Movement Ecology of Shortfin Makos off Texas and the Gulf of Mexico

Dr. Greg Stunz, Endowed Chair for Fisheries & Ocean Health and Director of the Center for Sportfish Science & Conservation, is spearheading a project that will provide new information on the movement patterns and stock structure of shortfin mako sharks (Isurus oxyrinchus) in the Gulf of Mexico (GOM) while concurrently documenting fishing mortality and the potential for interactions with fish aggregating devices, such as oil and gas infrastructure, using advanced tagging technology.

The shortfin mako shark is highly prized in recreational fisheries and as high-value bycatch in commercial pelagic longline fisheries. In Texas, mako sharks have been listed as a Species of Greatest Conservation Need in the Texas Conservation Action Plan and proposed for state listing as threatened. The most recent stock assessment was dire, suggesting the North Atlantic shortfin mako stock was overfished and experiencing overfishing, and that annual catch levels would need to be substantially reduced to begin rebuilding the stock. Recovery projections were long term (70 years) and uncertain.

Despite their imperiled status, mako shark management remains hindered by serious information gaps regarding the movement ecology of the species as well as unknowns regarding fishing mortality. Existing knowledge of mako shark distribution patterns and population dynamics is primarily informed by fisheries landings data and conventional tag-recapture studies. While these data are informative, they are limited by low recapture rates and are inherently biased by spatiotemporally variable fishing effort and the absence of information between the point of capture and recapture. These are potentially serious limitations to a robust stock assessment – especially if mako sharks are exposed to varying levels of fishing mortality during their migratory movements.

To overcome these limitations and fill key knowledge gaps, this project will cooperatively engage charter captains to deploy SPOTs (smart position or temperature transmitting tags) to provide fishery-independent observations of mako shark movement patterns, habitat use, and fishing mortality. In addition to providing important insights into the degree of connectivity between sub-regions of the GOM and beyond, recent advances in technology (e.g., Fastloc GPS) will also allow us to collect high-resolution data on the behavior and fate (i.e., mortality) of mako sharks following release.

Project objectives:

  1. Identify migration corridors and population connectivity of mako sharks to further our knowledge of stock structure;
  2. Determine the extent of spatiotemporal interactions between mako sharks and fish aggregating devices such as oil and gas infrastructure; and
  3. Estimate two sources of fishing mortality for mako sharks captured in the GOM recreational fishery.