Date of Award

5-2020

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology/Environmental Biology

First Advisor

Solange Brault

Second Advisor

Michael Rex

Third Advisor

Jarrett Byrnes

Abstract

North Atlantic right whales (Eubalaena glacialis) are verging on extinction. The purpose of this dissertation is to quantify local right whale abundance and use biological and physical predictors to explain the variations in abundance. I estimated local abundance using distance sampling methodology of line transect aerial survey data collected in and around Cape Cod Bay. I measured the time a whale would be in view from the aircraft, and collected dive and surface time data to estimate availability bias, which varied monthly (from 0.27 to 0.85). Right whale population estimates increased from 1990 to 2010, and have since declined; however, local abundance estimates in peak months increased at a faster rate (10% yr-1) than the population, with large monthly and yearly variations. To identify the mechanisms driving local abundance I constructed three structural equation models including local (Cape Cod Bay), regional (Gulf of Maine), and basin-wide (North Atlantic) variables. Population size and zooplankton patchiness had a direct positive relationship (90% credible intervals (CI) = 1.00 = 1.01, and 1.02 = 1.18), and the spring transition date had a direct negative effect on local abundance (90% CI = 0.88 – 0.97). The direct relationship between regional C. finmarchicus density and local abundance varied by month (90% CIs: January = 0.9997 – 0.9999, February = 0.99 – 1.00, March = 0.99 – 1.00, April = 0.99 – 1.00, May = 0.99 – 1.00). It is virtually certain that years of earlier spring transition dates had higher local abundance than years of later spring transition dates (>= 99%). The total effect of the NAO 2 yr-lag on local abundance depended on the month. It was about as likely as not that higher Gulf Stream North Wall latitudes had higher local abundance than years of lower latitudes (51% - 63%). My study identifies key variables to track when predicting local habitat use as the Gulf of Maine continues to change. Understanding the differential impact of climate change on these drivers will be imperative for crafting conservation measures.

Comments

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