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By Paige Radcliffe (Marine Resources Program Monitor, Ocean County)
The Rutgers University Marine Field Station (RUMFS) bridge netting survey is the second longest ongoing study of its kind on the east coast with this year marking 35 years. It provides a valuable time series for studying fish biology and species’ shifts in response to climate change, which are useful for informing fisheries management. The survey has also benefited dozens of students, professionals, and volunteers as a fisheries training opportunity. I was fortunate to join two sampling events in August 2024 to convey those experiences and highlight the scientific value of this survey in part of the Earth Day Every Newsletter series. Volunteers can also be part of this long standing project. Read on to learn how.
Driving down “Seven Bridges Road” (i.e., Great Bay Boulevard) in Tuckerton, NJ you will begin to see the Field Station at the end of the peninsula. Out in the untouched marsh with very little development in sight, there is an inherent connection to this place as few like it remain. Once a U.S. Coast Guard Station, the building adopted its scientific role as RUMFS in 1972 which is described in Ken Able’s book, Station 119 (Figure 1). The unique position of the field station; miles out in the Mullica River Estuary, stands as one of the last of its kind as a true hold out for marine science, braving the tides for monitoring and research.
Figure 1: Glimpse of the Rutgers University Marine Field Station (RUMFS).
The weekly bridge netting “ichthyoplankton” study has been an ongoing effort since 1989 and is currently led in part by Roland Hagan, the Field Station Operations Manager. Roland is a distinguished and well rounded scientist with years of fieldwork experience under his belt as a fisheries observer for Alaska’s high seas driftnet fishery and along the east coast. However, this survey was started by the highly revered Dr. Ken Able (Professor Emeritus, Rutgers University) who served as the Director of RUMFS for more than 35 years. Dr. Thomas (Motz) Grothues is another long standing member of the RUMFS team serving as an Associate Research Professor and also the Research Coordinator for the partnering Jacques Cousteau National Estuarine Reserve. Motz and his colleagues use the data collected during the bridge netting time series to study larval fish ecology and rates of species change as response to physical factors such as warming seas and shifting ecosystem characteristics. These scientists are deeply rooted to the field station as it is a true testament to their life’s work and passion with echoes of each other’s efforts intertwined with one another.
The year round netting from Little Sheepshead Bridge occurs once a week at night on different days and times depending on the arrival of the incoming tide. A study of this kind would not be possible without hard working and dedicated volunteers. Dedicated volunteers included Nicole, who also volunteers with ReClam the Bay and drove over 100 miles to be here, Peter who drove over 70 miles, and Lucas a college student who drove from Albany NY just to participate in the weekly bridge netting study. Nicole Fox, a Rutgers PHD student in the department of Ecology and Evolution led the evening sampling event (Figure 2).
Figure 2: Retrieval of net and emptying of codend into sampling bucket.
The survey’s longevity is beneficial to species population studies and development of fishery management plans for sustainable stock levels. Roland says, “as everything in this environment is connected, it is important to study species and environmental variation.” He expressed importance of recognizing variation and looking at systems change from a linear perspective. The bridge where the study occurs is named Little Sheepshead Creek Bridge, named after the sheepshead, a southern fish that is more common in warmer waters. This species, along with many other tropicals such as the permit, are having more of a presence in New Jersey’s estuaries and ocean waters. However, the Sheepshead Bridge was named on maps in the 1800s, so perhaps these fish were present in the past and can be seen as “a matter of change” in a series of time.
A changing climate has added an influx of non-native and unusual species into New Jersey’s coastal waters that are more commonly seen in warmer areas. Factors such as warming ocean temperatures, sea level rise, and ocean acidification are causing changes in the spatial distribution and stock status of many important species (Kitchel & Zemeckis, 2021). This has been noted in the bridge netting study as tow samples are taken from the same weekly location of Little Sheepshead Bridge within the Mullica River estuary therefore documenting change over time (Figure 3). Estuaries are a critical water body that are vulnerable to the effects of climate change due to shallow water depths and their location close to human-induced stressors while providing habitat to larval fish (Able, 1998).
Figure 3: Map of Mullica Bay Estuary and Little Sheepshead Creek Bridge. (Image Credit: Morson et al. 2019.)
Life and death on a salt marsh are a common occurrence as the tide is not always forgiving. Phytoplankton make oxygen daily while the sun is up but when the sun goes down tide pools with their anaerobic sediment consume oxygen and cut off the supply to killifish, silversides, and other fish species. The fish are forced to gulp oxygen during this anaerobic event which draws in birds looking for a quick meal contributing to the food web of predators and prey.
The study consists of weekly sampling of ichthyoplankton, or free floating larval fish using a 1 mm mesh conical net 3 meters deep with a 1 meter wide mouth. This net is cast off the Little Sheepshead Creek Bridge for 3 tows that are roughly 10 minutes long. The net is deployed with a flow meter within the net itself as well as adjacent to it to act as a variable when keeping track of the turning tide. The net is then hoisted up and the catch from the codend is emptied into a bucket and taken back to the field station for sorting. Larval fish less than 30mm are sorted using forceps and placed in vials. Larger fish are placed on a measuring board to record lengths from 20 fish per tow to establish a median (Figure 4).
Figure 4: After tows larval fish less than 30mm are sorted and placed in vials. Larger fish are placed on a length board to attain 30 lengths per tow to establish a median.
The preserved larval fish are stored for later identification back in the lab. This task of identifying larval fish requires a great deal of expertise (and patience!) while working under a microscope. Identifying the larval fish in the lab requires twice the effort as collecting them in the field. The steps include sorting, identifying, and measuring each larval fish, and then recording, entering, and checking all of the data. To be qualified in larval fish identification, 100 hours of morphometrics training must be completed to become capable of identifying fish by fin ray counts and other key characteristics that cannot be identified without a microscope (Figure 5).
Figure 5: Vialed and preserved fish that have been identified by their morphology.
A second consecutive week of participation in the August survey I gained a grasp of variation within the weekly catches (Figure 6). This week a scorpena “scorpion fish”, which is a tropical fish species, was identified in the catch. This was the second one spotted during the 34 year study, with the last seen in 2017. Amazingly, another scorpion fish came up in the second tow on the same night! With more volunteers this week, including Dr. Thomas (Motz) Grothues, we were able to sample the tow catches at a quicker pace. A walk down the pier at the end of a long shift, the chatter of crickets and knowing you contributed to something that will be etched in science is a reward in itself.
Figure 6: A lookdown, which is a more tropical species found in the bridgenetting survey.
Large takeaways from the study have shown that the northern species caught throughout the decades of study have decreased while southern species have increased in occurrence (Morson et al. 2019). Species diversity and density of samples has also increased over time. The scientific contribution of this study is representative evidence of the impact climate change on fisheries assemblage in the Mid-Atlantic from data shown in this larval fish estuarine study. The field station will be a beacon of long-term data collection for years to come. If you’d like to find out more or participate in the weekly volunteer bridge netting contact Christine Moran (christine.moran@marine.rutgers.edu), Volunteer Coordinator at JCNERR. Additionally, stay tuned for the full feature documentary on RUMFS- titled “Stories From the Marsh” that is being produced with the help of Rutgers University Interns Delia Lasek and Andie Zou under Dena Seidel.
References
Able, Kenneth W. (1998) The First Year in the Life of Estuarine Fishes in the Middle Atlantic Bight. Rutgers University Press.
Alexander, Andrea (2022) Rutgers Marine Field Station: On the Edge of Climate Change. Rutgers Today. www.rutgers.edu/news/rutgers-marine-field-station-edge-climate-change
Kitchel & Zemeckis (2021) Climate Change Impacts on New Jersey’s Marine Fisheries. Rutgers- New Jersey Agricultural Experiment Station. Cooperative Extension Bulletin E369. E369: Climate Change Impacts on New Jersey’s Marine Fisheries (Rutgers NJAES)
Morson JM, Grothues T, Able KW (2019) Correction: Change in larval fish assemblage in a USA east coast estuary estimated from twenty-six years of fixed weekly sampling. PLOS ONE 14(11): e0225526. journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0224157
Roland Hagan preparing for night time surveying.