Abstract

Atlantic bluefin tuna and blue marlin are highly migratory species that commonly cross ocean basins or political boundaries, and thus the fate of each species in influenced by activities (i.e. fishing) throughout their home range. Here, we examine the role of the Gulf of Mexico as essential fish habitat (EFH) of bluefin tuna and blue marlin, and report on the movement and stock structure of individuals that frequent this marginal sea at some part in their life history. Data from several of sources support the premise that the Gulf serves as EFH of bluefin tuna and blue marlin, and the region appears critical to the sustainability of both species. Observer data and logbook catch records from the U.S. long-line fleet demonstrate that both species frequent the Gulf and occupy the northern section of this basin during presumed spawning periods. Larval distribution data support the assertion that the Gulf represent critical spawning habitat of both species as well as other large pelagic species, which commonly aggregate along “hot spots” of productivity in the northern region. Electronic tagging and otolith chemistry data further document utilization patterns in the Gulf and highlight the unique nature of bluefin tuna and blue marlin populations. For bluefin tuna, residency times are limited and directed movements out of Gulf occur after spawning in a predictable manner. Long-distance movement often occurs after leaving the Gulf and a similar pattern of movement occurs for the eastern stock (spawns in Mediterranean Sea), which intermingle with Gulf-spawned individuals as they migrate into the western and central Atlantic. In contrast, movements of blue marlin out of the Gulf appear less directed with a large fraction of the population remaining in the Gulf from summer spawning periods into the winter. As a result, the Gulf component of blue marlin may have a separate migration pathway from the Atlantic population. The theory of distinct population components or contingents appears to apply to both Atlantic bluefin tuna and blue marlin in the Gulf, and further information on movement and population structure of both species is clearly needed to effectively manage these pelagic voyagers

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