By Jennifer Pyle, Senior Biologist, and
Shana Fehring, Senior Wildlife Worker
August 11, 2020
INTRODUCTION - HISTORY OF THE DELAWARE RIVER SEINE SURVEY
The Delaware estuary, New Jersey's largest estuary system, is a semi-enclosed body of water where fresh water from the Delaware River mixes with saltwater from the Delaware Bay. The estuary is a migratory route for many recreational and commercial fish and provides critical spawning and feeding grounds and nursery areas for many species.
The success of a species is contingent upon the survival of their young. The Delaware estuary provides a suitable nursery environment for young fish to grow. Monitoring populations of these juvenile fish is essential for fishery managers to estimate abundance and evaluate the success of the population. These assessments provide a means to predict population trends and future harvest potential of monitored species.
Bureau of Marine Fisheries biologists conduct several surveys each year to study the status of species populations within the estuary. One of these surveys is the Delaware River Seine Survey.
The seine survey is a Fishery Independent Monitoring Project required by the Interstate Fisheries Management Plan for Striped Bass. It is currently the Bureau of Marine Fisheries' longest running fishery-independent survey. It began in 1980 when striped bass stocks were severely depleted and is primarily a juvenile striped bass abundance survey. Data collected provides an annual abundance index for this species, reported as the number of young-of-year per seine haul. Results have been corroborated by other independent surveys, such as the Delaware Division of Fish & Wildlife's striped bass spawning stock survey.
A unique aspect of this survey is its longevity - it has been conducted for 40 consecutive years. Data from such a large period of time is highly beneficial to species population studies. Not only does this survey tell us how many fish there are from year to year, but the data also contributes to the development of fisheries management plans and projections of sustainable harvest levels.
For more information about the value of this survey, see the article from the 2006 Marine Digest: Striped Bass Survey Well Worth the Cost (pdf, 290kb).
Data Summary of 2019 Delaware River Seine Survey (pdf, 1.5mb)
Data Summary of 2018 Delaware River Seine Survey (pdf, 195kb)
Data Summary of 2017 Delaware River Seine Survey (pdf, 210kb)
Data Summary of 2016 Delaware River Seine Survey (pdf, 185kb)
Data Summary of 2015 Delaware River Seine Survey (pdf, 195kb)
Data Summary of 2014 Delaware River Seine Survey (pdf, 210kb)
Data Summary of 2013 Delaware River Seine Survey (pdf, 250kb)
Data Summary of 2012 Delaware River Seine Survey (pdf, 113kb)
Data Summary of 2011 Delaware River Seine Survey (pdf, 97kb)
Data Summary of 2010 Delaware River Seine Survey (pdf, 115kb)
Data Summary of 2009 Delaware River Seine Survey (pdf, 110kb)
Click on the links below for more Delaware River Seine Survey information:
- SURVEY LOCATIONS
- CATCH HISTORY
- WATER QUALITY
- THE FUTURE OF DELAWARE RIVER FISHERIES
- HOW YOU CAN HELP
Setting and pulling in the net.
Click on images to enlarge.
EQUIPMENT / METHODOLOGY
Survey methodology has remained fairly consistent through the years. The boat used for this survey is a 20-foot Privateer, Roamer skiff. This fiberglass boat has a side console and a 115-horsepower Evinrude E-tec 2-stroke outboard engine. The net used is a 100-foot long, 6-foot deep seine net with ¼-inch mesh that has a bag in the middle where the fish are collected.
One end of the net is held close to shore by a crewmember on the beach while the rest of the net is set off the bow of the boat as it backs away from the beach. The boat sets the net with the current, before turning back towards the beach to form a "U" shape. To complete the haul, the net is pulled onto the beach from both ends and the catch is funneled into the bag in the center of the net.
After a seine haul is complete, and the net has been pulled onto the beach, all fish captured are sorted by species, counted and sub-samples of target species are measured. In addition to striped bass, target species include white perch, American shad, bay anchovy, Atlantic croaker, weakfish, blueback herring, Atlantic menhaden, Atlantic silverside, alewife, spot, blue crab, bluefish, hickory shad, winter flounder, black drum and summer flounder.
To learn about what it's like to spend a day on the seine survey, please check out our series, A Day in the Life of a Marine Fisheries Hourly: A Day on the Delaware River - Striped Bass Recruitment Survey.
Since the survey's inception, sampling crews have set a beach seine 8,639 times and caught 1,534,212 fish. Fish & Wildlife has averaged 180 fish per haul since 1980, with 91 different species identified. The five most abundant species caught include blueback herring, Atlantic menhaden, bay anchovy, white perch and American shad. The primary target species (striped bass) is the tenth most commonly captured.
Over the past few years, a couple invasive species have shown up in seine surveys hauls: Northern snakeheads and green sunfish. These species are not native to the Delaware estuary, and are considered dangers to the local ecosystem. Snakeheads are top level predators and can negatively impact the populations of smaller species. Green sunfish have large mouths and will outcompete native fish. If caught, neither species should be released alive. Snakeheads should be destroyed and submitted to New Jersey Fish & Wildlife for identification verification.
Summary Table of All Species Caught 1980-2019 (pdf, 195kb)
Water quality parameters such as salinity, water temperature, dissolved oxygen (DO) and pH are recorded at every station with a handheld dissolved oxygen (DO) meter that simultaneously measures several different water quality parameters. The meter has a probe attached to it with a long cord. This probe is lowered over the side of the boat and placed into the water, just below the surface. The DO meter gives readings within a matter of seconds and provides surveyors with fast, accurate measurements. The pH meter is smaller than the DO meter. The cap serves as a sample cup, which holds the water sample while the meter takes a reading. Because all water quality parameters are influenced by many outside factors, it is necessary to record this data at the site of each seine haul.
In the 1940's, the water quality of the Delaware River was considered to be "grossly polluted." In 1972, the Federal Clean Water Act was enacted and water quality began to improve. Levels fluctuated until the mid-1980's when major improvements were finally seen. In 1989, striped bass catches in the river were at a much higher level than previous years. This showed that the striped bass population was rebounding, and water quality was beginning to improve. The information provided in this report contains water quality data from 1992 through present day.
Salinity is the saltiness, or dissolved salt content, of a body of water. In the Delaware River seine survey, it is measured in parts per thousand (ppt) which is the measure of grams of salt per liter of water. In a tidal estuary, there are many factors which influence salinity. Freshwater run-off from rainstorms lowers salinity levels, while droughts lead to an influx of saltwater from the ocean. In this survey, Region 1 is the southernmost area, closest to the Delaware Bay and has the highest salinity averages, ranging from 0.8 ppt in 2019 to 6.4 ppt in 1995. Region 2 is a brackish water area, with averages ranging from 0 ppt to 1.6 ppt in 1997. While still tidal, Region 3 is almost completely freshwater. Survey averages have ranged from 0 ppt to 0.323 ppt in 2017. Overall, trends show the salinity of the Delaware River has remained fairly constant through the years.
Salinity Graph (pdf, 175kb)
Water temperature is also affected by many factors, including water depth, tides, and the weather. On average, the water temperature during this survey, measured in degrees Celsius, has increased over the years. The lowest average temperatures in all three regions occurred in the early 1990s. In Region 1, high averages were collected in 2019, measuring 25.5° C. In Region 2, the average high of 24.6° C was collected during 2002. Finally, Region 3 peaked out in 2005 at 24.6° C.
Water Temperature Graph (pdf, 175kb)
Dissolved oxygen (DO) is a measure of the amount of gaseous oxygen that is dissolved in water. It is measured in milligrams per liter (mg/L). Oxygen gets into the water by diffusion from the surrounding air. This happens through a number of methods including rapid water movement (tides, run-off or boat traffic) and air movement above the water (wind or storms). Trends show a slight decrease in the overall average of DO in the Delaware River from 1992 to 2012. Recent years have shown a gradual increase in averages. Numerous studies suggest that these values will continue to support a healthy, diverse population of species. Region 1 peaked at an average of 7.9 mg/L in 1996 and bottomed out in 2008 at 6.5 mg/L. Region 2, had its highest average in 1996 at 7.5 mg/L and lowest in 2002 at 6.2 mg/L. Like Region 1, Region 3 had its highest average in 1996 at 8.1 mg/L and its lowest in 2005 with a value of 5.8 mg/L.
Dissolved Oxygen Graph (pdf, 180kb)
Water quality meters for temperature, DO and pH
Click to enlarge.
pH (potential of hydrogen) is a value based on a defined scale from 0 to 14, defining how acidic or basic a body of water is. The lower the number, the more acidic the water is. The higher the number, the more basic it is. A pH of 7 is considered neutral. The 2016 sampling year was the first year pH has been recorded during this survey. Region 1 has consistently provided the highest pH averages. Average values collected during 2019 were much closer to neutral levels than the previous two years. Averages for 2016-2019 by region are summarized here:Average pH By Year and Region
2016 2017 2018 2019 Region 1 8.0 9.2 7.7 8.2 Region 2 7.9 8.9 7.6 8.3 Region 3 7.9 9.0 7.3 8.2
Regions 1 and 2 are historical striped bass spawning grounds. Results of this seine survey in recent years have confirmed that these regions are just as important now as they were in decades past. In fact, data from this and similar surveys in other states have reflected an increase in the striped bass population along the entire East Coast. Surveys like this are just the beginning of the stock assessment process for many species.
In addition to striped bass, biologists recently analyzed the trends of forage fish in the Delaware River using data collected during this survey. This data provides an annual juvenile abundance index for many species, and contributes to the development of fisheries management plans and projections of sustainable harvest levels. To read more about this analysis and what the trends showed, please view the document, Wildlife Populations: Marine Fisheries (pdf, NJDEP Division of Science, Research, and Environmental Health)
Since the inception of the survey, the abundance of several species has declined including spot, weakfish, Atlantic croaker and white perch. While it is not completely certain why these species populations are decreasing, future research is planned to determine the underlying causes.
Seine surveys, as with all fishery surveys, are important for ecosystem management. Not only do they provide information on species abundance, but they also provide a broader source of data on interactions with other species and associations with environmental factors. Without these surveys, biologists could not identify species interactions that might predict future fishery management needs. With consistent monitoring along the entire New Jersey coast, we can identify declines in species abundance and implement management actions before it's too late.
Anglers have an important opportunity to help biologists collect valuable data through the Division's Recreational Saltwater Angler Survey. Interested anglers are encouraged to log on at www.njfishandwildlife.com/marinesurvey.htm to enter information about personal fishing trips. All information collected helps improve the management of our marine resources and the sustainability of New Jersey's marine fisheries.
Don't forget to register before fishing - it's FREE! For more information on the New Jersey Saltwater Recreational Registry Program, please visit: www.SaltwaterRegistry.nj.gov.
Funding for this survey is supported by the federal Sport Fish Restoration Program administered by the U.S. Fish & Wildlife Service.