This spring marks a decade since New Jersey’s Bureau of Marine Fisheries first deployed acoustic receivers to track the migratory patterns of the endangered Atlantic sturgeon in the Delaware Bay. For the researchers tasked with monitoring this fragile, prehistoric fish species, the past 10 years have been an exercise in hope — and occasional surprise.
“There are signs that the population has started a slow recovery,” said Brian Neilan, a senior fisheries biologist who leads the monitoring program for the bureau. “At least relative to the numbers when the [Atlantic coastwide] fishing moratorium on sturgeon went into effect in 1998.”
In mid-March, Neilan and his team deployed 19 acoustic receivers throughout the New Jersey side of the bay, from Cape May to Egg Island Point, in Cumberland County. The receivers pick up frequencies pinged from sturgeon and other fish implanted with radio tags that are similar to the microchips used for household pets. “It’s like E-ZPass for fish,” said Neilan.
On April 12, the first dataset was pulled from the receivers. Of the over 600 detections recorded, 66 came from just five sturgeon. “Those numbers are pretty on par for what we see during March and early April,” Neilan said. “May is typically when we get the most detections, because that’s when the sturgeon are using the bay the most, to go up to their spawning grounds in the river and then come back down and back out into the ocean.”
Like other depleted, culturally significant fish species in the Delaware Estuary, sturgeon are anadromous, meaning they spawn in fresh water, where they remain for the first couple years of their life before migrating to the ocean.
What sets sturgeon apart
What sets sturgeon apart from the estuary’s other anadromous fish species, however, is their slow growth. The American shad’s lifespan is about eight years; the striped bass can live up to 30 years. The Atlantic sturgeon can live for 50 years or more. A female sturgeon will not return to the estuary for her first spawn until she is around 15 years old.
“Sturgeon are very slow to mature,” Neilan said. “It takes close to between 10 and 12 years for a female to be mature, so when it takes that long, they’re interacting with so many different fisheries, or facing other threats, that they can easily die before they even have a chance to spawn once. That just compounds the issue of their life history.”
It has been estimated that before the industrialization of the Delaware Estuary, sturgeon numbered in the hundreds of thousands there. William Penn made note of the immense numbers in the river. Accounts from fishers in the early 1800s describe scenes of chaos, with gill nets overwhelmed and destroyed by sturgeon 6-7 feet long and hundreds of pounds, and boats nearly capsized by the bony, dinosaur-like fish jumping onboard.
In those days, the sturgeon was of little value. But by the latter part of the 19th century, the fish’s roe had become a delicacy sought by caviar importers around the world. With the largest Atlantic sturgeon population in the United States, the taking was easy and bountiful throughout the estuary: In Gloucester County in the 1870s, the Fancy Hill Fishery reported 117 sturgeon in one haul. The 1898 season alone yielded just over 5,000 fish and 1,067 kegs of caviar worth $2.1 million in today’s dollars. The rush reached fever pitch that same year, when the governors of New Jersey and Delaware had to arrange a special summit in Camden to avert the outbreak of a “sturgeon war” between their states’ fishers.
The intensity of the fishery, of course, was unsustainable. After only a decade, even as New Jersey, Delaware and Pennsylvania enacted regulations to protect juvenile sturgeon, the boom triggered a population collapse. To compound the stress on the fish, upriver pollution, between Wilmington and Philadelphia, stripped dissolved oxygen from the water. Just off the riverbank of Marcus Hook in Delaware County, Pennsylvania, a key spawning ground, the pollution was so great by the mid-20th century that sturgeon — and most other fish species — were unable to survive.
Genetically unique stock
In 2012, the National Marine Fisheries Service officially declared the Atlantic sturgeon, which includes a genetically unique population that migrates through and spawns in the Delaware Estuary, to be endangered. Today, there are less than 300 spawning adults left in the estuary — roughly half of Fancy Hill Fishery’s single-day haul in the 1870s.
While the Delaware Estuary is much cleaner today than it was 50 years ago, pollution remains a persistent problem for sturgeon, which are particularly sensitive to low dissolved oxygen. But modern life has also brought newer, wider-ranging problems.
Dredging of the Delaware River main channel has been one of the most devastating contemporary impacts on the fish. To spawn, sturgeon require flowing freshwater with hard-packed river bottom, which, in the Delaware Estuary, is predominately found in or adjacent to the Delaware River Main (shipping) Channel.
To accommodate newer and larger merchant ships, the channel must be constantly maintained and periodically expanded and deepened. To lessen the impact of the dredging, the Army Corps of Engineers, which conducts the work, must adhere to a moratorium that typically runs from March through June, when the sturgeon, shad and striped bass spawn is underway.
Nuclear reactors, propeller strikes
The Salem 1 and 2 nuclear reactors, located on the banks of the upper bay in Salem County, however, cannot shut down to accommodate the estuary’s anadromous fish species. The reactors utilize water intake systems that, despite being retrofitted with safeguards, suck in and destroy over 14 billion fish, eggs and larvae each year — a significant portion of them in the spring months.
The plant has a permit that allows them to “take” a certain amount of fish, and “they have to report every interaction with sturgeon,” Neilan said. “If they go past their allowed takes, they would have to shut down or change their operating to avoid having anymore takes.”
“Salem 1 and 2,” said Maya van Rossum, the Delaware Riverkeeper’s CEO, “is really the largest predator in the Delaware Estuary.”
Propeller strikes are also a major factor in sturgeon mortality in the bay and river. “They can be killed by anything from a huge container vessel down to regular people like us driving our center consoles through the bay,” Neilan said.
And as is the case with so many fish that are not the primary targets of commercial fisheries, bycatch is always a looming threat for the Atlantic sturgeon. “In the ocean and bay, they get caught in gill nets and trawls,” Neilan said. “Because they’re susceptible to low dissolved oxygen, if they’re stuck and can’t swim, they’ll die rather quickly.”
“This is a genetically unique population of fish that only exists in the Delaware Estuary,” van Rossum said. “And it’s on the brink and being hit at every turn.”
Though the 1998 moratorium on Atlantic sturgeon takes was necessary to save what remained of the Delaware Estuary population, the lack of a fishery made determining population numbers difficult. Acoustic monitoring programs like New Jersey’s have been a significant help in bridging this gap.
It has also led to innovative conservation efforts. In 2018, University of Delaware postdoctoral researcher Matthew Breece and colleagues used data from tagged sturgeon to develop a text-alert system that notifies fishers of where sturgeon are in the bay, so that they can avoid those areas.
Building further on data collected from acoustic tagging, this year Breece and his team of collaborators from University of Delaware, Delaware State University, Delaware Sea Grant, and the Delaware Department of Natural Resources and Environmental Control (the equivalent of the New Jersey Department of Environmental Protection) developed a forecasting tool that applies an algorithm to tagging and weather satellite data to provide fishers with three-day outlooks on sturgeon movement throughout the bay.
The technology is similar to tools that help predict algal blooms, and Breece is working on getting it into the hands of both commercial fisheries and the government agencies that oversee them. “Now that we had a forecast, now that we had those estimates of Atlantic sturgeon occurrence given the environmental conditions in the Delaware Bay, we wanted to use that data to help reduce interactions with Atlantic sturgeon,” Breece told the University of Delaware’s UDaily.
Other surprises in the data
The monitoring program has also yielded some surprising data that points to greater, more ominous changes in the ocean.
Last year, one of the New Jersey Bureau of Marine Fisheries’ receivers pinged the presence of another prehistoric fish species, though one that requires warm water temperatures: a mature Atlantic tarpon that had been tagged in the Florida Keys in 2019. “That’s the first one we’ve seen since the program started,” Neilan said.
In another survey, Neilan caught a ladyfish, a species usually found only in tropical and subtropical waters. Stockton University, he said, recently pulled up in a survey a bonefish, another warmwater dweller.
Climate change is the most likely factor in those incidents. According to the National Oceanic and Atmospheric Administration, the waters of the Northeastern U.S. continental shelf have warmed faster than any other ocean region in the country.
For the Delaware Estuary’s sturgeon, climate change is no less dangerous. The warmer water temperatures have already led to fishers catching shad in the bay in February, about a month sooner than historically normal. Neilan suspects we will see the same changes in sturgeon migration.
Neilan also worries about shifting salinity levels. “Sea level rise will cause higher salinities to move up into the bay and tidal section of the river, and sturgeon spawning and nursery areas occur in specific areas with specific salinities,” he said. “As higher salinities move into these areas, this may have an effect on spawning success, as the eggs and larvae may not be able to tolerate the higher salinities.”
As the peak of the sturgeon monitoring program draws near, Neilan can’t help but wonder what unexpected finding will surface in the data this time around. “Every year,” he said, “we get something that makes us go, ‘That’s pretty interesting, haven’t seen that one before.’”