Fishing effects on age and spatial structures undermine population stability of fishes |
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Authors: | Chih-hao Hsieh Atsushi Yamauchi Takefumi Nakazawa Wei-Fen Wang |
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Institution: | (1) Institute of Oceanography and Institute of Evolutionary Biology, National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei, 10617, Taiwan;(2) Center for Ecological Research, Kyoto University, Hirano, 2-509-3, Otsu 520-2113, Japan;(3) PRESTO, Japan Science and Technology Agency, Honcho 4-1-8, Kawaguchi 332-0012, Japan |
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Abstract: | Overfishing has caused dramatic changes in structures of exploited populations as well as ecosystems. In this article, we
focus on fishing effects on age (size) and spatial structures of exploited fishes. Accumulating evidence has shown that large
and experienced spawning individuals are able to produce higher quality and quantity of eggs, known as maternal effects, and
that individuals of different age classes tend to spawn in different locations and times. These behaviors are associated with
a healthy age structure and contribute to bet-hedging capacity that is important in smoothing out short-term environmental
variability. Here, we document a widespread phenomenon of age (size)-truncation of exploited populations driven by size-selective
fishery removals. Such size-selective fishing may have evolutionary consequence and may be difficult to reverse. In addition,
fishing often reduces population spatial heterogeneity that also contributes importantly to bet-hedging. We review studies
showing that the effects of age truncation and reduction of spatial heterogeneity have reduced resilience and elevated the
fluctuation amplitude of exploited populations facing a changing environment. Recent analyses indicated that fish populations
often exhibit nonlinear nature and have potential to shift dramatically in a short time. All the evidence suggests that fishing,
by altering age or spatial structures, may make exploited fishes, more prone to catastrophic shifts. Therefore, to achieve
sustainable fisheries, management should conserve the age and spatial structure in addition to viable spawning biomass. |
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