Examining Fish Migration Issues in North Carolina’s Cape Fear River

For over a century, anadromous fish including American shad, striped bass and Atlantic sturgeon in North Carolina’s Cape Fear River have been in serious decline from overfishing and because dams constructed in the early 1900s have hindered their annual migration upriver to traditional spawning grounds.

Starting in 2021, Aaron Bunch, Ph.D. candidate at Clemson University (advisor: Dr. Troy Farmer), and Jake Mathews, Ph.D. student at the University of North Carolina, Wilmington (advisor: Dr. Fred Scharf), have worked with a diverse team of researchers from several organizations to address key questions and help to solve some of these longstanding problems.

Challenge

The research focused on American shad, striped bass and Atlantic sturgeon, which are classified as depleted, overfished and endangered, respectively. Efforts to understand fish movements in the river were centered about 100 kilometers from the ocean inlet at a nature-like fishway constructed at the first barrier to migration, Lock and Dam 1 (LD1) near East Arcadia. The fishway was originally constructed in 2012 to facilitate upriver fish passage and subsequently underwent modifications in 2021. In addition to LD1, there are two additional lock and dam structures further upstream that also create barriers for migrating fish but do not have fishways.

The team wanted to tabulate the number of fish that encountered each of the migration barriers and which ones successfully passed through the fishway at LD1, and then the subsequent lock and dam structures further upstream. The goal was to estimate passage efficiency at all three lock and dams and, specifically, to evaluate if the modifications in 2021 improved passage.

Equally important was the need to identify fine-scale positioning of fish in the vicinity (immediately below and above) of the nature-like fishway, to inform the timing of passage, route selection, and ascent duration, but conducting two studies at vastly different spatial scales in the same area presented unique challenges.

Solution

To address this, the researchers used Innovasea telemetry systems with different frequencies. They leveraged existing VR2W 69 kHz receivers that were deployed in the river from previous studies and combined them with a new array of high residence HR3 307 kHz receivers placed upstream and downstream of the fishway to maximize the likelihood of detection due to a high noise environment.

All American shad, striped bass, and Atlantic sturgeon were double tagged with Innovasea’s HTI 495 series 307 kHz tags, and V9 or V16 69 kHz tags. The 69 kHz system was used to study broad-scale patterns of movement throughout the river and to estimate fish passage efficiency at all three lock and dams, whereas the 307 kHz system was used to gather fine-scale data surrounding the nature-like fishway to understand fish positioning, ascent timing, route selection, and passage duration.

Result

Broad scale movement patterns revealed that American shad outperformed striped bass in passage efficiency at LD1, both before and after the nature-like fishway was modified, as well as both upriver lock and dam structures. Both species demonstrated modest increases in passage success at LD1 following the modification but still fell short of the original goal of 80 percent passage success when the nature-like fishway was originally constructed. No tagged Atlantic sturgeon passed through the fishway during the spring spawning season, but a single tagged adult Atlantic sturgeon was detected above LD1 during the fall of 2023.

Fine-scale fish positions revealed species-specific differences in both passage timing and ascent duration. Striped bass typically ascended in the morning and remained in the fishway longer while American shad passed mostly in the afternoon or evening and spent less time completing the journey through the fishway.

The fine-scale data also showed that while shad and bass generally engaged in staging and foraging behaviors below the fishway. Sturgeon aggregation areas were identified by the fine-scale positional data below the fishway.  The combined high detection density in both the broad- and fine-scale datasets suggest that the area below the nature-like fishway represents a spawning area for Atlantic sturgeon.