Seines solve process challenge for hatchery staff
June 5, 2020 By Chuck Pratt
The growing popularity of circular tanks in aquaculture has many traditional raceway fish culturists perplexed when thinking about crowding fish for sampling and transfer activities.
Staff at the William Jack Hernandez Sport Fish Hatchery have worked through this conundrum: progressing from three panel crowders to purse seines. Steady improvements in technique and tools have now made it possible for one person to easily seine a 26-foot tank.
In 2011, during the initial phase of the Hernandez Hatchery operations, culturists built three panel crowders for use in the 26-foot diameter by six-foot deep tanks, of which there are 31 in the hatchery. The crowders proved cumbersome to move around the production floor into the tanks. Once in the tank, crowding and pumping the first 90 percent of the population worked well. But removing the last 10 percent was frustrating and time-consuming.
Hatchery staff worked with Christiansen Net Works to develop seines with the proper mesh size for the smolt and catchable production areas. Improvements included pole pockets on the seine ends to aide in controlling the seine around the tank and prevent fish from escaping between the seine and the tank walls. A red cork installed at the center of the seine helps to maintain a symmetrical bag when pumping.
Over the years, staff have learned techniques and added tools to make the seining process smooth and efficient. Seining the tank in the direction of the current allows the culturist to easily guide the seine around the tank. After sampling, releasing fish by opening the upstream side of the seine allows the fish to swim away calmly. Clamp on pole handles for leverage while trying to keep the seine tight against the tank improved ergonomics. The judicious use of a plunger helps to move fish away from the seine edges into the bag. For smolt, adding pool noodles to the middle section of the corks minimized fish loss over the top of the seine between the corks when pumping from a tight bag.
A pole bracket clamped to the side of the tank holding the purse end of the seine is by far the biggest improvement. Now, one person is able to seine a tank. The bracket slides over the seine pole and holds the stationary end tight against the tank while a culturist circles the tank with the net. Once the purse line is pulled, the clamps holding the bracket are released, poles pulled up then rings pulled over the side to complete the set.
The crowders now rest against the wal, not having been used in years. Seines are used exclusively in all tanks now – 10 feet, 16 feet and 26 feet diameter. Culturists now can’t remember how vexing this operational challenge was or how the initial surge of cold water into leaky raceway waders previously felt.
Chuck Pratt is a supervisor in the broodstock development center at the William Jack Hernandez Sport Fish Hatchery of the Alaska Department of Fish and Game in Anchorage, Alaska.
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