Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 9082
Title: Old-growth fishes become scarce under fishing
Author: Lewis Barnett, Trevor A. Branch, R. A. Ranasinghe, T. E. Essington
Publication Year: 2017
Journal: Current Biology
Volume: 27
Pages: 2843-2848
DOI: 10.1016/j.cub.2017.07.069

Researchers have long recognized the importance of
ecological differences at the species level in structuring
natural communities yet until recently have
often overlooked the influence of intraspecific trait
variation, which can profoundly alter community dynamics
[1]. Human extraction of living resources can
reduce intraspecific trait variation by, for example,
causing truncation of age and size structure of populations,
where numbers of older individuals decline
far more with exploitation than younger individuals.
Age truncation can negatively affect population and
community stability, increasing variability in population
and community biomass [2¿6], reducing productivity
[7¿10] and life-history diversity in traits such as
the spatial and temporal pattern of reproduction and
migration [4, 11¿16]. Here,we quantified the extent of
age truncation in 63 fished populations across five
ocean regions, as measured by how much the proportions
of fish in the oldest age groups declined
over time. The proportion of individuals in the oldest
age classes decreased significantly in 79% to 97% of
populations (compared to historical or unfished
values, respectively), and the magnitude of decline
was greater than 90% in 32% to 41% of populations.
The pervasiveness and intensity of age truncation
indicates that fishing is likely reducing the stability
of many marine communities. Our findings suggest
that more emphasis should be given to management
measures that reduce the impact of fishing on age
truncation, including no-take areas, slot limits that
prohibit fishing on all except a narrow range of fish
sizes, and rotational harvesting.

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Theme: Recovery and rebuilding of marine and coastal species
Foci: Describe the relationships between human activities and species recovery, rebuilding and sustainability.
Characterize the population biology of species, and develop and improve methods for predicting the status of populations.