Why Release Salmon Smolt During the Day?

Question: I was listening to an outdoor radio show last weekend where the host was telling his audience that salmon smolts from Coleman and other Central Valley hatcheries were being released from the acclimation pens during daylight hours – into the maw of thousands of seabirds and other predators. The discussion was over why these smolts could not be released during darkness. First, is it true that they are being released at daylight? If so, why? If not, would it be wiser to release them in the dark, say two hours before daylight? I speculated that small fish would simply ball up until daylight for safety but perhaps releasing them at night is a good idea. Got an answer? (Frank G.)

Answer: Great question! This concept has actually been tested before and we’ve found from previous experience that releasing the fish at night serves no advantage for several different reasons. According to senior hatchery manager, Armando Quinones, here’s how this whole smolt transport, introduction and acclimation process works from the hatchery to the Bay …

First, the fish hatchery trucks are prepared with 1,200–2,800 gallons of fresh, cool, well-oxygenated water. Salt is added to the water to help calm the fish for the journey and to prepare them for introduction into brackish water. The smolts are then loaded into the trucks and driven to San Pablo Bay where there are two acclimation net pen sites. The tide cycle at that time of day will be the determining factor of which net pen is used.

The hatchery trucks then back up to the pens and each offloads their shipment. Up to six trucks may load into the net pens that have five different compartments. The pens are then covered with netting to prevent predation from any waiting birds, or the escape of any of the new possibly disoriented jumping fish. The fish are then allowed to settle and acclimate in the pens to the new water conditions for between one to three hours. Once the tides are right and flowing out to sea, the nets are towed out into the deep water channel, and the smolts released. By doing it this way, we have found the greatest survival success rate.

As for your question regarding why not to release the fish at night, previous studies with striped bass and other fish introductions have shown no advantage. Operating at night poses a safety concern for the staff and requires the use of big flood lights to be used when working in the darkness. Adding lights into the equation actually draws greater attention from any potential predators as they are then drawn in to see what all of the excitement is about. Many of the potential predators are nocturnal feeders, and by adding light to the operations, we’d actually be tipping them off and congregating them to the operation.

Maybe most important to this whole situation is that operations are going extremely well this year just as they are. We have successfully transported and introduced nearly 12 million smolts into the Bay to date, and our goal is to assure a survivorship and return of 1 percent of this total. A certain degree of mortality is inherent in any process but our greatest goal is to get these fish past all of the obstacles within the Delta system and the many water diversions that they would otherwise encounter.

Of course, we can’t control what happens once they get to the ocean. But, by giving them this extra advantage of getting them past many of the obstacles and assuring that they don’t get lost along the way from their natal streams, we’re giving these fish their best opportunity for survival. If all goes well and ocean conditions improve, we hope to see a bumper crop return of these smolts as spawning adults by 2011.

FYI:Statewide Free Fishing Days – June 7, 2008 and Sept. 27, 2008. The Department of Fish and Game wants to see more people out fishing, and so each year the Fish and Game Commission sets aside two days when fishing licenses are not required. On these two Saturdays only, everyone can give fishing a try without having to purchase a fishing license. Just remember, all regular fishing regulations still apply (such as bag limits, size limits, gear restrictions, fishing hours, etc.) and the appropriate report cards are still required for everyone fishing for abalone, steelhead, sturgeon, spiny lobster or salmon in the Klamath-Trinity River System. Free Fishing Days provide a great, low-cost way to encourage families, friends and everyone who’s interested in trying some fishing an easy opportunity to do so.

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Carrie Wilson is a marine biologist with the California Department of Fish and Game. While she cannot personally answer everyone’s questions, she will select a few to answer each week. Please contact her at CalOutdoors@dfg.ca.gov.

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