| Summary |
The overall purpose of this dissertation is to increase understanding of migration and movement behaviors associated with a highly migratory elasmobranch species. In particular, I seek to determine whether sufficient evidence exists to warrant the separation of the northwest Atlantic Spiny Dogfish (Squalus acanthias) into separate management units. These management units are not genetically distinct, but rather would be based on unique behaviors adopted by hypothesized groups of dogfish that connect reproductive, feeding, and overwintering grounds ("contingents"). This dissertation includes an introductory chapter that introduces the reader to the Spiny Dogfish resource and recent management actions undertaken, followed by a chapter that provides technical and design recommendations based on a meta-analysis and a case study, which address the challenges of conducting behavioral research in dynamic environments through the use of acoustic telemtry. Approximately 30 percent of papers reviewed had no details on design specifications. Meta-analyses suggest that more fish were redetected when more acoustic equipment was deployed for longer periods of time, exemplifying the need for robust equipment that can withstand the rigors of an offshore, dynamic environment. In particular, we found that a heavy anchor, a subsurface float holding a mooring line, and a highflier-float system produced the best results in our case study. New behavioral information, derived from an analysis of data collected through a long-term conventional mark-recapture program and a multi-year acoustic tagging program, suggest that spiny dogfish tagged off North Carolina in overwintering grounds routinely make seasonal migrations to summer feeding habitats off southern New England (specifically, Massachusetts), but do not necessarily follow the same pathway each year. Sharks were often not detected on acoustic receivers for lengthy periods of time, and mark-recapture data indicated extremely lengthy times at liberty (1,000+ days). Spiny Dogfish were also noted to be locally abundant but exhibit short residency times on the Hatteras Bight acoustic array. An evaluation of potential environmental drivers of localized behavior in the southern extent of the Spiny Dogfish range noted that certain factors (i.e., water temperature and weather) had an effect on the presence and absence of dogfish in the Hatteras Bight. Finally, the dissertation discusses the Spiny Dogfish Contingent Hypothesis, which suggests that the northwestern Atlantic stock could comprise as many as five behaviorally distinct groups of Spiny Dogfish. The work presented in this dissertation identifies predictable behavioral patterns undertaken by individual Spiny Dogfish and inferred from recapture data, which can be used in context with future studies to further evaluate and refine the Spiny Dogfish Contingent Hypothesis. Despite many examples in the literature where Contingent Theory has been applied to describe spatially complex behavior in fish stocks, it is rarely applied in management plans. The current management structure in place for Spiny Dogfish is complex, has evolved to respond to fishery needs over the past 16 years, and involves multiple state and federal agencies, councils and commissions. Future research would likely need to quantify contingent "vital rates" and/or contribution to overall spawning stock biomass or fisheries to fully justify the development of a new management framework. |
