River herring (alewife, Alosa pseudoharengus, and blueback herring, Alosa aestivalis) have historically supported valuable fisheries along the Atlantic Coast and served as important components of coastal ecosystems.They are anadromous fish, meaning they live much of their lives in the ocean but migrate to freshwater to spawn. Herring typically spawn in the same streams where they were born. Over the past several decades, however, river herring numbers have declined significantly, leading to closures of fisheries including those in Chesapeake Bay.
Funded by the National Fish and Wildlife Foundation (NFWF) and the Smithsonian Institution, this project has a long-term goal of documenting and monitoring river herring spawning runs throughout the Chesapeake Bay watershed. This is being accomplished in two ways: assessment of presence or absense of herring to determine habitat use in tributaries AND the usage of cutting-edge technology to acquire accurate counts of herring.
Where do river herring spawn?
One question we're working to answer is: How far up tributaries are herring traveling to spawn? To answer this question, we have been visiting many sites along the Choptank, Deer Creek, Patapsco, Rappahannock, and Pamunkey Rivers to assess presence or absence of river herring.
We check for presence or absence three ways:
1) Visually. At each site we look for river herring and attempt to catch some in a net in order to determine whether they are Alewife or Blueback Herring. We also use a GoPro to record underwater video.
2) Collect an ichthyoplankton sample (fish eggs and larvae). We catch a sample of eggs or larvae, if present, from the current (photo above). These samples are sorted under a microscope in the lab to determine if river herring eggs are present. We have used genetic barcoding in some cases to determine whether eggs were Alewife, Blueback Herring or other similar species such as Hickory Shad.
3) Collect a DNA sample. We collect a water sample, which can be used to check for presence of herring DNA. This method, known as environmental DNA or eDNA, is under development but may be a more sensitive method for detecting the presence or absense of herring either at or upstream of the sampling location.
Below are some videos we took while sampling for river herring:
In this video, you can see the splashing caused by spawning activities of Blueback Herring in the Choptank River:
We're not the only ones interested in the river herring populations that spawn in the tributaries of the Chesapeake Bay! We captured a video of this blue heron attempting to feast upon Alewife at Big Gunpowder River in Maryland. Alewife and Blueback Herring are important prey for herons, eagles, ospreys, Striped Bass, and many other bay species:
In this video, you can see Alewife swimming in their spawning grounds of the Big Gunpowder River in Maryland:
The second major focus of our current work is using Dual-frequency Identification Sonar (DIDSON), also known as imaging sonar, to conduct run counts of river herring in tributaries of Chesapeake Bay (Choptank River in 2013, 2014, and 2015; Marshyhope Creek in 2013 and 2014; and Deer Creek in 2015). This cutting-edge technology allows us to record and count adult fish as they swim past a sonar station during their spawning runs, which usually occur from March to May. Imaging sonar allows us to overcome challenges to counting fish in tributaries of Chesapeake Bay such as turbid water, which prevents visual counts, and problems with obtaining accurate counts of schooling fish from net-based sampling methods. It also allows us to sample throughout the day and night without having to be present on site. See below for an example of what a DIDSON video looks like.
After the DIDSON has been deployed and footage collected, the footage is reviewed and analyzed in the lab to generate fish counts and size estimates. Species identifications are made by conducting additional sampling each week of the spawning run using electrofishing to determine the species composition of fish within the size range of river herring.
Below is an example of a DIDSON video. What are you seeing in this video? You are essentially looking down on the stream from above. The brightest spots that you see, if you notice, are not moving. Those are rocks on the bottom of the river bed. Each of the moving short bright lines is a fish. Dark spots that are moving are shadows cast by the fish. The fish moving from right to left are swimming upstream. We know that these fish are Alewife herring because we caught several and visually identified them at the site.
We are also using DIDSON to verify the accuracy of other, lower-cost methods of estimating the size of river herring runs. These other methods include electrofishing (photo to right) and tracking of ichthyoplankton (herring eggs and larvae) abundance. By exploring different methods of determining the size of spawning runs, we will be able to design a cost-effective combination of both highly accurate and less accurate but inexpensive methods of monitoring river herring runs throughout Chesapeake Bay.
Our work on river herring will help contribute to important body of research needed to direct efforts to restore herring populations to what they once were.
A special thanks to all of the volunteers who have helped us collect data and samples, and thanks to all of the land-owners who gave us permission to access their land in order that we could get to our tributary sampling sites. Your assistance is helping to make our project successful!