Atlantic salmon dynamics in the Foyle catchment (Ireland), a Bayesian approach

QH301 Biology

Dauphin, Guillaume ; Adams, Colin

University:University of Glasgow

关键词: Atlantic salmon, Bayesian modelling,fisheries, management, population dynamics, state-space model;   

Others  :  http://theses.gla.ac.uk/1744/1/2009Dauphinphd.pdf

来源: University of Glasgow

【 摘 要 】

Population dynamics is the study of the abundance of a species at different life stages of a species, theinteractions between these life stages and sometimes the interactions with other species. Stage-structuredmodelling is a popular approach for population dynamics studies. This approach examines populations basedon their ecology and allows the incorporation of complex dynamic processes. Model outputs are sensitive tothe parameter values. It then becomes crucial to accommodate and quantify parameter uncertainty. This is ofparticular importance when the population of interest is exploited and the risk of over-exploitaion orextinction needs to be assessed.When studying real world examples of populations exploited by fisheries, several additional problems oftenarise such as: multiple and heterogeneous sources of information (e.g. datasets collected at different spatialand temporal scales), missing observations, life stages of interest not directly observable. The Bayesianframework allows all of these issues to be handled within the general framework. Thus has proven itsparticular value in studying the dynamics of exploited populations. Indeed, unknown quantities haveassociated probability distributions reflecting their uncertainty. Dealing with variations in theinteractions/processes between life stages or limited and indirect ecological data is also facilitated byBayesian modelling.In this study, I examined a large Atlantic salmon population located in the Foyle catchment (Ireland). Thispopulation has been exploited for several centuries and particularly during the 20th century. This studyfocused on the period from 1959 to present for which most monitoring data is available from the LoughsAgency (formerly the Foyle Fisheries Comission). The Loughs Agency is responsible for the management ofthe salmon population. The aim of the agency is “to manage [the] fisheries towards maximum sustainableexploitation for commercial and recreational purposes”. In order to do so, it is important to understand theregulatory mechanisms occurring in the population in order to (i) estimate the number of fish returning toriver, i.e. pre-fishery abundances (PFAs), and (ii) to derive standard reference points for assessing thepopulation status with regards to its sustainable exploitation.To this end, a state-space model is implemented within a Bayesian framework. A life stage and spatiallystructured dynamic model describes the lifecycle of the Main components of Atlantic salmon in the Foylecatchment. Several empirical datasets related to the abundances of the stages at different scales of space andtime, over a period of 50 years are brought together. Observations and process errors are taken into accountultimately allowing PFAs to be estimated. A retrospective analysis was also carried out providing insights onthe historical status of the population and its exploitation.Geo unit specific abundances of the different states and their associated uncertainty are estimated. The mainstate of interest is the pre-fishery abundance (PFA), during the time-series considered (1959-2008) thesalmon population reached its apex in the mid 1960’s. This was followed by a steep decrease until the mid1970’s. From then to present, the population followed a slow declining trend with a slight recovery in themid 1980’s. This decline is shown to be mostly due to a decline of the 0+ juvenile to returning adult survivalwhich is accentuated some years by some overfishing.