Date of Award

Spring 5-10-2025

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Oceanography

First Committee Advisor

Damian Brady

Second Committee Member

Nicholas Record

Third Committee Member

Daniel Pendleton

Additional Committee Members

Kristina Cammen

Catherine Johnson

Abstract

North Atlantic right whales (Eubalaena glacialis) are critically endangered, with an estimated 372 individuals remaining. Right whales were heavily targeted during commercial whaling and have struggled to recover, presently threatened by ship strikes and entanglement in trap-pot fishing gear. Anthropogenic warming has resulted in changes in the northwest Atlantic ecosystem, leading to shifts in the availability of key prey resource, Calanus finmarchicus, and overall habitat suitability. As a result, right whales underwent a range shift utilizing new habitats. Decreased predictability of whale distribution patterns makes management challenging, and leaves whales susceptible to anthropogenic threats, hindering population recovery. Thus, understanding the interplay between oceanographic conditions, prey availability, and right whale density is critical to accurately informing management decisions. Addressing the question of how to consider these factors, specifically how to represent prey, in right whale density models is the focus of this dissertation.

This dissertation implemented and tested a series of models capturing right whale prey availability and estimating right whale density. Specifically, this research consists of three major components: 1) the development and implementation of a novel prey field modeling framework to address the gap in availability of modeled fields tailored to right whale foraging requirements, 2) the testing of these prey fields in right whale density models mimicking those used to inform management, and 3) exploring the effects of the oceanographic regime shift circa 2010 on right whale density estimates.

The first component of this research presented a novel modeling framework to capture right whale prey availability from C. finmarchicus abundance data. Potential thresholds defining a prey patch sufficient to sustain right whale feeding were derived from the literature and narrowed down using sensitivity analysis. We utilized a statistical model to effectively interpolate the C. finmarchicus data in the Mid-Atlantic Bight and the Gulf of Maine through the lens of right whale habitat suitability, producing a field of probabilities of occurrence of high-density copepod aggregations sufficient for right whale foraging. While there have been prior efforts to model C. finmarchicus, this was the first attempt that we know of from the perspective of whale foraging.

The second component of this research built directly on the first, testing the prey fields in a simplified right whale density surface model. Density surface models are an important component of whale management, allowing interested parties to simulate the impacts of potential strategies to mitigate fisheries interactions. We constructed a suite of density surface models relating right whale line transect survey data to environmental covariates with the goal of isolating the influence of prey fields. The approach from the first component of the dissertation was extended to produce fields representing two secondary right whale prey taxa, Centropages typicus and Pseudocalanus spp. We found that including prey fields, specifically C. finmarchicus, improves model performance and corrects spatiotemporal predictions to more closely resemble known right whale habitat use patterns.

The final component of this research aimed to explicitly investigate the influence of the 2010 oceanographic regime shift on right whale density estimates. The oceanographic regime shift likely drove the change in right whale habitat use patterns and has resulted in increased anthropogenic mortality. To understand the change in environmental conditions associated with right whale sightings across regimes, we implemented a breakpoint analysis to determine the year that right whale abundances began to decline. Then, we assessed the difference in the distributions of environmental variables pre- and post-2010 and produced two suites of density surface models: the first modeled all years of data and the second allowed the model to calibrate separate functions for pre- and post-2010. The results suggest that environmental conditions in the domain have changed significantly post-2010, specifically in the northernmost portion of the domain (e.g., Bay of Fundy area). We found that the probability of a C. finmarchicus patch associated with survey effort increased overall, but decreased when associated with right whale observations, suggesting that whales may be struggling to locate prey.

This dissertation research is novel in that it provides an alternative approach to resolving cetacean prey availability within a foraging domain. We demonstrated that this novel prey modeling approach improves the performance of density surface models used to inform parties interested in right whale conservation and increases density predictions in key right whale foraging grounds. Given the wide impacts of climate change on marine ecosystems, we also explored the impact of modeling oceanographic regimes separately and recommend that future models consider weighting recent data more heavily or potentially including climate indicators. Despite the threats facing right whales today, this species is worth our continued efforts.

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