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bluefin research
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bluefin research
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Background
Bluefin tuna have been studied for decades and while many important discoveries have been made about their life history and biology, there are still many questions left unanswered. This is due, in part, to the lack of access to the animals, their size and movement across entire ocean basins. Collaboration among scientists from around the world is making it easier to study this elusive fish. Below is a list of past and current research being conducted at the Large Pelagics Research Lab which is helping to answer some of the current issues surrounding bluefin tuna management.
In the early 90's, fishermen and representatives from the East Coast Tuna Association concerned about upcoming reductions to the western Atlantic bluefin quota (due to low estimates of abundance) approached the New England aquarium in hopes of initiating a project that would provide more accurate estimates of abundance. Fishermen were convinced that the numbers of bluefin tuna in the Gulf of Maine were higher than those estimated by management. To answer this questions researchers turned to volunteer bluefin spotter pilots. Armed with a laptop computer, GPS and camera, pilots photographed and documented bluefin schools in the Gulf of Maine. From 1993-1997 spotter pilots logged between 52,828-82,666 nautical miles of searching effort and photographed over 2,365 geo-referenced schools. The long-term goal of this project was to develop fishery-independent estimates of abundance. This information was the first of it's kind: fishery-linked spotter pilot surveys allowed researchers to learn more about the distribution and numbers of bluefin tuna without having to catch the fish to obtain the data. Independent estimates of abundance were needed since the relationship between fisheries catches and real abundance for a highly migratory species is rarely, if ever, associated. Aerial surveys also serve to help researchers understand the relationship of bluefin tuna to their environment and to their prey species.
An aerial survey was also conducted in 1995 in Great Bahama Bank in conjunction with the Southeast Fisheries Science Center, to document the apparent abundance and migration behavior of giant bluefin tuna. This survey was designed to compare results to prior surveys in the 1950s and 1970s. The number of bluefin observed was within the range of tuna counted in the prior survey. It was found that the schooling behavior of bluefin tuna traveling in "Tuna Alley" (where the survey was conducted) differed substantially from the behavior observed in tuna in the Gulf of Maine aerial surveys. The fish in the Bahamas survey spent little time at the surface and didn't exhibit cartwheeling behaviors (as seen above). All of the tuna observed during this survey were estimated by pilots to be large giants, while bluefin tuna documented in New England spanned a much broader range of class sizes.
Perhaps one of the most interesting finds was the observation of a small tuna school positioning into a "soldier formation" when a swimmer jumped into the water. This formation is thought to be a defense mechanism or hunting strategy.
Dr. Lutcavage and colleagues (Dr. Rich Brill, National Marine Fisheries Service, Jen Goldstein of UMass Boston, and Brad Chase and Greg Skomal of the Massachusetts Division of Fisheries), collaborated with commercial fishermen Jeff Tutein and Bill Chaprales to study bluefin tuna biology and behavior through hydroacoustic tracking. The goal of this research was to characterize how much time bluefin tuna schools spend at the surface, how fast they travel, and what their environmental preferences are. This information is important for developing direct assessments using aerial surveys, leading to better estimates of bluefin abundance. 
With the help of a spotter plane researchers located a bluefin school and using a modified harpoon (developed by Chaprales) attached a small sound-emitting device, called an acoustic "pinger" into one of the bluefin as it swam at the surface with it's school. The pinger emits a specified high frequency coded pulse that transmits information about the fish's location, depth, direction and speed. These signals were recorded by vessels equipped with specialized ultrasonic receivers that were attached to underwater hydrophones on a nearby vessel. Researchers listened for these signals and relayed to the captain which direction to go (see picture left).
Results from this research have shown that bluefin schools in the Gulf of Maine may travel as far as 30 miles per day (see tracks right). They spend very little time at the surface (where they can be seen by aircraft), but over 90% of their time in waters shallower than 110 feet. Giant bluefin made deep dives at dusk and dawn, sometimes traveling all the way to the bottom.
Population Modeling, Spatial and Environmental Analyses
Migration paths and movements of many large pelagic animals, usually long-lived species, are complex and highly variable. Their behavioral patterns vary by age, geographic region, oceanographic conditions, and whether they are feeding, traveling, or engaged in reproduction. Our research group is attempting to understand animal behavior through the development of movement models that use data obtained from tracking and tagging research. We can then use this information to describe and predict future behavior based on realistic biological and environmental inputs. Realistic movement models will help us better understand how and why pelagic animals alter their distributions, and should improve population assessments. Our modeling work also addresses basic ecological questions of optimal foraging patterns and environmental associations. This work has been undertaken with a diverse group of modelers that span broad areas of expertise in mathematics, ecology, and spatial statistics.
An example of movement models under development for bluefin tuna that use data from popup satellite tags (Sibert et al http://www.hawaii.edu/HIMB/Faculty/sibert.html,) is on the right. The upper panel shows results of a biased random walk, and the lower an advection-diffusion model. Each figure indicates the distribution of bluefin tuna after 12 months at liberty.
Our current projects and collaborators include:
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