Temperature Effects on Metabolic Rate of Juvenile Pacific Bluefin Tuna \u3ci\u3eThunnus Orientalis\u3c/i\u3e

Pacific bluefin tuna inhabit a wide range of thermal environments across the Pacific ocean. To examine how metabolism varies across this thermal range, we studied the effect of ambient water temperature on metabolic rate of juvenile Pacific bluefin tuna, Thunnus thynnus, swimming in a swim tunnel. Rate of oxygen consumption (MO2) was measured at ambient temperatures of 8–25°C and swimming speeds of 0.75–1.75 body lengths (BL) s–1. Pacific bluefin swimming at 1 BL s–1 per second exhibited a U-shaped curve of metabolic rate vs ambient temperature, with a thermal minimum zone between 15°C to 20°C. Minimum MO2 of 175±29 mg kg–1 h–1–1 was recorded at 15°C, while both cold and warm temperatures resulted in increased metabolic rates of 331±62 mg kg–1 h–1–1 at 8°C and 256±19 mg kg–1 h–1–1 at 25°C. Tailbeat frequencies were negatively correlated with ambient temperature. Additional experiments indicated that the increase in MO2 at low temperature occurred only at low swimming speeds. Ambient water temperature data from electronic tags implanted in wild fish indicate that Pacific bluefin of similar size to the experimental fish used in the swim tunnel spend most of their time in ambient temperatures in the metabolic thermal minimum zone

Seasonal Movements, Aggregations and Diving Behavior of Atlantic Bluefin Tuna (Thunnus thynnus) Revealed with Archival Tags

Electronic tags were used to examine the seasonal movements, aggregations and diving behaviors of Atlantic bluefin tuna (Thunnus thynnus) to better understand their migration ecology and oceanic habitat utilization. Implantable archival tags (n = 561) were deployed in bluefin tuna from 1996 to 2005 and 106 tags were recovered. Movement paths of the fish were reconstructed using light level and sea-surface-temperature-based geolocation estimates. To quantify habitat utilization we employed a weighted kernel estimation technique that removed the biases of deployment location and track length. Throughout the North Atlantic, high residence times (167±33 days) were identified in four spatially confined regions on a seasonal scale. Within each region, bluefin tuna experienced distinct temperature regimes and displayed different diving behaviors. The mean diving depths within the high-use areas were significantly shallower and the dive frequency and the variance in internal temperature significantly higher than during transit movements between the high-use areas. Residence time in the more northern latitude high-use areas was significantly correlated with levels of primary productivity. The regions of aggregation are associated with areas of abundant prey and potentially represent critical foraging habitats that have seasonally abundant prey. Throughout the North Atlantic mean diving depth was significantly correlated with the depth of the thermocline, and dive behavior changed in relation to the stratification of the water column. In this study, with numerous multi-year tracks, there appear to be repeatable patterns of clear aggregation areas that potentially are changing with environmental conditions. The high concentrations of bluefin tuna in predictable locations indicate that Atlantic bluefin tuna are vulnerable to concentrated fishing efforts in the regions of foraging aggregations

MIGRATORY MOVEMENTS OF PACIFIC BLUEFIN TUNA OFF CALIFORNIA

The genus Thunnus of the family Scombridae includes three species of bluefin tunas (Atlantic bluefin tuna – T. thynnus, Pacific bluefin tuna - T. orientalis and southern bluefin tuna - T. maccoyii). The bluefin tunas were first recognized as two independent species (Northern and Southern bluefin) based on subtle differences in morphological characters. Northern bluefin tunas are now recognized as morphologically, geographically and genetically separate species located in the Atlantic and Pacific oceans.The Pacific bluefin (T. orientalis) is the only species which remains unmanaged; this lack of management persists despite intensive fisheries on both sides of the Pacific. The current life history model indicates that these fish spawn in the western Pacific (Sea of Japan, Philippine Sea and East China Sea). Either late in the first year or early in the second year, a portion of the population migrates to the western coast of the United States and Mexico, a journey of over 8700 km (Bayliff et al., 1991). The young fish that have migrated into the eastern Pacific are thought to remain there for several years, feeding on sardines and anchovies in regions of intense upwelling (Bayliff et al., 1991, Bayliff, 1993). While these tuna are fished only seasonally off California and Mexico, they may be a year-round resident (Bayliff, 1991). The migrants then travel back to the western Pacific to spawn. Why some bluefin remain in the western Pacific while others migrate across the ocean basin is unresolved. How long they stay in the eastern Pacific, what habitats are most important, what triggers their return to the west is unclear

Influence of Swimming Speed on Metabolic Rates of Juvenile Pacific Bluefin Tuna and Yellowfin Tuna

Bluefin tuna are endothermic and have higher temperatures, heart rates, and cardiac outputs than tropical tuna. We hypothesized that the increased cardiovascular capacity to deliver oxygen in bluefin may be associated with the evolution of higher metabolic rates. This study measured the oxygen consumption of juvenile Pacific bluefin Thunnus orientalis and yellowfin tuna Thunnus albacares swimming in a swim-tunnel respirometer at 20°C. Oxygen consumption ( Mo2) of bluefin (7.1–9.4 kg) ranged from 235 ± 38 mg kg-1 h-1 at 0.85 body length (BL) s-1 to 498 ± 55 mg kg-1 h-1 at 1.80 BL s-1. Minimal metabolic rates of swimming bluefin were 222 ± 24 mg O2 kg-1 h-1 at speeds of 0.75 to 1.0 BL s-1. Mo2 of T. albacares (3.7–7.4 kg) ranged from 164 ± 18 mg kg-1 at 0.65 BL s-1 to 405 ± 105 mg kg-1 h-1 at 1.8 BL s-1. Bluefin tuna had higher metabolic rates than yellowfin tuna at all swimming speeds tested. At a given speed, bluefin had higher metabolic rates and swam with higher tailbeat frequencies and shorter stride lengths than yellowfin. The higher Mo2 recorded in Pacific bluefin tuna is consistent with the elevated cardiac performance and enhanced capacity for excitation-contraction coupling in cardiac myocytes of these fish. These physiological traits may underlie thermal-niche expansion of bluefin tuna relative to tropical tuna species

Acoustic Telemetry Monitors Movements of Wild Adult Catfishes in the Mekong River, Thailand and Laos

Research on fish movement and habitat use in large tropical rivers is urgently needed to protect fisheries that are a primary source of protein for millions of people. In this pilot study, acoustic telemetry was used to monitor movements of wild catfishes in a 94.6 rkm reach of Mekong River, where it functions as the border between Thailand and Lao People’s Democratic Republic (PDR). Twenty fish were tagged and released in May 2006 and monitored through May 2007 with 17 fixed-site acoustic receivers. Ten receivers had detection probabilities ranging from 0.67 to 1.00, and five receivers had detection probabilities of 0.50 or less. Detection probability was not correlated with river width. Eighteen (90%) of the tagged fish were detected by at least one receiver. Monitoring durations of individual fish ranged from 0.1 to 354.4 days. The longest total movement was 88.3 rkm, while the longest upstream movement was 52.1 rkm. Movement rates ranged from 0.1 to 156.7 rkm/d. This work provided preliminary data on movement patterns of wild Mekong catfishes. The methods and lessons learned from this study can be used for future positional telemetry research to address management-relevant uncertainties about migration corridors, habitat use, efficacy of fish reserves, and river development planning

Tissue Turnover Rates and Isotopic Trophic Discrimination Factors in the Endothermic Teleost, Pacific Bluefin Tuna (<em>Thunnus orientalis</em>)

<div><p>Stable isotope analysis (SIA) of highly migratory marine pelagic animals can improve understanding of their migratory patterns and trophic ecology. However, accurate interpretation of isotopic analyses relies on knowledge of isotope turnover rates and tissue-diet isotope discrimination factors. Laboratory-derived turnover rates and discrimination factors have been difficult to obtain due to the challenges of maintaining these species in captivity. We conducted a study to determine tissue- (white muscle and liver) and isotope- (nitrogen and carbon) specific turnover rates and trophic discrimination factors (TDFs) using archived tissues from captive Pacific bluefin tuna (PBFT), <em>Thunnus orientalis</em>, 1–2914 days after a diet shift in captivity. Half-life values for ¹⁵N turnover in white muscle and liver were 167 and 86 days, and for ¹³C were 255 and 162 days, respectively. TDFs for white muscle and liver were 1.9 and 1.1‰ for <em>δ</em>¹⁵N and 1.8 and 1.2‰ for <em>δ</em>¹³C, respectively. Our results demonstrate that turnover of ¹⁵N and ¹³C in bluefin tuna tissues is well described by a single compartment first-order kinetics model. We report variability in turnover rates between tissue types and their isotope dynamics, and hypothesize that metabolic processes play a large role in turnover of nitrogen and carbon in PBFT white muscle and liver tissues. ¹⁵N in white muscle tissue showed the most predictable change with diet over time, suggesting that white muscle <em>δ</em>¹⁵N data may provide the most reliable inferences for diet and migration studies using stable isotopes in wild fish. These results allow more accurate interpretation of field data and dramatically improve our ability to use stable isotope data from wild tunas to better understand their migration patterns and trophic ecology.</p> </div

Parameter estimates and 95% confidence intervals for metabolic constant (<i>m</i>) from time-based exponential fits to <i>δ</i>¹⁵N and <i>δ</i>¹³C data for Pacific bluefin tuna (<i>Thunnus orientalis</i>) white muscle and liver.

<p>Estimates and 95% confidence intervals of proportion of turnover due to growth (<i>P_g</i>) and metabolism (<i>P_m</i>) is shown for each tissue and isotope.</p