Date of Award

Spring 5-8-2020

Level of Access

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Marine Biology

Advisor

Yong Chen

Second Committee Member

Theresa R. Johnson

Third Committee Member

Jui-Han Chang

Additional Committee Members

Keith Evans

Burton Shank

Abstract

Understanding both the social and biological factors surrounding conservation is important for informing effective fisheries management. This dissertation examines conservation in the American lobster (Homarus americanus) fishery in a changing Gulf of Maine (GOM) using computer simulations informed by interviews with lobster fishers. In this fishery, v-notching, an important conservation measure intended to protect the spawning stock, has been hypothesized to have contributed to the dramatic increase in lobster landings and stock biomass since the 1990s in the GOM. Semi-structured and oral history interviews were analyzed to understand v-notching compliance and lobster fishers’ perceptions of v-notching. All lobster fishers interviewed described v-notching as important for the lobster fishery’s sustainability, while also reporting that the v-notching practice has been declining in recent years. Interviews suggest that the decline in v-notching was due to a decrease in the net benefits of v-notching resulting from increased lobster abundance. Given this decline in v-notching practice, evaluating the effect of v-notching on the fishery is important. An individual-based lobster simulator (IBLS), which can capture complex processes with a flexible probabilistic approach, was modified, parameterized, and applied to the fishery. To evaluate the impact of v-notching, scenarios examining different v-notching compliance rates and v-notch definitions were simulated using the IBLS with different recruitment dynamics scenarios. These simulation results suggest that the lobster fishery would not have experienced the observed large positive increases in biomass and landings without a high v-notching compliance rate (i.e. 90 or 100% compliance) or a strict definition of the notch. Although v-notching has contributed to the increases in the fishery and population, to fully understand the role of conservation, the stock-recruitment relationship (SRR) in a changing GOM needs to be better understood. The GOM bottom water temperatures have increased at a rate of 0.2°C per decade, which caused lobster settlement area to expand and size at maturity to change, adding to the complexity of understanding recruitment dynamics. To give more effective advice for fisheries management, the SRR for lobster was further investigated by including bottom water temperature as a covariate. The results showed that temperature had a strong effect on recruitment resulting in a temporal shift in productivity in the SRR in 2009. This dissertation also used a size-structured stock assessment model to assess the effect of a decrease in size at maturity and the resulting change in growth on the American lobster stock assessment model and SRR. Projections of the lobster fishery under different v-notching scenarios show that in the near future, although v-notching does not increase landings, v-notching still preserves the spawning stock. These results show that the v-notching conservation measure is a valuable tool for precautionary management. Overall, these results suggest that input controls, such as protecting the spawning stock, can provide benefits to both the fish population and fishery. The implications of a decline in the v-notching practice may have negative impacts for the future sustainability of the fishery if the spawning stock and productivity were to decline. Additionally, this dissertation demonstrates that climate driven SRRs and biological reference points should be considered for American lobster management. This dissertation highlights the importance of considering changes in compliance and productivity and the interactions between the two factors. The framework proposed in this study can be extended to evaluate the protection of spawning females in many other commercial fisheries influenced by climate change.

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