American sea scallop

According to the Atlantic Sea Scallop Fishery Management Plan, all scallops in the US EEZ belong to a single stock. However, the U.S. sea scallop stock was assessed in two separate components: the Mid-Atlantic Bight, and Georges Bank, and then combined (NEFSC, 2007). The latest stock assessment published in September 2007 incorporates improved data compilation and interpretation since the previous stock assessment in 2004, with new growth modeling and verification, a revised shell height/meat weight relationship, adjusted shucking capacity, and a re-estimation of selectivity in scallop dredges (Maguire, 2007). For the first time, the 2007 stock assessment incorporated data from many different sources, rather than merely NEFSC scallop dredge survey data. The primary assessment model used is known as CASA, which is size-structured and can directly treat the growth-increment probabilities, compared with other methods that rely on direct estimates of size at age. This model was improved for the most recent stock assessment, making it more precise, with reduced model-specification bias. This improvement, along with new scallop growth information, as well as recent information on increased gear selectivity towards larger scallops and area-based management (rotational closed areas) restrictions, has enabled the setting of new Biological Reference Points (BRP). Previous BRPs were calculated using recruitment estimates based only on the NEFSC dredge survey data and older information available on life history and selectivity. Both the previous and new biological reference points are based on yield-per-recruit, rather than stock size and recruitment estimates. This means the reference fishing mortality rate (F) used is FMAX rather than FMSY, and in order to produce optimum yield-per-recruit, the target F for the sea scallop fishery should be set between 0.20 and 0.30 (EPA, 2006). Since 1998, F has ranged from 0.18 to 0.34 (Figure 1), while FMAX in 2007 is 0.24 for Georges Bank (GB) and 0.25 for the Mid-Atlantic sea scallops (Hart, 2006b).

Figure 1. Scallop landings and fishing mortality rate, 1982-2005.
Data taken from (Hart, 2006b) Status of Fishery Resources off of the Northeastern U.S., NEFSC – Resource Evaluation and Assessment Division, December 2006 (Atlantic Sea scallop).

Keeping F under FMAX will prevent growth overfishing, but will not necessarily protect against recruitment overfishing, meaning the adult population could still be removed to an extent that compromises successful replenishment of stocks. Recent gear changes resulting in selection tendencies towards larger scallops appear to have helped improve yields, and decrease discards, which, together with closed areas, may help protect against recruitment overfishing. This may alleviate some of the concerns associated with using yield-per-recruit based reference points. Overall, sea scallops as a resource are inherently different from fish populations, as they have a benthic existence, but also form relatively sedentary communities. Their larval dispersal may allow for spawners in closed areas to contribute to an increase in overall stock, inside and outside of closed areas.

In the U.S., scientific advice and management decisions are given and made by the same organization: NOAA Fisheries Service. The decision making process is more complex than it sounds, however. The Northeast Fisheries Science Center (NEFSC), which runs under the auspices of the National Oceanic and Atmospheric Administration (NOAA) Fisheries Service, runs the fisheries independent scallop dredge survey, on which a large portion of the scientific advice is based. Advice from independent organizations, such as academic institutions and research organizations, is also closely followed when making management decisions. Data used in the Atlantic sea scallop stock assessment is contributed by: the NEFSC’s annual federal scallop dredge survey; the School for Marine Science and Technology at University of Massachusetts, Dartmouth (SMAST) video survey for reassessment of dredge survey selectivity for scallops less than 40 mm in shell height; the NEFSC Fisheries Observer Program; and Vessel Monitoring Systems (VMS) (NEFSC, 2004; Maguire, 2007). Although the scallop industry began to fund their own observer program in 2003, policy issues forced a suspension of the program from 2004-2007, during which time observers were provided and funded by the federal government. This resulted in a lower percentage of observed fishing trips during the suspension. In 2007, the implementation of Amendment 13 to the Atlantic Sea Scallop Fishery Management Plan enabled the reinstatement of the industry funded program.

Last updated on 19 Jan 2011

A new stock assessment for Atlantic sea scallops was published in September 2007. Both the previous and the new reference points are based on yield-per-recruit, rather than stock size and recruitment estimates. This means the reference fishing mortality rate (F) used is FMAX, or, Fthreshold, rather than FMSY. Therefore, assigning a simplified biomass target value is attempted solely as a convenience and/or necessity for management. In the new stock assessment, estimates of F and biomass (B) have made considerable progress since the previous assessment update in 2005. The Mid-Atlantic and Georges Bank (GB) areas are now modeled separately before results are combined (NEFSC, 2007). There are several reasons for this, the most prominent one being there was an observed difference in recruitment patterns between the two areas.

The 2005 F estimate was 0.22, which is below the threshold or FMAX of 0.24 (used as a proxy for FMSY), but above the target F (80% of threshold, or 0.20). The new stock assessment shows an increase in the suggested estimate of FMAX from 0.24 to 0.29 since the previous stock assessment update in 2005. Although F has been above Ftarget (0.20) for most recent years, it remains below FMAX. Because F is different for each area, and there is rotational area management, it is difficult to maintain a rate below the target F. However, the recent increase in FMAX shows that F exceeding Ftarget is not currently a concern.

In previous stock assessments, relative sea scallop abundance was estimated by measuring the weight of scallops in kg/tow from annual scientific surveys. Estimates were based on older life history and selectivity information, and recruitment estimates were based solely on data from the NEFSC scallop dredge survey. These annual measurements serve as a good proxy for total biomass. Target biomass levels for 2006 were 5.6 kg/tow (calculated as BMAX x median recruitment and used as a proxy for BMSY) and the NEFSC dredge survey yielded actual biomass levels of 7.7 kg/tow, indicating biomass levels were well above target levels (NOAA, 2007; NEFSC, 2006b). The biomass threshold, below which the stock would be defined as overfished, is one half the target biomass level.

The new draft stock assessment estimates biomass in meat weights of the whole stock (just the weight of the scallop meats, i.e., minus the viscera and shell weights). These estimates are based on new life history and selectivity information, and recruitment estimates for the stock based on a new model, which allows for growth increments, rather than depending on size-at-age data. They also depend on well established shell height/meat weight relationships for each area.

Table 3. Biological Reference Points

Last updated on 19 Jan 2011

Since 1998, F has ranged from 0.8 to 0.34, while F_MAX in 2007 was 0.25 for the Mid-Atlantic Sea scallops (Hart, 2006b). The 2005 F estimate was 0.22, which is below the threshold or F_MAX of 0.24 (used as a proxy for F_MSY), but above the target F (80% of threshold, or 0.20). Since the previous stock assessment update in 2005, the suggested estimate of F_MAX increased from 0.25 to 0.29. Although F has been above F_target (0.20) for most recent years, it remains below F_MAX.

Historically, the Atlantic sea scallop fishery has experienced dramatic cycles of biomass oscillations (usually more than ten years per cycle), categorizing it as a “boom and bust” fishery. In 1994, when landings and biomass were at a low point in their cyclical variation (Figures 3, 4), fishery managers closed three large areas on Georges Bank to scallop fishing. Portions of these areas have been reopened to fishing for intermittent periods since 1999. This system of rotational closures has aided an increase in scallop biomass, and may help prevent stock collapse, as well as conserve biodiversity (Hart, 2006a). In the period between 1998 and 2001, landings increased 264% from 5,879 tonnes to 21,404 tonnes (Baskaran and Anderson, 2005). The dramatic increase was due partially to the opening of Closed Area II in 1999. Exploitable biomass also increased dramatically from 55,014 tonnes in 1998 to 116,350 tonnes in 2001. Landings and biomass peaked in 2004 at the high point of the current cycle (Figures 3, 4). Even during the downwards portion of the cycle, projections account for these cyclical decreases, which helps to manage the resource effectively, and allow for the stock to remain at a healthy status.

Figure 3. Biomass in open and closed areas, 1979-2005.
Data taken from (Hart, 2006b) Status of Fishery Resources off of the Northeastern U.S., NEFSC – Resource Evaluation and Assessment Division, December 2006
Source : (Status of Fishery Resources off the Northeastern US).

Figure 4. Total commercial landings of scallops, 1887-2005.
Data taken from (Hart, 2006b) Status of Fishery Resources off of the Northeastern U.S., NEFSC – Resource Evaluation and Assessment Division, December 2006
Source : (Status of Fishery Resources off the Northeastern US).

The Atlantic Sea Scallop Fishery Management Plan (FMP) was implemented in 1982, and until 1994, was primarily controlled with a minimum average meat weight requirement for landings (NEFSC, 2004). Amendment 4 in 1994 changed the management strategy to effort control in the US EEZ. A combination of management measures has been implemented since this time, primarily to reduce fishing effort. These include: restrictions on days-at-sea (DAS) in open areas; rotational closed areas; access area trip limits; and gear regulations (check online legislation at Electronic Code of Federal Regulation) .

According to estimates, the target F should be set between 0.2 and 0.3 in order to achieve optimum yield. The current target F is set at 0.2. Even though the same organization and sector (government) houses both the scientific research and management bodies, each region has a fisheries management council made up of fisheries scientists, managers, and fishermen that is tasked with collecting the best scientific advice available, reviewing it and inviting outside, non-affiliated reviewers to participate, as part of a transparent process in a public arena. At times, even the one agency has to consider so many different interests that it appears to be more like many parties than just one. Eventually, they must come to a consensus in their policy making decisions. Atlantic sea scallops are managed under the Atlantic Sea Scallop Fisheries Management Plan, by the New England Fisheries Management Council in collaboration with the Mid-Atlantic Fisheries Management Council as the resource can be found in both regions.

The Access Area Program for the limited access scallop fleet has to comply with specific regulations in defined areas called scallop access areas, of which there are currently five (Figure 2, NERO, 2007). These areas may be closed or opened on a rotational basis, so that not all may be open at any one given time (Table 1). When a vessel makes a trip to a scallop access area, it is permitted to fish in this particular access area and this area only.

Figure 2. Map of Scallop Access and Closed Areas.
Closed Area II (CAII), Nantucket Lightship Closed Area (NLCA), Closed Area I (CAI), Elephant Trunk Access Area (ETAA), and Hudson Canyon Access Area (HCAA) (NERO, 2007).

Table 1. 2008 Schedule for Scallop Access Areas.


Source : (Access Area Schedule)

There is a limited access scallop fleet and a general category scallop fleet, each with different regulations. General category scallop vessels are generally smaller day-boats, and are allowed to land 400 lb (~ 180 kg) per day, or trip, whichever is more restrictive, meaning if a boat fishes on a two day trip, it can bring back 800 lb, but if a boat catches and lands 400 lb in one morning, it cannot go back to sea until the following day. The general category fleet is scheduled to be regulated under an IFQ program beginning March 1, 2009, and has become a limited entry fishery. Both the limited access fleet and the general category fleet have trip limits to the access areas, which are subject to change (Table 2).

Table 2. Number of access area trips allocated to scallop fleet.


a) Full-time scallop vessels have the following access area trip options:
2008:3 trips in Elephant Trunk Access Area (ETAA) (after March 1), and 1 trip in Closed Area I (CAI) or 1 trip in Nantucket Lightship Closed Area (NLCA) if approved (after June 15);
b) Part-time scallop vessels have the following trip options: 2008: 1 trip in CAI or 1 trip in NLCA if approved (after June 15), and 1 trip in ETAA (after March 1); or 2 trips in ETAA;
c) Occasional scallop vessels have the following trip options: 2008: 1 trip in ETAA (after March 1) or 1 trip in CAI or NLCA if approved.
Source : (Access Area Schedule)

The access area trip possession limits for limited access vessels depend on their permit class. Full-time and part-time permitted vessels may land 18,000 lb (~ 8,180 kg) per access area trip, and occasional permitted vessels may land 7,500 lb (~ 3,400 kg) per access area trip. When a vessel takes an observer, the observer’s costs are offset by added possession limits or added DAS. Unlike on regular open area trips, there is no crew limit on access area trips.

Although Illegal, Unreported and Unregulated (IUU) fishing is not an inherent problem in the United States, there are a few cases over the years of illegal sea scallop fishing recorded by NOAA’s Office of Law Enforcement. For example, a North Carolina sea scallop vessel was caught making repeated crossings into a sea scallop access area in the Hudson Canyon in 2006, even though vessels are only allowed to enter and exit once per trip in order to manage effort in these access areas. This allowed the vessel to circumvent DAS management measures (DOC NOAA, 2006a). In another case, three general category scallop vessels (this category is only permitted to land 400 lb (~180 kg) of scallops per trip or day, whichever is more restrictive, see section 1c. Managers’ Decisions) in Virginia were convicted in February of 2006 for landing and selling scallops over the 400 lb limit on numerous occasions (15-24), and submitting false vessel trip reports. Several dealers involved in buying these scallops and submitting false dealer reports were also convicted (DOC NOAA, 2006b).

NOAA Office of Law Enforcement continues to strictly enforce the Atlantic sea scallop regulations, and those that do not comply are heavily fined, both monetarily, and with suspended licenses.

Fisheries observers have recorded sea turtle interactions with scallop dredge and trawl gear in the mid-Atlantic since 2001 (Murray, 2007). There are five species of protected sea turtles in the Northwestern Atlantic Ocean: loggerheads (Caretta caretta) are listed as a threatened species under the US Endangered Species Act of 1973; and the leatherback (Dermochelys coriacea), hawksbill (Eretmochelys imbricata), Kemp’s ridley (Lepidochelys kempii), and certain populations of the green (Chelonia mydas) are listed as endangered. Improved observer training allowed for the majority of sea turtle interactions observed in the mid-Atlantic in 2001-2002 (88%) to be positively identified as loggerhead sea turtles, while the remaining 12% were unidentified (Murray, 2004). All interactions were observed in between June and November. In order to decrease incidental catch of sea turtles in scallop dredges, vessels are required to use sea turtle chain mats on dredges between May 1 and November 30 when fishing south of 41˚09.0’ N. latitude (NERO, 2007). The vast majority of sea turtle interactions in the sea scallop fishery occur in the mid-Atlantic, however, the first interaction on Georges Bank was recorded in 2005 with a Kemp’s ridley (Murray, 2007). There are more observed interactions with scallop trawl gear (similar to otter trawls, but modified for scallop fishing) than with dredge gear. Overall, the sea turtle bycatch remains low in this fishery. However, due to the vulnerability of these species, there is extensive research ongoing that aims to mitigate and/or maintain low levels of sea turtle bycatch in this and in other fisheries.

Provided a vessel holds a valid permit to land groundfish (NE multispecies) or any other species, these species may also be landed, but only if the total amount is less than 300 lb (~ 136 kg) per trip (NERO, 2007). These species may include, but are not limited to cod (Gadus morhua), haddock (Melanogrammus aeglefinus), yellowtail flounder (Limanda ferruginea), and monkfish (Lophius americanus).

The limited access scallop fishery is allocated 10% of the yellowtail flounder TAC for the Southern New England/Mid Atlantic stock (for Nantucket Lightship) and for the Georges Bank stock (for Closed Areas I & II). The scallop fishery is constrained by the yellowtail flounder TAC, which aims for specific mortality targets for the stock (NOAA, 2006). All bycatch of yellowtail flounder in access areas is monitored using observer data. Observed haul data is recorded and used to extrapolate bycatch for unobserved hauls and trips. According to projections, it is unlikely the scallop fishery will reach their yellowtail flounder TACs for the coming years, but if the annual yellowtail flounder TAC is reached, the area is closed to fishing for the rest of the year. Similar regulations exist for U.S./Canada shared resources of Georges Bank cod, haddock, and yellowtail flounder.

Other bycatch species include skates, juvenile scallops, other flounders, ocean quahogs, sea ravens, sculpins. Some of these species, such as winter skates, are overfished, or near their threshold levels.

Adult sea scallops are widely found on sand, gravel, shells, and rock bottom (NOAA, 2004). Some studies on the impacts of scallop dredging on bottom habitat have found that sand bottom recovers relatively quickly (Garcia et al., 2006; Stokesbury & Harris, 2006). However, because most studies are performed in areas that have been fished for many years, it remains unclear as to whether or not this would be true, had these experimental areas never been dredged. One study (Stokesbury & Harris, 2006), focusing on Georges Bank, used the closed area as a control area, and found that the New Bedford style dredge used in the U.S. may have less impact than the toothed dredges used in the EU and Australia; and that a limited, short-term scallop fishery alters the epibenthic community less than the natural, environmental dynamics on Georges Bank. Despite these results, it is important to remember that determining impacts to bottom habitat is difficult, therefore further studies are expected and required.

Last updated on 19 Jan 2011

A number of areas closed to scallop fishing are currently in place over the US continental shelf (Figure 2; “Managers’ Decisions” section). Marine reserves and other long term closures of areas to fishing help sea scallop biomass increase and may have possible effects on fishery yield, assuming effective and high mixing of larvae with open areas. With these types of marine reserves, it is difficult to measure how they are working. According to Hart (2006a), most other models of long-term closures do not indicate increased yield when the fishing mortality in open areas is at or less than FMSY or applicable proxy. This, however, does not mean that the reserves are not useful. The long-term closures may help prevent stock collapse; help conserve biodiversity, as well as have other conservation benefits; and serve as a control area for scientific research. They may also help increase yield when fishing mortality levels are high. Marine reserves should be established with these hopes in mind, rather than to help reach optimal yield.