Climate Change

Climate directly impacts ocean conditions.  Ocean temperature is one of the most important factors affecting the survival of young herring. Temperature directly controls the rates of the metabolic processes and in turn these affect, for example, swimming activity, enzyme activity, and digestion rate.  Warmer temperatures increase the rates of these processes and cause more larvae and juvenile herring to die.  Temperature also has indirect effects through, for example, changing feeding conditions and how predators are distributed. In British Columbia, warmer temperatures cause a shift in herring’s primary food: zooplankton.  In particular, the composition of the plankton shifts from large lipid-rich northern species to smaller, less nutritious lipid-poor southern species. Warmer temperatures also cause southern predators such as Pacific mackerel and hake that feed on herring, to become more abundant.

Temperature is not the only climate-related variable that impacts herring populations.  Wind speed and direction drive the upwelling of deeper, colder and nutrient rich ocean water to the surface.  Fuelled by sunlight, the nutrients drive phytoplankton and zooplankton growth which in turn influence the growth and survival of herring larvae.  When the combination of ocean temperature, wind, light, and salt content (salinity) are right, herring larvae can survive in strong numbers.

Additional climate related factors that may impact herring in the future are hypoxia (oxygen deficiency) related to ocean circulation, and acidification, which is related to increasing concentrations of atmospheric carbon dioxide (CO2).


Photo: Mark Wunsch

Friday, January 24, 2014