Anadromous Fish Reintroduction
The connection between the marine and riverine systems of the Bronx River has been severed since the 1600’s when the first dam was erected at what is now the 182nd Street Dam. Through our stocking efforts, and proposed installation of fish passageways (PDF, 562KB), we will re-establish this connection. Alewife and other diadromous fish will once again be able to pass from river to ocean.
Alewife (Alosa pseudoharengus) and blueback herring are collectively referred to as river herring. They are anadromous fish, which means they live in the ocean as adults and travel upstream into freshwater streams, rivers and lakes to spawn. After adults spawn in the spring, they leave the freshwater within weeks and return to the ocean. The freshly spawned eggs hatch into larvae and develop into juvenile fish that stay in freshwater to feed and grow for 1-4 months. By mid-fall, the juveniles migrate to the ocean where they remain for 3-5 years until they have reached reproductive maturity.
Alewife reintroduction is part of an effort to increase habitat availability regionally and support and increase biodiversity locally. Alewife and blueback herring populations are declining throughout the northeast due to a number of factors including pollution, poor fisheries management and barriers to migration. Stocking alewife in the Bronx River will provide the species as a whole with additional habitat. Alewife recolonization can also result in a net import of nutrients to the riverine system, which potentially can increase decomposition rates within the river.
Project Partners include New York City Parks & Recreation Natural Resources Group (NRG), Connecticut Department of Environmental Protection Inland Fisheries Division (CTDEP), Lehman College, Bronx River Alliance, and Wildlife Conservation Society (WCS).
Anadromous Fish Reintroduction Map
Click on the photo to view a larger image
The initial stocking occurred on March 21st, 2006 in the impoundment above the 182nd Street Dam (Delancey Lighting Dam) and below the Twin Zoo Dams (Bolton Dam). March 21st was chosen as the target date because it falls during the natural spring run. Alewife return to the rivers in which they are born in the spring around the same time every year. Also the river water is still cold at this time of the year which means that the fish will not be submitted to as much stress. This freshwater stretch of river has slower, deeper sections that provide suitable spawning habitat for alewife.
The 201 alewife used in this reintroduction project were collected by the CTDEP from Bride’s Brook in East Lyme, CT. Fish were transported via a CTDEP stocking truck, complete with a release flume and circular storage tank. The release flume was extended and alewife were released out of the circular tank, down the release flume and into the river where they will spawn.
Lehman College and NRG conduct post-stocking monitoring. Monitoring occurs from the day of the stocking event until the fall, when all alewife will have left the system. We will continue monitoring the success of the project for years to come.
The release of 400 additional alewife occurred on April 5, 2007. Alewife were once again collected by the CTDEP and released into the Bronx River by NRG staff members, WCS and Lehman College staff. Monitoring continued after release for mortality and of egg larvae to see if the alewife spawned. "Popping" surveys will run from July through September.
Electronic Fish Counter
The electronic fish counter may be installed when river herring are expected to return to the Bronx River, in the spring of 2009. The fish counter would then collect data continuously until the fall when river herring migrate out of the system and before winter when the fish ladder would be inactive.
An electronic fish counter should be installed on a fish ladder to maximize the percentage of migrating fish it can count. The installation of a fish ladder is planned to occur at the 182nd Street dam on the Bronx River. The installation of an electronic fish counter is contingent on the installation of a fish ladder at the 182nd Street dam and the availability of funds.
Returning Adult Survey
Returning Adult Survey Goals
- To determine presence of returning adult river herring
- To estimate the success of the project
- To identify the beginning, peak and end of the spring run
Observe river between March 1st and June 1st of 2009 on at least a weekly basis. Spring of 2009 is the start date for collection because river herring require three to five years to reach sexual maturity. Alewife are expected to return to the Bronx River beginning in 2009, since they were first released into the Bronx River on March 21, 2006.
Monitoring should occur in the northern most area accessible to anadromous fish. On the Bronx River, this area is located south of the 182nd Street dam, near River Park.
Estuarine Trawl Survey Goals
- To confirm a spawning event
- To determine the presence of larvae
- To examine the condition of eggs and larvae
- To determine the diet and fitness of juvenile alewife
The trawl for eggs and larva was scheduled one month after the spawning event. The trawls for juvenile river herring were scheduled to occur once at the end of July and again at the end of August. These trawls are scheduled to coincide with the out-migration of juvenile river herring to the ocean.
Trawls should be conducted in areas that are accessible by motorized boat. On the Bronx River the acceptable location is at the mouth of the Bronx River, in the estuarine section near Soundview Park and Hunt’s Point.
To monitor for the presence of alewife in the Bronx River system, NRG is employing a technique developed by the Connecticut Department of Environmental Protection Inland Fisheries Division. The popping surveys take advantage of the natural feeding behavior of juvenile river herring. Popping refers to the rippling of the water surface as a result of feeding. Juvenile river herring feed on invertebrates that rise to the surface of the water at dusk. The juveniles will break the water surface while feeding, hence the term popping. This behavior can be easily observed from shore and requires very little experience to recognize.
Popping Survey Goals
- To confirm presence of juvenile river herring
- To estimate relative numbers of juveniles or amount of activity
- To determine general location of juveniles
- To compare number or activity of juveniles at different sites
- To compare number or activity of juveniles over a series of years
Observations are made at dusk. For the 2006 season, observations began July 18th and will continue until September 28th and are conducted three times per week. For the 2007 season, observations began July 17th and will continue through the end of September to allow for comparability of data.
Egg and Larvae Collection
Although the probability of capturing a significant quantity of river herring eggs and larva is low, collecting any river herring larva or eggs confirms the occurrence of a spawning event. The effort required to collect the eggs and larva is minimal when compared to the potential benefits of the collection.
- To estimate spawning success
- To examine the condition of the eggs and larva
- To confirm a spawning event
Egg and larvae collections are conducted two weeks after water temperatures have been maintained above 14°C. For the 2006 season collection began on June 6th. Collections were made on a weekly basis for 13 weeks. The number of drift net samples taken will be restricted to limit the amount of eggs and larvae collected and therefore the impact on the spawning success of the river herring.
Collection should occur in areas where the streambed is soft enough to allow the nets to be staked and consolidated enough to support the weight of an adult. Sampling locations should be accessible with hip waders. In the Zoo, this is located just south of the Double Zoo dams, in the impoundment.
River Bank and Channel Survey
Anadromous fish stocking in the Bronx River occurred on March 21st in the impoundment above the 182nd Street Dam (Delancey Lighting Dam) and below the Twin Zoo Dams (Bolton Dam). Through our stocking efforts, and proposed installation of fish passageways, alewife and other diadromous fish will once again be able to pass from the Bronx River to the ocean. Lehman College and NRG will conduct post-stocking monitoring until the fall of 2006, when all alewife will have left the system. We will continue monitoring the success of the project for years to come.
River Bank and Channel Survey Goals
- To estimate adult river herring survival and condition
- To identify date of spawning activity
River bank and channel surveys were conducted twice-weekly beginning two days after stocking. These surveys continue until water temperatures remain above 14°C for 3 weeks, approximately 2 weeks post-spawning. Alewife typically spawn between April and May.
Monitoring should occur on the furthest upstream stretch of the river accessible to river herring, suitable for spawning, and easily accessible by humans, with close access to the water or good views of the channel bed. In the Zoo, this was the section of the Bronx River from the bridge in the Bronx Zoo parking lot north to the Double Zoo dams.
No dead fish were reported for 2006, 2007.