Stock assessment and risk analysis for the school shark (Galeorhinus galeus) off southern Australia

1998 ◽  
Vol 49 (7) ◽  
pp. 719 ◽  
Author(s):  
André E. Punt ◽  
Terence I. Walker
Keyword(s):  
Stock Assessment ◽  
Catch Rate ◽  
Data Series ◽  
Structured Population ◽  
Population Dynamics Model ◽  
Equilibrium Size ◽  
Structured Population Dynamics ◽  
Pup Survival ◽  
Galeorhinus Galeus ◽  
Selection Of

A spatially aggregated age- and sex-structured population dynamics model was fitted to standardized catch-rate data from the school shark resource off southern Australia. The model incorporates the peculiarities of shark populations and fisheries, including the pupping process and the selectivity characteristics of gill-nets. Estimates are determined by a Bayesian approach that incorporates prior distributions for virgin biomass, the parameter that determines productivity, and the variation in pup survival. Tests of sensitivity include changing the data series used, varying the value of adult natural mortality, and changing the prior distribution for the productivity parameter. The point estimates of the mature biomass at the start of 1995 range from 13% to 45% of the pre-exploitation equilibrium size, depending on the specifications of the assessment. The results are notably sensitive to the selection of a catch-rate series. Results suggest that the current fishing intensity will lead to further declines in abundance, that a reduction of ~20% in fishing mortality would achieve a 0.5 probability of not declining further, and that a reduction of 42% would achieve with a probability of 0.8 the management goal of not being below the 1996 mature biomass at the start of 2011. Extra keyword: CPUE.

Stock assessment of school shark, Galeorhinus galeus, based on a spatially explicit population dynamics model

2000 ◽  
Vol 51 (3) ◽  
pp. 205 ◽  
Author(s):  
André E. Punt ◽  
Fred Pribac ◽  
Terence I. Walker ◽  
Bruce L. Taylor ◽  
Jeremy D. Prince
Keyword(s):  
Population Dynamics ◽  
Spatial Structure ◽  
Stock Assessment ◽  
Dynamics Model ◽  
Point Estimates ◽  
Population Dynamics Model ◽  
Equilibrium Size ◽  
Assessment Approach ◽  
The Status ◽  
Galeorhinus Galeus

The school shark (Galeorhinus galeus) resource off southern Australia is assessed by use of an assessment approach that takes account of the spatial structure of the population. The population dynamics model underlying the assessment considers the spatial as well as the age-specific characteristics of school shark. It allows for a series of fisheries (each based on a different gear type), explicitly models the pupping/recruitment process, and allows for multiple stocks. The values for the parameters of this model are determined by fitting it to catch-rate data and information from tagging studies. The point estimates of the pup production at the start of 1997 range from 12% to 18% of the pre-exploitation equilibrium size, depending on the specifications of the assessment. Allowing for spatial structure and incorporating tag release–recapture data lead to reduced uncertainty compared with earlier assessments. The status of the resource, as reflected by the ratio of present to virgin pup production and total (1+) biomass, is sensitive to the assumed level of movement between the stocks in New Zealand and those in Australia, with lower values corresponding to higher levels of movement.

scholarly journals Optimal immune specificity at the intersection of host life history and parasite epidemiology

2021 ◽  
Vol 17 (12) ◽  
pp. e1009714
Author(s):  
Alexander E. Downie ◽  
Andreas Mayer ◽  
C. Jessica E. Metcalf ◽  
Andrea L. Graham
Keyword(s):  
Life History ◽  
Life History Traits ◽  
Reproductive Maturity ◽  
Structured Population ◽  
Specificity And Sensitivity ◽  
Population Dynamics Model ◽  
Structured Population Dynamics ◽  
Host Life ◽  
The Relationship ◽  
Shed Light

Hosts diverge widely in how, and how well, they defend themselves against infection and immunopathology. Why are hosts so heterogeneous? Both epidemiology and life history are commonly hypothesized to influence host immune strategy, but the relationship between immune strategy and each factor has commonly been investigated in isolation. Here, we show that interactions between life history and epidemiology are crucial for determining optimal immune specificity and sensitivity. We propose a demographically-structured population dynamics model, in which we explore sensitivity and specificity of immune responses when epidemiological risks vary with age. We find that variation in life history traits associated with both reproduction and longevity alters optimal immune strategies–but the magnitude and sometimes even direction of these effects depends on how epidemiological risks vary across life. An especially compelling example that explains previously-puzzling empirical observations is that depending on whether infection risk declines or rises at reproductive maturity, later reproductive maturity can select for either greater or lower immune specificity, potentially illustrating why studies of lifespan and immune variation across taxa have been inconclusive. Thus, the sign of selection on the life history-immune specificity relationship can be reversed in different epidemiological contexts. Drawing on published life history data from a variety of chordate taxa, we generate testable predictions for this facet of the optimal immune strategy. Our results shed light on the causes of the heterogeneity found in immune defenses both within and among species and the ultimate variability of the relationship between life history and immune specificity.

Why the Atlantic cod (Gadus morhua) stock off eastern Nova Scotia has not recovered

2001 ◽  
Vol 58 (8) ◽  
pp. 1613-1623 ◽  
Author(s):  
Caihong Fu ◽  
Robert Mohn ◽  
L Paul Fanning
Keyword(s):  
Nova Scotia ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Commercial Fishing ◽  
Sudden Increase ◽  
Annual Variations ◽  
Structured Population ◽  
Population Dynamics Model ◽  
Structured Population Dynamics ◽  
Age Structured

An age-structured population dynamics model, incorporating interactions between Atlantic cod (Gadus morhua), the fishery, and the grey seal (Halichoerus grypus) population, was applied to the cod stock off eastern Nova Scotia (Northwest Atlantic Fisheries Organization Divisions 4Vs and 4W, commonly abbreviated to 4VsW), a stock that has dramatically declined since the late 1980s. Mortality was modeled as having three components: fishing mortality (F), seal predation (Mp), and all other sources of natural mortality (M). Specifically, M was assumed to be distinct for immature cod (ages 1–4; Mi) and mature cod (age 5 and older; Mm), and respective annual variations were estimated. Parameters estimated also included recruitment (cod abundance at age 1; R), F, and Mp. Based on our estimates of F, Mp, and M, it is unlikely that the collapse of the 4VsW cod stock can be attributed to a sudden increase in M; fishing appears to have been the primary cause for the stock's decline. However, after the moratorium on commercial fishing in 1993, increasing Mp and Mm and low R may have contributed to the failure of the 4VsW cod stock to recover.

Long-Time Behavior of Spatially and Size-Structured Population Dynamics with Delayed Birth Process

2017 ◽  
Vol 27 (03) ◽  
pp. 1750032 ◽  
Author(s):  
Dongxue Yan ◽  
Xianlong Fu
Keyword(s):  
Population Dynamics ◽  
Semigroup Theory ◽  
Sufficient Conditions ◽  
Time Behavior ◽  
Birth Process ◽  
Structured Population ◽  
Population Dynamics Model ◽  
Structured Population Dynamics ◽  
Long Time ◽  
Asynchronous Exponential Growth

This paper is devoted to the study of a spatially and size-structured population dynamics model with delay in the birth process. We investigate some dynamical properties of the equation by using [Formula: see text]-semigroup theory and spectral analysis arguments, through which we obtain some sufficient conditions of asymptotical stability, asynchronous exponential growth at the null equilibrium as well as Hopf bifurcation occurring at the positive steady state of the system. Some examples are presented and simulated to illustrate the obtained results.

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