natural mortality

natural mortality
a measure of the rate of removal of fish from a population from natural causes, not through fishing. Includes predation, cannibalism, senility, disease, pollution, etc. The balance that must be struck between natural mortality and fishing mortality to ensure an effective fishery is difficult. Natural morality can be reported as either annual or instantaneous. Annual mortality is the percentage of this fish dying in one year. Instantaneous mortality is the percentage of fish dying at any one time. Natural mortality is very high for young fish, with more than 99% dying in the first few months of life. Natural mortality for recruited fish is fairly steady at about 0.2, i.e. 2 fish in every 10, for groundfish, lower for Sebastes spp. (ca. 0.1), and higher for small pelagic fish. At a rate of 0.2, the chance of dying of natural causes in 1 in 5 at whatever age the fish happens to be. For a year class however, at a rate of 0.2, 45% of new recruits would die in less than 4 years from recruitment but 1% would survive more than 23 years

Dictionary of ichthyology. 2009.

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  • natural mortality — Deaths of fish from all causes except fishing. It is often expressed as a rate that indicates the percentage of fish dying in a year; e.g. a natural mortality rate of 0.2 implies that approximately 20% of the population will die in a year from… …   Fisheries — dictionary

  • natural mortality — (M) Deaths in a fish stock caused by predation, pollution, senility, etc., but not fishing …   Fisheries — dictionary

  • natural mortality — (M) Deaths in a fish stock caused by predation, pollution, senility, etc., but not fishing …   Fisheries — dictionary

  • instantaneous rate of natural mortality — When natural and fishing mortality operate concurrently it is equal to the instantaneous total mortality rate, multiplied by the ratio of natural deaths to all deaths. Also called: force of natural mortality …   Fisheries — dictionary

  • instantaneous rate of natural mortality — When natural and fishing mortality operate concurrently it is equal to the instantaneous total mortality rate, multiplied by the ratio of natural deaths to all deaths. Also called: force of natural mortality …   Fisheries — dictionary

  • force of natural mortality — instantaneous rate of natural mortality (when natural and fishing mortality operate concurrently it is equal to the instantaneous total mortality rate, multiplied by the ratio of natural deaths to all deaths (Ricker, 1975). Abbreviated as M) …   Dictionary of ichthyology

  • instantaneous rate of natural mortality — when natural and fishing mortality operate concurrently it is equal to the instantaneous total mortality rate, multiplied by the ratio of natural deaths to all deaths (Ricker, 1975). Abbreviated as M. Also called force of natural mortality …   Dictionary of ichthyology

  • conditional natural mortality rate — The fraction of an initial stock that would die from causes other than fishing during a year (or season), if there were no fishing mortality. Also called: annual natural mortality rate, seasonal natural mortality rate …   Fisheries — dictionary

  • conditional natural mortality rate — The fraction of an initial stock that would die from causes other than fishing during a year (or season), if there were no fishing mortality. Also called: annual natural mortality rate, seasonal natural mortality rate …   Fisheries — dictionary

  • annual natural mortality rate — annual mortality rate (the ratio between the number of fish which die during a year from causes other than fishing and the number alive at the beginning of that year. Also called conditional natural mortality rate and seasonal natural mortality… …   Dictionary of ichthyology

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