Density-dependence can be revealed by modelling the variance in the stock-recruitment process: an application to flatfish (original) (raw)
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Background/Question/Methods Understanding the density dependence of fish reproduction is critically important for management and conservation of commercial fisheries. Stock-recruitment relationships describe how reproductive output changes relative to the number of fish in a population. Common models used to fit fisheries data include the Beverton-Holt model, which describes a system where total recruitment levels off at higher spawner densities (called compensation), and the Ricker model, where total recruitment declines at high densities (overcompensation). While large amounts of data allow an appropriate model to be chosen for a species or population, no clear method has been developed to objectively determine the appropriate stock-recruitment relationship for commercial species where limited or no stock-recruitment data exist. To address this gap, we developed a hierarchical model that uses Bayesian inference to link stock-recruitment parameters among species, taxonomic orders (...
Survival variability and population density in fish populations
Nature, 2008
To understand the processes that regulate the abundance and persistence of wild populations is a fundamental goal of ecology and a prerequisite for the management of living resources. Variable abundance data, however, make the demonstration of regulation processes challenging. A previously overlooked aspect in understanding how populations are regulated is the possibility that the pattern of variability--its strength as a function of population size--may be more than 'noise', thus revealing much about the characteristics of population regulation. Here we show that patterns in survival variability do provide evidence of regulation through density. Using a large, global compilation of marine, anadromous and freshwater fisheries data, we examine the relationship between the variability of survival and population abundance. The interannual variability in progeny survival increases at low adult abundance in an inversely density-dependent fashion. This pattern is consistent with models in which density dependence enters after the larval stage. The findings are compatible with very simple forms of density dependence: even a linear increase of juvenile mortality with adult density adequately explains the results. The model predictions explain why populations with strong regulation may experience large increases in variability at low densities. Furthermore, the inverse relationship between survival variability and the strength of density dependence has important consequences for fisheries management and recovery, and population persistence or extinction.
ICES Journal of Marine Science, 2021
Beverton and Holt’s (1957. On the dynamics of exploited fish populations. UK Ministry of Agriculture, Fisheries and Food. Fisheries Investigations, 2: 533 pp.) monograph contributed a widely used stock–recruitment relationship (BH-SRR) to fisheries science. However, because of variation around a presumed relationship between spawning biomass and recruits, the BH-SRR is often considered inadequate and approached merely as a curve-fitting exercise. The commonly used and simplified version of the BH-SRR has eclipsed the fact that in their classic monograph, the derivation accounted for mechanistic recruitment processes, including multi-stage recruitment with explicit cohort-dependent and -independent mortality terms that represent competition between recruits and extrinsic, cohort-independent factors such as the environment or predation as two independent sources of mortality. The original BH-SRR allows one to recreate recruitment patterns that correspond to observed ones. Doing so sho...
A conceptual framework for enhancing and studying recruitment of marine fish stocks
The possibility of enhancing and studying recruitment of commercially important marine fish stocks is discussed in general, and for North-east Atlantic cod stocks, Gadus morhua L.,in particular . Current knowledge concerning the relative importance of different physical and biological factors influencing survival of early stages is addressed in relation to cost-benefit of release programmes . The cost of producing large juveniles is relatively high compared with the expected yield per recruit . Because large juveniles also eventually become too expensive to release, emphasis should he put into releasing the offspring as early as possible . Special attention is given to evaluation of the optimal time for survival of larvae and juveniles and thus the possibility to enhance recruitment by releasing the offspring when environmental factors are favourable . The prey energy available for larval and juvenile fish varies during ontogeny . The period at the onset of exogenous feeding and the...