Short answer: in spring, in rivers, on warming water. In Chesapeake Bay's rivers the eggs peak between the third week of April and the first week of May. In the Hudson, big tagged spawners crowd the spawning reaches from late April through May and are mostly gone by early June.
And yes, striped bass reproduce in the wild, in fresh water. They spawn in the tidal fresh stretch of a river, then spend most of the year in salt water. The fish you catch along the Massachusetts coast did their spawning weeks before you saw them, hundreds of miles to the south.
Where they spawn: tidal fresh water
The cleanest look at where the eggs are comes from the Virginia Institute of Marine Science. George Grant and John Olney towed plankton nets through the York, James and Rappahannock river systems from 1980 to 1983 and counted striped bass eggs and larvae.
The eggs turned up within the first 40 km (25 miles) of tidal fresh water, and peak densities were "nearly always" in fresh water. In the drought spring of 1981, when salt water crept up the James River, peak spawning moved 15 km (9 miles) upriver ahead of it. In the other rivers, the center of the spawn moved less than 2 km from year to year.
So can striped bass breed in fresh water? That is where they breed.
When: a few sharp weeks in spring
| River | Evidence | Years | Peak |
|---|---|---|---|
| York River system, Virginia | eggs in plankton nets | 1980, 1983 | 4th week of April |
| James River, Virginia | eggs in plankton nets | 1981, 1983 | 1st week of May |
| Rappahannock River, Virginia | eggs in plankton nets | 1982, 1983 | late April |
| Hudson River, New York | 66 tagged fish over 27 in | 2017, 2018 | half had arrived by Apr 18–27; most gone by early June |
In Virginia the egg peaks were "sharp and of limited duration", and Grant and Olney note that peak spawning at the same time is typical for the Potomac and the upper Chesapeake.
The Hudson fish carried acoustic tags put in 100 large spawners in 2016 by a team led by David Secor. They entered the river between April 4 and May 11, and half of each group had left the spawning reaches by May 21–30.
The season may be getting shorter. In Maryland's spawning survey of the Potomac and the upper Bay, 1985–2020, Angela Giuliano found warmer water since the 2000s, no significant change in when spawning starts, but an earlier end.
The temperature: a rising river, not a magic number
Grant and Olney found striped bass eggs across a wide band, 8.0 to 21.2°C (46 to 70°F). But the peaks were "limited to rapidly rising temperatures" between 13.7 and 19.5°C (57 to 67°F).
The Rappahannock in 1983 shows what that means. Egg numbers were climbing in mid-April when a cold snap dropped the river from 13–14°C (55–57°F) to 11–12°C (52–54°F), and only scattered eggs turned up. Once the water warmed again in the last week of April, eggs hit their season high: 477 per 100 cubic meters.
In the Hudson, the number of tagged fish on the spawning reaches climbed fastest between 10 and 12°C (50 to 54°F), and most left by the beginning of June as the river approached 20°C (68°F). But the temperature at which half a group had arrived moved a lot between two springs: 10.1 and 11.8°C (50 and 53°F) in 2017, then 6.1 and 8.0°C (43 and 46°F) in 2018, a slower-warming year. In the authors' words, the runs were "influenced, but not tightly cued by temperature."
The Chesapeake shows the same direction across decades. Alexander Peer and Thomas Miller analyzed a long run of Chesapeake gill-net catches and found spring water temperature was the main factor in when females moved onto the spawning grounds: warmer springs, earlier runs. In cool years, when the run came late, more egg-bearing females were caught before they could spawn.
Then they swim here
Spawning is why the big fish arrive when they do.
In the Potomac, Secor's team tagged 100 fish in 2014 and followed them through early 2018. Every fish that left Chesapeake Bay for the ocean ended up in Massachusetts. "All arrows point to Massachusetts," the authors wrote. The spring transit took between 17 and 96 days, 47 on average.
The Hudson spawners moved along the south shore of Long Island and into Massachusetts waters from May through June, averaging about 10 km (6 miles) a day, and stayed until late September.
Fish tagged here confirm the circuit. Of 159 adults, 26 to 43 inches, tagged in Massachusetts between 2008 and 2012, 125 were detected elsewhere on the coast, including on the spawning grounds of the Chesapeake, the Delaware and the Hudson (Jeff Kneebone and colleagues). All three stocks summered here, with the Chesapeake appearing the largest contributor in 2008–2010. That is a count of tagged fish heard on spawning grounds, not a census, so we will not turn it into a percentage. Why some fish make the trip and others stay home is its own story, told in our post on where stripers spend the winter.
What it means on a Massachusetts beach
- Spring fish here are post-spawn fish. The spawning grounds those Massachusetts tags found were all to the south. By the time big fish reach Cape Cod Bay, they have already spawned and traveled.
- A Virginia river's temperature is not your water's. 57°F is when a Chesapeake river's eggs can peak. It says nothing about when fish show up off Plymouth, and the Massachusetts tagging studies measured no arrival temperature.
- A late, cold spring down south may push things back. Cool springs delayed the Chesapeake run onto the spawning grounds. That a late spawn also means a late arrival here is our inference; nobody has measured the link in Massachusetts.
- Expect a spread, not a date. A 17-to-96-day trip from one river puts weeks between the first fish and the last.
How StripedLines uses this
StripedLines is built for striped bass. It rates feeding water, and Massachusetts fish do their spawning somewhere else. The spawning it pays attention to in spring is the bait's: from April through June, water near the mapped alewife and blueback herring run mouths can rate higher, because those fish are heading upriver to spawn. The rating ranks places against each other. It is never a chance of catching.