The 2020 American Lobster Benchmark Stock Assessment and Peer Review Report indicates record high stock abundance and recruitment in GOM and GBK, and record low abundance and recruitment in SNE. The GOM/GBK stock is not overfished and not experiencing overfishing. Conversely, the SNE stock remains severely depleted with poor prospects of recovery.

Given extensive research showing the connections between environmental conditions and American lobster life history and population dynamics, the 2020 assessment applied new methods to account for changing environmental influences when assessing the lobster stocks. Environmental data time series included water temperatures at several fixed monitoring stations throughout the lobster’s range, average water temperatures over large areas such as those sampled by fishery-independent surveys, oceanographic processes affecting the environment, and other environmental indicators such as lobster prey abundance. Environmental time series were analyzed for regime shifts, which indicate a significant difference in the lobster’s environment and population dynamics from one time period to another and can impact the stock’s capacity for recruitment and supporting different levels of catch. The assessment also quantified the effect of temperature on the catchability of lobster in surveys, and corrected trends in estimated abundance by accounting for these effects.

Model-estimated abundance time series were also analyzed for shifts that may be attributed to changing environmental conditions and new baselines for stock productivity. Regime shifts were detected for the GOM/GBK stock in 1996 and 2009 and one shift was detected for the SNE stock in 2003. New reference points were developed to account for the changing regimes.

The 2020 assessment used three reference points to characterize stock abundance (Figure 2). The abundance threshold is calculated as the average of the three highest abundance years during the low abundance regime. A stock abundance level below this threshold is considered significantly depleted and in danger of stock collapse. This was the only abundance reference point recommended for the SNE stock due to its record low abundance and low likelihood of reaching this threshold in the near future (Figure 3). The abundance limit is calculated as the median abundance during the moderate abundance regime. Stock abundance that falls below this limit is considered depleted because the stock’s ability to replenish itself is diminished. The fishery/industry target is calculated as the 25th percentile of the abundance during the high abundance regime. In this case, when abundance falls below this target, the stock’s ability to replenish itself is not jeopardized, but it may indicate a degrading of economic conditions for the lobster fishery.

Two reference points are used to evaluate the fishing mortality condition of the stocks. The exploitation threshold is calculated as the 75^th percentile of exploitation during the current abundance regime. The stock is considered to be experiencing overfishing if exploitation exceeds the exploitation threshold. The exploitation target is calculated as the 25^th percentile of exploitation during the current abundance regime.

Gulf of Maine/Georges Bank

GOM/GBK stock abundance has increased since the late 1980s, and at an accelerated pace since 2008. The GOM/GBK stock shifted from a low abundance regime during the early 1980s through 1995 to a moderate abundance regime during 1996-2008, and shifted once again to a high abundance regime during 2009-2018 (Figure 2). Current spawning stock abundance and recruitment and are near record highs. Exploitation (commercial landings relative to stock abundance) declined in the late 1980s and has remained relatively stable since.

The GOM/GBK stock is in favorable condition based on the recommended reference points. The average abundance from 2016-2018 was 256 million lobster, which is greater than the fishery/industry target of 212 million lobster. The average exploitation from 2016-2018 was 0.459, below the exploitation target of 0.461. Therefore, the GOM/GBK lobster stock is not depleted and overfishing is not occurring.

Southern New England

SNE stock abundance increased from the early 1980s, peaked during the late 1990s, then declined steeply through the early 2000s to a record low in 2018. Additionally, recent recruitment estimates are the lowest on record. The assessment regime shift analysis indicates the SNE stock shifted from a high abundance regime during the early 1980s through 2002 to a low abundance regime during 2003-2018 (Figure 3).

Declines in population abundance are most pronounced in the inshore portion of the stock where environmental conditions have remained unfavorable to lobster since the late 1990s. The contraction of the SNE stock has continued since the last assessment and is now becoming apparent in the offshore portion as well, according to survey encounter rates. It is believed the offshore area of SNE depends on nearshore larval settlement and offshore migration as the source of recruits (e.g., young of the year lobster).

Based on the new abundance threshold reference point, the SNE stock is significantly depleted. The average abundance from 2016-2018 was 7 million lobster, well below the threshold of 20 million lobster. However, according to the exploitation reference points the SNE stock is not experiencing overfishing. The average exploitation from 2016-2018 was 0.274, falling between the exploitation threshold of 0.290 and the exploitation target of 0.257.

Peer Review Panel Recommendations

The Panel endorsed the stock assessment findings that the GOM/GBK  stock is not depleted and the SNE stock is significantly depleted, and recommended the assessment be used for management advice. In particular, the Panel recommended significant management action be taken to provide the best chance of stabilizing or improving abundance and reproductive capacity of the SNE stock.

The Panel also recognized the consideration of environmental and climatic drivers on stock dynamics as a major advancement in the assessment. Given rapidly changing environmental conditions, the Panel recommended changes to stock abundance and settlement indices be monitored through an annual data update process to allow for more timely reactions to any concerning trends in the interim between the next stock assessment. Links to the Benchmark Stock Assessment and Peer Review Report, as well an overview of the assessment findings, can be found below under Stock Assessment Reports.