Coastal shark populations have been subject to increasing anthropogenic pressure over the past two decades. This study focused on two lemon shark (<italic> Negaprion brevirostris</italic>) populations, the site-attached maturing sub-adults at the Island of Bimini, Bahamas, threatened by a large-scale resort development, and adults forming winter aggregations off the coast of Jupiter, Florida, subject to direct fishing pressure. For the sub-adult population, analysis was carried out on the long-term temporal patterns in abundance and population structure, relative to potential driving factors, and the influence of variables affecting longline catch- rates used as the basis for stock assessment. For the aggregating adult population, life-history aspects of population structure and distribution were investigated for relative implications on the species' vulnerability status. The following analysis and methodologies were utilised to investigate the two populations: longline catch records from 1982&ndash;2008 monitoring of variables potentially affecting longline catch-rates documentation of shark behavioural interactions with longline equipment using underwater video surveillance aerial surveying for abundance estimates comparison of spatial utilisation patterns with longline catch locations external tagging the utilisation of archival satellite tags passive tracking with Vemco acoustic monitoring system and research collaborations with other scientific groups utilising the same acoustic monitoring system. The key findings of this study were that in the northwest Atlantic, <italic>N. brevirostris</italic> populations are experiencing considerable anthropogenic pressure at all life-stages. In Bimini, the effects of a large-scale resort development have resulted in a significant decline in abundance, to a level (-52 individuals) well below the temporal average (-158). On the U.S. east coast, seasonal aggregating behaviour has further increased vulnerability through increased catchability, beyond the highly vulnerable status already attributed to this species, and targeted <italic>N. brevirostris</italic> fisheries appear to be currently operating at unsustainable levels. Shark longlinc catchability was noted to be significantly influenced by multiple shark presence, resulting in greater susceptibility for <italic>N. brevirostris</italic> (and other similar species) that naturally exhibit group behaviour. Incidental encounterability and predation risk significantly influenced longlinc catch-rates. Adult <italic> N. brevirostris</italic> exhibited large-scale seasonal migrations on the U.S. east coast, which, in addition to documented international transitions, supports existing evidence for genetic mixing across the distribution. Water temperature was found to be a significant driver of <italic>N. brevirostris </italic> behaviour at all life-stages, with an apparent adult temperature preference of 24&deg;C. This study represents the first long-term abundance assessment for sub-adult <italic>N. brevirostris</italic>, and the first in-depth study to focus on an adult <italic>N. brevirostris</italic> population. The results provide essential life-history information, revealing that at all life-stages <italic>N. brevirostris</italic> appear to be highly sensitive to anthropogenic activities, relative to other species, and therefore require enhanced management for species protection. It is therefore highly recommended that <italic>N. brevirostris</italic> be added to the U.S. prohibited species list.

The mechanisms and functions of shark grouping behaviour have received relatively little scientific attention to date. The current widespread use of social network analysis to study animal groups, in concert with rapid advances in animal tracking technology, now allows us to test specific hypotheses about how and why sharks form groups. This thesis uses replicated laboratory experiments to investigate some of the mechanisms underpinning aggregation in a model species of benthic, oviporous elasmobranch, the small spotted catshark (Scyliorhinus canicula L. 1758; Scyliorhinidae). Acoustic tracking of this species in the wild is also conducted to explore how network analyses can be adopted to study the localized movements, habitat connectivity and ranging behaviour of adult sharks. Groups of juvenile S. canicula were characterized by non-random social preferences, crucially, only when individuals were familiar with one another suggesting social recognition is important in young sharks of this species. Genetic analyses of parent and offspring DNA revealed very high levels of multiple paternity in this species, likely due to male sexual harassment and multiple mating, which leads to increased genetic diversity between juvenile sharks. Perhaps unsurprisingly, there was no evidence of kin relatedness structuring social interactions between conspecifics. Furthermore, testing the effects of environment on social behaviour provided evidence that these juveniles aggregated more in structurally complex environments than simple ones. However, at the individual level sharks showed consistency in their social network positions through time and across different habitat types. This result is indicative of personality traits in S. canicula. Using data gathered via passive acoustic telemetry of wild shark behaviour, network analysis provided a useful tool with which to quantify movement between receivers. One chapter has been dedicated to the application of these methods, highlighting a number of different analyses for predicting movement behaviour from such data. Finally, these methods were adopted to address ecological questions in this sexually segregated species. Persistent site fidelity to a localised inshore area by both male and female sharks suggested that segregation occurred at a relatively small spatial and temporal scale. Despite strong evidence of segregation, analyses of movement networks and individual co-occurrences revealed distinct periods of behavioural synchronicity during the months of March, April and May. In addition, habitat complexity appeared to be a significant driver of female behavioural strategy. Enhancing our knowledge of the social and environmental drivers of aggregation and movement in sharks is of great importance given the ecological threat facing many of our ocean’s top elasmobranch predators.