State of physical, biological, and selected fishery resources of Pacific Canadian marine ecosystems in 2009
Monitoring the physical and biological oceanographic conditions and fishery resources of the Pacific Region is done semi-regularly by a number of government departments, to understand the natural variability of these ecosystems and how they respond to both natural and anthropogenic stresses. This eleventh report of an annual series updates the state of physical, biological, and selected fishery resources of Canadian Pacific marine ecosystems.
One of the biggest stories for 2009 was the return of far fewer Sockeye salmon than expected. Accurately forecasting salmon returns is difficult as there are few observations of salmon between the time adults spawn in fresh water, and the time the next generation returns to British Columbia waters. Scientists base predictions of numbers of returning adult Sockeye salmon primarily on the empirical relationship between stock size (spawners, returns, or smolts depending on the stock) and consequent recruitment. For 2009, the forecast indicated there was a 90% probability the total run would be between 3.5 and 37.6 million Sockeye, yet the actual number was less than 2 million. Efforts to incorporate ocean indices to improve forecast performance were examined, and show promise for certain stocks; however, not Fraser River sockeye salmon at this time.
Ocean temperatures off the west coast on Canada were cooler than normal at the beginning of 2009 but warmed through the summer and autumn. By early 2010 most regions along the American and Canadian west coast were above normal in temperature. The shift from cool to warm is likely in response to a change from La Ni a to El Ni o conditions in the tropical Pacific and a shift in ocean temperature patterns all across the North Pacific Ocean, called the Pacific Decadal Oscillation. The North Pacific Current has declined in strength from its peak flow in 2008. This eastward current splits into a northward flowing Alaska Current and southward flowing California Current, when it approaches the west coast of North America. The Alaska Current flow, in 2009, was the strongest in the eight years of continuous observations provided by the International Argo Program.
Zooplankton are small animals drifting in the ocean’s currents. The type of zooplankton available is thought to determine the growth and survival rates of juveniles of many endemic marine species. Species off the coast of Oregon and British Columbia, in the spring of 2009, were dominated by cool water groups that might be a better food source for endemic (native) marine life. These cool-water zooplankton dominated for the past three years of cooler ocean temperatures, although the dominant groups shifted to warm-water species in late summer 2009, along the outer continental shelf of southern Vancouver Island. Perhaps in response to the dominance of cool-water zooplankton in spring and early summer, many endemic species of seabirds on Triangle Island and in Pacific Rim Nature Preserve successfully raised chicks. Pink (smooth) shrimp numbers off the west coast of Vancouver Island increased in the May surveys of 2008 and 2009, from very low levels during 2004-2007. Such increases appear related to colder water when the shrimp were young, and to low abundances of Pacific hake. Many juvenile salmon from the Columbia River and west coast of Vancouver Island were larger in size or more numerous, or both, through spring and early summer of 2009, but their growth rates through summer and early autumn were low. Biomass of adult herring off Vancouver Island were low, attributed to several factors, including warmer ocean temperatures prior to 2007, when these adults were young and most sensitive to ocean temperatures and to the predators and prey associated with these conditions. Catches of Albacore tuna in Canadian waters, in 2009, were lower than average, attributed to these cooler ocean temperatures. As noted above, several species along the west coast of Vancouver Island appear sensitive to interannual changes in ocean temperature; elsewhere this link is not as clear, and the timing of spring conditions or presence of predators might be more relevant. For example, herring in the Strait of Georgia are relatively high in number and year-to-year changes in their biomass does not follow changes in temperature.
Humboldt squid appeared off the west coast in record high numbers in 2009. They were most abundant at several hundred metres depth, just seaward of the continental shelf among schools of Pacific hake, and were likely feeding on hake. Many of these squid were also observed closer to shore, and scores were found dead on west coast beaches. The biomass of Pacific hake off the Canadian coast seemed low, but assessment was difficult due to the many squid also observed among them.
Several highlights are specific to the waters of central and northern British Columbia, which form the Pacific North Coast Integrated Management Area (PNCIMA). This region warmed later in the year than the Oregon, Washington and southern British Columbia coasts. Zooplankton species here also continued the dominance of cool-water groups. There are three stocks of herring in PNCIMA, and the biomass of adults of all three stocks is relatively low. Their biomass might increase if hake numbers remain low. The abundance of central and north coast Chinook salmon seems to be rebounding, from a low in 2008.
Surface temperatures were generally above normal at most lighthouse stations in 2009 in the Strait of Georgia and Juan de Fuca Strait, but below the surface the waters remained relatively cool. Very high concentrations of phytoplankton were observed during the ship-based survey in April in the Strait of Georgia and in summer in Juan de Fuca Strait. Both were dominated by diatoms, as is normal for these regions. Satellite observations provide estimates of the concentration of phytoplankton at the ocean surface, when ship-based sampling is unavailable. These satellite observations reveal that when a plankton bloom appears very early in the Strait of Georgia, it is often associated with a bloom that is found in Malaspina Strait and also in Jervis Inlet. When viewed from space this bloom sometimes takes on the shape of a dragon, and it has acquired the name “Malaspina Dragon.” These satellite measurements became available in 2001, and the Dragon appeared in 2005, 2008, and 2009.
Finally, measurements of contaminants in cores from the bottom of the Strait of Georgia reveal past changes in the relative concentrations of contaminants in this region. Most contaminants that have been banned for many years, such as lead in gasoline and PCBs, are declining in concentration. In contrast, the concentration of flame retardant polybrominated diphenyl ethers (PBDEs) is increasing rapidly in sediment, despite its recent ban in Canada.