The Pacific Decadal Oscillation (PDO) has been described by some as a long-lived El Nino-like pattern of Pacific climate variability, and by others as a blend of two sometimes independent modes having distinct spatial and temporal characteristics of North Pacific sea surface temperature (SST) variability. A growing body of evidence highlights a strong tendency for PDO impacts in the Southern Hemisphere, with important surface climate anomalies over the mid-latitude South Pacific Ocean, Australia and South America. Several independent studies find evidence for just two full PDO cycles in the past century: “cool” PDO regimes prevailed from 1890–1924 and again from 1947–1976, while “warm” PDO regimes dominated from 1925–1946 and from 1977 through (at least) the mid-1990's. Interdecadal changes in Pacific climate have widespread impacts on natural systems, including water resources in the Americas and many marine fisheries in the North Pacific. Tree-ring and Pacific coral based climate reconstructions suggest that PDO variations—at a range of varying time scales—can be traced back to at least 1600, although there are important differences between different proxy reconstructions. While 20th Century PDO fluctuations were most energetic in two general periodicities—one from 15-to-25 years, and the other from 50-to-70 years—the mechanisms causing PDO variability remain unclear. To date, there is little in the way of observational evidence to support a mid-latitude coupled air-sea interaction for PDO, though there are several well-understood mechanisms that promote multi-year persistence in North Pacific upper ocean temperature anomalies.

https://link.springer.com/content/pdf/10.1023%2FA%3A1015820616384.pdf

The Pacific Decadal Oscillation

The Atlantic bluefin tuna is at the centre of an international debate in fisheries conservation. Last summer the western Atlantic bluefin tuna fishery collapsed and some conservationists say it will not recover unless the International Commission for Conservation of Atlantic Tunas adopts a tougher regime. Results from an electronic tagging programme on bluefin tuna are presented this week, and they make alarming reading. Western tagged bluefin tuna are shown to migrate freely across the international stock boundary into the eastern Atlantic, where they are vulnerable to European fisheries; and both known spawning grounds, in the Gulf of Mexico and the Mediterranean Sea, are shown to be linked to the endangered western Atlantic fishery. Electronic tags that archive or transmit stored data to satellites have advanced the mapping of habitats used by highly migratory fish in pelagic ecosystems1,2,3,4,5,6. Here we report on the electronic tagging of 772 Atlantic bluefin tuna in the western Atlantic Ocean in an effort to identify population structure. Reporting electronic tags provided accurate location data7,8,9 that show the extensive migrations of individual fish (n = 330). Geoposition data delineate two populations, one using spawning grounds in the Gulf of Mexico and another from the Mediterranean Sea. Transatlantic movements of western-tagged bluefin tuna reveal site fidelity to known spawning areas in the Mediterranean Sea. Bluefin tuna that occupy western spawning grounds move to central and eastern Atlantic foraging grounds. Our results are consistent with two populations of bluefin tuna with distinct spawning areas that overlap on North Atlantic foraging grounds. Electronic tagging locations, when combined with US pelagic longline observer and logbook catch data, identify hot spots for spawning bluefin tuna in the northern slope waters of the Gulf of Mexico. Restrictions on the time and area where longlining occurs would reduce incidental catch mortalities on western spawning grounds.

Electronic tagging and population structure of Atlantic bluefin tuna

The deployment of electronic data storage tags that are surgically implanted or satellite-linked provides marine researchers with new ways to examine the movements, environmental preferences, and physiology of pelagic vertebrates. We report the results obtained from tagging of Atlantic bluefin tuna with implantable archival and pop-up satellite archival tags. The electronic tagging data provide insights into the seasonal movements and environmental preferences of this species. Bluefin tuna dive to depths of >1000 meters and maintain a warm body temperature. Western-tagged bluefin tuna make trans-Atlantic migrations and they frequent spawning grounds in the Gulf of Mexico and eastern Mediterranean. These data are critical for the future management and conservation of bluefin tuna in the Atlantic.

/pdf/migratory-movements-depth-preferences-and-thermal-biology-of-2mwl59uvxf.pdf

Migratory movements, depth preferences, and thermal biology of Atlantic bluefin tuna.

Fish population variability and fisheries activities are closely linked to weather and climate dynamics. While weather at sea directly affects fishing, environmental variability determines the distribution, migration, and abundance of fish. Fishery science grew up during the last century by integrating knowledge from oceanography, fish biology, marine ecology, and fish population dynamics, largely focused on the great Northern Hemisphere fisheries. During this period, understanding and explaining interannual fish recruitment variability became a major focus for fisheries oceanographers. Yet, the close link between climate and fisheries is best illustrated by the effect of “unexpected” events—that is, nonseasonal, and sometimes catastrophic—on fish exploitation, such as those associated with the El Nino–Southern Oscillation (ENSO). The observation that fish populations fluctuate at decadal time scales and show patterns of synchrony while being geographically separated drew attention to oceanograph...

http://www.stccmop.org/files/images/Journal%20of%20Climate%202006%20Lehodey(1).pdf

Climate Variability, Fish, and Fisheries

Both old and new information on the biology and ecology of Atlantic bluefin tuna have confronted scientists with research challenges: research needs to be connected to current stock- assessment and management issues. We review recent studies on habitat, migrations and population structure, stressing the importance of electronic tagging results in the modification of our perception of bluefin tuna population dynamics and behaviour. Additionally, we question, from both scientific and management perspectives, the usefulness of the classical stock concept and suggest other approaches, such as Clark's contingent and metapopulation theories. Current biological information confirms that a substantial amount of uncertainty still exists in the understanding of reproduction and growth. In particular, we focus on intriguing issues such as the difference in age-at-maturity between West Atlantic and Mediterranean bluefin tuna. Our description of Atlantic bluefin tuna fisheries places today's fishing patterns within the two millennium history of exploitation of this species: we discuss trap fisheries that existed between the 17th and the early 20th centuries; Atlantic fisheries during the 1950s and 1960s; and the consequences of the recent development of the sushi-sashimi market. Finally, we evaluate stock status and management issues since the early 1970s. While important uncertainties remain, when the fisheries history is confronted with evidence from biological and stock-assessment studies, results indicate that Atlantic bluefin tuna has been undergoing heavy overfishing for a decade. We conclude that the current exploitation of bluefin tuna has many biological and economic traits that have led several fish stocks to extreme depletion in the past.

/pdf/atlantic-bluefin-tuna-population-dynamics-ecology-fisheries-3z8u3ya3ga.pdf

Atlantic bluefin tuna: population dynamics, ecology, fisheries and management

Twenty giant bluefin tuna were captured in September and October 1997 and tagged and released with pop-up satellite tags programmed to jettison from March through July, 1998. Seventeen tags success...

Results of pop-up satellite tagging of spawning size class fish in the Gulf of Maine: do North Atlantic bluefin tuna spawn in the mid-Atlantic?

Since 1997, 58 single point and 21 light-sensing pop-up archival satellite tags (Microwave Telemetry, Inc., Columbia, MD) were deployed on giant bluefin tuna (Thunnus thynnus) (178-266 cm SFL) in the western north Atlantic The goals of the initial deployments were to test external tag attachments and the tags themselves, which evolved to include greater data logging capacity, additional sensors, and increased power. All of the tags were deployed on fish from New England and Canadian commercial or charter fishing vessels (harpoon, rod and reel, trap, and purse seine) using tag attachment techniques developed by the U.S. fishermen (Murray, Chaprales, Mendillo, and Genovese). Attachment periods ranged from 5 365 days, although the majority of tags detached from the fish over the presumed spawning period (April July). Tag reporting success rates were 59% for single point tags and 79% (15 out of 19 due) for the archival tags. Three tags (shed from large fish in Canada) reported from land. Without exception, results from 1997-2000 tagging showed that all tagged fish were in the central Atlantic when their tags reported, and 30-58 % annually were in the eastern management area. Our high tag reporting success rates is attributed to the experience of fishermen tagging partners, appropriate handling of the bluefin tuna during capture and tagging, careful tag placement, and proper storage and handling of the satellite tags. Data capable of depicting full migration paths and environmental associations (80 270 days) of ten fish (193-266 cm) are now available. Data successfully returned from the archival tags will generate geolocation estimates and errors associated with light-derived data. In 2000, the deployment of pop-up archival tags for 365-500 day attachments is planned.

Paul W Howey

Papers

Results of pop-up satellite tagging of spawning size class fish in the Gulf of Maine: do North Atlantic bluefin tuna spawn in the mid-Atlantic?

Summary of pop-up satellite tagging of giant bluefin tuna in the joint us-canadian program, gulf of maine and canadian