Biologging tools for investigating the study of fine-scale linkages between animal behavior and the physical microstructure of the marine habitat are technically limited by substantial size, high cost or low sensor resolution. However, recent advances in electronic technologies and process techniques present attractive alternatives to current tag designs. Motivated by the need for a low-cost, compact CTD biotag for medium-sized marine animals, the University of South Florida Center for Ocean Technology developed a multi-sensor biotag for quantitative measurements of ocean salinity. This dissertation describes the development and performance of a novel CTD biotag used for animal-borne measurements of the physical microstructure of marine ecosystems. Printed circuit board processes were used to fabricate a liquid crystal polymer- based conductivity, temperature and depth sensor board. Tests performed in the laboratory exhibited good sensor repeatability between the measured and the predicted variables indicating that the initial design and fabrication process is suitable for the construction of a CTD sensor board. The conductivity cells showed good sensor integrity for the entire conductivity range (0- 70 mS/cm), thus demonstrating the potential for a highly resolved salinity system. The CTD sensor board was integrated into two initial multi-sensor biologging systems that consisted of reconfigurable modular circuit boards. The design and initial performance of a 4-electrode conductivity cell circuit was discussed and preliminary tests showed a sensor accuracy of 0.0161 mS/cm. A potential packaging material was analyzed for use on the temperature and pressure sensors and initial tests showed good sensor sensitivities (-2.294 °C/kohms and 1.9192 mV/dbar, respectively). Underwater packaging of the biotag was presented in this work along with three different field observations. Vertical profiles of conductivity, temperature and depth in the Gulf of Mexico were obtained and compared to a commercial instrument. On the West Florida shelf, conductivity, temperature, depth and salinity data were obtained from loggerhead turtle deployments. Data collected showed that the tagged turtle encountered a highly variable salinity range (30.6- 35.3) while at depth (20 m). This data trend captured was in agreement with shelf characteristics (tidal fluxes and water mass features) and moored instruments. Finally, observations that were undertaken in Bayboro Harbor showed no biofouling to the conductivity electrodes during a 14 day deployment. This biotag is the first to use a PCB-based low-cost CTD to collect animal-borne salinity measurements.

In response to the drastic decline of the European eel (Anguilla anguilla (L.)) fisheries have been reduced and elvers are stocked in areas where natural abundances are low. Are these measures adequate? To answer different aspects of this question, we have analysed more than a century of eel tagging, using both traditional and more novel capture – recapture analyses. Based on these long-term data, we have evaluated the impact of the Swedish eel coastal fisheries using Survival analysis. Our analysis indicates that the fishing mortality just prior the 2009 fishing restrictions were in the order of 10%. More recent tagging programs have focused on issues related to the fate of stocked fish. If and how they migrate out of the Baltic Sea and further on towards the Atlantic Ocean. Both earlier and our new studies reveal that all eels recaptured on the Swedish East Coast, no matter of their origin, migrate at a reasonable speed and direction towards the outlets of the Baltic Sea. Even though it is sometimes difficult to determine their origin, our analyses indicate that stocked fish were scarce among the recaptures. In an experiment on the Swedish West Coast, we knew the individuals’ origin (stocked or wild) and they had similar migration patterns. In contrast, silver eel in Lake Mälaren – assumed to have been stocked as elvers or bootlace eels – seemed to have difficulties in finding the outlets. Instead they overwintered and lost weight. However, weight losses are also significant among non-stocked individuals in the Baltic Sea, both if they overwinter and if they appear to be on their way out from the area. It remains an open question whether eels from the Baltic region in general, and whether the overwintered fish in particular, manage to reach the spawning area in the Atlantic Ocean. Based on current knowledge, I advocate invoking the precautionary approach and to concentrate Swedish eel stockings to the West Coast and allow the young fish to spread out on their own. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Manuscript.</p><p> </p>