Assessment of factors leading to oyster mortality in Tracadie Bay (NB) and development of physical and biological tools for management

Description

In August 2016, significant mortality of up to 75% of suspended oysters in some leases occurred in the northern branch of Tracadie Bay. Field observations were consistent with an anoxic event (i.e., water conditions characterised by an absence of dissolved oxygen and elevated hydrogen sulfide levels in the water conditions) caused by the eutrophication of the ecological system through an increase in nutrient concentration. As eutrophication is a major threat globally, it is important to increase knowledge and understanding of how productivity of cultured stocks might be impacted by the ecosystem in which they exist, and of how aquaculture operations impact the ecosystem.

The objectives of this project are to: 1) develop a hydrodynamic model capable of reproducing current flow patterns within Tracadie Bay; 2) determine areas within the bay that are at risk of hypoxia; and 3) determine thresholds of effect of anoxia, hydrogen sulfide and temperature on cultivated oysters using a combination of field and laboratory work. Together, field and laboratory work will provide powerful tools for managing Tracadie Bay and other shellfish aquaculture areas for the foreseeable future. The hydrodynamic model, in conjunction with the spatial assessment of organic content and benthic flux, will help identify areas at risk of nutrient-induced impacts.

While the capacity to predict areas at risk of impact is useful for management, it is also directly applicable for shellfish growers and their operations. Ultimately identifying thresholds of oyster survivorship will provide baseline information for early warning signs and, potentially, indicators for growers to take action in the event of a future anoxic event. Findings from this work also will be of relevance for other fixed gear aquaculture around the world, resulting in an increase in scientific capacity of the aquaculture industry.