Fishing season estimation for tuna troll line fishing fleet at Palabuhanratu Nusantara Fishing Port, Sukabumi, Indonesia

We evaluated the behavior of skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye tuna (T. obesus) associated with drifting fish aggregating devices (FADs) in the equatorial central Pacific Ocean. A total of 30 skipjack [34.5–65.0 cm in fork length (FL)], 43 yellowfin (31.6–93.5 cm FL) and 32 bigeye tuna (33.5–85.5 cm FL) were tagged with coded transmitters and released near two drifting FADs. At one of the two FADs, we successfully monitored the behavior of all three species simultaneously. Several individuals remained around the same FAD for 10 or more days. Occasional excursions from the FAD were observed for all three species, some of which occurred concurrently for multiple individuals. The detection rate was higher during the daytime than the nighttime for all the species, and the detection rate for bigeye tuna was higher than for yellowfin or skipjack tuna. The swimming depth was deeper during the daytime than nighttime for all species. The fish usually remained shallower than 100 m, but occasionally dived to around 150 m or deeper, most often for bigeye and yellowfin tuna during the daytime. The swimming depth for skipjack tuna was shallower than that for bigeye and yellowfin tuna, although the difference was not large, and is probably not sufficient to allow the selective harvest of skipjack and yellowfin tuna by the purse seine fishery. From the detection rate of the signals, bigeye tuna is considered to be more vulnerable to the FAD sets than yellowfin and skipjack tuna.

Bigeye tuna (Thunnus obesus) have much greater vertical mobility than yellowfin (T. albacares) and skipjack (Katsuwonus pelamis) tunas, due to an apparent greater tolerance of the changes in ambient temperature and oxygen occurring with depth. In an attempt to identify physiological processes (e.g., effects of temperature on cardiac function) responsible for these behavioral differences, we examined enzyme activities (at 12 °C, 17 °C, and 25 °C) of cardiac muscle in all three species. Contrary to our expectations, we found few differences and no clear explanatory patterns in maximum enzyme activities (V max ) or enzyme activity ratios. For example, citrate synthase (CS) activity was the same in bigeye and skipjack tunas, but ≈ 40% lower in yellowfin tuna, whereas carnitine palmotoyltransferase (CPT) activity in skipjack tuna was approximately double that in the other two species. The ratio of CPT to pyruvate kinase (PK) activity, a measure of the tissues’ preference for fatty acids as metabolic substrates, was the same in bigeye and yellowfin tunas, but elevated skipjack tuna. The ratios of lactate dehydrogenase (LDH) to CS activity and of PK to CS activity (anaerobic–aerobic enzyme activity ratios – taken as measures of the tissues’ ability to tolerate hypoxia) were both elevated in yellowfin tuna cardiac tissue relative to the other two species. We also found no differences in temperature sensitivity (Q10 values) when comparing cardiac enzyme activities across species, nor effects of temperature on the substrate affinity (K m ) of LDH. In sum, our results do not suggest any clear metabolic difference in the cardiac muscle that would explain the apparent greater tolerance of bigeye tuna to acute hypoxia and ambient temperature changes or their substantially greater vertical mobility.

Highly migratory tuna species play an important economic role and ecosystem function worldwide. They are mainly caught in tropical and subtropical areas of the Pacific, Atlantic and Indian oceans. Data collected by the Chinese longline fishery in the high seas of the Eastern Pacific Ocean from 2014 to 2015 were analysed to estimate the catch per unit effort (CPUE), length and weight frequency, length-weight relationship, relative condition factor and Fulton’s condition factor for albacore tuna (Thunnus alalunga), yellowfin tuna (Thunnus albacares) and bigeye tuna (Thunnus obesus). The results showed that this fishing technique was highly selective for these three species. Albacore tuna represented the major portion of the catches at 76.17%. Yellowfin and bigeye tuna represented 8.24 and 11.68% of the total of specimens, respectively. The remaining 3.9% were bycatch such as Katsuwonus pelamis, Acanthocybium solandri, Ruvettus pretiosus, Xiphias gladius, Lampris guttatus, Carcharodon carcharias and Scomberomorus guttatus. The average fork length for albacore tuna was 90-100 cm; yellowfin tuna, 100-130 cm and bigeye tuna, 125-165 cm. The average weight for albacore tuna was 15-20 kg; yellowfin tuna, 20-50 kg and bigeye tuna, 35-55 kg. The CPUE (based on fish per one thousand hooks) for albacore, yellowfin tuna and bigeye tuna ranged from 1.6 to 9.82, 1.07 to 2.66 and 1.06 to 3.45, respectively. The parameters of the length-weight relationship showed a negative allometric growth regression of 2.7135 for albacore tuna, 2.3275 for yellowfin tuna and 2.4047 for bigeye tuna. Nevertheless, the albacore and yellowfin tuna females were characterised by positive allometry (b>3). The analyses also showed that the relative condition factors (Krel) of the three fish species were greater than one, implying that they were in good physiological condition, good water quality and healthy organisms. Keywords: China, Fishing effort, Fish per hook, Tuna

A preliminary study on species composition of a Korean purse seine catch landed at cannery was conducted in April 2011. In the cannery, all tuna catch are sliding through a sorting grid panel that filters and drops fish in the buckets by size class (above 9kg, 3.4-9kg, 1.8-3.4kg, 1.4-1.8kg and below 1.4kg). In cannery processing, species sorting was made for skipjack tuna and yellowfin tuna only from catches greater than 3.4kg during filtering but not for bigeye tuna because of difficulties in species identification between bigeye tuna and yellowfin tuna under frozen state. As no species identification was carried out for catch groups less than 3.4kg in the cannery process, this study focused on sorting out skipjack tuna and yellowfin tuna from these groups and then identifying bigeye tuna from all size groups of yellowfin tuna. Using the mixture rate of species obtained from the samples taken, species composition of the landed catch was estimated. As results, cannery research showed 95% for skipjack tuna, 3% for yellowfin tuna and 2% for bigeye tuna in species composition, while vessel logbook data represented 96%, 3% and 1% for skipjack tuna, yellowfin tuna and bigeye tuna, respectively. The proportion of bigeye tuna identified in the cannery was slightly higher than shown in logbook data by 1%.

Indonesian archipelagic waters, including the Fisheries Management Areas (FMAs) 713, 714 and 715, have significant potential for tropical tuna fisheries. The government has prepared harvest strategies to optimize the utilization of these tuna species such as skipjack (SKJ), yellowfin tuna (YFT), and bigeye tuna (BET) in these waters. This paper aims to provide an overview of the characteristics of these fisheries in Indonesian archipelagic waters based on a descriptive analysis of fishing logbook and observer program data received by the Ministry of Marine Affairs and Fisheries. The study shows that during the 2019-2021 period the number of purse seine (PS) trips was relatively stable while hand line (HL) and pole and line (PL) tended to increase. In 2021, the catch composition of PS was dominated by SKJ (73%) and YFT (27%). PL caught SKJ 83% and YFT 17%, while HL's catch was significantly comprised of YFT (95%), BET (2%), and SKJ (3%). BET was predominantly distributed in FMAs 714 and 715, whereas the fishing grounds for YFT closely resembled those for SKJ. The results also provided information that the size composition of tuna species varied based on the fishing gears operated. The mean length of each species caught by PS was smaller than other gears, namely SKJ at 36.9 cm, YFT at 40.22 cm, and BET at 52.87 cm. Therefore, immediate management actions are needed to prevent juvenile capture in the area to ensure the sustainability of tropical tuna fisheries.

Rumpon, as a fish-aggregating device, has long been used by tuna handline fishermen in Bone Bay, South Sulawesi Province, Indonesia. Information on the characteristics of tuna handline fishing in the area is very limited and is very much needed as study material for tuna fishing strategies and fisheries policies. This research aims to understand the results of handline catches and sustainable solutions for tuna fisheries in rumpon areas. The data used is the result of observations using 19 ships based at PPI Lonrae and data collection for 5 years (2018-2022). The results show that the composition of the main catch is dominated by yellowfin tuna (Thunnus albacares), bigeye tuna (Thunnus obesus), and skipjack tuna (Katsuwonus pelamis). In general, the size of fish that are not suitable for catching for the yellowfin tuna, bigeye tuna, and skipjack tuna, consecutively, is 54.0%, 45.1%, and 31.9%. This finding further clarifies that the percentage of tuna and skipjack tuna that are not suitable for catching is still very large. Continuous and large-scale fishing of juvenile tuna could cause fish resources to continue to decline in the future. Technically, what fishermen need to understand is, in addition to the strategy of lowering fishing gear deeper, the time of fishing and the type of bait used.

Abstract. Hidayati D, Oclandhi B, Maulidinia N, Sa’adah NN, Nurhayati APD. 2019. Short Communication: The species and body size composition of pelagic fishes that caught by troll line in the fish landing of Sendang Biru, East Java, Indonesia. Biodiversitas 20: 1764-1769. Troll line is the most used pelagic fishing gear for fishermen in Sendang Biru, the part of Indian ocean at East Java, which have an impact on the catch composition. The study was aimed to obtain data on species composition and size of pelagic fish caught in troll line in Sendang Biru, East Java, Indonesia. Fish samples were collected from nine different vessels landed in Sendang Biru for three days in April 2018. The composition of fish species was measured based on relative abundance. The fish size composition was obtained by measuring fork length which is also used to determine the stage of development of juvenile (Jv) or adult (Ad) fish. The results of the research showed there were four pelagic fish species which dominated by Katsuwonus pelamis or skipjack tuna (50.05%) and Thunnus albacares or yellowfin tuna (47.95%) and a small amount of Coryphaena hippurus and Makaira mazara. According to the body size, the fish caught by troll line in Sendang Biru is dominated by adult skipjack tuna (41-60 cm) and juvenile yellowfin tuna (21-78 cm).

Defining the stock structures of key commercial tunas in the Pacific Ocean I: Current knowledge and main uncertainties

The influence of multiple anchored fish aggregating devices (FADs) on the spatial behavior of yellowfin (Thunnus albacares) and bigeye tuna (T. obesus) was investigated by equipping all thirteen FADs surrounding the island of Oahu (HI, USA) with automated sonic receivers (“listening stations”) and intra-peritoneally implanting individually coded acoustic transmitters in 45 yellowfin and 12 bigeye tuna. Thus, the FAD network became a multi-element passive observatory of the residence and movement characteristics of tuna within the array. Yellowfin tuna were detected within the FAD array for up to 150 days, while bigeye tuna were only observed up to a maximum of 10 days after tagging. Only eight yellowfin tuna (out of 45) and one bigeye tuna (out of 12) visited FADs other than their FAD of release. Those nine fish tended to visit nearest neighboring FADs and, in general, spent more time at their FAD of release than at the others. Fish visiting the same FAD several times or visiting other FADs tended to stay longer in the FAD network. A majority of tagged fish exhibited some synchronicity when departing the FADs but not all tagged fish departed a FAD at the same time: small groups of tagged fish left together while others remained. We hypothesize that tuna (at an individual or collective level) consider local conditions around any given FAD to be representative of the environment on a larger scale (e.g., the entire island) and when those conditions become unfavorable the tuna move to a completely different area. Thus, while the anchored FADs surrounding the island of Oahu might concentrate fish and make them more vulnerable to fishing, at a meso-scale they might not entrain fish longer than if there were no (or very few) FADs in the area. At the existing FAD density, the ‘island effect’ is more likely to be responsible for the general presence of fish around the island than the FADs. We recommend further investigation of this hypothesis.

The Biochemical properties of myosins prepared from the frozen muscle of a few marine fish species and tilapia (a tropical freshwater fish) have been compared. 1) For various myosin preparations ATP-sensitivity values varied between 2 and 5. 2) Skipjack tuna myosin was found to retain remarkably high Ca2+-ATPase specific activity, while those of yellowtail and bigeye tuna had comparatively lower values. 3) Certain effectors, such as KCl, Ca2+ and Mg2+ showed essentially the same effects on fish myosin ATPases as they do on rabbit skeletal muscle myosin. 4) The sulfhydryl group contents (moles per 5×105g) were found to be 37-38 for skipjack tuna, yellowfin tuna and white marline myosins along with that of tilapia. Myosins of yellowtail and bigeye tuna were found to contain as few as 30-33 sulfhydryl groups. 5) When the relative thermo-stabilities of these myosins were compared in terms of the inactivation of Ca2+ATPase at 35°C, the sequence was found to be: tilapia, skipjack tuna, yellowfin tuna, white marline, bigeye tuna and yellowtail in decreasing order. 6) The ability of various fish myosins to combine with rabbit actin was determined by measuring the ATP-sensitivity and the stabilization of Ca2+ATPase to thermal denaturation. It was noted that myosins from tilapia, skipjack tuna, yellowfin tuna and white marline ratain fairly good actin combining ability.

Epipelagic fish communities dominate fish assemblages and are an important part of marine ecosystems due to their high abundance, vertical migration behavior, and global distribution. Purse seine fisheries are key components of marine fisheries in the tropical Western and Central Pacific Ocean (WCPO), primarily targeting skipjack tuna (Katsuwonus pelamis, SKJ), yellowfin tuna (Thunnus albacares, YFT), and bigeye tuna (Thunnus obesus, BET). In this study, WCPO purse seine fishery data from 2014 to 2022, combined with environmental factor data, were used, and Mantel tests and correlation analysis were employed to analyze the diversity, fish coexistence mechanisms, and environmental responses of catch communities under the following two different fishing strategies: free–swimming schools (FSCs) and drifting fish aggregating devices (DFADs). Mantel tests indicated that nitrate (NO3−), the Oceanic Niño Index (ONI), and pH significantly impact the diversity of the FSCs community, whereas NO3− significantly affects the diversity of the DFADs community. Based on the correlation analysis results, in the FSCs community, yellowfin tuna was positively correlated with bigeye tuna, and yellowfin tuna was negatively correlated with skipjack tuna and black marlin (Istiompax indica, BLM). In the DFADs community, yellowfin tuna was only positively correlated with skipjack tuna and bigeye tuna. In addition, species with high correlations were also positively correlated. The results of this study provide a theoretical basis for the biodiversity conservation of catch communities under two different purse seine fishing strategies in the WCPO.

The selective capture of tunas; bigeye tuna (Thunnus obesus), skip jack tuna (Katsuwonus pelamis) and yellow fin tuna ((Thunnus albacares) is important for Japanese seine net fisheries. Classification of the species composition by using acoustic information before catching them will significantly contribute for the selective catch. Target strength spectra (TSSP) of each species were measured by a broadband split beam system. Each tuna species was separately kept in a enclosure, which sized 8 × 8 m square and approximately 5 m in depth. This system was able to measure not only TSSP but also a swimming track of individual in 3D. The differences of TSSP among three species were confirmed. For example, the target strength value of begeye whose tilt angle was 0 degree about 10 dB higher than skip jack tuna one. Swimbladder sizes were measured for each species by soft X-ray because skip jack tuna are physoclist species, and others are physostome species. There were differences of the swimbladder shape between bigeye tuna and yellow fin tuna. The TSSP seemed to be depend on not only body size (fork length), but also swimbladder shape. The TSSP could be useful information to classify among tunas.

Ten separate experiments monitoring the simultaneous behaviors of 26 skipjack (Katsuwonus pelamis), 26 bigeye (Thunnus obesus), and 33 yellowfin (T. albacares) tunas within large multi-species aggregations associated with drifting fish aggregating devices (FADs) were investigated using ultrasonic telemetry in the equatorial eastern Pacific Ocean. Experiments were conducted during a research cruise aboard a chartered purse seine vessel. Purse seine sets were made on the tuna aggregations associated with FADs at the termination of six of the ten experiments. Seventeen of the 44 tagged tunas were not recaptured indicating the transient nature of the associative behavior of tunas with FADs. Although there was considerable overlap in the depths of the three species, by day and night, there were some species-specific differences and diel differences within species. While we documented spatial and temporal differences in the schooling behavior of the three tuna species, the differences do not appear sufficient such that modifications in purse seine fishing practices could effectively avoid the capture of small bigeye and yellowfin tunas, while optimizing the capture of skipjack tuna in purse seine sets on FADs.

The biological aspect is a piece of basic information that is commonly presented in assessing the level of environmental friendliness of fishing gear or fishing vessel. This study was conducted to analyze the biological aspects of the main catch of the troll line at the Palabuhanratu Fishing Port, Sukabumi, Indonesia. The biological aspects analyzed consisted of length frequency distribution, length-weight relationship, to the average feasibility status of the caught target fish. There were three main target commodities for fishing from the troll line that was identified during the research activity, namely yellowfin tuna (Thunnus albacares), skipjack tuna (Katsuwonus pelamis), and frigate tuna (Auxis thazard). A total of 14 troll line fleets were obtained as a source of research data based on the accidental sampling method. The total number of 1404 fish consisting of 480 yellowfin tuna, 475 skipjack tuna, and 449 frigate tuna were obtained as research data objects. The stratified random sampling method was used in determining the observed sample fish data. Yellowfin tuna were distributed at size 29 – 148 cm, skipjack tuna at size 29 – 88 cm, and frigate tuna at size 23 – 82 cm. Analysis of the length-weight relationship showed a negative allometric growth pattern in the three main fishing target commodities. The analysis of the feasibility of the average fish caught based on compared of L50% to ½ L∞ shows that the average size of tuna and frigate tuna caught is undersize for catching, while the average skipjack caught has reached a legal size. The results of this study indicate that there is a need for a review of the use of fishing hooks in the fishing activity of the troll line fishing fleet. Increasing the hook size can be used to avoid catching fish that are at a size that is not suitable for catching.

Archival and acoustic tagging were carried out in the exclusive economic zone (EEZ) of Papua New Guinea (PNG) in the western Pacific Ocean during 2006–07 to investigate the vertical behavior of tropical tuna found in association with large arrays of anchored FADs. Industrialized purse-seine fishing on anchored FADs has existed in the PNG EEZ for more than a decade. Archival tags were implanted in bigeye (n = 40; length 40–90 cm FL) and yellowfin (214; length 42–126 cm FL) tuna in the Bismarck and Solomon Seas. Acoustic tags were released in the same areas in 195 tuna (10 bigeye, 116 yellowfin, 69 skipjack). In addition, 27 tuna (eight bigeye, 19 yellowfin) received both an archival and an acoustic tag. Archival tag data from 32 recaptures were categorized into the three distinct vertical behavior modes for bigeye, and the three distinct modes for yellowfin that have been described in the published literature. The depth distribution for each of the categories was then calculated to examine potential vulnerability to industrial purse-seine capture in this region. A region-specific analysis was considered important as oceanographic conditions in this region are distinctly different to the conditions reported in the published literature from other locations. Analysis of acoustic data reveals short residence times at FADs and strong school cohesion. Vertical behavior of skipjack, yellowfin and bigeye tuna that were simultaneously present at the same FAD, as determined by depth transmitting acoustic tags, suggested some vertical separation of these species. However, there was a high degree of depth overlap, particularly during early morning hours when purse seining on floating objects normally occurs in this region. This overlap limits the potential for targeting particular species or size classes of tuna through fishing depth selection. This observation was confirmed from the archival tag depth records for yellowfin and bigeye during the same time period regardless of behavior type exhibited. The recapture of bigeye and yellowfin tuna implanted with both acoustic and archival tags allowed the observation of the natural vertical behavior of these fish when they were close to anchored FADs equipped with acoustic receivers. Occupation of shallow (<100 m) depths over a 24 h period was identified as the dominant behavior exhibited on FADs.