Short answer: yes, and more than most anglers would guess. When Massachusetts biologists opened 3,006 striped bass stomachs between June and September, 1997 to 2000, crustaceans (mostly crabs, small lobsters and sand shrimp) made up 45 percent of the diet by weight on the North Shore, 33 percent in Cape Cod Bay and 53 percent in Nantucket Sound. In Nantucket Sound that is more than the fish.
The less obvious part is which bass eat them. The bigger the fish, the more of its meal came off the bottom.
Which crabs
Nelson and colleagues found food in 1,720 of those stomachs. By share of total prey weight:
| Prey | North Shore | Cape Cod Bay | Nantucket Sound |
|---|---|---|---|
| Rock crab | 14.7% | 10.5% | 5.7% |
| Lady crab | none | 9.7% | 18.9% |
| Green crab | 6.8% | 3.9% | 4.4% |
| All crustaceans | 44.6% | 32.6% | 52.9% |
| All fish | 50.4% | 57.9% | 40.3% |
Rock crab is the North Shore crab. It turned up in about one in five North Shore stomachs with food, and it follows the rock: bass of roughly 17 to 25 inches caught on rocky shoreline in June and July carried 31.8 percent rock crab, while small bass from the estuaries carried almost none.
Lady crab is the southern one. In Nantucket Sound it was the heaviest single named prey of any kind, ahead of sand eels, sea robins and menhaden.
Green crab is everywhere and never large: under 7 percent in every region, and most important to bass under about 27 inches in estuaries and off beaches.
The rest barely register. Jonah crab was 1.3 percent on the North Shore, blue crab 0.5 percent in Nantucket Sound, and spider crabs under half a percent anywhere. A resample of Salem Sound in 2012 to 2016 found Asian shore crab, absent from the 1990s table, in four stomachs.
The crabs were small. Rock crabs from the stomachs averaged 30 mm (1.2 inches) across, against 140 mm (5.5 inches) for the ones the commercial fishery landed in northern Massachusetts in 2000. More on prey size in big bait, big fish.
The bigger the bass, the more crab
The textbook line is that striped bass turn into fish-eaters as they grow. In Massachusetts summer water, the stomachs lean the other way.
On North Shore rocky shoreline, bass of roughly 27 to 38 inches (175 stomachs with food) ate 31 percent small lobster and 17 percent rock crab by weight from June through September, and under 1 percent menhaden. Smaller bass on the same rocks ate crab in early summer too, then shifted to fish, mostly menhaden, in August and September. The big fish stayed on crustaceans all summer.
Offshore in Nantucket Sound, 36 stomachs from bass of about 32 to 40 inches held 34 percent lady crab, 20 percent sea robin and 18 percent cephalopods, likely squid, and no menhaden.
The authors wrote that their data "did not clearly support" the fish-eater rule, and with reason: in Cape Cod Bay, small bass were not collected offshore and big ones were not collected in the estuaries, and Nantucket Sound split much the same way, so size and place are tangled. The rocky North Shore comparison, one habitat and two sizes, is the cleaner one.
A second look came from new fish. Murphy, Nelson and Grabowski caught 158 bass on rod and reel around Salem Sound from 2012 to 2016 and split them at about 30 inches. Above that line, crabs and lobster were 35.5 percent of the diet by weight and showed up in half the stomachs with food. Below it, 13.2 percent, in about a third. Fish were 79.5 percent of the smaller bass's diet and 61.2 percent of the bigger bass's.
Carbon isotopes in the muscle, which record more than one meal, agreed: as the summer went on the big bass fed more off the bottom and the small ones did not. The big bottom-feeders also carried relatively larger livers, which the authors read as better energy reserves. Their explanation is that a heavy fish pays more to chase fast baitfish than to pick up slow prey; they say other explanations are not ruled out.
What the stomachs cannot tell you
They stop at the end of September. Every number above is a June-to-September number. The one Massachusetts study that reached October, Ferry and Mather's 1999 survey of 13 estuaries, pooled September with October and looked mostly at 15- to 19-inch fish, whose autumn diet added juvenile menhaden. We could find no published October or November stomach contents for big bass in Massachusetts. What a 35-inch fish eats on its way south is not measured.
Weight favors heavy prey. One small lobster outweighs a pile of sand shrimp. In the Salem Sound study rock crab turned up in the same share of stomachs as lobster, about one in six, yet made up a fifth as much of the diet by weight: 4.3 percent against 19.9.
The most dramatic numbers sit on tiny samples. 48 percent lobster comes from 15 stomachs of fish around 35 inches; 58 percent lady crab from five stomachs of Cape Cod Bay's biggest bass; 44 percent rock crab, in a later reanalysis of the same stomachs, from 17 of the oldest fish in late summer. Treat them as hints.
These are mostly fish that bit, before noon. Most came on rod and reel (some by gillnet and long-line), and 77 to 90 percent were caught between 6 a.m. and noon. They show what fish willing to take an offering had eaten that morning.
What to do with it
Inference from the diet, not a tested rule: nobody has measured catch rates by lure against these stomachs.
- For the biggest summer fish, think bottom. Crab-shaped, crab-colored presentations worked slowly near rock and cobble on the North Shore, or over clean sand in the sounds, look like what those fish had been eating.
- Fish the crab of the place, and keep it small. Rock crab and small lobsters on northern rock, lady crab on southern sand, green crab in the estuaries, most of them an inch or so across.
- Do not carry it into October on faith. For smaller fish the late-summer story is menhaden (bunker is an autumn bait); for big fish after September, we found no one who has looked.
How StripedLines uses this
StripedLines is built for striped bass. Crabs and juvenile lobster are among the baits the app can suggest you match, tied to the bottom they live on: rock crab and lobster on rock and cobble, lady crab on sand in the open sounds. The pick shows as the spot's likely bait, with a prompt to look for it first. The app does not know what size of bass you are after; the big-fish crab pattern is yours to apply.