Bays, and the authors cite Cape Cod and Nantucket studies only as background on fall spawning, so applying its findings here is CPWB's inference. Today scallops and the eelgrass they depend on are gone from the bay (see WHOI chemist explains why eelgrass has vanished from Waquoit Bay), and an EPA-led assessment tied the collapse of scallop harvests to nitrogen from the land (see How much nitrogen is too much for eelgrass?).
If scallops are ever restored here, the Peconic record shows what a returning population may lean on and where it is fragile. The authors suggest that a scallop born in the fall that spawns in its second year may give the population a second chance, and that this may matter most in a year when the usual spring and summer spawn fails. But in some years and places almost none of the adults were fall-spawned, and the Peconic scallop population crashed in 2019 despite years of restoration. Fall spawning may act as a buffer, but it is not a guarantee.
Read the paper
Tettelbach, S. T., Bonal, D. M., Tobi, H., Tomasetti, S., & Czaja, R., Jr. (2026). Insights into temporal patterns of late season spawning and other biological parameters in Bay Scallop populations over a 30-year period. *Northeastern Naturalist*, 33(3), 431–460. https://doi.org/10.1656/045.033.0308
License: The article is published in Northeastern Naturalist by the Eagle Hill Institute and distributed through BioOne, whose terms limit use of the PDF to personal, educational and non-commercial use. It is not openly licensed, so we link to the publisher's copy through the DOI and do not host the PDF. The summary is based on the full paper. The card image is a title card made from the citation.
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