Population growth of northern anchovy and Pacific sardine using stage-specific matrix models

Abstract

We applied a stage-specific population matrix, the Lefkovitch matrix, to the northern anchovy Engraulis mordax and the Pacific sardine Sardinops sagax to determine which vital rates in the life history have the most effect on population growth. Three vital rates considered are the daily stage-specific instantaneous mortality rate, stage duration and daily age-specific fecundity per female. The models incorporate variability in growth rates among individuals and link simpler stage-based and more complicated individual-based modeling approaches. The elasticity of population growth rate for anchovy (percentage change from a 1 % change of a vital rate) was greatest for mortality in yolk-sac larvae, fecundity of 2 yr old fish (111 to 135 mm), and stage duration in late larvae (11 to 35 mm). For sardine, elasticity was greatest for mortality in life stages of egg and yolk-sac larvae, fecundity of 5 and 6 yr old fish (211 to 250 mm), and stage duratlon in the early larvae (5 to 10 mm). When stage duration was variable, elasticity was !:;(l as large as when stage duration was constant, indicating that sensitivity of populations to changes in vital rates IS reduced by variation In growth rates. Population growth rates for both specles increased with variance in individual growth rates. Thus, a population with individuals that grow at varying rates is more likely to increase. Our models indicate that growth rates are important determinants of population growth and recruitment and it is likely that growth and mortality rates are linked. We suggest, therefore, that inexpensive estimates of larval growth rates could be used to help forecast future recruitment.

Larval stage controls on Pacific sardine recruitment variability: high zooplankton abundance linked to poor reproductive success

“…Based on stage-based models, Lo et al (1995) and Smith et al (1992) show that the largest changes in sardine population growth come from a relative change in the mortality rate of egg and larval stages, concluding that mortality rates of these stages are the primary determinants of recruitment success. Reductions in mortality rates due to predation could occur during warm years and clearly have the potential to enhance recruitment success.…”

Importance of pre-recruitment life-history stages to population dynamics of the woolly sculpin Clinocottus analis

“…As in other studies of nearshore fishes (Lo et al 1995, Pfister 1996, λ was highly sensitive to hypothetical variation in early adult survivorship (high elasticity of λ to P 2 and P 3 ). However, changes in these terms did not account for differences in λ observed over time.…”

Understanding population dynamics of a numerically dominant species at hydrothermal vents: a matrix modeling approach

“…S1 in Supplement 1 at www.int-res.com/articles/suppl/m403p113_app.pdf). The stage-specific survival probabilities (σ i ) (Table S1 in Supplement 2 at www.int-res.com/articles/suppl/ m403p113_app.pdf) were then calculated as (Vaughan & Saila 1976, Lo et al 1995:…”

“…This second estimate of λ was substituted back into the equation to recalculate γ i , and the iteration stopped when the difference between 2 consecutive values of λ was < 0.0001 (Levin & Huggett 1990, Lo et al 1995. G i and P i were calculated from σ i and γ i as (Crowder et al 1994, Caswell 2001 …”

“…Demographic analysis using matrix models has a long history in terrestrial (Leslie 1945, Lefkovitch 1965, Sondgerath & Richter 1990, Horvitz & Schemske 1995 and shallow marine systems (Crouse et al 1987, Levin & Huggett 1990, Brault & Caswell 1993, Lo et al 1995. Its general use for describing the population dynamics of species with widely different life-history strategies testifies to the flexibility and power of the technique.…”