Showing papers by "Molly Lutcavage published in 2001"

Understanding Environmental Influences on Movements and Depth Distributions of Tunas and Billfishes Can Significantly Improve Population Assessments

Abstract: The vulnerability of the highly mobile tunas (family Scombridae) and billfishes (fami- lies Istiophoridae and Xiphiidae) to various fishing gears and detection by aerial surveys is influenced by their depth distributions, travel speeds, residency times, and aggregation. As a result, understand- ing the effects of the physical environment on fish behavior is critical for robust population assess- ments. Numerous studies have attempted to understand the movements and habitat requirements of tunas and billfishes by correlating catch statistics with environmental conditions averaged over time and space. Such correlations do not necessarily elucidate the requisite relationships because the data are not gathered simultaneously, and because error terms are often too broad to demonstrate meaning- ful relationships. More important, using catch statistics to determine the effects of environmental conditions on catch statistics can never prove causation and result in tautology, unless independent measures of fish abundance are available. The situation is not necessarily improved when catch statis- tics are correlated with satellite-derived sea surface temperature data. Tunas and billfish fish do not always live at the surface and, more importantly, regularly move through vertical thermal gradients (1°C m -1 ) that are orders of magnitude steeper than horizontal gradients ( 1°C km -1 ). Sea surface temperature gradients per se are, therefore, unlikely to influence horizontal movements or aggrega- tion. Direct observations of tuna and billfish behaviors (collected via acoustic telemetry or electronic data-recording tags) can, however, be readily combined with information on their physiologically- based environmental tolerances, forage abundance, and appropriate oceanographic data. The result- ing models can correct both traditional catch-per-unit effort data and aerial survey data for differences in gear vulnerability, and thus significantly improve population assessments.

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

Abstract: 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.

From Individuals to Local Population Densities: Movements of North Atlantic Bluefin Tuna (Thunnus Thynnus) in the Gulf of Maine/Northwestern Atlantic

Abstract: North Atlantic bluefin tuna have high rates of spatial redistribution and display complex aggregation behavior in response to changes in their environment. This paper presents preliminary results obtained from an analysis of individual movements of giant bluefin tuna derived from tracking studies conducted in association with aerial surveys in the Gulf of Maine (NW Atlantic). From the perspective of a correlated and biased random walk movement model, we examined how alternative behavioral modes of tuna movement affect estimation of local population density. We summarize information needed to link movements and behavior of individuals and schools (i.e., depth and surfacing behaviour, spatial mixing, residency, and school and size distribution) in order to portray spatial and temporal dynamics of the bluefin assemblage. Our goals are to integrate hydroacoustic tracking and aerial survey movement data in order formulate a modeling and simulation framework that will generate predictions and estimates of local population densities. This will support the development of fishery-independent assessments of adult bluefin tuna that are crucial to accurate monitoring, management, and rebuilding of the Atlantic population.