Even if you never eat a fish pulled from the Delaware River, or never swim in its waters, it's important to know what is living below the surface.

Fish, plants and other species in New Jersey waters indicate pollution levels and climate. They show whether ocean fishing alongside this coastal state is sustainable.

The Delaware is the longest un-dammed river east of the Mississippi, 330 miles long from New York state south to the state of Delaware and the Atlantic Ocean.

The Delaware's 13,539-square-mile watershed, the nonprofit Delaware Riverkeeper Network says, "drains only four-tenths of one percent of the total continental U.S. land area," yet "15 million people — about 5 percent of the nation's population — rely on the Delaware River Basin for their drinking water. This includes the largest and fifth largest cities in the nation — New York and Philadelphia."

One way of measuring the river's health is through the annual survey of fish species, conducted by the state Department of Environmental Protection for 35 years. The 2014 results, a snapshot of what's swimming with you in the Delaware, were released this month.

The report paints a far different picture than that first survey in 1980. That year biologists made 28 hauls, one-tenth of the 284 made in 2014, and caught a single American Shad.

One.

Last year this native migratory fish, an important food source to Native Americans and generations of settlers, topped the list, with 7,208 netted.

Second on the list is Blueback herring. In 1980 the catch yielded 659, almost exactly one-tenth of the 6,504 in last year's combined catch.

So what?

Everyone should care because "everyone's downstream from something," said Steve Meserve, whose family's Lewis Fishery in Lambertville has seen the ups and downs of a shad fishery for the past century and expects to start seining for shad this year on April 4.

"In order to maintain everything, everything has to be maintained," he said. Otherwise "the dominoes start falling."

He points out that results from the 1980 DEP fish species survey could have been skewed by time of year and location of the hauls. American Shad, for instance, swim upriver in spring to spawning grounds. In the fall juvenile shad head downstream to the ocean.

Some species are common in the lower Delaware, below the falls at Trenton; others prefer the upper reaches of the river.

Having said that, Meserve pulled up fishery data and said 1980 "was an off year for us." Crews netted 1,920 shad, but that was over 148 hauls, for an average of 13 shad per haul.

In 1981 that number increased four-fold, to 54 American shad per haul.

Life cycles can make fish numbers cyclical. For instance, Delaware River floods in September 2004 and April 2005 hit shad at vulnerable times and affected hauls three-to-five years out.

That's the same reason, Merserve said, that the effects of the 1972 federal Clean Water Act weren't immediately noticeable. The 1980s, he said, was "the best decade" for fishing the Delaware River since the 1930s, when the fishery netted 30,000 fish.

"You can tell when the wars were" by reading the fishery's records, he said. "From1915-18 the numbers dropped. The '40s were fairly bad years," with the Philadelphia Naval Shipyard in high gear and "raw sewage" dumped in the river.

Steep declines ensued, and the Lewis Fishery didn't net a single American Shad in 1953 or 1956. "There was no real rebuilding until they were actively cleaning up the water" in the wake of the Clean Water Act, said Meserve.

"The water's wonderful right now," Merserve said, referring to Delaware River quality. "1980 was on the cusp of cleaning up the water; it's only gotten better since then."

Frenchtown's new sewage plant, for instance, is discharging effluent in the river, borough Mayor Warren Cooper said, that is considered cleaner than the river flow it's joining.

Meserve and the Lewis Fishery crew also help the state keep an an eye on river health by tagging fish and reporting haul numbers. The crew is required to return to the river any game fish it nets, such as striped bass — one of the predatory species with a taste for shad.

Because American shad spend most of their lives in the ocean, Meserve said, commercial trawlers in the Atlantic also take their toll on this and other species.

"If you're not looking for a bottom swimmer, why are you dragging the bottom?" he wondered. "They're trying to make nets that allow some species out, but it's tough when the fish" being harvested are "about the same size" and are "swimming in the same column.

"If shad are caught in the ocean and killed in those nets, they never make it upriver to spawn. You can't make a fish reproduce at will."

Renee Kiriluk-Hill may be reached at rkhill@hcdemocrat.com. Follow her on Twitter @ReneKirilukHill. Find The Hunterdon County Democrat on Facebook.