Sustainability of a new mechanical clam harvesting rotation plan to manage the hard clam (Mercenaria mercenaria) fishery in North Carolina

Sustainability of a new mechanical clam harvesting rotation plan to manage the hard clam (Mercenaria mercenaria) fishery in North Carolina

Clam kicking is a controversial method of mechanical clam harvesting, practiced only in North Carolina. However, clam kicking in Core Sound, Carteret County, NC, is no longer sustainable due to overharvesting. This has resulted in adoption of a rotation plan in which a new area in nearby Pamlico Sound was opened in December, 2001, to clam kicking while part of Core Sound was closed as the start of a rotation cycle. We do not know if this new rotation plan will achieve sustainability without environmental harm. Therefore, we have a unique opportunity to evaluate the impacts of clam kicking on the stocks in Pamlico Sound to assess potential negative environmental impacts on clam recruitment and seafloor habitat quality, and to document recovery processes in the closed area of Core Sound as a means of assessing the effectiveness of a two-year rotation cycle. We plan to evaluate the effects of clam kicking on relative population size, size- and age-structure in the fishable population and recruitment of juvenile clams in the Pamlico Sound area for comparison to the same parameters in Core Sound. We sampled in spring and fall 2001 (before the new area was opened to kicking in December 2001) and will return in spring and fall 2002 after one season of kicking. Sampling for adult population size and size-and age-structure was done from a commercial clam kicking boat to provide densities that can be related to area, and sampling for clam recruits and associated benthic organisms was done by suction dredge. Our results will answer critical questions regarding the management of the North Carolina hard clam fishery. Specifically, we will determine if the rotation between Core and Pamlico Sounds is a sustainable way to manage the fishery and minimize damage to the habitat.

John Vavrinec,¹* Robert S. Steneck,¹ Douglas C. McNaught.^{2 1}University of Maine Darling Marine Center, Walpole ME, USA; ²Brown University, Providence RI, USA.

Serial depletion of sea urchin populations led to a rolling phase shift along the coast of Maine in the last decade. Southern parts of the state were the first to switch from coralline dominated urchin barrens to fleshy macroalgal beds, but the transition has steadily progressed to the northeast with shifting fishing pressures. These areas experienced a rapid succession from primarily filamentous algal species to kelp usually within two or three years of urchin extirpation. Theory predicts these kelp should outcompete other algal forms and remain dominant in this alternate stable state. However the succession along the southern coast continued beyond this "climax" community and over time a complex understory algal assemblage became established. This understory appears to be competitively equal, or even superior, to the kelp. Given the differing oceanographic conditions along the coast, it is uncertain if this algal succession will lead to the same turf community or kelp beds as the phase shift continues northeast. While kelp beds may be able to support limited numbers of urchins under their higher canopy, the red algae understory assemblage can spatially dominate the substrate and virtually excludes all urchins. Therefore, this increased algal density, diversity, and complexity may be important in maintaining and understanding the stability of the fleshy macroalgal state.


Fooled by sampling frequency: an example using demise and recovery of seagrass in Indian River Lagoon, FL

Robert W. Virnstein,* Lori J. Morris, Edward W. Carter, and Lauren Hall. St. Johns River Water Management District, P.O. Box 1429, Palatka, FL 32178.

Seagrass in Indian River Lagoon (30,000 ha total seagrass) is monitored by two main methods: (1) mapping every 2-3 years since 1986 based on aerial photos and (2) field monitoring of 85 fixed transects twice a year since 1994. These two methods generally show similar temporal patterns throughout the Lagoon. However (isn’t there always a “however”?), seagrass in one small segment showed highly disparate patterns, depending on the monitoring method and frequency. This segment is a poorly-flushed but relatively pristine area whose drainage basin is a relatively undisturbed hardwood swamp and marsh system.

What happened? It depends. Based on the Lagoon-wide mapping, the amount of seagrass varied little over time. However, based on the higher-frequency monitoring of transects plus additional field checks, over 100 ha of seagrass completely disappeared from this segment in summer 1997, but had fully recovered by summer 2000. This demise was preceded by a shift from predominantly Halodule wrightii plus patchy Halophila engelmannii to Ruppia maritima in 1996. Recovery occurred in the reverse sequence—first, recruitment by Ruppia seedlings followed by dominance by Halodule plus Halophila.