ORIGINAL ARTICLE: Comparison of demographic and direct methods to calculate probabilistic maturation reaction norms for Flemish Cap cod (Gadus morhua)

Alfonso Pérez‐Rodríguez,Marie Joanne Morgan,Fran Saborido‐Rey

doi:10.1111/j.1752-4571.2009.00084.x

Alfonso Pérez‐Rodríguez, Marie Joanne Morgan + Show 1 more

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https://doi.org/10.1111/j.1752-4571.2009.00084.x

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Journal: Evolutionary applications	Publication Date: Jul 31, 2009
Citations: 19	License type: cc-by

Affiliation: Institute of Marine Research

Abstract

Age and length at maturation have declined in many fish populations and this has been hypothesized to be a genetic change caused by high fishing mortality. Probabilistic Maturation Reaction Norms (PMRNs) have been used as a tool to gain a better understanding of the possible genetic nature of these changes. The demographic and direct methods are two ways to calculate PMRNs. The data requirements are more often met for the demographic method than for the direct method which requires the identification of recruit spawners. However, the demographic method relies on more assumptions than the direct method, typically assuming equality of growth and mortality rates for immature and mature individuals within an age class. This study provides the first direct comparison of demographic and direct methods and shows that both methods produce comparable results. Differences between methods are hypothesized to be owed to possible differences in growth rate between mature and immature individuals in Flemish Cap cod.

Highlights

The maturation process is the most important life-history transition in plants and animals which comes with large changes in energy allocation (Dieckmann and Heino 2007; Roff 1992, Stearns 1992; Bernardo 1993)
These different maturity stages were identified following Saborido-Rey and Junquera (1998): immature females were identified when all the oocytes were in the primary growth stage and no evidence of previous spawning activity was found; recruit spawner females had oocytes in the cortical alveoli stage (CA) or vitellogenic stage (VO) but not postovulatory follicle (POF) nor atretic oocyte stage (AO); repeat spawner females were identified by the presence of CA, VO, POF and/or AO
Logistic models for the DemPMRNs and the direct method for PMRNs estimation (DirPMRN) methods were fit for every cohort grouping option (Tables 2 and 3)

Summary

Introduction

The maturation process is the most important life-history transition in plants and animals which comes with large changes in energy allocation (Dieckmann and Heino 2007; Roff 1992, Stearns 1992; Bernardo 1993). While a fish is immature, energy is allocated to increase survival and growth. Energy is required for reproduction and this may decrease survival, deplete body reserves and reduce growth (Roff 1992; Berner and Blanckenhorn 2007; Saborido-Rey and Kjesbu, unpublished manuscript). As fecundity, egg size and egg quality can increase with fish size and age (Trippel 1995; Marshall and Frank 1999), females maturing at smaller size and younger age suffer from reduced reproductive success (Solemdal 1997; Trippel et al 1997). The decrease in age and length at maturation of individuals can produce a a 2009 The Authors Journal compilation a 2009 Blackwell Publishing Ltd 2 (2009) 291–298 decrease in reproductive potential, (Domınguez-Petit 2007), and make the recruitment process more sensitive to environmental variability (Saborido-Rey and Kjesbu, unpublished manuscript)

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