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Climate Variability & Marine Fisheries

How Does Climate Variability Affect Fish Populations?

Marine ecosystems are not in a steady state, but are affected by the environment, which varies on many spatial and temporal scales. Fish populations respond to the variation in different ways. As examples, during short term weather changes such as storms, fish may take refuge from rough conditions through minor changes in distribution. Interannual or El Niño scale changes in the ocean environment may result in changes in the distribution patterns of migratory fishes and can affect reproduction and recruitment in other species. Decadal and longer scale variations may have other impacts, potentially including cyclic changes in the production level of marine ecosystems in ways that may favor one species or group over another. Scientists at the Pacific Fisheries Environmental Laboratory and their collaborators strive to understand how these mechanisms work and to incorporate this knowledge into the management and conservation of the nation's living marine resources.

Temperature is one way we measure ocean variability, but temperature is also an indicator of more complex ocean processes. Changes in temperature are related to alterations in oceanic circulation patterns that are affected by changes in the direction and speed of the winds that drive ocean currents and mix surface waters with deeper nutrient rich waters. These processes in turn affect the abundance and variety of plankton which are food for small fish. The biological responses to those ocean processes are complex and not well understood.

Most fish species have a fairly narrow range of optimum temperatures related both to the species basic metabolism and the availability of food organisms that have their own optimum temperature ranges. Depending on the species, the area it occupies may expand, shrink or be relocated with changes in ocean conditions. Some small pelagic fish, such as sardine and whiting, migrate seasonally between southern California breeding grounds and southern British Columbia feeding grounds and the length of these migrations is affected by climatic variations. Some resident fish such as rockfish do not make alongshore migrations but they may move into deeper cooler water during periods of warm water. El Niño and other longterm climatic variations have marked affects on both resident and migratory fishes.

Long-term records of the abundance for most species are limited to historical commercial and recreational landings. These records are often influenced by economic factors such as the relative price paid for different types of fish, and changes in fishing methods or fishing effort. These non-climatic factors often obscure climate related trends in fish abundance. Most studies of variations in ocean climate and their relationships with fish abundance have been on inter-year time scales, such as El Niño and La Niña cycles and the North Pacific Decadal Oscillation. We can only speculate at what prolonged warming over the next century could bring, and our best guesses would be based on the types of variability in fish observed in the inter-year and decadal scales.

Here are some examples of the response of different species to climate variability:
shim Short-term Changes -- El Niño Scale
shimshim Temporary Changes in the Distribution of Warm Water Fish During El Niño Ocean
Warming Events -- (US West Coast)


Reduced Catches of Squid During El Niño Warming Events -- (California)

shim Intermediate to Decadal Scale Changes

Collapse of Anchovy Fisheries and the Expansion of Sardines In Upwelling Regions -- (Worldwide)

shimshim Reduced Abundance of Zooplankton and Temperate Fish Off Southern California During
Two Decades of Warming
shimshim Salmon Populations From Alaska Increased at the Same Time Salmon Stocks From
California, Oregon, and Washington Declined
shimshim Decadal-scale Changes in Ecosystem-wide Productivity in the Northwestern Hawaiian Islands

shim Long-term Climate Variability and Fisheries Fluctuations
shimshim Historical Variability of Fish Populations From Sediment Records

shim Potential Impacts of Global Climate Change on Marine Fisheries
shimshim Alaska Sockeye Salmon Could Be Restricted In Ocean Distribution By Prolonged Warming
shimshim Expected Changes in Distribution of Migratory vs Sedentary Fish on the U.S. Atlantic
Continental Shelf From Ocean Warming
shimshim Impacts of Warming On Estuarine Dependent Marine Species on the Atlantic Coast

Climate Variability & Marine Fisheries
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