PCSGA Tidings

The rapid growth of the oys­ter aqua­cul­ture indus­try in Rhode Island has raised ques­tions about how many oys­ter farms Nar­ra­gansett Bay and the state’s salt ponds can sup­port. But a study by a Uni­ver­sity of Rhode Island grad­u­ate stu­dent has found that these ecosys­tems can with­stand con­tin­ued high rates of aqua­cul­ture growth with­out caus­ing eco­log­i­cal harm.

Car­rie Byron, a doc­toral stu­dent in the URI Depart­ment of Fish­eries, Ani­mal and Vet­eri­nary Sci­ence, exam­ined the eco­log­i­cal car­ry­ing capac­ity of the waters that cur­rently con­tain leases for oys­ter aqua­cul­ture in the state, includ­ing Nar­ra­gansett Bay and five South County salt ponds.

‘The farms are part of a greater ecosys­tem, and we want to make sure the whole sys­tem remains healthy,’ said Byron, a native of Mans­field, Mass. ‘The affect of the oys­ters doesn’t stop at the farm bound­ary — it extends from the bac­te­ria in the sys­tem to the birds and the top preda­tory fish. We iden­ti­fied all those key species that are active play­ers in the system.’

What she found was that Nar­ra­gansett Bay could sup­port the growth of 1.3 tons of oys­ters per acre, whereas just .002 tons of oys­ters per acre are cur­rently being har­vested from these waters. The car­ry­ing capac­ity of the salt ponds is 3.2 tons per acre, and farm­ers now har­vest about .05 tons per acre.

At present farm­ing den­sity rates, this means that nine per­cent of the sur­face area of Nar­ra­gansett Bay and 46 per­cent of the sur­face of the salt ponds could be leased for oys­ter aqua­cul­ture before the waters would suf­fer adverse effects. Less than two per­cent of these waters are being used for aqua­cul­ture today. State aqua­cul­ture reg­u­la­tions indi­cate that no more than five per­cent of the sur­face waters of the salt ponds can be leased for aquaculture.

‘I was expect­ing to be sur­prised by my results, but it was still sur­pris­ing,’ Byron said. ‘I knew there was a lot of food out there for oys­ters, but I didn’t know there was that much.’

The major dif­fer­ence between the car­ry­ing capac­ity of the Bay and the salt ponds is due to the quan­tity of zoo­plank­ton in the waters.

‘Zoo­plank­ton in the Bay are very heavy graz­ers on the same food the oys­ters eat, so there is com­pe­ti­tion for that food,’ Byron said. ‘Zoo­plank­ton come into the Bay from the ocean, and they are not com­ing into the ponds nearly as much, so there is less com­pe­ti­tion for food in the ponds.’

Byron noted that Rhode Island’s aqua­cul­ture indus­try, while small com­pared to other parts of the world, has great poten­tial for con­tin­ued growth due to the abun­dance of micro­scopic organ­isms upon which the oys­ters feed.

By com­par­i­son, she said that the car­ry­ing capac­ity of oys­ter aqua­cul­ture in New Zealand, which has a very large aqua­cul­ture indus­try, is just 0.3 tons per acre, far below the 1.3 and 3.2 tons per acre in Rhode Island waters. Accord­ing to a study pub­lished five years ago, New Zealand farm­ers har­vest oys­ters at a rate of 0.1 tons per acre, about dou­ble the rate as in Rhode Island.

Byron’s study is the result of con­cerns expressed over the high rate of growth of the aqua­cul­ture indus­try in Rhode Island. An aqua­cul­ture work­ing group con­vened by the R.I. Coastal Resources Man­age­ment Coun­cil requested the study to enable the group to make rec­om­men­da­tions about how best to man­age the industry’s growth.

Byron said that there are other issues besides the eco­log­i­cal car­ry­ing capac­ity that reg­u­la­tors must address when deter­min­ing the future of the indus­try, includ­ing con­flicts with other users of state waters, but her study is an impor­tant first step.

‘This is likely the most detailed sci­en­tific deter­mi­na­tion to date of eco­log­i­cal car­ry­ing capac­i­ties for shell­fish aqua­cul­ture for a large estu­ary and coastal lagoons any­where in the world,’ said Barry Costa-Pierce, direc­tor of Rhode Island Sea Grant and Byron’s advi­sor. ‘Car­rie has com­pleted not only a mas­sive exer­cise in data min­ing and mod­el­ling, but also trans­lated these find­ings to a very engaged, statewide group of stake­hold­ers. Her results will impact shell­fish aqua­cul­ture devel­op­ments locally and globally.’

Source: Uni­ver­sity of Rhode Island

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