Ricardo P. Babaran

Discrimination of Juvenile Yellowfin (Thunnus albacares) and Bigeye (T. obesus) Tunas using Mitochondrial DNA Control Region and Liver Morphology

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.

Cryptic genetic divergence in Scolopsis taenioptera (Perciformes: Nemipteridae) in the western Pacific Ocean

We studied the phylogeny, population structure, and demographic history of Scolopsis taenioptera in the western Pacific Ocean. Using the 80 samples collected from four locations, we obtained the nucleotide sequences of mitochondrial cytochrome c oxidase subunit I and cytochrome b genes. We identified two distinct lineages showing a clear phylogeographic break that was possibly due to the Pleistocene sea-level change. One lineage was distributed in Iloilo (Philippines) and the other in Terengganu (Malaysia), Rayong (Thailand), and Ha Long Bay (Vietnam). The Terengganu and Rayong populations showed clear signs of demographic expansion; the Iloilo and Ha Long Bay populations were relatively stable or spatially expanded as geographically subdivided populations.

Rapid and cost-effective molecular identification of the three mackerel species of the genus Rastrelliger (Perciformes: Scombridae) using PCR-RFLP analysis

The three mackerel species, Rastrelliger kanagurta, Rastrelliger brachysoma, and Rastrelliger faughni, co-occur in the central part of the Indo-West Pacific Ocean, and together represent important fisheries resources. However, they have sometimes been collectively referred to as “Rastrelliger spp.” in the fisheries statistics, owing to their morphological similarity. Therefore, species-specific data on landings, effort, and population status are lacking, undermining the appropriate resource management. The present study provides a rapid and cost-effective method based on polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis to distinguish the three species. Digestion of the PCR products of 1247 base pairs of mitochondrial DNA encompassing the complete sequence of cytochrome b gene using two restriction enzymes yielded diagnostic restriction patterns for the three species, thereby enabling accurate identification.

Local Ecological Knowledge (LEK) on Fish Behavior Around Anchored FADs: the Case of Tuna Purse Seine and Ringnet Fishers from Southern Philippines

Abstract The Fishing Industry in the Philippines plays an important role in the food and employment need of Filipino fishers. By using anchored Fish Aggregating Devices (FADs or payao), the Philippine tuna fisheries was transformed into a million-dollar industry. Minimal studies on exploitation rates and fish behaviour around anchored FADs hampered further understanding of this fishery practice. Studies on fish behavior using Local Ecological Knowledge (LEK) are good complement where data is limited. A study using semi-structured interview (n=46) and three focus group discussions (n=39 participants) to record fishers’ knowledge and observations on the behavior of different fish species around anchored FADs was conducted. This particularly focused on attraction, retention, and departure behaviour of fishes in identified FAD sites. Based on the fishers’ knowledge, tuna schools are attracted to anchored FADs at 10 km distance. In anchored FADs, tuna form schools segregated by species and size. There was no relationship between the attraction distance and the reported school size and the various waiting times for fish to aggregate below the FADs. There was no variation between the species present at day or night time although fishers have reported a distinction of species found near the surface (0-10 m) and those found at other depths (11-20 m). Juvenile yellowfin tuna (Thunnus albacares), skipjack (Katsuwonus pelamis) and frigate and bullet tunas (Auxis spp.) are found to stay at 25-50 m from the FAD at a depth of >20 m. Adult oceanic tunas reside in deeper waters (75 m). The fish visual census produced similar results with the semi-structured interviews and FGDs but did not observe oceanic tunas at depths of 15-20 m in the anchored FADs examined.