ABSTRACT
Enric Cortés, Elizabeth N. Brooks, and Todd Gedamke
CONTENTS
15.1 Introduction ................................................................................................................................................................. 453 15.2 Population Dynamics ................................................................................................................................................. 454
15.2.1 Methodological Background ....................................................................................................................... 454 15.2.1.1 Demographic Unit or Stock ........................................................................................................ 454 15.2.1.2 Population Sampling Design ..................................................................................................... 459 15.2.1.3 Exponential vs. Logistic Population Growth ........................................................................... 460 15.2.1.4 Stock-Recruitment Curves ......................................................................................................... 463 15.2.1.5 Compensatory Responses to Exploitation ............................................................................... 463
15.3 Modeling Approaches ................................................................................................................................................ 464 15.3.1 Biomass Dynamic Models ........................................................................................................................... 464 15.3.2 Cohort-Structured Models ........................................................................................................................... 465
15.3.2.1 Age-Structured Demographic Models ..................................................................................... 465 15.3.2.2 Stage-Structured Demographic Models ................................................................................... 467 15.3.2.3 Yield-per-Recruit Models ........................................................................................................... 468 15.3.2.4 Age-Structured Stock Assessment Models .............................................................................. 468
15.3.3 Models for Data-Poor Situations ................................................................................................................. 470 15.3.3.1 Rapid Assessment Techniques .................................................................................................. 470 15.3.3.2 Statistical Analysis of Relative Abundance Trends ................................................................ 472 15.3.3.3 Ecological Risk Assessments ..................................................................................................... 472 15.3.3.4 Analytical Reference Points ....................................................................................................... 473 15.3.3.5 Catch-Free Assessment Model ................................................................................................... 475
15.4 Applications to Management .................................................................................................................................... 475 15.5 Summary and Conclusion ......................................................................................................................................... 477 Acknowledgments ................................................................................................................................................................. 477 References ................................................................................................................................................................................ 477
There is mounting evidence of declines in elasmobranch populations worldwide mainly as a result of overharvesting (Baum et al., 2003; Campana et al., 1999, 2001; Cortés et al., 2002, 2006; Dulvy et al., 2010; Myers et al., 2007; Simpfendorfer, 2000), although habitat loss and degradation are also of increasing concern (Dulvy and Forrest, 2010; Field et al., 2009; García et al., 2008; Simpfendorfer, 2007). The severity of several of these reported declines, however, has been questioned on the grounds that the data and methods of analysis may not have captured the real changes in relative abundance exhibited by the
populations under study (Baum and Myers, 2004; Baum et al., 2003, 2005; Burgess et al., 2005a,b). Within the past three decades, the links between life histories and the risk of overexploitation or even extinction of elasmobranch populations have been increasingly studied, mainly through demographic (life table or matrix population) models and formal stock assessment models.
