Abstract
Individual growth is an important parameter and is linked to a number of other biological processes. It is commonly modeled using the von Bertalanffy growth function (VBGF), which is regularly fitted to age data where the ages of the animals are not known exactly but are binned into yearly age groups, such as fish survey data. Current methods of fitting the VBGF to these data treat all the binned ages as the actual ages. We present a new VBGF model that combines data from multiple surveys and allows the actual age of an animal to be inferred. By fitting to survey data for Atlantic herring (Clupea harengus) and Atlantic cod (Gadus morhua), we compare our model with two other ways of combining data from multiple surveys but where the ages are as reported in the survey data. We use the fitted parameters as inputs into a yield‐per‐recruit model to see what would happen to advice given to management. We found that each of the ways of combining the data leads to different parameter estimates for the VBGF and advice for policymakers. Our model fitted to the data better than either of the other models and also reduced the uncertainty in the parameter estimates and models used to inform management. Our model is a robust way of fitting the VBGF and can be used to combine data from multiple sources. The model is general enough to fit other growth curves for any taxon when the age of individuals is binned into groups.
Highlights
Throughout ecology, growth is an important parameter that describes the life history of individuals and species (Austin, Robinson, Robinson, & Ricklefs, 2011; Einum, Forseth, & Finstad, 2012; Paine et al, 2012; Pardo, Cooper, & Dulvy, 2013)
By fitting our model and two other alternative versions of von Bertalanffy growth function (VBGF), to SWC-IBTS data for Atlantic herring (Clupea harengus), a species with a long-s pawning season, and Atlantic cod (Gadus morhua), a species with a short-spawning season (Datta & Blanchard, 2016), we demonstrate that the parameters can be sensitive to the version of the VBGF that we fit them to
We demonstrated that fitting to multiple surveys is a good way of reducing uncertainty when fitting the VBGF but existing methods of doing this are unsatisfactory
Summary
Throughout ecology, growth is an important parameter that describes the life history of individuals and species (Austin, Robinson, Robinson, & Ricklefs, 2011; Einum, Forseth, & Finstad, 2012; Paine et al, 2012; Pardo, Cooper, & Dulvy, 2013). An alternative way of combining data is to increase the age of fish according to the time of year at which the fish was surveyed (Chambers, Sidhu, O’Neil, & Sibanda, 2017; Sparre & Venema, 1998) In effect, this assumes that every fish spawned on January 1st, and its age is the number of winters survived plus the time of year at which it was caught, expressed as proportion. It is intuitive to think that of two fish, aged the same in the survey data but of different lengths, the larger fish spawned earlier than the smaller, especially if they were young With this in mind, in this study, we develop a model that uses information from previous studies about the spawning times of species (Datta & Blanchard, 2016) to infer the age of individual fish and allow multiple surveys to be combined.
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