An integrated Bayesian modeling approach for the growth of Indian Ocean yellowfin tuna

Abstract

The Indian Ocean Tuna Tagging Program provided a unique opportunity to collect demographic data on the key commercially targeted tropical tuna species in the Indian Ocean. In this paper, we focused on estimating growth rates for one of these species, yellowfin (Thunnus albacares). Whilst most growth studies only draw on one data source, in this study we use a range of data sources: individual growth rates derived from yellowfin that were tagged and recaptured, direct age estimates obtained through otolith readings, and length-frequency data collected from the purse seine fishery between 2000 and 2010. To combine these data sources, we used an integrated Bayesian model that allowed us to account for the process and measurement errors associated with each data set. Our results indicate that the gradual addition of each data type improved the model's parameter estimations. The Bayesian framework was useful, as it allowed us to account for uncertainties associated with age estimates and to provide additional information on some parameters (e.g., asymptotic length). Our results support the existence of a complex growth pattern for Indian Ocean yellowfin, with two distinct growth phases between the immature and mature life stages. Such complex growth patterns, however, require additional information on absolute age of fish and transition rates between growth stanzas. This type of information is not available from the data. We suggest that bioenergetic models may address this current data gap. This modeling approach explicitly considers the allocation of metabolic energy in tuna and may offer a way to understand the underlying mechanisms that drive the observed growth patterns

Modelling growth in tuna RFMO stock assessments: Current approaches and challenges

“…Vert-pre et al, 2013) Given these problems, it is possible that growth curves may already attract a disproportionate amount of research effort. For example, large-scale tagging studies have often been touted as the best fishery-independent data option for improving tuna assessments, and we note that a recent Fisheries Research special issue on tagging, which focused on (but was not restricted to) the Indian Ocean Regional Tuna Tagging Programme (Murua et al, 2015), resulted in four papers that presented new growth curve estimates Dortel et al, 2015;Eveson et al, 2015;Sardenne et al, 2015), one paper that provided tag-based mortality estimates (Hillary and Eveson, 2015), and no papers that presented quantitative tag-based abundance or movement estimates (though analyses which would contribute to such estimates were presented).…”

“…Laslett et al (2002) opted to develop a more flexible parametric growth function for southern bluefin tuna, which has also proved useful for several tropical tunas (e.g. Dortel et al, 2015;Eveson et al, 2015). This two stage growth model, VBlogK, consists of two von Bertalanffy curves for different age ranges (independent K, shared L ∞ ) and a logistic weighting function that provides a smooth (continuously differentiable) transition between the two (e.g.…”

“…Dortel et al (2015) demonstrated that fitting a VBlogK model to Indian Ocean yellowfin otolith data (without tags) resulted in a growth curve that asymptotes shortly beyond their oldest age estimate from otoliths. In contrast, Aires-da- show that von Bertalanffy and Richards growth curves extrapolate to unrealistically high asymptotes when fit to otolith data from eastern Pacific bigeye tuna.…”

“…Eveson et al, 2004;Dortel et al, 2015), and computationally-intensive, statistically-sophisticated methods can be employed. The latter is particularly relevant to modelling tag-recapture data because methods that properly account for individual variability in growth by modelling the joint probability density of release and recovery lengths (see previous Section) would be computationally challenging to implement within a stock assessment model.…”

Life history demographic parameter synthesis for exploited Florida and Caribbean coral reef fishes

“…Tag-recapture growth studies were quite rare in our literature search, even though this approach has proven useful for developing length-age functions for tropical fishes that are inherently difficult to accurately age from otoliths and other hard parts (Francis, 1988;Laslett, Eveson, & Polacheck, 2002;Welsford & Lyle, 2005). Likewise, we did not encounter length-age studies utilizing Bayesian model-fitting procedures (c.f., Dortel et al, 2015), although this may change in the future.…”