Monitoring fragile sturgeons in Delaware Bay | NJ Spotlight News

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Credit: (Mauro Orlando from Flickr; CC BY-NC-ND 2.0)
Black sturgeon

This spring marks a decade since the New Jersey Bureau of Marine Fisheries first deployed acoustic receptors to track the migratory patterns of endangered Atlantic Sturgeon in Delaware Bay. For researchers tasked with monitoring this fragile, prehistoric species of fish, the past 10 years have been an exercise in hope – and sometimes surprise.

“There are signs the population has started a slow recovery,” said Brian Neilan, a senior fisheries biologist who heads the monitoring program for the office. “At least in relation to the figures when the [Atlantic coastwide] the moratorium on sturgeon fishing entered into force in 1998. “

In mid-March, Neilan and his team deployed 19 acoustic receivers across the New Jersey side of the bay, from Cape May to Egg Island Point, Cumberland County. The receivers pick up the frequencies sent by sturgeons and other implanted fish with radio beacons similar to microchips used for pets. “It’s like E-ZPass for fish,” Neilan said.

On April 12, the first set of data was pulled from the receivers. Of the more than 600 detections recorded, 66 came from just five sturgeons. “These numbers are pretty comparable to what we see in March and early April,” Neilan said. “It is generally in May that we get the most detections, because it is at this time that the sturgeons use the bay the most, to go up to their spawning grounds in the river, then to descend and return to the ocean. . “

Like other depleted and culturally important fish species in the Delaware Estuary, sturgeons are anadromous, meaning they spawn in freshwater, where they stay for the first two years of their life before migrating to the sea. ‘ocean.

What sets sturgeon apart

However, what sets sturgeon apart from other anadromous fish species in the estuary is their slow growth. The lifespan of American shad is about eight years; striped bass can live up to 30 years. Atlantic sturgeon can live 50 years or more. A female sturgeon will not return to the estuary for her first spawning until she is about 15 years old.

“Sturgeons are very slow to mature,” said Neilan. “It takes 10 to 12 years for a female to mature, so when it takes that long, she’s interacting with so many different fisheries, or facing other threats, that she can easily die before she even dies. ‘have a chance. to spawn once. This only compounds the question of their life history. “

It was estimated that before the industrialization of the Delaware Estuary, sturgeons were numbered there in the hundreds of thousands. William Penn noted the immense numbers in the river. Fisherman’s accounts of the early 1800s depict scenes of chaos, with gillnets submerged and destroyed by sturgeons 6 to 7 feet long and hundreds of pounds, and boats nearly capsized by the bony fish resembling a dinosaur jumping on board.

At that time, the sturgeon was of little value. But by the end of the 19th century, fish roe had become a delicacy sought after by caviar importers around the world. With the largest population of Atlantic sturgeon in the United States, collection was easy and abundant throughout the estuary: in Gloucester County in the 1870s, the Fancy Hill Fishery reported 117 sturgeon in one single trait. The 1898 season alone produced just over 5,000 fish and 1,067 barrels of caviar worth $ 2.1 million in today’s dollars. The rush came to a head in the same year, when the governors of New Jersey and Delaware had to hold a special summit in Camden to avoid the outbreak of a “sturgeon war” between fishermen in their states.

Credit: (AP Photo / Ben Finley)
File photo: A baby Atlantic sturgeon

The intensity of fishing, of course, was not sustainable. After just a decade, even as New Jersey, Delaware and Pennsylvania passed regulations to protect juvenile sturgeons, the boom triggered a population collapse. To add to the stress on the fish, pollution upstream, between Wilmington and Philadelphia, has extracted dissolved oxygen from the water. Just off the shore of Marcus Hook in Delaware County, Pennsylvania, a key spawning ground, pollution was so great by the mid-20th century that sturgeon – and most other fish species – were unable to 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 and spawns in the Delaware Estuary, is Endangered. Today, fewer than 300 breeding adults remain in the estuary, about half of Fancy Hill Fishery’s one-day transport in the 1870s.

While the Delaware estuary is much cleaner today than it was 50 years ago, pollution remains a persistent problem for sturgeons, which are particularly sensitive to low dissolved oxygen. But modern life has also brought newer and larger problems.

One of the most devastating impacts on fish today has been the dredging of the main channel of the Delaware River. To spawn, sturgeons need running fresh water with a compact river bottom, which in the Delaware Estuary is mostly found in or next to the main channel of the Delaware River.

To accommodate newer and larger merchant ships, the canal must be constantly maintained and periodically widened and deepened. To mitigate the impact of dredging, the Army Corps of Engineers, which carries out the work, must adhere to a moratorium that typically runs from March to June, when sturgeon, shad and striped bass are In progress.

Nuclear reactors, propeller strikes

The Salem 1 and 2 nuclear reactors, located on the shores of the Upper Bay of Salem County, however, cannot close to accommodate the anadromous fish species from the estuary. The reactors use water intake systems which, despite being modernized with protective measures, suck up and destroy more than 14 billion fish, eggs and larvae each year – a significant portion of them in the spring.

The plant has a permit that allows them to “catch” a certain amount of fish, and “they have to report every interaction with the sturgeon,” Neilan said. “If they exceed their allowed outlets, they should stop or change their operation to avoid having more outlets.”

“Salem 1 and 2,” said Maya van Rossum, CEO of Delaware Riverkeeper, “is really the biggest predator in the Delaware Estuary.”

The impacts of propellers are also a major factor in the mortality of sturgeons in the bay and the river. “They can be killed by anything from a huge container ship to ordinary people like us driving our center consoles across the bay,” said Neilan.

And as with so many fish that are not the primary targets of commercial fisheries, bycatch is still an imminent threat to Atlantic Sturgeon. “In the ocean and the bay, they’re caught in gillnets and trawls,” Neilan said. “Because they’re sensitive to low dissolved oxygen, if they get stuck and can’t swim, they’ll die pretty quickly.”

“This is a genetically unique fish population that only exists in the Delaware Estuary,” said van Rossum. “And he’s about to be hit at every turn.”

Acoustic monitoring

Although the 1998 moratorium on Atlantic sturgeon catches was necessary to save what was left of the Delaware Estuary population, the lack of fishing made it difficult to determine population numbers. Acoustic monitoring programs like those in New Jersey have gone a long way in filling this gap.

It has also led to innovative conservation efforts. In 2018, University of Delaware postdoctoral researcher Matthew Breece and his colleagues used the tagged sturgeon data to develop a text alert system that informs fishermen of the sturgeon’s location in the bay. , so that they can avoid these areas.

Relying further on data collected from acoustic tagging, Breece and his team of collaborators from the University of Delaware, Delaware State University, Delaware Sea Grant, and Delaware Department of Natural Resources and Environmental Control (the New Jersey Department of Environmental Protection equivalent) developed a forecasting tool that applies an algorithm to tagging and meteorological satellite data to provide fishermen with a three-day outlook on sturgeon movements in the bay.

The technology is similar to tools that help predict algal blooms, and Breece is working to put it in the hands of commercial fisheries and the government agencies that oversee them. “Now that we had a forecast, now that we had these estimates of Atlantic Sturgeon occurrence given the environmental conditions in Delaware Bay, we wanted to use this 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 produced startling data indicating larger and more disturbing changes in the ocean.

Last year, one of the New Jersey Bureau of Marine Fisheries receivers reported the presence of another prehistoric fish species, albeit one that requires warm water temperatures: a mature Atlantic tarpon that had been scored in the Florida Keys in 2019. “This is the first one we’ve seen since the program started,” said Neilan.

In another investigation, Neilan captured a ladybug, a species typically only found in tropical and subtropical waters. Stockton University, he said, recently found in an investigation a bonefish, another inhabitant of warm waters.

Climate change is the most likely factor behind these incidents. According to the National Oceanic and Atmospheric Administration, the waters of the northeastern US continental shelf have warmed faster than any other ocean region in the country.

For the Delaware estuary sturgeon, climate change is no less dangerous. Warmer water temperatures have already led fishermen to catch shad in the bay in February, about a month earlier than normal. Neilan suspects that we will see the same changes in sturgeon migration.

Neilan is also concerned about the change in salinity levels. “Rising sea levels will cause higher salinities to rise in the bay and tidal section of the river, and sturgeon spawning and nursery areas occur in specific areas with specific salinities,” did he declare. “As higher salinities move into these areas, it can have an effect on spawning success, as eggs and larvae may not be able to tolerate the higher salinities.”

As the peak of the sturgeon monitoring program approaches, Neilan can’t help but wonder what unexpected finding will appear in the data this time around. “Every year,” he said, “we get something that makes us say, ‘It’s pretty interesting, I’ve never seen this one before. “”



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