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A Day Spent Gill Netting for River Herring


by Rachel Reinhard, Hourly Fisheries Technician
Bureau of Marine Fisheries
July 23, 2018

NOTE: This article is one in the series, A Day In the Life Of a Marine Fisheries Hourly.

River herring, a term that includes both the alewife (Alosa pseudoharengus) and blueback species (Alosa aestivalis), were once a commercially important fish for the state of New Jersey. Alewife and blueback herring are anadromous, meaning they spawn in freshwater but return to saltwater to live. These fish are typically distributed from Newfoundland to South Carolina.

The two species look very similar but can often be differentiated based on eye size and body shape. In the past couple of decades, the population sizes of these fish have dropped dramatically and over time they have become a species of concern.

Blueback Herring and Alewife Comparison
Adult blueback and alewife herring
Click to enlarge

The introduction of dams in waterways and construction projects around rivers are just some of the major obstacles facing the species. These dams inhibit the species' ability to migrate to spawning sites. Overfishing, bycatch and the return of striped bass populations have also contributed to the decline in numbers.

After assessing the scope of problems facing river herring, the Atlantic States Marine Fisheries Commission (ASMFC) put a ban on the harvest of any river herring in 2013. One year before the ban, a project was introduced by the Division of Fish and Wildlife's Marine Fisheries Administration to research herring species and to track their population sizes.

Typically, river herring spawn in the spring, from March until the end of May. During this time, Marine Fisheries conducts a gill-netting survey for herring and some other target species.

A typical day of gill-netting starts at 6:30 a.m. at the Nacote Creek Research Station in Atlantic County. Once the crew arrives at the station, the van is packed with personal gear, such as boots, gloves, rain bibs and rain jackets. The boat is then checked to ensure that all the necessary equipment is aboard. This includes two gill nets, baskets to hold the nets, buoys, anchors, pliers and picks, pH and dissolved oxygen meters, measuring boards, a live-well to hold fish, dip nets, data sheets and buckets.

When everyone is ready to go, we trailer the boat to either the Maurice or Great Egg Harbor River. At the river, the team puts on their bibs and boots and we launch the boat into the water. Once on the water, we head north to our first sampling location and deploy the first gill net.

The first net we set is 174' in length with a 3" mesh. First, the small buoy is hooked to the float line of the net and one of the anchors is attached to the lead line. Both the anchor and buoy are thrown over the bow of the boat and two team members work together to feed the net out of its basket. Once we reach the end of the net, the large buoy is attached to the float line and another anchor is clipped to the lead line.

To straighten the net out in the water, the float line and lead line are held by team members and the boat is put into reverse. Once the gill net is straightened out, each team member lets go of their line; the net is now set.

Next, I calibrate the dissolved oxygen meter and collect readings for salinity, dissolved oxygen, water temperature, pH and air temperature which are all recorded onto datasheets. These same steps are repeated for the second, southerly location. The only difference is that the net for the second location is a bit smaller at 141' with a 3" mesh size. Nets are typically allowed to soak for 90 minutes.

After the soak time is completed, we retrieve the nets and assess our catch. Two team members simultaneously pull the net in over the bow by the lead and the float line.

As we are pulling in the net, a third person picks any fish that may be caught in the mesh and transfers them to the live well.

Once the entire net is pulled in and placed back in its basket, we can begin measuring the fish. Counts and measurements are taken for all fish, including both target species and bycatch. Target species include any river herring species (alewife, blueback herring, shad) and striped bass. When target species are found, fork and total tail measurements of length are recorded. Only fork measurements and counts are taken for bycatch species. Some common bycatch species that we often find in the nets include white perch, white catfish, and chain pickerel.

River herring are sexed and we determine if the females have spawned recently or if they have yet to release their eggs. When a striped bass is caught, scale samples may be taken. The scales are then brought to the lab and used to determine the age of the fish. After the necessary data is collected for each fish, they are released back into the water and we repeat the process at the second location. On some occasions, a sample of river herring species collected in the nets will be taken back to the lab as samples for further research.

In the summer months, biologists at Marine Fisheries continue herring research by seining for juvenile target species within the same rivers. These two surveys are essential in monitoring the health of river herring populations and New Jersey Fish and Wildlife hopes to see that the statewide harvest ban is helping herring populations to become numerous again.

Measuring the length of a fish
Using a measuring board to measure the length of a chain pickerel
Click to enlarge

To learn more about river herring and these surveys please see the following:

River Herring Status: Research Holds the Key (eRegs, 2018 Marine Digest)
River Herring Status: Research Holds the Key (pdf, 2018 Marine Digest, 1.6mb)
Studying River Herring - 2016 Report
River Herring - Species of Concern (pdf, NOAA website)

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Last Updated: July 24, 2018