Showing papers by "Molly Lutcavage published in 2016"

Discovery of a spawning ground reveals diverse migration strategies in Atlantic bluefin tuna (Thunnus thynnus)

Abstract: Atlantic bluefin tuna are a symbol of both the conflict between preservationist and utilitarian views of top ocean predators, and the struggle to reach international consensus on the management of migratory species. Currently, Atlantic bluefin tuna are managed as an early-maturing eastern stock, which spawns in the Mediterranean Sea, and a late-maturing western stock, which spawns in the Gulf of Mexico. However, electronic tagging studies show that many bluefin tuna, assumed to be of a mature size, do not visit either spawning ground during the spawning season. Whether these fish are spawning in an alternate location, skip-spawning, or not spawning until an older age affects how vulnerable this species is to anthropogenic stressors including exploitation. We use larval collections to demonstrate a bluefin tuna spawning ground in the Slope Sea, between the Gulf Stream and northeast United States continental shelf. We contend that western Atlantic bluefin tuna have a differential spawning migration, with larger individuals spawning in the Gulf of Mexico, and smaller individuals spawning in the Slope Sea. The current life history model, which assumes only Gulf of Mexico spawning, overestimates age at maturity for the western stock. Furthermore, individual tuna occupy both the Slope Sea and Mediterranean Sea in separate years, contrary to the prevailing view that individuals exhibit complete spawning-site fidelity. Overall, this complexity of spawning migrations questions whether there is complete independence in the dynamics of eastern and western Atlantic bluefin tuna and leads to lower estimates of the vulnerability of this species to exploitation and other anthropogenic stressors.

Declining Mercury Concentrations in Bluefin Tuna Reflect Reduced Emissions to the North Atlantic Ocean

Abstract: Tunas are apex predators in marine food webs that can accumulate mercury (Hg) to high concentrations and provide more Hg (∼40%) to the U.S population than any other source. We measured Hg concentrations in 1292 Atlantic bluefin tuna (ABFT, Thunnus thynnus) captured in the Northwest Atlantic from 2004 to 2012. ABFT Hg concentrations and variability increased nonlinearly with length, weight, and age, ranging from 0.25 to 3.15 mg kg–1, and declined significantly at a rate of 0.018 ± 0.003 mg kg–1 per year or 19% over an 8-year period from the 1990s to the early 2000s. Notably, this decrease parallels comparably reduced anthropogenic Hg emission rates in North America and North Atlantic atmospheric Hg0 concentrations during this period, suggesting that recent efforts to decrease atmospheric Hg loading have rapidly propagated up marine food webs to a commercially important species. This is the first evidence to suggest that emission reduction efforts have resulted in lower Hg concentrations in large, long-live...

Sailfish migrations connect productive coastal areas in the West Atlantic Ocean

Abstract: Isla Mujeres, Mexico is home to one of the most well-known aggregations of sailfish. Despite its fisheries prominence, little is known about this sailfish assemblage, or its relationship to other aggregation sites in the western Atlantic. In January 2012, April 2013 and 2014, we deployed 34 popup satellite archival tags on sailfish in order to study their behavior, population connectivity and biophysical interactions. Sailfish were monitored for up to one year, and displayed (1) predominantly shelf associated activity (2) occupancy of the Yucatan Current near Isla Mujeres for up to five months and (3) subsequent dispersals from the Yucatan to productive coastal areas in the Gulf of Mexico, the Caribbean Sea and along the South American coast. Tagged sailfish occupied a median temperature of 26.4°C (interquartile range, IQR = 2.5 °C; range = 12.3-33.3 °C) and median depth of 4.4 m (IQR = 19 m; range = 0-452 m). Diel activity was present and individuals made distinctive descents before sunrise and sunset. Tracking missions of sufficient duration (~1 year) revealed previously undetected connectivity between western Atlantic sailfish fisheries and pelagic longline catches, and highlighted how fishery independent tagging can improve understanding of sailfish migrations and behavior for assessment and management.

Fish tagging via RFID and bluetooth: Crowdsourced fish tracking through better reporting tools

Abstract: Conventional tagging methods using plastic streamer tags have been the most widely used tool for elucidating fish movements in the last half century. With a very high failure rate, these methods for fish tagging and tracking are unreliable and prohibitively expensive for tracking global fish populations. Under the current method, fishermen are required to remember the time and location of the catch, the size of the fish, and the weight of the fish. In order to report a tagged fish, a fisherman cuts off and keeps the tag from the fish. Later, the fisherman must go back and submit the form using the information they can remember from earlier in the day or even several days ago. The long delay and relative difficulty between catch and data entry creates a barrier to data collection. The Olin College of Engineering Intelligent Vehicles Laboratory, in partnership with The Large Pelagics Research Center, has been developing a new, automated method for reporting data from fish tags. In the proposed process, a fish will be tagged with a modified streamer (“spaghetti”) tag carrying a rice grain RFID chip. A fisherman can scan the tag at or near the moment of capture with a compatible RFID reader, which will transmit the fish's data file to a personal smartphone pre-installed with our reporting application (the HI Tag App). From the application, the fisherman has the option to save the form directly as generated, input any missing data, or add richer data (i.e. a photo of the fish) before saving the form and storing the data on internal memory. When the application has detected a cellular or wireless connection, the data will be immediately uploaded to the Pacific Islands Fisheries Group database. Tests conducted off the island of Hawaii (Summer 2016) demonstrated that the HI Tag application greatly improved the process of fish tagging and reporting with respect to automating the process of collecting, parsing, and transmitting data without requiring supervision from the user. In this way, the reporting can be integrated into the fishing experience itself. Minimizing the barrier between catching and reporting the fish should create a direct relationship between identifying and reporting the tag, thereby improving “catch and release” fishing activities while enabling scientists and researchers access to richer data, collected from the same tag over the entire lifetime of a fish.

Reply to Safina and Walter et al.: Multiple lines of evidence for size-structured spawning migrations in western Atlantic bluefin tuna

Abstract: Walter et al. (1) and Safina (2) raise numerous concerns regarding our study (3). Specifically, they question our conclusions that (i) a majority of spawning occurs outside the Gulf of Mexico, (ii) western North Atlantic bluefin tuna mature earlier than currently estimated, and (iii) additional spawning locations and younger age at maturity mean that the western Atlantic bluefin tuna are less vulnerable to anthropogenic impacts, including exploitation.