Juvenile tarpon tagging

The overall goal of this project is to quantify the residency, habitat use, and timing of outmigration of juvenile tarpon (~1-2 ft) using acoustic telemetry. In the past, HRI has used this technology to successfully track the movements of sharks, spotted seatrout, red drum, black drum, cobia, and red snapper in Texas’ offshore, nearshore, and inshore waters. Acoustic telemetry provides researchers critical access to observing movements by fitting animals withcoded acoustic transmitters (“pingers”) and tracking them with an array of omnidirectional acoustic receivers (“listening stations”) strategically placed throughout the study area (Figure 1). When tagged fish are within the detection range of a receiver (typically < 400 m in our bays), the receiver stores a unique tag identification code and timestamp on the unit’s hard drive. Conveniently, receivers will monitor for fish presence or absence 24/7 while deployed; however, receivers must be recovered and downloaded at regular intervals (e.g., quarterly) to retrieve stored data. For this study, acoustic transmitters will be surgically implanted in 20 juvenile tarpon. Fish will be captured from 2-3 “drains” within Oso Bay, and movements, residency, and fidelity to tagging sites will bemonitored withan array of 16 VR2Wacoustic receivers for approximately 2.5 yrs (Figure 2). To increase the probability of capturing outmigration events, transmitters will have an expected battery life of 860 days. Water quality loggers will also be deployed at each tagging site and at regular intervals within the bay system to continuously capture water temperature and salinity measurements during the study period. These timestamped measurements will later be associated with juvenile tarpon presence and absence records to estimate habitat preferences for these important variables. The information collected from this project will help answer critical questions regarding the life history of juvenile tarpon including physiological (water quality preferences), spatial (core use areas), and temporal (time period using this type of nursery habitat). Additionally, data would aid in the identification of other nursery areas within the region and provide support for protecting specific nursery areas if interannual site fidelity to specific drains is observed.

Nursery Habitats and Early Life Ecology of Tarpon along the Texas Coast

Port Aransas, Texas was once known as the “Tarpon Capital of the World” when large schools of tarpon (Megalops atlanticus) would pass along the coast.  By the 1960’s the fishery had collapsed, which was initially attributed primarily to overexploitation of adults, and the loss of suitable habitat and prey resources for juveniles (Holt et al. 2005).  An examination of fishing records of tarpon caught between 1908 and 1998 in Port Aransas, Texas indicated a lack of small fish caught after 1960 while large fish were still present.  Scientists have speculated that the collapse of the tarpon fishery in Texas was the result of recruitment failure to the area.  In fact, Winemiller and Dailey (2002) modeled population dynamics of tarpon using life history data and determined that small declines in juvenile survival resulted in marked reductions in the abundance of adults. Thus, the collapse of the fishery in Texas appears linked to the quality and availability of nursery habitats used by juvenile tarpon during the first year of life.  Unfortunately, our understanding of basic habitat requirements of juvenile tarpon in Texas is very limited, precluding our ability to assess population trends and develop sound conservation strategies.

The goal of this project is to develop a standardized survey that will provide critical baseline data on the occurrence, abundance, and habitat requirements of juvenile tarpon in Texas.  The proposed project will allow us to better understand the ecological value of estuarine nursery habitats used by this species and guide future management decisions to rebuild a sustainable tarpon fishery in Texas.