Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 8080
Title: Spatio-temporal variation in fish condition is not consistently explained by density, temperature, or season for Northeast Pacific groundfishes
Author: James T. Thorson
Publication Year: 2015
Journal: Marine Ecology Progress Series
Volume: 526
Pages: 101-112
DOI: 10.3354/meps11204
Keywords: Condition factor, spatial analysis, weight at length, Northeast Pacific groundfish, ,

 Condition (the relationship between individual weight and length) has been researched in fisheries science for over 100 years and is an integrated measure of physiological status for fishes.  Spatial or temporal variation in condition can contribute to otherwise unexplained variation in the relationship between spawning biomass and recruitment.  Condition is also included in age-structured population models, which use weight at age to convert population estimates between numbers and biomass.  However, no study has analyzed spatial and temporal variation in condition for multiple marine species.  Here, I apply recent improvements in spatial modeling to analyze coastwide variation in condition for 28 groundfishes in the California Current.  I show that 22% of individual-level variation in condition can be explained via persistent and annually varying spatial differences in condition, and condition for many species varies 10-20% spatially and among years.  While population density, bottom temperature, and calendar date are parsimonious descriptors of condition in several species, the sign of these coefficients varies and their magnitude is small relative to the magnitude of residual spatial and temporal variation.  Additionally, annually varying spatial differences have nearly twice the magnitude of persistent spatial differences in condition.  I therefore conclude that dynamic habitat conditions contribute a substantial portion of variation in individual condition for these groundfishes.  Spatial and temporal variation in condition will be important for population models that covert between numbers, fishery catch, and population biomass, and may also clarify unexplained variability in productivity for marine fishes.


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Theme: Recovery and rebuilding of marine and coastal species
Foci: Characterize the population biology of species, and develop and improve methods for predicting the status of populations.
Develop methods to use physiological, biological and behavioral information to predict population-level processes.