[6] DFO's Latest Ocean Report Good News For Salmon Numbers

The North Pacific ocean has cooled off considerably over the past couple of years, but just how much? A new report by Canada's Department of Fisheries and Oceans said the Gulf of Alaska in January was the coldest in the past 35 years.

"This local cooling was the global exception," says the report. The cooling has been good news for salmon and steelhead going to sea. The scientists expect improved survival rates for many Canadian stocks migrating to sea in 2008.

"Blame it on La Nina. (Or thanks to La Nina if you love coldwater fish)", said the report, which noted winter winds over the past couple of years have blown from a more westerly direction, rather than the more typical warm southwesterly.

A series of robotic buoys that periodically rise from the deep to measure and transmit temperature and salinity data showed an unexpected strengthening of the easterly bearing North Pacific Current and increased flow into the California Current "which may have contributed to cooling of near shore oceans observed through 2007."

But according to the report, weather systems weakened the mechanism that pushes warm water offshore, and led to warmer summer sea surface temperature on the outer coast from California to SE Alaska in 2007, which "was likely poor for local marine life."

However, in February 2008, sampling by a research ship found increased concentrations of nutrients and a deepened mixed layer in the ocean, similar to the pattern of the strong La Nina of 1999.

Zooplankton species shifted to cool-ocean types in 2007, from the warmer water species of the previous report, which means better food for young fish, and contributes to larger body size and higher energy content.

The report also noted that warm-water loving hake populations off BC have declined 27 percent since 2005--and closest to the lowest recorded biomass seen in 2001. That's more good news for salmon, since hake are thought to be a heavy predator of young migrants. The hake survey also found populations had scattered, which might be related to the reduced abundance of their preferred food--T. spinifera, small, shrimp-like crustaceans. The presence of jumbo squid may also have scattered hake populations, since squid like to eat them.

Sardines had spread farther into northern BC waters, helped by a strong year-class from 2003 when waters were warm.

But herring populations on the west coast of Vancouver Island are at historically low levels, and researchers didn't expect that trend to turn around until predator numbers declined from the change in ocean conditions.

The report also noted that sockeye returns in the Fraser were extremely low in 2007. The low returns were "almost certainly" due to the unusually poor ocean conditions in 2005 once the fish left the river, which were worse in Georgia Strait than offshore. Fraser stocks are less influenced by La Ninas and El Ninos than coastal stocks because they enter the ocean in more protected estuarine waters. But these waters warm up later and stay warmer longer than the ocean-which generally means a delayed adverse effect from El Ninos. Marine survival of the Chilko Lake sockeye in 2005 tied for the second lowest in more than 50 years of recordkeeping. The Chilko is the largest producer on the Fraser system.

But a funny thing happened on the way to the Gulf of Alaska. In another report published recently by Canadian fish scientists, they were happy to report, but truly mystified by the huge 2007 juvenile sockeye migration from the lake. At about 78 million smolts, that is about twice the previous highs in the mid-1990s. "Something truly mysterious began in 2005 that made Chilko Lake far more friendlier for sockeye salmon than normal."

They said at the lowest marine survivals they've even observed, the Chilko return would still be around one million fish. At average survival, it would be around 6 million, and if better-than-average, as they consider 2007 to be, "what a spectacular vintage it will be." -B. R.

The following links were mentioned in this story:

State of the Oceans - Pacific Region, Fisheries and Oceans Canada, July 31, 2008

2009 Vintage of Fraser River Sockeye Salmon: A Complex Full Bodied Red with Mysterious Bouquet

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