Many management strategies are available to fishery managers to improve the sustainability of a fishery; however, it is not always clear how implemented strategies interact with the demographics of the exploited species. Management decisions are often made in order to maximize egg production and recruitment or to preserve specific size classes to increase reproductive output. Consequences of these strategies could include variation from a natural size structure of the population, exaggerated sexual dimorphism, skewed sex ratios, and suboptimal mating conditions. To examine the possibility of these consequences, I ran a series of deterministic models to simulate the fished and unfished population dynamics of two clawed lobster species, American lobster (Homarus americanus) and European lobster (Homarus gammarus), under a variety of management strategies. Protection of ovigerous females takes two forms in this model. The American fishery in the Gulf of Maine requires fishers to v-notch ovigerous females for up to four years of protection from fishing. The European fishery in southern Norway bans the harvest of ovigerous females, which translates to one year of protection. I compared the relative impact of the two levels of ovigerous female protections on factors that may be important for reproductive success: size structure, dimorphism, sex ratio, and egg production for both species. I then considered a case study on European lobster to evaluate the interaction of a no-take marine protected area with a slot limit to compare relative impacts to egg production, overall size structure and dimorphism. Results showed that American lobster females benefitted greatly from strict protections such as v-notching in terms of mean size increase and egg production, but mean size dimorphism and the overall proportion of females also increased with higher fishing pressure. European lobster females also benefitted from protections, but less dramatically than American lobsters, and with lower size dimorphism. In the case study, European lobsters benefited most from the implementation of a no-take marine protected area in combination with a slot limit to preserve the largest individuals of both sexes which improved overall egg production. By taking a simulation approach to evaluate these different management strategies on two closely related species of lobster, this thesis provides a basis for understanding how fishery decisions can achieve their sustainability goals in addition to quantifying some of the unintended impacts of management on parameters that may be important to overall reproductive success. / Master of Science / Fishery managers make decisions about a fishery based on the species' biology to optimize catch while also ensuring that enough individuals remain to keep the population alive for years to come. However, it is not always clear what types of unintended consequences these decisions may have. Management decisions are often made in order to maximize egg production, to keep small individuals alive until they can reproduce, or to preserve the large individuals that have high reproductive potential. Some consequences of these strategies could include a reduction in the number of large individuals with high fishing pressure, increased female body size compared to males, unequal numbers of females and males, and less optimal conditions for mating. To examine the possibility of these consequences, I ran a series of models to simulate the fished and unfished populations of two clawed lobster species, American lobster (Homarus americanus) and European lobster (Homarus gammarus), under a variety of management strategies. The American lobster fishery in the Gulf of Maine requires a practice known as v-notching, which protects egg-bearing females for up to four years. The Norwegian fishery for European lobster bans the harvest of egg-bearing females, which is protection that lasts for one year. I compared the impact of the two types of egg-bearing female protections on factors that may be important for reproductive success: abundance of large lobsters, unequal numbers of females and males, difference in size between females and males, and overall production of eggs for both species. I then considered a case study on European lobster to test how a no-take marine protected area and a slot limit (minimum and maximum harvest size limits) affected those same factors. Results showed that American lobster females benefited greatly from longer lasting protections by growing to larger sizes and producing more eggs, but the average size difference between females and males and the overall proportion of females also increased as fishing became more intense. European lobster females also benefitted from protections, but less dramatically than American lobsters, and with lower mean differences in size between females and males. In the case study, European lobsters benefitted most from the no-take marine protected area in combination with a slot limit to preserve the largest individuals of both sexes which improved overall egg production. Using a simulation makes it easier to tease apart the effects of these different management strategies on two closely related species of lobster. This thesis helps managers see how fishery decisions affect lobsters in both desired and unintended ways. With this information, managers can better improve the sustainability of the fishery through considering what a specific species needs to improve reproductive success.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/113415 |
| Date | 24 January 2023 |
| Creators | Theberge, Kaitlyn |
| Contributors | Fish and Wildlife Conservation, Kindsvater, Holly, Pugh, Tracy, Castello, Leandro |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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