a doctoral student in the shark biology & fisheries science lab at texas a&m university at galveston (tamug) is studying the movement and habitat patterns of bull sharks in galveston bay with support from texas sea grants grants-in-aid of graduate research program thomas tinhan is tagging juvenile bull sharks (carcharhinus leucas) to learn more about their habitat preferences through long- and short-term movement tracking texas estuaries are essential nursery habitats for the sharks but these areas vary greatly in habitat type and regularly experience drastic changes in environmental conditions like temperature and salinity by tagging the sharks and then observing where they go over time tinhan hopes to learn more about how they respond to these changes ive always had an interest in studying the behavior of apex predators he said they typically play very important roles in marine ecosystems by studying one of the top predators in galveston bay tinhan said that more can be learned about the food chain as a whole which can then be used to inform management and fishing practices in texas bays some ecosystems are very tightly linked he said if you adjust the population of one species it could affect several other species or it might not but its important we understand how much influence that might have and the first step of getting at that is understanding the first link in the chain tinhan has long been fascinated by sharks he volunteered at the university of hawaiis shark lab studying tiger sharks and hammerheads while working toward his undergraduate degree in marine biology he has a specific interest in bull sharks because they are infamous for their ability to do something that very few other sharks can do: regularly travel deep into freshwater systems with no apparent ill effects bull sharks are uniquely adept at regulating the salt content in their bodies and their tolerance for varied salinity grows with their size tinhan said that spending time in fresh water may be a trade-off especially for smaller sharks the lower the salinity the more energy it takes them to regulate that he said but because fewer species can inhabit low salinities juveniles can go up into those habitats and remain relatively unthreatened by larger sharks he added that being in fresh water reduces a sharks buoyancy by about eight times making it far more taxing for it to swim when the salinity is low but for small sharks it is thought that all of these extra energy expenditures are preferable to being eaten bull sharks have been found all over the world in rivers and lakes that are connected to oceans but the extent to which they do this in texas isnt well known texas parks and wildlife has a coastal monitoring program thats been going on for about 30 years but they dont sample into freshwater systems tinhan said we know that bull sharks move into low salinity areas near river mouths but we dont know how far theyre actually moving into them he adds that its not rare for bull sharks to be found in fresh bodies of water in texas but how often it happens is hard to quantify fishermen who are attempting to catch other species in rivers will catch bull sharks occasionally but its hard to tell how often it happens because theyre typically not fishing for an animal that large so bite-offs are common tinhan hopes that observing the sharks movement patterns over the course of a year will shed some light on that mystery and provide a clearer picture of why they spend their time where they do he will track the sharks by fixing each animal that is caught with an acoustic transmitter these tags send out a signal every few minutes that can be picked up by the listening stations his team has scattered throughout different habitats in galveston bay tinhan began tagging sharks during summer 2017 in part with the aid of texas sea grants funding but his project was interrupted by hurricane harvey in late august however tagging has since resumed and tinhan said they plan to deploy another 20-30 tags before next summer the team will begin monitoring the sharks movements for a full year after the last tag is deployed texas sea grants grants-in-aid of graduate research program is a competitive program that provides small grants to graduate students enrolled at texas a&m university texas a&m university at galveston and texas a&m university-corpus christi whose research projects are both relevant to texas and marine-related the program is designed to promote scientific research by supporting students in their early academic careers for more information about research at the shark biology & fisheries science lab visit http://wwwwellsfisherieslabcom/