The comparison scores every group at once. This page is for the moment you already have a pair of names in mind — mayfly or stonefly, scud or sowbug, shad or alewife — and want the structures that keep them apart, in one look. Nothing here is a current hatch.
The differences, and nothing else
Best separating check: Deep, slab-sided bodyAt a glance It separates Sand lance (sand eel) from Menhaden (bunker, pogy) cleanly, and every pair of groups still in play differs on it and you can check it at a glance.
What to look at
Sand lance (sand eel)
Menhaden (bunker, pogy)
No pelvic fins underneath at alldecisiveIn hand
Yes
No
Dorsal fin layoutdecisiveClose look
One dorsal running most of the back
None of these
Long thin body, eel-likedecisiveAt a glance
Yes
No
Sawtooth belly keel you can feeldecisiveIn hand
No
Yes
Deep, slab-sided bodydecisiveAt a glance
No
Yes
Dives into clean sand and vanishesdecisiveWatch it
Yes
No
Rows of small spots behind the shoulder spotdecisiveClose look
No
Yes
Dark spot behind the gill coverdecisiveAt a glance
No
Yes
Reported size
4–300 mm
30–500 mm
Water it is recorded in
surf, inshore, nearshore, offshore
surf, inshore, nearshore
How it moves
dives head-first into the sand at sixty to seventy-five degrees and disappears; leaves the sand at twenty to sixty degrees, accelerating to about 120 cm per second within the first metre and a half
dense schools that ripple or splash at the water surface; young fish corralled at the surface or tight to the shoreline in a feeding blitz
Reference seasonality
Winter spawn on sand: Nov, Dec, Jan, Feb, Mar
Inshore season: May, Jun, Jul, Aug, Sep, Oct
The same for both: life stages.
Rows come from the reviewed diagnostic weights the comparison scores with. “Decisive” means one answer puts them at least four points apart — the carrier's own rule for a structure that separates a pair.
The two entries, side by side
Ammodytidae
Sand lance (sand eel)
A fish that solves the predator problem by becoming part of the beach.
First check
Look at the underside where the pelvic fins should be. If there is nothing there, on an eel-thin body with one dorsal running most of the back and a forked tail, that is a sand lance.
What it is
Most small silver fish deal with being eaten by schooling tighter and swimming faster. Sand lance took a different route: they dive into the seabed. Head first, at sixty to seventy-five degrees, wriggling until about a quarter buried, then settling to a shallower angle and stopping. A researcher with a stopwatch measured them leaving again at fifty to eighty centimetres a second and accelerating to a hundred and twenty within the first metre and a half off the bottom. That is not a fish hiding. That is a fish with an exit strategy.
Stages
Larva and first year (4–60 mm through the larval period) · Full-grown (76–200 mm typical; the northern species reported over 300 mm)
Water
surf, inshore, nearshore, offshore
Separates from Menhaden (bunker, pogy)
Run a finger up the belly. Sharp scutes forming a sawtooth keel is a clupeid; a sand lance has only a soft fold of skin there.
Typical windows
Winter spawn on sand (adult)
Patterns (correspondence)
Surf Candy
Limits
The two Atlantic species are not separable by eye, and one synthesis reports that the standard DNA barcoding gene cannot split them either. This entry does not offer that call.
Everyone knows the shoulder spot. The shoulder spot is not the answer.
First check
Find the shoulder spot, then look BEHIND it. Rows of smaller spots trailing back is menhaden. A single spot on its own settles nothing.
What it is
A menhaden is a deep, slab-sided, oily fish with a head about a third of its body, swimming with its mouth open and straining plankton through a basket of gill rakers. In a school they ripple and splash at the surface, and when something is under them the young ones get corralled tight to the shoreline in what Massachusetts calls, in an official publication, a blitz. That is the animal most of the coast is actually fishing over.
Stages
First year (30–150 mm; the NOAA staging runs larva under 30, prejuvenile 30–38, juvenile above 38) · Full-grown (152–500 mm depending which source you read — see the limitations)
Water
surf, inshore, nearshore
Separates from Sand lance (sand eel)
This entry does not name Sand lance (sand eel) as a look-alike. That is a gap in the prose, not proof they cannot be confused.
Typical windows
Inshore season (adult)
Patterns (correspondence)
None mapped yet.
Limits
Adult size is stated five incompatible ways across five agencies, one of them exceeding another's stated maximum.