Seeding the Seedbeds: Enhancing oyster recruitment and production in Delaware Bay, USA.

Transcription

1 Seeding the Seedbeds: Enhancing oyster recruitment and production in Delaware Bay, USA. David Bushek Haskin Shellfish Research Laboratory Rutgers University Port Norris, NJ, USA Russell Babb and Jason Hearon Bureau of Shellfisheries New Jersey Department of Environmental Protection Port Norris, NJ, USA Bureau of Shellfisheries

2 Outline 1. General structure of Delaware Bay oyster fishery 2. Current problem of low recruitment on seedbeds 3. Demonstration project to use spat from high recruitment / high mortality zone 4. Preliminary results of large scale plantings

3 Washington DC The oyster fishery is viable, but struggling in Delaware Bay Delaware Bay Dredge boat fishery dependent upon natural production Chesapeake Bay

4 Oystering in Delaware Bay Seed Beds Leased grounds Seedbeds in the upper bay provide oysters for leased grounds and direct marketing

5 Round Island Upper Arnolds Arnolds Middle Cohansey Sea Breeze Ship John Shell Rock Bennies Sand Bennies Nantuxent Hog Shoal New Beds Strawberry Hawks Nest Beadons Vexton Egg Island Ledge Bed Mean All Beds Oystering in Delaware Bay Long-term ( ) Weighted Prevalence (Mackin Scale, 95% CI) (2004 only) Seed Beds Leased grounds MEAN 2004 Seedbeds in the upper bay provide oysters for leased grounds and direct marketing Disease (dermo) and predation increase with salinity

6 Oystering in Delaware Bay Seed Beds Leased grounds Seedbeds in the upper bay provide oysters for leased grounds and direct marketing Disease (dermo) and predation increase with salinity but growth and quality of oysters are better in higher salinity areas of the lower bay.

7 Oystering in Delaware Bay Seed Beds Leased grounds Seedbeds in the upper bay provide oysters for leased grounds and direct marketing Disease (dermo) and predation increase with salinity but growth and quality of oysters are better in higher salinity areas of the lower bay. Thus, oysters that are not direct marketed are planted on leased grounds to enhance growth and quality before harvesting oysters for market.

8 Problem: 5 years of low recruitment on seedbeds Unprecedented in 52 year dataset

9 Low recruitment has shifted size frequencies toward larger animals Shell Height (mm) No recruitment = Increase in mean size of oysters Market oysters have become more abundant with few small oysters to replace them

10 Purpose: Increase seedbed recruitment Industry choice: move oysters from authorization further up bay author Alternative: without move spat from high recruitment / high disseminate mortality zone in not lower baydo

11 July 2003: 20,000 bushels of surf clam shell (Spissula solidissima) planted to collect spat Methods September 2003: 16,000 bushels recovered with spat and planted on a 2.6 hectares on Bennies Sand seedbed 2004 to date monitored growth, dermo disease, mortality and abundance Monitoring not planned, afterthought

12 Surf clam shells were readily available from local processors. Methods A vessel is planting shell at site. A vessel is loaded with surf clam shells. Collecting monthly sample Planted shell contained nearly 1800 spat per bushel compared to 25 spat per bushel of natural set on site; a 75-fold increase

13 Fall 2005 ho riz Spring 2005 se m in at e w ith ou ta ut ho ra ut Summer 2004 D o no td is Fall 2003 at io n Results Planted oysters were easy to identify in monthly samples because surf clam shell is not native to the area.

14 Growth was excellent Growth was excellent Growth during 2004 and 2005 Clam Shell Plant Seedbed Average Planted oysters doubled in sized during Many are now market size. Shell Height (mm) Feb-04 Apr-04 Jun-04 Aug-04 Oct-04 Dec-04 Feb-05 Apr-05 Jun-05 Aug-05 Oct-05 Dec-05

15 Dermo Disease Dermo Disease Dermo Weighted Prevalence Feb-04 Apr-04 Jun-04 Aug-04 Oct-04 Dec-04 Feb-05 Apr-05 Jun-05 Aug-05 Oct-05 Dec-05 Clam Shell Plant Seedbed Average Dermo disease is lower on planted oysters Infection intensity (Mackin Scale 0 to 5)

16 Mortality Comparison Mortality Comparison R 2 = R 2 = Clam Shell Plant Seed Bed Average Feb-04 Apr-04 Jun-04 Aug-04 Oct-04 Dec-04 Feb-05 Apr-05 Jun-05 Aug-05 Oct-05 Dec-05 Box Count Mortality (percent) Mortality is generally lower than native set on the seedbeds

17 Estimated enhancement 16,000 bushels of clam shell planted 1800 spat per bushel = 28.8 x 10 6 spat Across 2.6 hectares = 1108 spat m -2 Mortality estimates predict 220 oyster m -2 remain as of August 2005 The 2004 stock assessment estimated about 20 oysters m - 2 across the seedbed region Thus, this planting has provided a 11-fold increase

18 Conclusions Shell planting, once a common practice by the industry, should be revitalized Spat from high mortality areas can be used to enhance production elsewhere This effort has generated state and federal assistance for a larger scale shell planting effort A portion of the effort involves utilizing lower bay recruitment, remainder is direct planting Shell resources are limited

19 New Efforts: 2005 Shell Planting Six direct plantings 1 Crushed surf clams 3 Dredged Maryland Oyster shell 1 Crushed Ocean quahog 1 Mixed quahog and Maryland shell Two lower bay plants Maurice River Cove Cape Shore surfclam

20 Preliminary 2005 Shell Planting Results Site Material Spat /bushel planted material Lower middle dredged MD oyster shell 49 Jigger Hill dredged MD oyster shell 130 Shell Rock (4) dredged MD oyster shell 265 Shell Rock (12) Maryland oyster + quahog = 537 Shell Rock (43q) ocean quahog 550 Shell Rock (43s) surf clam 512 Bennies Sand Cape Shore surf clam replanted 888 Maurice Cove surf clam 0 (fouled with Sabellaria)

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