Efficient use of harvest data: a size‐class‐structured integrated population model for exploited populations

Abstract

Many animal populations are subject to hunting or fishing in the wild. Detailed knowledge of demographic parameters (e.g. survival, reproduction) and temporal dynamics of such populations is crucial for sustainable management. Despite their relevance for management decisions, structure and size of exploited populations are often not known, and data limited. Recently, joint analysis of different types of demographic data, such as population counts, reproductive data and capture–mark–recapture data, within integrated population models (IPMs) has gained much popularity as it may allow estimating population size and structure, as well as key demographic rates, while fully accounting for uncertainty. IPMs built so far for exploited populations have typically been built as age‐structured population models. However, the age of harvested individuals is usually difficult and/or costly to assess and therefore often not available. Here, we introduce an IPM structured by body size classes, which allows making efficient use of data commonly available in exploited populations for which accurate information on age is often missing. The model jointly analyzes size‐at‐harvest data, capture–mark–recapture–recovery data and reproduction data from necropsies, and we illustrate its applicability in a case study involving heavily hunted wild boar. This species has increased in abundance over the last decades despite intense harvest, and the IPM analysis provides insights into the roles of natural mortality, body growth, maturation schedules and reproductive output in compensating for the loss of individuals to hunting. Early maturation and high reproductive output contributed to wild boar population persistence despite a strong hunting pressure. We thus demonstrate the potential of size‐class‐structured IPMs as tools to investigate the dynamics of exploited populations with limited information on age, and highlight both the applicability of this framework to other species and its potential for follow‐up analyses highly relevant to management.

Age‐specific survival rates, causes of death, and allowable take of golden eagles in the western United States

“…IPMs take advantage of the direct relationship between demographic rates and population size by formally combining the available information on all relevant parameters to obtain more precise estimates of each (Kéry & Schaub, 2012 ; Schaub & Abadi, 2011 ). The use of IPMs to help estimate allowable take rates with the PTL approach is a relatively new concept (Gamelon et al, 2021 ), thus our analysis represents an important contribution to the joint application of these two methods.…”

Ninety years of change, from commercial extinction to recovery, range expansion and decline for Antarctic fur seals at South Georgia

“…The IPMs considered separate demography and population dynamics by sex, given the large differences in life history between females and males. Sex structure in IPMs is preferable, although uncommon (but see Cleasby et al, 2017;Gamelon et al, 2021;Péron & Koons, 2012;Plard et al, 2019), and in our case it was justified by between-and within-sex differences in data types and data record periods, in a species with a high degree of sexual dimorphism.…”

Contrasting demographic responses to size‐selective harvesting among neighbouring wild fish populations

“…This is similar to cases in which fisheries collapse could not be detected from catches alone (Walters & Martell, 2004). The mismatch between age‐ and length‐at‐harvest and age‐ and size‐distribution across years in harvested populations is concerning, given that age‐ and size‐at‐harvest are often used to monitor population (Gamelon et al, 2021; Walters & Martell, 2004).…”