Volume 19 Issue 2 MARCH/APRIL 2018
RESTOCKING
PROFILE
The Right Stuff How efforts by government agencies in California contributed to a record salmon return at the Mokelumne River Fish Hatchery BY MATT JONES
ast year was a good one for the Mokelumne River Fish Hatchery in Clements, California. Over 19,650 salmon returned to the hatchery, breaking the previous record of 18,000 set in 2011. Representatives for the East Bay Municipal Utility District (EBMUD) attribute the high numbers to specific steps taken on the river and in the hatchery to make conditions favourable for the salmon. One of the primary efforts has been river restoration, says Jose Setka, manager of fisheries and wildlife for EBMUD. A $1.3 million partnership between EBMUD, the California Department of Fish
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EBMUD intern Ryan Ham holds an alevin caught at a juvenile trap located seven miles downstream from Camanche Dam. The fish is measured, weighed and released farther downstream to avoid duplicate counting.
and Wildlife and the US Fish and Wildlife Service has seen roughly 75,000 cubic yards of gravel added to key spawning areas in the upper region of the usable area for salmon. These efforts brought the depth of the water to one to three feet - the salmons’ preferred level for spawning. The shallow water also creates higher velocities which the salmon prefer for making redds and depositing their eggs. “It’s returned a tremendous benefit in terms of continued on page 9
BY JUSTIN HENRY
arly maturation in net pen farmed salmon was identified as an economic liability decades ago, and can still be a problem today. The ability to improve salmon growing conditions using RAS has compounded this problem. Indeed, optimal culture conditions for salmonids in RAS is still not clear. That was the message from a few presenters during the Aquaculture Innovation Workshop (AIW) held in Vancouver, Canada last November. In particular, it is still unclear what environmental conditions will minimize early maturation in salmon grown to harvest size in RAS. Steve Summerfelt from the Freshwater Institute in Virginia,
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Manāki Whitebait: Breaking new ground with an old staple A unique New Zealand facility produces whitebait species which it sells commercially to fund restoration efforts. BY BEN NORMAND
RAStech
RAS Is For Girls
Giant Kōkopu embryo (Photo: Stephen Moore).
USA, presented a study by his group comparing maturation rates of two strains of Atlantic salmon grown in RAS under continuous light for 24 months post-hatch. In this trial the Gaspe strain grew faster, reaching 4 kg. However, a serious challenge for the RAS farmer became clear in that greater than 50% of the male St. John River strain fish matured early. The Gaspe strain were all females and no females matured from either strain. Could it be that RAS is just for girls? P R E C O C I O U S M AT U R AT I O N
Early maturing Atlantic salmon are called grilse, while early maturing Pacific salmon are called jacks (boys) or jills (girls). By the time the mature ones can be identified, the quality can be slightly or severely compromised, depending on how good the farmer is at identifying them early. During the maturation process pigment comes out of the flesh and pigment goes into the skin; oil content in the flesh decreases as energy goes into gonad production. When determining what percentage of the fish are maturing
f all the ways to hunt and fish, few are more quintessentially Kiwi than the act of gathering Whitebait. In New Zealand, Whitebait refers to the larval form of five Galaxiid species. These larval fish are caught as they return upstream from the ocean to continue growing and, eventually, to spawn. From August/September through the end of November, it’s rare to find a stream that flows into the ocean without someone standing watch over their whitebait net. To call it a popular Kiwi hobby is nearly an understatement. Across the country, however, recreational and commercial catches have been in decline. Of the five species one can catch, four are labelled by the New Zealand Department of Conservation as declining or threatened. This is due to a variety of factors including an increase in river and stream pollution from industry and farming, and the introduction of aggressively
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Male Atlantic salmon like these can mature prematurely in RAS. It is easier to prevent early maturation by using all-female stock.
early, the farmer must decide whether or not to grade out these maturing fish. Additional labour is required to grade, and there is an additional handling of the fish with the associated stress and reduced feeding. If the farmer decides to leave the fish and not grade, the quality of the maturing fish will continue to decline and they will start to die off. W H Y D O M A L E S M AT U R E E A R LY ?
Maturing a year or two earlier than the rest of their cohorts is one of the mechanisms used by salmon continued on page 13
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