Fish Mortality Story: The FAQ from NJDEP

In response to Clean Ocean Action’s push on the state and federal levels for answers and solutions to the abundant menhaden, or bunker fish, die off along the Navesink and Shrewsbury rivers, the NJ Department of Environmental Protection (DEP) has issued the following released statement and Frequently Asked Questions (FAQ) and answers …

The NJ Department of Environmental Protection (NJDEP) continues to investigate large menhaden die-offs impacting the Navesink and Shrewsbury rivers of Monmouth County.

These mortality events appear to be only affecting Atlantic Menhaden, also known as bunker, an extremely abundant member of the herring family primarily harvested for bait and non-food commercial purposes. Similar largescale die-offs have been reported since the fall in coastal areas from Rhode Island to New Jersey.

Tests by the Division of Fish and Wildlife indicate that the bacterium causing these mortalities is Vibrio anguillarum, one of numerous Vibrio species that commonly occur in marine and estuarine environments.

The DEP continues to work on better understanding the disease caused by this Vibrio infection in bunker and is working with the Atlantic States Marine Fisheries Commission and other states in the region to better understand these mortalities.

Bunker appear to be the only species impacted at this time and it is believed that they may be more susceptible to the impacts of this bacterium. This is likely driven by stressors present during the spring, including fluctuating water temperatures which may suppress the fish’s immune system combined with the abundance and dense schooling nature of these fish, which enhances transmission of the bacterium.

Menhaden are typically not eaten by people or fished recreationally. There is no indication that any other fish, shellfish, bird or wildlife species are being impacted by this bacterium. It is safe to continue eating other species of fish that prey on menhaden. However, it is always advised to properly cook all fish or shellfish before consuming and to never collect and consume dead fish or any that appear ill.

This bacterium is generally not known to be harmful to humans. However, contact with water in areas where fish die-offs are occurring should be avoided as a precaution. Handling of dead or unhealthy appearing fish should be avoided, including collecting for bait. If handling is necessary for disposal purposes, wear appropriate protection, including gloves.

Menhaden die-offs are expected to continue in the near term. The DEP will continue to provide information to local governments as appropriate and provide any public advice or advisories as necessary. The fish will naturally decompose and become part of the nutrient cycle in affected waterways. Local governments, at their discretion may remove fish from their riverbanks.

To report a fish die-off, contact the DEP’s hotline at 877-WARN-DEP (877-927-6337).

Frequently Asked Questions

Since the fall, New Jersey has seen large numbers of mortalities of menhaden in coastal areas. What is causing the fish kills?
This mortality has been observed to only affect Atlantic Menhaden (bunker). Based on necropsy and laboratory testing, the fish are infected with a bacterium known as Vibrio anguillarum, which causes the disease known as vibriosis. The DEP is continuing with research to characterize this bacterium and the disease it is causing in the bunker. Histopathology and microbiological testing demonstrated that this bacterium is causing a systemic infection impacting multiple organs of the fish, including the brain. Bacterial infection of the brain and its associated damage is most likely causing the neurologic signs observed in the fish.

These neurologic signs can be seen as fish circling at the surface, swimming erratically or uncontrolled, and sometimes lethargic and unresponsive to stimuli. V. anguillarum is a common bacterium found in marine environments and outbreaks with the disease can be the result of other factors that may stress or compromise the immune system of the fish. In the spring and fall when these mortalities occur, fluctuating water temperatures may play a role in making fish more vulnerable to infection. The abundance and dense-schooling nature of bunker also enhance the transmission of the bacterium.

Where are the fish kills occurring?
In New Jersey, reports of the fish kills have come primarily from the Raritan Bay area, including the Navesink and Shrewsbury Rivers. However, in the fall of 2020, reports of menhaden fish kills were reported in every state from New Jersey to Rhode Island, inclusive. Pathology tests were not conducted for all reported fish kills, but the timing of the kills and similarity of symptoms reported from kills throughout the region suggest they were all likely related.

What are possible effects on other species of fish and wildlife?
The mortality events have thus far only been documented in Atlantic Menhaden. No other fish or wildlife species have been documented to be affected by these mortality events. V. anguillarum has been reported in the literature to cause vibriosis in a variety of marine finfish (including but not limited to salmonids, Striped Bass, Winter Flounder, and Atlantic Cod), shellfish (including but not limited to hard clams and oysters), and crustaceans (including lobsters and shrimp).

Though this bacterium is often an opportunistic pathogen in a wide range of marine species, these mortality events have thus far only impacted Atlantic Menhaden. This may be related to a number of factors including susceptibility of fish species to the bacterium, bacterial transmission factors that may be enhanced in dense schooling fish such as Atlantic Menhaden, and that Atlantic Menhaden may be particularly sensitive to some environmental stressors, such as fluctuating water temperatures. At this time, since no other species have been observed impacted, we do not believe that other fish and wildlife are being impacted.

What are the possible effects on humans?
Generally, V. anguillarum is a pathogen causing vibriosis in a wide range of marine finfish, shellfish and crustaceans. Though there are rare reports of V. anguillarum infecting humans, particularly when immunocompromised, this bacterium is generally not known to be pathogenic to humans. During bacterial epizootics in Atlantic Menhaden, it is likely that fish with vibriosis are shedding bacteria into the surrounding water.

It is recommended that the public avoids handling the dead or diseased fish. If the fish must be handled for disposal, then proper protective equipment, such as gloves should be worn. Diseased or dead fish should not be consumed by humans and these fish should not be handled to be utilized as bait for other marine species.

What are the possible effects on the menhaden population?
Atlantic Menhaden is an abundant species that ranges between Nova Scotia, Canada and northern Florida. A recent stock assessment conducted by the Atlantic States Marine Fisheries Commission (ASMFC) reports that total biomass of the Atlantic Menhaden stock is over 4.5 million metric tons (www.asmfc.org/species/atlantic-menhaden), or approximately 10 billion pounds.

Although the number of fish seen washing up on area beaches and waterways may appear alarming, the impact to the population as a whole has so far been negligible. The population model explicitly accounts for all sources of mortality, both natural (such as fish kills) and harvest. Menhaden mortalities have been reported as near annual events in the spring since the 1950s, though the numbers of fish impacted varies from year to year. The next stock assessment is scheduled to be conducted in 2022 and will incorporate information gathered from the ongoing mortality event.

What is DEP doing to monitor the situation?
Since the fall of 2020, DEP staff have responded to many calls regarding fish kills with visual inspection of the sites and collection of samples for pathology testing. In addition, NJDEP is working with other states and ASMFC to track the duration and magnitude of these events on a regional scale. If you see a fish kill and wish to report it, you should contact 877-WARN-DEP (877-927-6332).

NJDEP has deployed three continuous monitoring buoys in the Raritan Bay/Two Rivers area. These monitoring buoys collect water quality data for numerous parameters including dissolved oxygen and temperature. The buoys are deployed from May through October. The data collected may provide insight to the stressors and environmental factors impacting menhaden. One buoy is located in the Navesink River east of the Rt 35 bridge, the other two are in Keansburg and Keyport. The buoys should be in the water by mid- to late May and transmitting data to our continuous monitoring web page: https://njdep.rutgers.edu/continuous/.

What should I do (or not do) and who should I contact if I see a fish kill?
Generally, the bacterium affecting the menhaden is pathogenic to marine finfish, shellfish, and crustaceans. As with any wildlife, the New Jersey Division of Fish and Wildlife recommends people do not handle, collect, or consume any dead fish or those showing signs of disease. If you see a fish kill, please contact the DEP at 877-WARN-DEP (877-927-6332).

Will rising temps make this situation improve or get worse?
Water temperature is an important factor in the ecology of disease in aquatic species. The efficiency of a fish’s immune system is temperature-dependent and oftentimes cold-water temperatures will suppress a fish’s immune system. Unlike mammals, fish are poikilotherms, meaning their body temperature fluctuates with the external water temperatures.

In the fall and spring when water temperatures fluctuate, this may be an important stress factor that makes fish more susceptible to disease in these seasons. V. anguillarum has been reported in the literature to be most common in late summer and early fall when water temperatures are elevated.

This is not consistent with observations we see in Atlantic Menhaden when these outbreaks are occurring during colder water temperatures. It is hard to say if warmer water temperatures will worsen the impact of this bacterium in the fish population, but it is suspected that if there are wider temperature swings during the fall and spring, then this could worsen the impact of these mortality events.

Will concerns cited in the past like oxygen depletion compound the problem?
Low dissolved oxygen is a significant stressor to fish populations. Atlantic Menhaden are a highly active species and the high metabolism related to this activity makes them sensitive to low dissolved oxygen. To date, vibriosis-related mortality events have been associated with cool water which holds relatively more oxygen than warm water does.

Atlantic Menhaden mortality events linked to depleted dissolved oxygen occur most frequently in the summer months, though heavy congregation of menhaden schools in smaller and/or poorly flushing estuaries during any time of year may cause depleted dissolved oxygen and mortality. If dissolved oxygen is depressed to sub-lethal levels, then this will likely be an additional stress factor to Atlantic Menhaden that can make them more vulnerable to opportunistic infections, such as vibriosis.

Is it possible the bacteria is more prevalent based on local population densities?
Atlantic Menhaden form large, dense schools which facilitate the transmission of disease among individuals. This bacterium is likely spread between fish through the water. It is suspected that fish with clinical vibriosis are shedding large amounts of the bacterium. It is possible that some fish are persisting in our region during the cooler months instead of migrating to southern or offshore waters. This may expose fish to cooler water and larger temperature swings, which could suppress the fish’s immune system and leave them more vulnerable to opportunistic bacterial infections.

Will the decomposing fish affect water quality locally?
Fish kills occur naturally and generally do not cause any long-term effects on water quality. However, in the short term, it is recommended that bathers avoid swimming, surfing, etc. in areas of active fish kills. Anyone entering the water in an affected area should wash exposed skin and clothing thoroughly with soap and water after contact with the water. The NJ Bureau of Marine Water Monitoring has been informed of the fish kills and is working in conjunction with Fish & Wildlife to analyze potential stressors which may impact the menhaden as well as monitoring water quality.

New Jersey’s beach program partners with the NJ Department of Health, County and local Health Departments to monitor recreational bathing beaches. NJ beaches typically open on Memorial Day and begin preseason testing two weeks prior. There are no recreational bathing beaches on the Navesink or Shrewsbury Rivers, but there are recreational bathing beaches on Raritan Bay. Pathogen testing will occur prior to opening bathing beaches to ensure water quality is within recreational bathing standards and safe for primary contact. Information and beach monitoring data is available at https://njbeaches.org.

Who is responsible for cleaning up areas and disposing of fish?
Small to moderate sized fish kills generally take care of themselves over time, through scavenging by birds, fish, crabs, and other wildlife, and by fish washing out with the tide. Larger fish kills, or areas with low flushing rates where fish may accumulate or persist longer, such as lagoons and marinas, will also eventually clear up if left alone. However, this natural process takes time and may result in aesthetic impacts.

If residents, businesses, or local officials are concerned about possible impacts, the property owner or municipality may take steps to remove the dead fish from the beach and surrounding areas. Residents and business owners should take necessary precautions to limit contact, by wearing protective equipment such as boots and gloves if collecting fish. Fish may be bagged and discarded with other refuse. The DEP is continuing to discuss and work with local government officials on more scaled clean up options. Questions regarding disposal may be directed to the Division of Solid and Hazardous Waste at 609-633-1418.

Can you expand on other partnering organizations who are assisting with the research?
The DEP continues to coordinate with the New Jersey Department of Health. Further, New Jersey has been in regular contact with staff from the New York State Department of Environmental Conservation (NYSDEC) regarding fish kills in shared waters of the Raritan Bay, and is cooperating with the Atlantic States Marine Fisheries Commission who are coordinating a multistate effort to monitor the situation on a regional level.

Staff from the Office of Fish and Wildlife Health and Forensics have also been collaborating with partners from numerous fish health laboratories, such as Cornell University and the US Geological Service to identify and research the underlying cause of mortality.

Have other species been reported affected?
V. anguillarum has been observed in other species of fish, shellfish, and crustaceans in both wild environments and aquaculture systems. However, at this time, there is no indication that other species are being affected during this mortality event.

Is it safe to eat other fish who may have eaten menhaden affected by the bacteria?
There is no indication that other fish species are being impacted by this mortality event. It is advised to always avoid eating any fish that shows obvious disease signs and to cook your fish thoroughly before consumption. If following these guidelines, then it is safe to consume the fish.