Helping farmers through a mass mortality event

Oysters in a machine

At SED Graders, we know that oyster farming isn’t easy work. So, when you have a mass mortality event that affects your crop, it can be a stressful threat to your farm… and your income.

We’re proud to be part of the solution with our SED water grader and oyster grading systems that not only reduce the highly labour intensive work of grading oysters, but also reduce mortality rates.

Here, we touch on the significant impact of Pacific Oyster Mortality Syndrome on Tasmanian oyster farms and how we were able to provide an innovative and effective solution to a mass mortality event.

Bunch of Oysters

The impact of a mass mortality event


In December 2015, Southern Tasmania was hit with an outbreak of Pacific Oyster Mortality Syndrome (POMS).

POMS is a disease that only affects Pacific Oysters (Crassostrea gigas) and is caused by a virus called OsHV-1 micro variant.

Oyster mortality resulting from this disease can be very rapid. This led to a control area for the entire state of Tasmania. As a result of POMS, oyster farms reported devastating losses ranging from 10% to 90%.

The oyster farming community needed to find ways to recover from the sudden threat to their industry. While several strategies emerged, they were not enough to help farms in the short term as finances were hit, including loss of income and cash flow, restocking costs and a lack of replacement stock as the hatcheries were also affected.

This meant that while farmers, for example, may have half of live oysters left in their system, the extra cost of labor in recovering them by hand is prohibitive at a time of lost income and cash flow. In past mass mortality events, a loss of 50% represented a 100% loss to the farmer as the cost of the live recovery was higher than the sale price, so all oyster batches affected would be discarded.

Basket of Oysters in a warehouse

Our innovative SED water grader


The solution was to select the live oysters from the dead stock with a grader as they grew. Unfortunately, they found that the remaining live oysters were stressed and any rough handling would result in more losses. This ruled out using traditional grading systems such as shaker or dry barrel.

Fortunately, the SED water grader was designed for gentle handling, so Tasmanian oyster farmers with access to one were able to save most of their remaining incredibly stressed oyster crop. The gentle action of the underwater grading successfully graded out dead oysters, allowing the remaining live oysters to be on-grown and sold.

The SED Water Grader uses the way juvenile oysters behave underwater to gently grade, with far greater consistency. This removes oyster stress caused by traditional barrel and shaker graders as well as the high cost and laborious work of hand grading.

Shellfish equipment inside a warehouse

Dramatically reducing mortality rates


Developed in partnership with local oyster farmers, the SED Water Grader dramatically decreases handling damage and reduces mortality rates to as low as 1.5%.

In fact, the main hatchery in Tasmania reported that their previously recorded mortality rate of 20% across their 1.5 – 25mm seed and juvenile oysters dropped to less than 1.5% after installing the water grader.

Man standing beside an equipment inside a warehouse

Fast and efficient


The SED Water Grader protects your bottom line by increasing your potential oyster output and reducing labour costs. On average, the largest model machine (pictured) grades up to 200,000 20-30mm oysters per hour.

Fully automatic, the SED Water Grader frees oyster farmers and workers from the laborious task of grading. A single operator is required to fill the hopper or seed table. Oysters are then automatically sorted underwater into three sizes.

Finally, the SED Water Grader delivers the oysters to collection points via three small conveyors. Most farms then use the SED bagger to refill baskets to on-grow. It’s really that easy.

Are you ready to make every oyster count and reduce mass mortality rates? Find out more about our productivity-boosting oyster graders and equipment. Contact the team at SED Graders today.

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