Spisula Solidissima) Using a Spatially Northeastern Continental Shelf of the United States

300 Abstract—The commercially valuable Atlantic surfclam (Spisula so- Management strategy evaluation for the Atlantic lidissima) is harvested along the surfclam (Spisula solidissima) using a spatially northeastern continental shelf of the United States. Its range has con- explicit, vessel-based fisheries model tracted and shifted north, driven by warmer bottom water temperatures. 1 Declining landings per unit of effort Kelsey M. Kuykendall (contact author) (LPUE) in the Mid-Atlantic Bight Eric N. Powell1 (MAB) is one result. Declining stock John M. Klinck2 abundance and LPUE suggest that 1 overfishing may be occurring off Paula T. Moreno New Jersey. A management strategy Robert T. Leaf1 evaluation (MSE) for the Atlantic surfclam is implemented to evalu- Email address for contact author: [email protected] ate rotating closures to enhance At- lantic surfclam productivity and in- 1 Gulf Coast Research Laboratory crease fishery viability in the MAB. The University of Southern Mississippi Active agents of the MSE model 703 East Beach Drive are individual fishing vessels with Ocean Springs, Mississippi 39564 performance and quota constraints 2 Center for Coastal Physical Oceanography influenced by captains’ behavior Department of Ocean, Earth, and Atmospheric Sciences over a spatially varying population. 4111 Monarch Way, 3rd Floor Management alternatives include Old Dominion University 2 rules regarding closure locations Norfolk, Virginia 23529 and 3 rules regarding closure du- rations. Simulations showed that stock biomass increased, up to 17%, under most alternative strategies in relation to estimated stock biomass under present-day management, and The Atlantic surfclam (Spisula solid- ally not found where average bottom LPUE increased under most alterna- issima) is an economically valuable temperatures exceed 25°C (Cargnelli tive strategies, by up to 21%. When bivalve common to the sandy bot- et al., 1999). Atlantic surfclams are incidental mortality caused by the toms off the northeastern coast of the relatively sessile planktivorous filter fishery increased, the benefits seen United States and Canada (Weinberg, feeders that rarely vacate their bur- under the alternative management 2005). The range of the Atlantic surf- row unless resuspended by storms or were enhanced. These outcomes suggest that area management involv- clam before recent effects of global they are escaping predators (Ropes ing rotating closures could be valu- warming spanned the western North and Merrill, 1973; Prior et al., 1979), able in insulating the stock and the Atlantic Ocean continental shelf from after which they rapidly reburrow commercial fishery from further de- Nova Scotia to northern South Caro- into the substrate (Weinberg, 2005). clines as a northerly shift in range lina, at depths of 10 m to 50 m, and The life span of Atlantic surfclam is proceeds. temperature determines the range approximately 30 years and has a boundaries (Goldberg and Walker, maximum-recorded shell length (SL) 1990; Weinberg, 1998; Jacobson and of 226 mm (Fay et al.3; Cargnelli et Weinberg1; NEFSC2). They are gener- al., 1999; Munroe et al., 2016). The range of Atlantic surfclam 1 Jacobson, L., and J. Weinberg. 2006. At- has been shifting north and offshore lantic surfclam (Spisula solidissima). In since approximately 1970, driven Manuscript submitted 28 June 2016. Status of fishery resources of the North- primarily by warming bottom water Manuscript accepted 27 March 2017. eastern US (R. Mayo, F. Serchuk, and E. temperatures (Cargnelli et al., 1999; Fish. Bull. 115:300–325 (2017). Holmes, eds.), 1–8 p. Northeast Fish. Online publication date: 4 May 2017. Sci. Cent., Woods Hole, MA. [Available doi: 10.7755/FB.115.3.3 from website.] 2 NEFSC (Northeast Fisheries Science Center). 3 Fay, C. W., R. J. Neves, and G. B. Par- 2013. 56th Northeast Regional Stock due. 1983. Species profiles: life his- The views and opinions expressed or Assessment Workshop (56th SAW) as- tories and environmental requirements implied in this article are those of the sessment summary report. U.S. Dep. of coastal fishes and invertebrates (mid- author (or authors) and do not necessarily Commer, Northeast Fish. Sci. Cent. Ref. Atlantic) surf clam. U.S. Fish. Wildl. reflect the position of the National Doc. 13-04, 42 p. [Available from web- Serv., FWS/OBS-82/11.13, U.S. Army Marine Fisheries Service, NOAA. site.] Corps Eng., TR EL-82-4, 23 p. Kuykendall et al.: A management strategy evaluation for Spisula solidissima 301 Weinberg, 2005; Munroe et al., 2013; Hofmann et al., have been reported to be similar across much of the in press). Early evidence of this trend is the disappear- range of the Atlantic surfclam before the 1999 mortal- ance of Atlantic surfclams in Virginia and Maryland ity event (Cargnelli et al., 1999). Increased bottom wa- state waters between the 1970s and the 1990s (Loesch ter temperatures above approximately 20°C negatively and Ropes, 1977; Powell4; Hofmann et al., in press) and affect Atlantic surfclam nutrition by reducing ingestion the shift of the southern fishery from the Delmarva rate and leading to a reduction in growth rate, condi- Peninsula to ports north (Powell et al., 2015). From the tion, and maximum size (Marzec et al., 2010; Munroe 1997 to 1999 period, the Atlantic surfclam population et al., 2013; Munroe et al., 2016). Munroe et al. (2016) was considered to be near carrying capacity (NEFSC2). found that the maximum size had, in fact, declined Abundances were once high on the continental shelf off for much of the stock since 1980. Simulation modeling the Delmarva Peninsula, but declines in growth, maxi- of Atlantic surfclam population dynamics shows that mum size, and tissue weight (Weinberg, 1998, 1999) this outcome can be derived solely from rising bot- were accompanied by increased mortality in this region tom water temperatures (Munroe et al., 2013, 2016), (Weinberg, 2005; Weinberg et al.5). Separate fisheries- although a change in food supply would result in the independent surveys conducted in 2002 by the North- same outcome. east Fisheries Science Center of the National Marine Along the Mid-Atlantic coast, the Atlantic surfclam Fisheries Service (NMFS) and the New Jersey Depart- has supported a fishery since the 1960s that reached ment of Environmental Protection revealed that a large total revenues of $29 million in 2011 (Weinberg, 1999; mortality event had occurred sometime after 1999 that Weinberg et al.5; NEFSC2). The average rate of fishing- extirpated Atlantic surfclams from the southern in- induced mortality (commonly termed “fishing mortal- shore region off Delmarva Peninsula, followed by stock ity”) in the stock south of Hudson Canyon has been declines in both state and inshore federal waters off higher than the fishing mortality rate over the whole New Jersey (Powell4; Kim and Powell, 2004). An addi- stock and of the northern region since 2002; however, the tional survey conducted in 2004 (Weinberg et al.5) con- fishing mortality rate, which historically has been less firmed the northward and offshore shift in the Atlantic than 25% of the natural mortality rate (M=0.15/year), surfclam stock. remains below the natural mortality rate (NEFSC2). One result of these mortality events was the re- For the last 30 years, most of the commercial land- distribution of the stock north: namely an increasing ings within the U.S. Exclusive Economic Zone have abundance off the coast of Long Island, New York; the been harvested along the coast of New Jersey and expansion of the population on Georges Bank; and the the Delmarva Peninsula (Weinberg, 1999; NEFSC2). movement of the seaward boundary of the southern Landings in this region within the last decade have portion of the stock offshore in response to increased declined coincident with the latest phase of contrac- bottom water temperatures (Weinberg, 2005; Munroe tion in the distribution range of this species. According et al., 2013; NEFSC2). Simulations by Narváez et al. to the latest stock assessment, the Atlantic surfclam (2015) based on stock assessment data from the North- is not overfished, and overfishing is unlikely to occur east Fisheries Science Center and bottom temperature in the next 5–7 years (NEFSC2). However, declining time series obtained through implementation of the stock abundance has led to the termination of a once Regional Ocean Modeling System for the northwestern thriving clam fishery in the most southerly portions Atlantic indicated that episodic warm years caused el- of its range since 2000. A decline in landings per unit evated mortality events in older and larger clams and of effort (LPUEs), coupled with rising fishing moral- that these events have occurred with increasing fre- ity rates, has generated concern for the sustainability quency over the last several decades of the 20th centu- of the stock off New Jersey (Powell4; Weinberg et al.5; ry. In the simulation study, Narváez et al. (2015) found NEFSC2). The reopening of Georges Bank for harvest- that thermal stress decreased the Atlantic surfclam ing of clams in 2010 (NOAA, 2012)—an area that was stock by 2–9% on the shelf regions that coincide with a closed in 1990 owing to the risk of harvesting clams majority of the regions used by the commercial fishery. contaminated with paralytic shellfish poison (Jacobson The Atlantic surfclam reaches marketable sizes of and Weinberg1) —allowed some relief from fishing pres- 120 to 150 mm SL within 6–7 years depending upon sure in other regions, but landings over much of the food availability and water temperature (Weinberg, remainder of the stock continue to produce the steady 1998; Cargnelli et al., 1999; Weinberg et al., 2002; decline observed since 2008 (Fig. 1) (NEFSC2). NEFSC2). Growth rates within the first 3 to 5 years Declining abundance and LPUE south of Hudson Canyon have driven stakeholders’ desire to enhance production in the New Jersey portion of the stock (Fig. 4 Powell, E. N.

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