Pacific herring, small, silver-coloured fish, are the most abundant fish species in Canada's Pacific coastal waters. About 500 linear kilometres of British Columbia's coastline turn milky-white every March and April, as a result of the herring's release of countless sperm around the eggs (roe) spawned on algal beds.
Pacific herring are central to the marine food web, contributing 30 - 70% to the summer diets of chinook salmon, Pacific cod, lingcod, and harbour seals in southern B.C. waters. Herring eggs constitute an important part of the diets of migrating seabirds and grey whales, as well as invertebrates.
Pacific herring are important to Native peoples, other Canadians, and Japanese as traditional food, delicacies, fishing bait, and food for zoos and aquariums.
Pacific herring spawn in coastal areas, requiring abundant algal beds and uncontaminated waters. Herring generally spawn annually beginning at age three. Survival and abundance of a herring year-class (herring born in the same year) vary considerably as a result of complex ocean factors, including predators.
Pollution and other coastal human stresses, particularly near coves, inlets, and estuaries, can destroy, contaminate or alter algal beds used by spawning herring, thus affecting herring survival and growth. However, it is often difficult to assess local pollution impacts on herring stocks because, although the herring return to spawn in the same general area each year, they do not always return to the same specific location.
Survival and growth of Pacific herring are sensitive to natural fluctuations in ocean climate and ecology. One of the more important natural factors is ocean temperature which influences herring survival and growth and alters the abundance of herring predators, principally Pacific hake. Waters off the West Coast of Vancouver Island undergo alternate warm and cool periods. Warm periods since 1976 have been intensified by strong El Niño events.
During these warm periods, survival and growth of young herring are weak due to the abundance of Pacific hake and the high water temperature, frequently associated with El Niños. Strong El Niño events further reduce young herring survival because large numbers of Pacific mackerel migrate north into B.C. waters and feed on herring, salmon, and other species during the summer. Conversely, survival and growth are relatively strong when the summer biomass of hake is low and the annual water temperature is cool, in the range of 10°C.
Natural predators, rather than the fishery catch, account for most herring mortality. The eight most abundant predatory fish off the West Coast of Vancouver Island consume approximately six times the average annual herring fisheries harvest.
A combination of intense harvesting pressure and unfavorable ocean conditions may create a crash in herring stocks. An example of this occurred in the mid-1960s, when the abundance of all herring stocks in British Columbia underwent a drastic crash. Conservative management of the herring harvest lessens the combined effects of environmental factors and commercial fishing on herring abundance. This, in turn, enhances the long-term sustainability of the Pacific herring resource.
Herring Spawn Video Survey
Ocean Ecology has been using their benthic video camera technology to observe herring spawn deposition. This work is a part of a number of research projects funded by the Herring Conservation and Research Society (HCRS; see link) for the purpose of supporting the conservation and management of Canada's Pacific Herring resources and the sustainability of herring fisheries. In 2009, an experimental survey method for herring spawn was developed ("Big Bay Experimental Herring Video Survey"). A summary of the work was presented to HCRS at their September 23, 2009 meeting (see link). Further research was carried out in 2010, including trial studies using a high defintion drop video camera system ("2010 Experimental Herring Video Survey Final Report").
In the above video clip, the herring spawn is visible as white patches and traceries on the kelp blades, and as small round clusters on stringy seaweed. Two red laser dots are visible, and can be used to estimate the size of objects in the video, as the distance between the dots is always a constant 4 cm.