Abstract
Yellowfin tuna, Thunnus albacares (Bonnaterre, 1788) and bigeye tuna, Thunnus obesus (Lowe, 1839) are two of the most economically important tuna species in the world. However, identification of their juveniles, especially at sizes less than 40 cm, is very difficult, often leading to misidentification and miscalculation of their catch estimates. Here, we applied the mitochondrial DNA control region D-loop, a recently validated genetic marker used for identifying tuna species (Genus Thunnus), to discriminate juvenile tunas caught by purse seine and ringnet sets around fish aggregating devices (FADs) off the Southern Iloilo Peninsula in Central Philippines. We checked individual identifications using the Neighbor-Joining Method and compared results with morphometric analyses and the liver phenotype. We tested 48 specimens ranging from 13 to 31 cm fork length. Morpho-meristic analyses suggested that 12 specimens (25%) were bigeye tuna and 36 specimens (75%) were yellowfin tuna. In contrast, the genetic and liver analyses both showed that 5 specimens (10%) were bigeye tuna and 43 (90%) yellowfin tuna. This suggests that misidentification can occur even with highly stringent morpho-meristic characters and that the mtDNA control region and liver phenotype are excellent markers to discriminate juveniles of yellowfin and bigeye tunas.
Highlights
Yellowfin tuna (Thunnus albacares) and bigeye tuna (T. obesus) are the second and third most important large tuna commodity in the Philippines by catch weight, after skipjack tuna [1,2,3]
Juveniles of yellowfin tuna and bigeye tuna, especially at sizes less than 40 cm Fork Length (FL), are difficult to distinguish using external morphology while DNA-based methods and liver morphology are more reliable for obtaining species identifications (e.g.[8,16])
Tuna species can be identified using several genetic markers developed in population-based studies
Summary
Yellowfin tuna (Thunnus albacares) and bigeye tuna (T. obesus) are the second and third most important large tuna commodity in the Philippines by catch weight, after skipjack tuna [1,2,3]. Reliable estimates of the numbers of these two species are very important in fisheries management to illustrate annual production, demonstrate utilization rates, monitor catch quotas, estimate fishing mortality and to calculate catch per unit effort especially in light of declining population due to overfishing in recent years [2]. Differentiation of these tuna species in commercial landings poses a problem since the two species are morphologically very similar, especially at sizes less than 40 cm Fork Length (FL). The difficulty in distinguishing these two species, to non-expert field staff has long been problematic in Philippine fisheries statistics as yellowfin and bigeye tuna data were collectively grouped as yellowfin [5]
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