RELATIVE EFFICIENCY OF TWO CLAM 



RAKES AND THEIR CONTRASTING IMPACTS 



ON SEAGRASS BIOMASS 



Fishing gear and techniques are continually being 

 developed and modified as alternatives to tradi- 

 tional fishing methodologies. As new equipment 

 becomes available, most individual fishermen carry 

 out their own field trials and peer interviews to deter- 

 mine which gear best meets their needs. Neverthe- 

 less, both quantitative comparisons of the relative 

 efficiencies of alternative methodologies (e.g., Med- 

 cof andMacPhail 1964; Caddy 1973) and controlled 

 scientific tests of the environmental impacts of con- 

 trasting techniques (e.g., Glude and Landers 1953; 

 Caddy 1973;Fonsecaetal. ) are necessary to provide 

 the biological basis for resource managers to devel- 

 op sound management policies. Quantitative data on 

 the relative costs and benefits of alternative fishing 

 methodologies are especially important in the es- 

 tuaries, where fishing intensity often brings the 

 demands of different fisheries into conflict. 



Here we provide relative cost and benefit data for 

 two different clam rakes, both available to hard clam 

 (Mercenaria mercenaria) fishermen along the east 

 and gulf coasts of the United States. At a study site in 

 coastal North Carolina, we estimated the efficiency 

 of hard clam capture by each rake in two habitats — a 

 seagrass bed and a sand flat. We also employed repli- 

 cate trials of both clam rakes within the seagrass bed 

 to estimate relative impacts of raking on seagrass 

 biomass. We chose damage to seagrass as a measure 

 of important environmental impact because most 

 coastal resource managers now recognize the direct 

 and indirect contributions of seagrass beds to coastal 

 zone fisheries production (e.g., Thayer et al. 1975). 



Materials and Methods 



The Contrasting Gear 



We compared two clam rakes, known in North Car- 

 olina as the pea digger and the bull rake (Fig. 1). The 

 pea digger (also called the potato rake in New Eng- 

 land) is a traditional implement of hand rakers in 

 North Carolina. It resembles a garden rake, having a 

 wooden shaft (handle) about 1.2 m long, leading to a 

 steel head with 3-6 prongs, each about 14 cm long, 

 with 3.5 cm gaps. It is used by making forward and/or 



' Fonseca, M.S., G. W. Thayer, A. J. Chester, and C. Foltz. 1981. 

 The impact of scallop harvesting on eelgrass (Zostera marina L.) 

 meadows. Unpubl. manuscr., 15 p. Southeast Fish. Cent. Beau- 

 fort Lab., Natl. Mar. Fish. Serv., NOAA, Beaufort, NC 28516. 



backward strokes which penetrate the sediments to a 

 shallow depth (3-8 cm, depending upon substrate 

 compaction and habitat). Whenever a rake prong en- 

 counters a clam, a distinctive scraping noise signals 

 the clammer to excavate more deeply and to unearth 

 the catch. The pea digger used in this study weighed 

 1.2 kg, had a wooden shaft 1.3 m long, and prongs 14 

 cm long. 



The bull rake (also known as the shinnecock rake) 

 has been introduced recently to North Carolina from 

 Long Island Sound (see description in Glude and 

 Landers 1953). It is a heavier, more robust imple- 

 ment, usually weighing from 8 to 1 1 kg. The rake con- 

 sists of a steel basket attached to a metal (steel or 

 aluminum) shaft which ends in a t-shaped handle. 

 The basket has a rectangular opening (usually 18 X 

 48 cm) with teeth extending outward along the lower 

 lip of the basket. The basket is formed by a grate of 

 steel bars spread about 2-3 cm apart. The rake is 

 used by pushing the teeth to a 14 cm depth into the 

 sediments and then pulling it with short, quick jerks. 

 The depth of penetration varies only slightly with 

 substrate type. As the rake is pulled along through 

 the sediments, clams, shells, and (if present) sea- 

 grass and debris are forced into the basket. When the 

 rake seems heavy enough to suggest a full basket, it is 

 removed from the water where the clams can be sort- 

 ed. Because of its longer (and extendable) handle, the 

 bull rake is often used from boats and can extend the 

 depth at which hand clammers can work effectively. 

 The bull rake used in this study (Fig. 1) weighed 8.6 

 kg, had a 1.8 m steel shaft and teeth 4 cm long, ex- 

 tending from a basket made of 0.7 cm steel rods 2.2 

 cm apart. 



Although other hand rakes are used by clammers 

 along the east and gulf coasts (including especially 

 the "Jersey" rake), we chose to test the pea digger 

 and bull rake because they fall at opposite ends of a 

 size spectrum. Of all commonly used clam rakes, the 

 pea digger is the lightest implement, has the fewest 

 teeth, and digs to the shallowest depths in the sedi- 

 ments, whereas the bull rake falls at the opposite ex- 

 treme for each of those three criteria. 



The Study Site 



Gear trials were conducted during June 1 98 1 in two 

 habitats along the southern (barrier island) margin of 

 Back Sound, near Beaufort, N.C. This general study 

 area and its physical environment are described in 

 several previous publications (Sutherland and Karl- 

 son 1977; Nelson 1979; Peterson 1982). Water tem- 

 perature was about 22°C during our study. Specific 

 sites were chosen in an unvegetated sand flat and a 



FISHERY BULLETIN: VOL. 81, NO. 2, 1983. 



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