License-funded tagging study nearing completion

The N.C. Division of Marine Fisheries conducts research and monitoring projects using Coastal Recreational Fishing License funds. These projects align with strategically planned management goals, and enhance the Division’s efforts to manage, protect, restore, develop, cultivate, conserve and enhance North Carolina’s marine resources. Data obtained from these projects supports management plans and policy decisions.

One project based out of the division’s Wilmington Office, regionally located near the Cape Fear River and its tributaries, is coming to a completion. The project entitled Mark-Recapture Study to Determine Population Size and Fishing Mortality Rate of Cape Fear Striped Bass was initiated in 2011 to develop an estimate of population size and mortality rates of striped bass in the Cape Fear River using a tag return model. The current tagging program is a five-year continuation of the original study and should provide additional data as well as a longer time series to inform the model.

Mark-recapture studies rely on determining the number of fish that were tagged, the number of fish recaptured, the tag return rate, the tag retention rate, and the percent of fish that immigrate or emigrate. Many mark-recapture programs that rely on fishermen to report the recapture of tagged fish often have problems estimating tag return rate and tag retention rate. To avoid this problem, passive integrated transponder tags were implemented for this study.

Passive integrated transponders, or PIT tags, are tracking tags that use an internal microchip coded with a unique identification number for each fish that is read by a handheld scanner. These tags are similar to the tags used by veterinarians to identify lost pets. Using PIT tags removes the need for fishermen reporting, which eliminates the need to estimate the tag return rate.

The overall goal of the project is to develop an estimate of population size and total mortality rates for striped bass in the Cape Fear River. Division staff is estimating the population size using state-of-the-art modeling techniques. These estimates will be used to determine if the current harvest moratorium and stocking programs are sufficient to increase the population to sustainable levels.

The estimates from a tag return model can be updated annually. Therefore, management can respond in a timelier fashion than with traditional models which may take several months to accumulate the data and run the model. Management triggers can be established through the fishery management plan. Additionally, fish collected for this project are also tagged with internal anchor tags that are used throughout the state as part of the division’s Multi-species Tagging Program. Aging structures (scales) and DNA samples (fin clips) are also collected.

Division of Marine Fisheries staff in Wilmington, in collaboration with the N.C. Wildlife Resources Commission and the Cape Fear River Watch, have worked diligently to carry out the objectives of this project and are in the process of modeling data. They expect to publish the results in 2020 and the report will be used in place of a traditional stock assessment as part of the Estuarine Striped Bass Fishery Management Plan being developed jointly with the N.C. Wildlife Resources Commission.