Oyster Harvest at Kouei Suisan

October 26 was the first day of Oyster Harvest in the town of Murotsu, near Himeiji City, Hyogo Prefecture. We visited Mr. Koichi Isobe’s oyster farm – Kouei Suisan –June 1st of this year (see Blog Post 6 Kouei Suisan: An Oyster Farm on Japan’s Inland Sea). We returned to the farm on August 1st to check the oysters’ growth and again on October 26, the first day of oyster harvest (Photos 1 & 2).

Photo 1: The Isobe Family in front of their waterfront oyster facility, Kouei Suisan, August 1, 2011. Their teenage daughter studies English and would like to visit America. Ami and Marina came along to learn about oyster farming.

Photo 2: Sign at roadside stand in Murotsu: ‘Oyster Harvest Begins October 26’.

When we visited Isobe-san June 1st, he had just finished putting out his oyster ‘seed’ – approximately 8-10 million baby oysters. The oysters were attached to scallop shells (30-40 per shell) that were suspended on ropes (25 shells per rope) and hung from rafts (1,000 ropes per raft, on ten rafts). These ‘seeds’ were actually 9-10 month old oysters, 2-3 mm long (0.1 inches). They had grown to 10 mm (0.4 inches) after just a few weeks at Kouei Suisan, where the water temperature June 1st was 23OC (73.4OF, see Photo 3). At this time, the oyster rafts floated high in the water and were anchored close to shore to avoid storm damage (Photo 4).

Photo 3: Oysters on June 1, 2011 had already reached 10 mm in length.

Photo 4: On June 1st the oyster rafts were anchored close to shore to avoid typhoon damage (compare to Figure 10). The rafts floated high in the water at this time (compare to Figures 6, 7 & 11).

By August 1st, the water had warmed to 33 C (91.4 F) and the oysters had grown to 60-90 mm (2.4-3.6 inches; Photo 5). The rafts had submerged 125 mm (5 inches) since June, due to the greater weight of the oysters (Photos 6 & 7). The warm, nutrient rich water supports a rich ‘soup’ of plankton, the oysters’ food. Many other organisms compete for plankton and may grow on the oysters (see Photos 5 & 8). These fouling organisms are particularly common on the outermost lines of each raft. By comparison, oysters on the second row of lines grow faster. They have good access to plankton, but without so many fouling organisms. Because these outer rows of oysters grow faster, they are the first to be harvested. As the outer oysters are removed, the oysters toward the middle of the raft have better access to plankton and eventually will grow to market size. Thus, oysters can be harvested over several months.

Photo 5: Oysters on August 1, 2011 were 60-90 mm in length. There are approximately 30 oysters attached to the scallop shell at the center of this cluster. Note the many fouling organisms attached to the oysters, particularly the light brown ‘sea squirts’ (tunicates).

Photo 6: Isobe-san with a rope of oysters. The oysters are attached to scallop shells. Note the position of the raft relative to the water (compare to Figures 4 & 11).

Photo 7: Isobe-san measures the height of the raft relative to sea level. The raft had submerged 125 mm (5 inches) since June 1st.

Photo 8: Many organisms grow on the oysters. These fouling organisms include seaweeds (green algae visible here), anemones, and many competing types of plankton feeders such as tunicates, barnacles and mussels.

Isobe-san pointed out the open shells of his oysters in the water (Photo 9). These ‘smiling faces’ indicate healthy oysters: feeding and breathing. In bad conditions, oysters will ‘clam up’, stop growing, and may die. In 2009, Isobe-san lost 70% of his oysters in late July and early August, the most dangerous time for oysters. Red tides (blooms of toxic plankton) can poison oysters and deplete the water’s oxygen; typhoons can damage the rafts and dump too much freshwater into the sea. The government tests the water weekly for toxic plankton and other contaminants. As of August 1st, conditions had been good, but Isobe-san was still concerned about the next two weeks.

Photo 9: These oysters have partly open shells (note the black lines at the bottom of the photo), a good sign for oyster farmers. Oysters move water over their gills to breath the oxygen, and to filter feed on the plankton. Also visible are the many ‘open mouths’ of fouling organisms attached to the oysters.

During the early summer, oyster rafts are kept close to shore, to protect them from typhoons. At the end of typhoon season Isobe-san moved his rafts further offshore to deeper water (see Photo 10). At this time, his oysters were well established and he expected them to grow well until harvest.

Photo 10: Oyster rafts were moved offshore after typhoon season. This picture was taken October 26, the first day of oyster harvest (compare to Figure 4).

We returned to Kouei Suisan on the first day of harvest, October 26th.  Isobe-san began work before dawn, headed out to his rafts, and hauled in 60 ropes laden with oysters. He harvested 12 ropes of oysters at a time (see Photos 11-14). Oysters were stripped from their ropes by force of gravity and a special winch that dropped them onto the boat deck, followed by a mechanical stripper (Photos 15 & 16). The oysters were collected in a net, rinsed in the ocean, and then brought into port (see Photos 17-19 and Video: Oyster Harvest).

Video: Twelve ropes of oysters are moved from the raft to the boat. The oysters are dropped onto the dock to knock them off their ropes (four drops in total, not all shown in video). Any remaining oysters are stripped from the ropes mechanically. The oysters are collected into a net and rinsed in the ocean (four times).

Photo 11: The man on the raft gathers 12 oyster lines for pickup by the boat. Note that the raft is partly submerged due to the increased weight of the oysters.

Photo 12: On the boat, Isobe-san prepares a net to hold the oysters.

Photo 13: Isobe-san begins to pull the oyster out of the water.

Photo 14: The oysters are dropped onto the deck to knock the oysters off the ropes. Isobe-san repeats this process for a total of four drops.

Photo 15: Isobe-san removes any remaining oysters from the ropes.

Photo 16: After all the oysters have been removed from the ropes, they are gathered into a net, and then rinsed in the ocean.

Photo 17: The net full of oysters is dumped into the ocean to rinse off fouling organisms, silt, and broken shells.

Photo 18: This photo was taken a moment after Figure 18. Note the difference in the water between these figures. Isobe-san rinsed the oysters four times before bringing the harvest to shore.

At the dock, oysters were offloaded and brought into the facility for processing (Photos 20 & 21). Here, the oysters are carried on a conveyor belt for initial inspection – the best looking shells are pulled aside for seru gaki (see below). Most oysters continue on to a metal basket and washing machine that mechanically removes fouling organisms and washes off the waste. After a third washing, the oysters finally enter the facility for shucking.

Photo 21: A forklift brings the oyster bin to the conveyor belt where the oysters will be sorted.

Inside the facility, 7 women and 3 men sat around a large table piled high with oysters (Photos 22 & 23). They shucked from morning to evening. Isobe-san and his wife also shucked oysters when not busy with other tasks (see Video: Oyster Shuck). Shucking is still done by hand, and this crew was fast. We visited just after lunch; at that time one shucker had finished her third case of 4 kg (8.8 pounds) – nearly 600 oysters. Once shucked, oysters enter a separate conveyor system for a final wash and bagging.

Video: Isobe-san demonstrates how to shuck oysters.

Photo 22: A busy crew shucked mountains of oysters from just after dawn until dusk.

Photo 23: To shuck an oyster, a knife is inserted between the two shells and cuts the adductor muscle.

As mentioned earlier, the best looking shells were pulled aside for seru gaki (shell oysters). One man cleaned these shells with an electric brush to remove chips and fouling organisms (see Photo 24). These shells were then placed into baskets and will be hung from rafts for another few weeks (Photo 25). Seru gaki will be sold at a premium to restaurants and opened to order: oysters on the half shell.

Photo 24: This man cleans the seru gaki (shell oysters). These oysters were picked because their shells were relatively intact and clean of fouling organisms. An electric brush is used to further clean them of debris. They will be placed in special baskets and put back into the ocean for a few weeks before being sold to restaurants for oysters on the half shell.

Photo 25: Baskets filled with seru gaki (shell oysters).

Isobe-san was very excited about this year’s harvest. When we arrived, he took us back out to his rafts and harvested an additional 24 lines of oysters, so we could photograph the process (source of the earlier photos & video, and Photo 26). The rafts had submerged another 150 mm (6 inches) since August, and the oysters were now 100-150 mm in length (4-6 inches) more than a ten-fold increase in five months (see Photo 27). Those still in the water will continue to grow up to 200 mm (8 inches) before the last are harvested in early spring. It is an exceptionally good year and Isobe-san plans to be busy. He will work today until 6:30 or 7:00 PM, and be back at 1:30 AM. He will sleep 5 hours each night through the harvest, and he expects to take only two days off – for New Years – between now and April!

Photo 27: Harvested oysters in the net, October 26. These oysters ranged in size from 100-150 mm (4-6 inches), a 1000% increase in 5 months (compare to Photo 3).

As mentioned in the earlier blog, Isobe-san really enjoys his oyster farm. Moreover, he values natural resources and cares for both the sea and land around him. He washes his empty oyster shells and sells them to farmers for fertilizer. In the offseason, he cleans up any shells or other debris that might fall from his rafts.  Isobe-san is a gracious host. He welcomed us on several visits, and the girls in August (Photo 28). He sent us back to Kyoto with two beautiful bags of his pride and joy. We eagerly enjoyed them, washed down with amber Yebisu (see Photos 29 & 30).

Photo 28: Ami and Marina visit Kouei Suisan on August 1st, 2011.

Photo 29: Two freshly packed bags of namakaki (raw oysters) from Kouei SuisanSeto Naikai (Inland Sea), Japan.

Photo 30: A plate of fresh oysters with green onions and ponzu sauce, courtesy of Kouei Suisan, accompanied by a can of amber Yebisu, Sapporo Brewery.

This entry was posted in Japan Sabbatical by Robert Reavis. Bookmark the permalink.

About Robert Reavis

I study fish behavior and marine ecology through direct observation while diving. I also teach General Biology, Marine Biology, SCUBA and Scientific Diving at Glendale Community College. This year (2011-2012) I will be in Japan to study Traditional Fisheries and Modern Environmentalism.

One thought on “Oyster Harvest at Kouei Suisan

  1. Pingback: Season’s Greetings: Autumn in Kyoto | Glendale Community College Blog

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