Evaluating the effects of Atlantic menhaden management and environmental change on the northwest Atlantic Ocean ecosystem

Author

Maxwell T. Grezlik, Humboldt State UniversityFollow

Graduation Date

Fall 2021

Document Type

Thesis

Program

Master of Science degree with a major in Natural Resources, option Fisheries

Committee Chair Name

Dr. Andre Buchheister

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Dr. Mark Henderson

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Dr. Jose Marin Jarrin

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

Dr. David Chagaris

Fourth Committee Member Affiliation

Community Member or Outside Professional

Subject Categories

Natural Resources

Abstract

Atlantic Menhaden (Brevoortia tyrannus) is an abundant forage fish species whose management has recently shifted from using single species reference points to ecological reference points. This type of management allows for the ecological role (e.g., supporting predators) of the species to be considered when making management decisions, and is part of a growing global movement towards ecosystem-based fisheries management. One model that aided in this transition from single species to ecological reference points was the Northwest Atlantic Continental Shelf (NWACS13) model created using Ecopath with Ecosim (Buchheister et al. 2017). Here, I updated and expanded the NWACS13 model with four years of additional data and used it to address three main objectives. First, I evaluated the effects of different Menhaden fishing mortality rates on the relative biomasses of modeled species groups using 50-year projections. Second, I examined whether single species biomass target reference points would be achieved for five focal species of management interest (Striped Bass, Bluefish, Weakfish, Spiny Dogfish, Atlantic Herring) under different fishing rates for Menhaden and the focal species. Third, I implemented bottom-up, primary production forcing in the ecosystem model to explore the long-term consequences on biomass and catch of a 3.5% and 6% decrease in phytoplankton biomass that represents a range of climate-change effects from the literature. Results indicate that ecological reference points behaved as they were designed, to push Striped Bass biomass toward its target. Nearshore piscivorous birds and pelagic sharks were identified as species of concern and were not included in less complex models. The inclusion of a primary production forcing function strengthened the relationship between Atlantic Menhaden and Striped Bass biomass in model projections, a key interaction evaluated in setting ecological reference points for Atlantic Menhaden. The inclusion of climate change projections identified disproportionate negative impacts on the biomass and catch of several species groups including Weakfish, Atlantic Cod, Striped Bass, Bluefish, and Spiny Dogfish. This model and study can contribute to fisheries management by identifying species or interactions of concern that are sensitive to Menhaden fishing mortality rates. This work contributes to Menhaden management by providing insight into the benefits of adding further complexity to models currently used for management decision making. More broadly, this work contributes to the ecosystem-based management movement and shows how climate impacts can be considered in making management decisions.

Citation Style

Grezlik, M., Buchheister, A., Henderson, M., Marin Jarrin, J., Chagaris, D.. (2021). Evaluating the Effects of Atlantic Menhaden Management and Environmental Change on the Northwest Atlantic Ocean Ecosystem [Master's thesis]. Humboldt State University, Arcata, California.

Recommended Citation

Grezlik, Maxwell T., "Evaluating the effects of Atlantic menhaden management and environmental change on the northwest Atlantic Ocean ecosystem" (2021). Cal Poly Humboldt theses and projects. 519.
https://digitalcommons.humboldt.edu/etd/519