Some things have changed on the Hudson River. For example, on August 10, the tide washed up at my feet at Little Stony Point two different bags of proprietary, legal, branded marijuana.

Some things have remained the same. That same morning I observed several people dragging a trawl net through the bay, something people have been doing at this location for at least 5,000 years.

The technique has not changed much, with two exceptions. Native Americans used palm-sized pieces of sandstone instead of metal for the weights at the bottom of the net. At the end of the day, they left the weights on the shore so that the net could be carried home more easily.

“Who wants to carry a bunch of rocks around in their pockets, right?” asks Tom Lake, a naturalist with the state Environmental Protection Agency. “Although I don’t think they had pockets.”

Lake said that along the river you can still find old sandstone weights with notched edges.

The other innovation is a bag in the middle that bulges as the net is dragged along the river bottom. “Fish are pretty smart,” says Lake. “They know they can swim faster than we can drag the net.” But when the bag expands, the fish think it’s an opening and swim into it.

Catch bags were introduced about 100 years ago. “That worked for a long time,” says Lake. “Every time we release the fish, we’re afraid they’ll tell the others, ‘Don’t turn right when the net turns, keep swimming straight.’ So far they haven’t done that.”

There was one final difference. Native Americans fished to eat. “We fish to discover,” Lake said.

We weren’t the only ones dragging a net that morning. At eight locations along the river, from the Brooklyn Bridge to the confluence of the Mohawk and Hudson Rivers north of Albany, educators, naturalists and citizen scientists participated in the 13th annual Hudson River Fish Count.

“It’s a way to teach people about the fish that live in their river,” says Sarah Mount, a science educator with the Hudson River National Estuarine Research Reserve who, like Lake, has participated in every fish count for the past 13 years (as has Lake’s 14-year-old grandson, Thomas, who was with us on the beach at Little Stony Point with two dozen other volunteers and a half-dozen dogs).

The number and type of fish caught varies each year. On August 10, the water was 27 degrees and the salt front – the line where salty ocean water meets fresh water from the Adirondack Mountains – had retreated to Yonkers due to heavy rains. Normally, the salt front is between Little Stony Point and Beacon at this time of year.

Even the tides play a role in what we might find in the nets. “We have a new and full moon right now, so the tides are pretty weak right now,” said Lake, who correctly predicted that we would find mostly tiny herring in the nets. They are born in freshwater, swim to the sea when they grow larger, and return to the Hudson four years later to spawn.

With its tides, winds and muddy bottom, the river’s murky nature makes it an ideal place for juvenile fish to escape predators and a terrible place to snorkel. “If these fish were at Coney Island, they would have a life expectancy of about 90 seconds,” Lake said.

The Hudson is home to about 240 species of fish, half of which swim past Little Stony Point at some point during the year. Most of the fish the trawls brought in were blueback herring or alewives, two members of the herring family that look almost identical except that the stomach lining of the blueback herring is black while that of the alewive is pink.

Properly identifying our catch required, as Lake put it, a “mildly invasive procedure.” He then handed a wriggling fish over his shoulder to Thomas, who bit off the fish’s head, spat it out, and returned the body to his grandfather.

“Black!” Lake said, holding up the decapitated fish. (Lake later said he uses this trick when he leads field trips for fourth-graders and their attention lapses.)

Other identification methods were less drastic. Spottail shiners, three-inch-long minnows with a black spot near their tail, got their name in 1824 from Gov. DeWit Clinton, who “took the time to think about science and nature,” Lake said.

As the boats passed, rolling waves washed bass into the nets, attracted by food stirred up by the churning riverbed. A few juvenile striped bass showed up, as well as two “one-year-old” striped bass, which stay in the river for a year before heading to the sea, increasing their chances of survival.

For the fish that don’t stick around for a year, the outlook is grim. Lake estimates that only 10 percent make it back. The chances are slimmer for the herring pulled from the nets, as many herring can’t handle the stress and go belly-down when they’re put back in the river. “Nothing goes to waste,” Lake said, referring to the blue crabs and eels that feed on the dead fish that aren’t eaten by the dogs.

The catfish that sometimes get caught in the nets are a different story. “I could put a catfish in my pocket, go to the village, have dinner there, come back here and throw it back into the river and everything would be fine,” Lake said.

For Mount, the science teacher, the best part of the day is seeing people’s faces light up when they catch a fish for the first time. “It’s one thing to stand on the river bank and look out and intellectually know there are fish,” she said. “But when you see how many fish you can catch with a little net tip, you realise there’s a whole world down there.”

On September 14th, Lake will be back at Little Stony Point with a trawl at 3:00 p.m. as part of the Hudson River Valley Ramble.