Shellfish Harvest Opportunities

How much of our estuaries are open for shellfish harvesting and how has it changed over time?

The percentage of possible acre-days (i.e. the number of open acres multiplied by the number of days those acres were open for harvest) between 2012 and 2016 was 80% and 66% for the Great Bay and Hampton-Seabrook estuaries, respectively. This continues the long-term trend of a gradual increase in acre-days. The next reporting period may see continued increases as the Portsmouth wastewater treatment facility upgrade is completed in 2019.


Shellfish beds are closed—either temporarily or indefinitely—to commercial and recreational harvesting when there are high amounts of bacteria or other pollution in the water. Closures also occur for precautionary reasons related to wastewater treatment facilities (WWTFs). Therefore, the amount of time that shellfish beds are open for harvest can be used as an indicator of water quality.
Improve water quality and identify and mitigate pollution sources so that additional estuarine areas meet water quality standards for bacteria and for shellfish harvesting.
Figure 11.1 indicates open and closed areas of the Great Bay and Hampton-Seabrook estuaries for recreational shellfish harvesting. (Note that open areas may become temporarily closed after large rain events due to water quality issues). The percentage of possible acre-days between 2012 and 2016 was 80% and 66% for the Great Bay and Hampton-Seabrook estuaries, respectively (Figure 11.2). The Great Bay acre-days open data exhibits a saw tooth profile between 2006 and 2009, which is most likely caused by major storms, such as the Mother’s Day storm of 2006. The 2016 steep decrease in the Hampton-Seabrook acre-days open data was the result of a prolonged discharge of raw sewage from a broken 14-inch force main pipe under a salt marsh in the Town of Hampton. The pipe broke in late 2015 and was fixed in early 2016. The overall long-term trend of gradual improvements since the year 2000 may reflect improved pollution source management, such as efforts by NHDES and municipalities to identify and eliminate illicit discharges. Lower rainfall amounts in recent years may also have led to a decrease in the occurrence of bacterial pollution events related to stormwater runoff.

The areas designated as “conditionally approved” (open but subject to temporary closures due to water quality issues), “restricted” (closed due to chronic water quality problems) and “prohibited” (closed due to water quality issues that require further investigation) have remained fairly constant since 2004 (Figure 11.3). The most notable change occurred in 2014 with the conversion of over 1,300 acres that was “prohibited/unclassified” area (closed because the water quality is unknown) to “prohibited/safety zone.” This refers to areas closed due to pollution sources that may unpredictably affect the water quality of the area and create a potentially dangerous public health risk. These zones are most often related to WWTFs.

This 2014 conversion was a direct result of the December 2012 Portsmouth wastewater treatment facility (WWTF) dye study46, which examined how this primary WWTF affected water quality in the estuary, and how those effects might change once the facility upgrade is complete in 2019. The dye study indicated effluent travels further up river and faster than previously determined; this resulted in the reduction of harvest opportunities at the Little Bay and Bellamy River shellfish beds (Figure 11.1). Specifically, harvest days were reduced from seven days/week to Saturdays only, from 9 a.m. to 5 p.m.; this approach gives wastewater operators and the NHDES Shellfish Program more time to react in the event of a WWTF problem that occurs overnight. (Note: aquaculture operators in Little Bay are mandated to call the NHDES Shellfish Program before harvesting and so are not impacted by the new rule).

Maine waters, including areas of the Piscataqua River and Spruce Creek are also closed due to concerns about the Portsmouth WWTF. This facility is being upgraded from primary to secondary treatment, which should greatly reduce both the risk of bacteria/viral contamination during failure events as well as improve overall water quality. When the Portsmouth upgrade is complete, NHDES and Maine Department of Marine Resources will reassess the public health risks and modify harvesting classifications accordingly.

Figure 11.1 Map showing recreational shellfish harvest categories for the Great Bay and Hampton-Seabrook estuaries.

Figure 11.2 Shellfish harvest opportunities for Great Bay and Hampton-Seabrook estuaries. Percentage maximum possible “acre-days”, which is the number of open acres multiplied by the number of days those acres were open for harvest.

Figure 11.3 Shellfish closure acres by classification.