Abstract
Abstract Age–length key (ALK) methods generally perform well when length samples and age samples are representative of the underlying population. It is unclear how well these methods perform when lengths are representative but age samples are sparse (i.e. age samples are small or missing in many years, and some length groups do not have any age observations). With western Atlantic bluefin tuna, the available age data are sparse and have been, for the most part, collected opportunistically. We evaluated two methods capable of accommodating sparse age data: a novel hybrid ALK (combining forward ALKs and cohort slicing) and the combined forward-inverse ALK. Our goal was to determine if the methods performed better than cohort slicing, which has traditionally been used to obtain catch-at-age for Atlantic bluefin tuna, given the data limitations outlined above. Simulation results indicated that the combined forward-inverse ALK performed much better than the other methods. When applied to western Atlantic bluefin tuna data, the combined forward-inverse ALK approach was able to track cohorts and identified an inconsistency in the ageing of some samples.
Highlights
Atlantic bluefin tuna (ABFT) are managed by member nations of the International Commission for the Conservation of AtlanticTunas (ICCAT)
The difference in performance between FIAL and Cohort slicing (CS) was most pronounced in scenario 8, where additional years of age data brought considerable improvements to the performance of FIAL, as well as in scenarios 3 and 4, the scenarios in which the age sample is skewed towards larger individuals and recruitment variability is inflated by 50%, respectively (Table 2)
With simulated data designed to emulate several real world complexities, the FIAL key performed significantly better than the other two methods
Summary
Atlantic bluefin tuna (ABFT) are managed by member nations of the International Commission for the Conservation of AtlanticTunas (ICCAT). Atlantic bluefin tuna (ABFT) are managed by member nations of the International Commission for the Conservation of Atlantic. Though the two stocks mix throughout most of their foraging range (Block et al, 2005; Dickhut et al, 2009; Rooker et al., 2008; Wilson et al, 2015), they are managed as two separate units delineated by the 45 W meridian. ABFT are relatively long lived (up to 34 years of age; Ailloud et al, 2017) and carry out extensive migrations across the Atlantic Ocean where they are targeted by a wide range of fisheries that differentially harvest multiple age groups
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