To understand the processes affecting the abundance of wild populations is a fundamental
goal of ecology and a prerequisite for the management of living resources. Variable abundance, however, makes the investigation of ecological processes challenging. Recruitment,
the process whereby new individuals enter a given stage of a ?sh population, is a highly
variable entity. I have confronted this issue by developing methodologies speci?cally designed to account for, and ecologically interpret, patterns of variability in recruitment.
To provide the necessary context, Chapter 2 begins with a review of the history of
recruitment science. I focus on the major achievements as well as present limitations, particularly regarding environmental drivers. Approaches that include explicit environmental
information are contrasted with time-varying parameter techniques.
In Chapter 3, I ask what patterns of variability in pre-recruit survival can tell us about
the strength of density-dependent mortality. I provide methods to investigate the presence
of density-dependent mortality where this has previously been hindered by highly variable data. Stochastic density-independent variability is found to be attenuated via density
dependence.
Sources of recruitment variability are further partitioned in Chapter 4. Using time-varying parameter techniques, signi?cant temporal variation in the annual reproductive rate
is found to have occurred in many Atlantic cod populations. Multivariate state space models
suggest that populations in close proximity typically have a shared response to environmental change whereas marked differences occur across latitude.
Hypotheses that could result in consistent changes in productivity of cod populations
are tested in Chapter 5. I focus on a meta-analytical investigation of potential interactions between Atlantic cod and small pelagic species, testing aspects of the cultivation-depensation hypothesis. The ?ndings suggest that predation or competition by herring and
mackerel on egg and larval cod could delay recovery of depleted cod populations.
Chapter 6 concludes with a critical re?ection on: the suitability of the theories employed, the underlying assumptions of the empirical approaches, and the quality of the data
used in my thesis. Application of ecological insights to ?sheries management is critically
evaluated. I then propose future work on recruitment processes based on methods presented
herein.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:NSHD.ca#10222/13881 |
| Date | 24 May 2011 |
| Creators | Minto, Cóilín |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | en_US |
| Detected Language | English |
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