Humpback Whale Variability at an Ecological Hotspot: Reconciling Patterns with Processes

Jesus Pineda, Biology

2014 MMC Funded Project

Abstract

Humpback whales, sand lance fish, and small sharks are major components of the Massachusetts Bay pelagic community.  These organisms can be very abundant at Stellwagen Bank’s (SB) southwest corner, an ecological hotspot in the sense that density of key species is high.  This location is one of the most ecologically important areas within the Stellwagen Bank National Marine Sanctuary (SBNMS).  The southern flank of SB lies within the Northern Right Whale Critical Habitat Area, and is heavily fished commercially and recreationally.  Previous observations indicate sharp interannual variability of whales, fish, and sharks during the summer.  When the small sharks Squalus acanthias are abundant, humpback whales Megaptera novaeangliae and sand lance fish Ammodytes spp. tend to be rare.  Sand lance, a small zooplanktivorous fish, is the preferred prey of humpback whales in Massachusetts Bay, and small sharks also prey on these fish.

We propose to test the hypothesis the small sharks influence the distribution and interannual variability of humpback whales at Stellwagen Bank’s (SB) southwest corner through competition for sand lance prey.  We infer that high shark abundances lead to a decline in sand lance, resulting in a shift in humpback whale distribution to areas with fewer sharks and with more prey.  We will focus on patterns of covariance of humpback whales, small sharks, and their common prey, sand lance, to further understand how these species interact, and the spatial variability of these trophic relationships.  Fish and shark abundance will be assessed using acoustic and video approaches, whereas whale abundance and behavior will be assessed by expert observers.

Whale distribution at Massachusetts Bay is an issue of societal concern, with implications for large ship navigation, fishing gear deployment, and a source of tourism revenue for the whale watching fleet.  By investigating specific processes (e.g. foraging response and habitat characteristics), and the patterns of interannual variability in distribution, our study will contribute to untangling the complex web of processes influencing the ecology and distribution of humpback whales, their preferred prey, and a potential competitor.