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In the Western and Central Pacific Ocean (WCPO), which accounts for over half of world tuna production, purse seine effort and catch on floating objects have increased significantly due to a rapid increase in the use of fixed and free-floating fish aggregation devices (FADs). FAD fishing has had an impact on the current status of the stocks of the three main target tunas in the equatorial WCPO, skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye (T. obesus). FADs have been shown to influence the behaviour and movement patterns of the three tuna species with the juveniles of each species occupying shallower habitats when associated with FADs. Aggregation of tunas around drifting objects increases their vulnerability to purse seine gear, particularly for juvenile and small size classes. Further to the impacts on the target stocks, the use of FADs has increased the vulnerability of other fishes to the purse seine method, including some shark and billfish species. Given the concern over FAD-related fishing effort on target and bycatch species, there is a need to understand how FAD use affects target and bycatch stocks. Science needs to better support management decisions are highlighted including the need to identify the magnitude of broader community-level affects. [ABSTRACT FROM AUTHOR]

The Western and Central Pacific Ocean sustains the highest tuna production in the world. This province is also characterized by many islands and a complex bathymetry that induces specific current circulation patterns with the potential to create a high degree of interaction between coastal and oceanic ecosystems. Based on a large dataset of oceanic predator stomach contents, our study used generalized linear models to explore the coastal-oceanic system interaction by analyzing predatorprey relationship. We show that reef organisms are a frequent prey of oceanic predators. Predator species such as albacore (Thunnus alalunga) and yellowfin tuna (Thunnus albacares) frequently consume reef prey with higher probability of consumption closer to land and in the western part of the Pacific Ocean. For surface-caught-predators consuming reef prey, this prey type represents about one third of the diet of predators smaller than 50 cm. The proportion decreases with increasing fish size. For predators caught at depth and consuming reef prey, the proportion varies with predator species but generally represents less than 10%. The annual consumption of reef prey by the yellowfin tuna population was estimated at 0.8±0.40CV million tonnes or 2.17±1012±0.40CV individuals. This represents 6.1%±0.17CV in weight of their diet. Our analyses identify some of the patterns of coastal-oceanic ecosystem interactions at a large scale and provides an estimate of annual consumption of reef prey by oceanic predators. [ABSTRACT FROM AUTHOR]

8217 days of data downloaded from 47 archival tags, recovered from bigeye tuna ( Thunnus obesus ) 51–134 cm in length ( x ¯ = 86.9 c m ) , 0.87–3.44 years of age ( x ¯ = 1.89 years ) at liberty from 36 to 851 days ( x ¯ = 183 days ) in the equatorial central Pacific Ocean, are evaluated herein. Analyses of depth and temperature records resulted in the classification of three daily behavior types: characteristic, associative (associated with floating objects), and other. For three defined length classes, 54–79.9 cm, 80–99.9 cm, and 100–134 cm, when exhibiting characteristic behavior, the proportions of time and average durations of events were 45.3% ( x ¯ = 5.1 days ) , 62.6% ( x ¯ = 8.5 days ) , 79.2% ( x ¯ = 17.5 days ) , and the average daytime depths and temperatures were 284 m and 12.6 °C, 305 m and 12.7 °C, and 312 m and 12.1 °C, respectively. For the same three length classes, when exhibiting associative behavior, the proportions of time and average durations of events were 9.5% ( x ¯ = 1.9 days ) , 4.8% ( x ¯ = 1.9 days ) , and 6.0% ( x ¯ = 1.8 days ) , and the average daytime depths and temperatures were 101 m and 23.2 °C, 105 m and 23.1 °C, and 74 m and 22.3 °C, respectively. There is a significant positive correlation between the proportion of time fish exhibits characteristic behavior and fish length, and significant negative correlations between the proportion of time bigeye tuna exhibit associative and other behavior with fish length. Behavior and habitat preferences of bigeye tuna should be considered for standardizing catch-per-unit of effort (CPUE) data from both longline and purse-seine fisheries targeting tropical tunas in the Pacific, in an effort to provide more reliable estimates of relative abundance. [ABSTRACT FROM AUTHOR]

In the western and Central Pacific Ocean mark-recapture experiments have been an integral part of monitoring tuna stocks since the late 1970s. The data from tagging campaigns have been included in stock assessments since the 1980s and in integrated analyses since the late 1990s. Ensuring that tagging experiments are implemented in a manner that satisfies the incorporation of the data in stock assessment is important to maximize the return on investment. We review three large scale tuna experiments implemented in the western and central Pacific Ocean to synthesize the lessons learned so that future tagging programmes can save considerable time and money, and maximize the quantity and quality of the data needed to obtain more accurate and precise assessments of stock status. We highlight particular knowledge gaps that require further attention, and suggest some approaches, both technological and methodological, from which future studies could benefit in order to improve our understanding of tuna biology. [ABSTRACT FROM AUTHOR]

A total of 31,242 bigeye tuna was captured, tagged, and released, 30,793 with dart tags (DTs) and 449 with geolocating archival tags (ATs), in the equatorial central Pacific Ocean along the 140° W, 155° W, 170° W, and 180° meridians, during 2008 through 2012, of which 10,029 (32.1%) of the DTs and 74 (16.5%) of the ATs were returned. A subset of high-confidence filtered DT data was retained for 5807 fish at liberty for 30 d or more, for evaluating linear displacements from release to recapture positions. For the filtered DT data, days at liberty ranged from 30 to 1701 d (median = 187 d). Linear displacements ranged from 1 to 5372 nautical miles (M) (median = 936 M), with 71% eastward and 29% westward, and 95% within 3614 M of their release positions. The data indicate significant differences in the linear displacements by release locations, days at liberty, and fish length at release. An unscented Kalman filter model with sea-surface temperature measurements integrated (UKFsst) was used to process 48 AT data sets from bigeye tuna at liberty for 30 d or longer, to obtain most probable tracks, improved estimates of geographic positions, and movement parameters. The 95% volume contours surrounding the position estimates, along the most probable tracks from bigeye tuna releases along the 140° W, 155° W, 170° W, and 180° meridians show substantial overlap. For the pooled AT data sets, the median parameter estimates from the UKFsst model for errors in longitude ( σ x ) and latitude ( σ y ) were 0.52° and 1.75°, for directed eastward and northward movements ( u and v ) were −2.01 M/d and −1.41 M/d, and for dispersive movement ( D ) was 496.7 M 2 /d. The linear displacements and most probable tracks obtained from these tagging data demonstrate constrained latitudinal dispersion, some regional fidelity, some extensive eastward longitudinal dispersion, and substantial mixing of bigeye tuna between release longitudes. The amount of mixing of bigeye tuna among these release areas in the equatorial central Pacific Ocean, with those in adjacent areas of the equatorial eastern and western Pacific Ocean, is dependent on distances between areas, with, in general, the greatest mixing occurring between the areas that are closest to one another. [ABSTRACT FROM AUTHOR]