Information on Blue Crab Adaptive Management

Three advisory committees of the N.C. Marine Fisheries Commission met in September 2024 to discuss adaptive management in the blue crab fishery. The advisory committees received a short presentation on the status of the blue crab stock and had a collaborative discussion with Division of Marine Fisheries staff about options available under the Adaptive Management framework adopted in Amendment 3 to the Blue Crab Fishery Management Plan. 

The advisory committee meetings can be viewed on the DEQ YouTube channel at the links below:

Northern Regional Advisory Committee

Southern Regional Advisory Committee

Shellfish/Crustacean Advisory Committee

Following full implementation of Amendment 3 management measures in 2021, division monitoring programs continued to observe historically low commercial landings, coupled with continued low abundance of all blue crab life stages (e.g., male and female juveniles, male and female adults, mature females). In response to stock concerns expressed by commercial crabbers and continued poor trends in abundance since adoption of Amendment 3, the division began updating the stock assessment with data through 2022, adding six years of data to the benchmark assessment. As an assessment update, there were no changes to model parameters and a peer review was not conducted, as the model configuration of the prior peer reviewed model was maintained. Results of the model update indicate the magnitude and trends for estimated recruitment, female spawner abundance, and fishing mortality were similar to the prior benchmark assessment (Figure 1), however, the Maximum Sustainable Yield (MSY) based reference points used to determine stock status for both female spawner abundance and fishing mortality both drastically changed with the update time series (Figures 2-3). Due to the magnitude of the change in reference points, the division requested an external review of the updated stock assessment.

This external review was completed in late December 2023. The reviewers identified concerns with model specifications and results and strongly recommended resolving these issues before basing any management decisions solely on the assessment update. Suggestions provided by reviewers can only be incorporated with a new benchmark stock assessment. Given concerns with the assessment update identified by the division and external peer reviewers, the division does not recommend using results of the 2023 stock assessment update to inform harvest reductions. 

Regardless of the availability of management advice from an updated stock assessment, stock concerns raised by commercial crabbers and trends in available data clearly show Amendment 3 management measures have not worked to reverse declining population trends as intended. Amendment 3 adopted management measures were only projected to result in a 2.4% harvest reduction with a 50% probability of achieving sustainable harvest, the minimum required by statute. 

In addition, declines in the North Carolina blue crab stock are not unique, as blue crab stocks in other Atlantic coast states have shown similar declines. In January 2023 the South Carolina Department of Natural Resources released a status report for the South Carolina blue crab fishery. The report concluded the South Carolina blue crab stock has been in decline for nearly two decades and provided recommendations to prevent overharvesting, gradually reduce fishing pressure, prevent overexploitation, and strengthen enforcement capabilities. Concerns for the Chesapeake Bay blue crab stock have also persisted. While the Chesapeake Bay blue crab stock is not depleted and overfishing is not occurring, juvenile abundance remains low. Precautionary management, focusing on protecting mature females and juveniles, has been recommended for the Chesapeake Bay stock and a benchmark stock assessment has been started to better understand the population.     

The original North Carolina Blue Crab Fishery Management Plan (FMP) was adopted in December 1998, Amendment 1 was adopted in December 2004, and Amendment 2 was adopted in November 2013. The Amendment 2 adaptive management strategy relied on annual updates to the Traffic Light Assessment (TLA) to provide information on relative condition of the stock. Based on results of the TLA update with 2015 data, management action was required by the North Carolina Marine Fisheries Commission (MFC). To improve the condition of the blue crab stock, the MFC adopted management measures documented in the May 2016 Revision to Amendment 2.

Comprehensive review of the Blue Crab FMP was originally scheduled to begin in July 2018, but at its August 2016 business meeting, the MFC voted to begin formal review immediately to assess the status of the blue crab stock and identify more comprehensive management strategies. Consequently, development of Amendment 3 began in August 2016.  

Amendment 3 Background

As part of Amendment 3 to the North Carolina Blue Crab FMP, a benchmark stock assessment was undertaken using data from 1995-2016. Based on assessment results, the N.C. blue crab stock was classified as overfished in 2016. The probability the stock was overfished was 98% with the average spawner abundance in 2016 estimated at 50 million crabs (below the threshold estimate of 64 million crabs). Overfishing was also occurring in 2016 with a 52% probability. The average fishing mortality in 2016 was estimated at 1.48 (above the fishing mortality threshold of 1.46). 

The North Carolina Fishery Reform Act of 1997 requires the State specify a time period not to exceed two years to end overfishing and achieve a sustainable harvest within 10 years of the date of adoption of the plan. To meet the legal requirement, the division determined reductions in commercial harvest were necessary. A harvest reduction of 0.4% (in numbers of crabs) was projected to end overfishing and a harvest reduction of 2.2% was projected to achieve sustainable harvest and rebuild the blue crab spawning stock within 10 years with a 50% probability of success (Table 1).  

Prior to adoption, the division recommended that, at a minimum, the MFC should adopt a commercial harvest reduction of 2.2% (50% probability of success) but encouraged the MFC to consider a further reduction to at least 5.9% (90% probability of success). Further, the division encouraged the MFC to adopt a management strategy that included a prohibition on immature female hard crab harvest, a 5-inch minimum size limit for mature females, and a continuous closure period resulting in a reduction of at least 4.6% to make up the remainder of the preferred reduction. A comprehensive list of Amendment 3 sustainable harvest options can be found in Table 4.1.12 and Table 4.1.14 of Amendment 3.  

Prior to adoption in February 2020, and after advisory committee recommendations and public comment, the MFC selected their preferred management strategy in November 2019. The initial recommendations included:

• North of the Highway 58 Bridge: A January 1 through January 31 closed season, a 6.75” mature female hard crab maximum size limit, and prohibiting immature female hard crab harvest.
• South of the Highway 58 Bridge: A March 1 through March 15 closed season and prohibiting immature female hard crab harvest.
• Replacing the current pot closure period and remaining closed in entirety (could not be reopened early).
• Maintain the 5% cull tolerance established in the 2016 Revision to Amendment 2. 
• Adopt proposed adaptive management framework and allow measures to be relaxed if the assessment update indicated the stock was not overfished and overfishing was not occurring and recommend updating the stock assessment once 2019 data is available. 

It was estimated this initial recommendation would result in a 3.7% harvest reduction with a 50-67% probability of success. This reduction would be just above the statutory required minimum (2.2%) needed to rebuild the stock to the threshold abundance level, but below the harvest reduction level needed to reduce F to the target (5.9%) or to increase spawner abundance to the target (19.8%).   
Following legislative review and before voting on these recommendations for final approval, at their February 2020 meeting commissioners discussed a perceived inequity between crabbers in the north and south due to the preferred management strategy selected in November 2019. At issue, was the maximum size limit for mature female crabs for only the northern part of the state. To address the inequity, the MFC removed their recommendation to implement a maximum size limit for mature females in the northern region and replaced it with a 5-inch minimum size limit for mature female crabs statewide, consistent with the division recommended minimum size. The adopted management strategy was estimated to result in a harvest reduction lower than the initial recommendation and provided an estimated 2.4% harvest reduction with a 50% probability of success. This reduction would be just above the statutorily required minimum (2.2%), but below the harvest reduction level needed to reduce F to the target (5.9%) and the reduction needed to increase spawner abundance to the target (19.8%). Additionally, in consideration of the burden updating the stock assessment would put on division staff and understanding the stock assessment would be updated through the adaptive management framework, the MFC removed their recommendation to update the stock assessment with data through 2019. Amendment 3 management strategies have been fully in place since January 2021. Amendment 3 also maintained all measures implemented with the May 2016 Revision to the Blue Crab FMP. A summary of all management measures in place through Amendment 3 can be found in the annual FMP Update or in the Amendment 3 flyer. 

Adaptive Management

In addition to management strategies to reduce harvest, Amendment 3 also includes the following adaptive management framework:  

1. Update the stock assessment at least once in between full reviews of the FMP, timing at the discretion of the division.
   • If the stock is overfished and/or overfishing is occurring or it is not projected to meet the sustainability requirements, then management measures shall be adjusted using the director’s proclamation authority.
   • If the stock is not overfished and overfishing is not occurring, then management measures may be relaxed provided it will not jeopardize the sustainability of the blue crab stock.
2. Any quantifiable management measure, including those not explored in this paper, with the ability to achieve sustainable harvest (as defined in the stock assessment), either on its own or in combination, may be considered.
3. Use of the director’s proclamation authority for adaptive management is contingent on:
   • Consultation with the Northern, Southern, and Shellfish/Crustacean advisory committees.
   • Approval by the Marine Fisheries Commission.

Upon evaluation by the division, if a management measure adopted to achieve sustainable harvest (either through Amendment 3 or a subsequent Revision) is not working as intended, then it may be revisited and either: 1) revised or 2) removed and replaced as needed provided it conforms to steps 2 and 3 above.