chapter  15
21 Pages

Life History Patterns, Demography, and Population Dynamics

ByEnric Cortés

CONTENTS 15.1 Introduction .................................................................................................................................. 449 15.2 Life History Patterns .................................................................................................................... 450

15.2.1 Comparative Life History Patterns ................................................................................. 450 15.2.2 Life History Relationships .............................................................................................. 451

15.3 Population Dynamics ................................................................................................................... 453 15.3.1 Methodological Background........................................................................................... 453

15.3.1.1 Demographic Unit or Stock............................................................................. 457 15.3.1.2 Population Sampling Design ........................................................................... 457 15.3.1.3 Stock-Recruitment Curve................................................................................. 458

15.3.2 Biomass Dynamic Models .............................................................................................. 458 15.3.3 Cohort-Structured Models............................................................................................... 459

15.3.3.1 Static Models ................................................................................................... 459 15.3.3.2 Dynamic Age-Structured Models .................................................................... 461

15.3.4 Models Incorporating Uncertainty and Stochasticity..................................................... 461 15.4 Conclusions .................................................................................................................................. 464 Acknowledgments.................................................................................................................................. 464 References .............................................................................................................................................. 464

15.1 Introduction There is mounting evidence of recent declines in a number of elasmobranch populations as a result of overharvesting (Campana et al., 1999, 2001, 2002; Simpfendorfer, 2000; Cortés et al., 2002; Baum et al., 2003), and two species of skate have even become locally extirpated or almost extinct (Brander, 1981; Casey and Myers, 1998). Yet our knowledge of life history traits of most species is still limited and we are just beginning to gain insight into the life history patterns shared by some species and the relationships among life history traits (Compagno, 1990; Cortés, 2000; Frisk et al., 2001). Within the past two decades, our scant but increasing knowledge of the life history of numerous species (Compagno, 1984) has given rise to the development of demographic (life table and matrix population) models for elasmobranchs that attempt to characterize the vulnerability to exploitation of the populations under study. Increased fishing pressure on some species (Hoff and Musick, 1990), largely due to an increase in demand for shark fins (Bonfil, 1994), also prompted the emergence of population models to assess stock status.