Date of Award

2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Oceanography

Specialization

Biological Oceanography

Department

Oceanography

First Advisor

Jeremy S. Collie

Abstract

Marine mammal foraging and diet in southern New England is not well known and has therefore been largely ignored as a component of habitat, distribution, and bycatch. Incorporating prey components into marine mammal management is key to improving management of these species, especially as fisheries management progresses towards ecosystem-based management, climate change results in shifting distributions of marine mammals, and we are faced with new management challenges stemming from offshore wind development. This dissertation aims to address data gaps for species highly impacted by human activities, specifically the North Atlantic right whale (Eubalaena glacialis) and the harbor porpoise (Phocoena phocoena), and a suite of species along the continental shelf break that may be subject to future offshore energy development.

The first chapter assesses harbor porpoise diet in southern New England, an area of recently increased bycatch where no diet information was previously available. The results of this study could be incorporated into ecosystem-based management, assess likely shifts in habitat due to climate changes, and inform future bycatch management regulations. For this study we examined stomach contents from 46 bycaught harbor porpoises collected over 24 years (1994-2017) between January and May on the continental shelf south of New England. Clupeids, true hakes (Urophycis), cephalopods, and silver hake (Merluccius bilinearis) constituted 85.5% of all estimated biomass, while cusk eels (Ophidiidea) and small flatfish (Pleuronectiformes) were frequently consumed (found in 29.8% and 27.7% of all stomach samples), but each made up less than 1% of estimated biomass due to their small size. Porpoises were found to preferentially select their prey by size and species, overlapping little with gillnet catch, and average prey size was larger for larger porpoise, females, and during the first half of our study (1994-2006 compared to 2007-2017).

The second chapter investigated North Atlantic right whale prey choices on the continental shelf south of New England. Researchers recently found that these highly endangered whales inhabit the continental shelf south of Rhode Island and Massachusetts year round, and are present and feeding in higher numbers during the late winter and early spring. However, little is known about right whale foraging in this region and the factors driving distribution of their prey. During a short research cruise in April of 2018 we opportunistically investigated potential right whale prey choices in southern New England. After spotting two diving right whales in an area with numerous documented sightings in the previous two weeks, we sampled the water column for possible prey and physical oceanographic parameters using a variety of instruments. Our sampling revealed a consistent dense layer at about 35-40 m associated with a slight pycnocline that appeared to consist primarily of ctenophores and marine snow. However, net sampling throughout the water column showed a mix of Pseudocalanus and Calanus finmarchicus that were not visible in the echosounder or Video Plankton Recorder data. Our sampling suggest possible foraging on ctenophores and a zooplankton assemblage more diverse than most right whale feeding regions, but similar to Cape Cod Bay.

The third chapter demonstrates the use of echosounding to model marine mammal distribution and abundance with direct measurements of prey rather than proxies. The study applies a published algorithm to classify echosounding data into four organism types on the shelf break south of New England, an area of potential offshore energy development rich with marine mammals. We built Generalized Additive Models (GAMs) for seven species using only these acoustically derived variables to explain marine mammal distribution. The resulting GAMs explained between 1% and 36% of model deviance, on par with other published studies that employed a suite of variables that served as proxies for water-column components driving marine mammal distribution.

The research in this dissertation aims to provide data and methods to improve management of marine mammals by considering how ecosystem components such as prey resources influence the distribution of marine mammals. Currently consideration of prey resources does not play a large role in most regional marine mammal management analyses, despite this consideration becoming more important with recent shifts in the ocean environment. This research lays the groundwork for considering prey distributions in ecosystem-based management.

Available for download on Sunday, August 15, 2021

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