By Elizabeth Wulfhorst
FAIR HAVEN – There is a not-so-pleasant sight on a tiny strip of sandy ground at the end of Fair Haven Road: at least a dozen dead fish.
While not a rare occurrence, the presence of these lifeless menhaden here and at other locations throughout the Two River area, is a cause for concern for a number of reasons, explained Swarna Muthukrishnan, Ph.D., the staff scientist at Clean Ocean Action, a local nonprofit that works to improve the water quality along the Jersey Shore.
The menhaden – also known as bunker – an oily feeder fish that sits at the bottom of the food chain, can end up in shallow water after being chased there by larger predators. The shallower waters at times have less dissolved oxygen and can’t accommodate the influx of fish so some die. Muthukrishnan called this a “natural cause in a natural situation.”
But the concern, she said, is, “at least in the Navesink and the Shrewsbury (rivers), we have been observing this more frequently.” The reasons for the increase are difficult to pinpoint and could be explained by a number of factors.
Oxygen variation in the coastal waters has a “diurnal pattern,” said Muthukrishnan. This means the levels fluctuate between the daytime and nighttime. But as climate change brings warmer weather to the region sooner than expected, “tremendously higher and warmer temperatures much much earlier on in the season” can create a problem for the fish, she said. As recently as 2018, hundreds of the fish washed up in both rivers and along the Sandy Hook Bay. Muthukrishnan said normal dissolved oxygen levels in healthy water are around 8 to 10 milligrams per liter; readings have gone as low as 2 mg/L, which is alarming.
Another potential factor is “stormwater runoff from improperly managed fertilizer application,” she said. Severe weather events, which have been occurring more frequently, drive nutrients into the waters which creates algal blooms. These nutrient-rich blooms also need dissolved oxygen for survival, depriving the native aquatic life of it and causing them to die, a process called “eutrophication.”
“We are watching the temperature and the weather so we are wanting to kind of have a handle on this, because, especially in the Navesink,… we definitely know that runoff is a problem,” Muthukrishnan said.
Still another possible cause of the excess of dead fish is disease.
An unusual number of dead menhaden showed up on New Jersey shores in November and December, typically colder months when low oxygen levels should not have been an issue. Muthukrishnan said she and Alison Jones, COA’s watershed program coordinator, spotted a few fish washed up in the Red Bank area in December 2020 when they were collecting water samples.
The New Jersey Division of Fish and Wildlife had been investigating occurrences and attributed the deaths to a disease, possibly a bacterial infection, that caused multiple-organ failure. Another disease, called “spinning disease,” effects the fishes’ nervous system and can cause them to become disoriented and listless in the water.
Rather than the deaths being caused by just one of these factors, Muthukrishnan said most scientists believe all of them are working in consort against the lowly menhaden. But why so much concern over a relatively small fish not even suitable for human consumption?
Menhaden filter up to four gallons of water a minute, cleaning the marine environment and keeping it healthy. Without menhaden, phytoplankton grow unchecked, killing other species, which in turn affects the entire food chain. Osprey, egrets and seagulls and many larger fish like tuna and bluefish, call the menhaden food.
And the unexplained deaths of these fish aren’t the only issue: Menhaden have been harvested in droves for years for their rich omega-3 oil, used in supplements, livestock feed and many other applications, and they are perfect as chum when fishing.
The Atlantic States Marine Fisheries Commission has begun limiting the Atlantic menhaden harvest to try to ensure a balance between maintaining a healthy ecosystem and the needs of the fishing industry.
Muthukrishnan said the community can help the menhaden by letting organizations like COA know when they spot dead fish on the shore.
“We want to try to assemble all the information that we can possibly get from these mortalities,” to determine if the cause is something that’s fixable, she said. “That is our goal.”
The article originally appeared in the April 1 – 7, 2021 print edition of The Two River Times.
