FEATURES 



WILLAPA OYSTER STUDIES-USE OF THE PASTURE HARROW 

 FOR THE CULTIVATION OF OYSTERS 



By Clyde S. Sayce^'^ and Charles C. Larson** 



The EnglisJi pasture harrow is used in oyster cultivation to break apart and scatter clusters of oysters. 

 It is also used to prepare oysters for harvest by loosening them from the substrate and removing fouling 

 growth. An area of the Long Island Oyster Reserve, Willapa Bay, Wash., was divided into a control and 

 three lanes to test the effect of the harrow upon Pacific oysters (Crassostrea qigas j^ The control was un- 

 dragged, lane 1 was dragged once, lane 2 ten times, and lane 3 three times. Condition of samples of 

 oysters was determined for each lane every week during dragging and once each month for 6 months 

 after completion of the experiment. The experiment showed that Pacific oysters spawned shortly after 

 being dragged while undragged oysters spawned later. Total mortality of oysters dragged 10 times was 

 no higlier than that of oysters dragged once only. Dragging oysters once and 3 times increased Pacific 

 oyster spatfall 3 and 5 times, respectively, but dragging more than 3 times did not increase spatfall 

 further. 



INTRODUCTION 



Farm harrows, both disc and tooth, modified plows, and oyster and clam dredges have 

 been used in Long Island Sound, New York, to aid the cultivation of oysters by burying oyster 

 drills. In the gradual mechanization of the oyster industry of Willapa Bay, Wash., straight- 

 tooth drags, spring-tooth harrows, and tractor harrows were tried and discarded while the 

 pasture harrow has been used most successfully in cultivation of Pacific oysters (Crassostrea 

 g igas) . 



The commercially available English pas- 

 ture harrow is used by farmers to break up 

 dirt clods in pasture leveling. This harrow is 

 formed of triangular-shaped linkages with a 

 4 -inch long tooth at the base of each leg. The 

 legs are about 8 inches long and adjacent links 

 are held together by a loop at the apex of the 

 triangle and rings at each leg. This arrange- 

 ment gives a loose linkage of triangles made 

 of ^-inch diameter rod with 4 -inch teeth 

 spaced 4 to 6 inches apart; rows are 6 to 7 

 inches apart (fig. 1). The toothed harrow sec- 

 tion is 10 feet wide and 6 feet long, has a total 

 length of 10 feet, including weights and towing 

 bar, and has a total weight of about 250 pounds. 

 (Fig. 2). 



-Detail of the linkage of teeth of the English pasture harrow. 

 (Photo by C. S. Sayce) 



The first use of this harrow in Willapa 

 Bay was to break apart clusters of growing 



*Fisheries Biologist, Washington Department of Fisheries, Willapa Shellfish Laboratory, Ocean Park, Wash. 

 **Assistant District Biologist, Alaska Department of Fish and Game, Juneau, Alaska, 

 Note: The material for this article is from the overall Economic Development Administration (EDA) Technical Assistance Project 



No. 627, Oyster Research, Pacific County, Wash., performed under Bureau of Commercial Fisheries Contract No, 14-17-0007-218. 



U. S. DEPARTMENT OF THE INTERIOR 



Fish and Wildlife Service 



Sep. No. 772 



21 



