Habitat preferences by individual humpback whale mothers in the Hawaiian breeding grounds vary with the age and size of their calves

Abstract

We investigated whether calf age and calf size influence habitat choice by humpback whale mother-calf pairs in their breeding grounds. During 1997-2008, we conducted focal follows of mother-calf pairs in Hawaiian waters. Tail-fluke identification photographs and calf lengths (measured through videogrammetry) were obtained. Water depth and sea-bed terrain type were derived from GPS data. Identification photographs were matched so that the habitat choices could be established within breeding seasons. Across 72 mother-calf pairs resighted over various intervals within a breeding season, magnitude of depth change between initial and final sightings increased significantly with resighting interval. There was a significant increase from initial depth to final depth for relatively long resighting intervals (27-51 days), but no significant difference for relatively short resighting intervals (2-26 days). Although there was no preference for sea-bed terrain type by mother-calf pairs at their initial sighting, there was a preference for rugged terrain at their final resighting. A resource selection model indicated that the relative probability of a location being used by a mother-calf pair increased (as a function of water depth and rugged sea-bed terrain type) from initial to final sighting; a finding supported by subsequent tests of habitat preference versus availability. For 96 measured calves, calf length and water depth were positively correlated, even when ordinal day of measurement was controlled for statistically; a finding confirmed by a general linear model that simultaneously investigated the relationship between water depth, sea-bed terrain type, number of escorts, ordinal day and calf size. Thus, both calf age and size influence habitat choice by mother-calf pairs in their breeding grounds. The movement of mothers and their maturing calves into deeper waters where they favour rugged sea-bed terrain appears to be part of a suite of behavioural changes during the pre-migratory phase of residency in the breeding grounds.

Acoustic crypsis in southern right whale mother–calf pairs: infrequent, low-output calls to avoid predation?

“…Migrating mother-calf pairs of grey whales (Eschrictus robustus), right whales (Eubalaena spp.) and humpback whales (Megaptera novaeangliae) move close to shore in shallow waters while on their breeding grounds, compared with conspecific adults unaccompanied by a calf (Whitehead and Moore, 1982;Payne, 1986;Swartz, 1986;Pack et al, 2017). Specifically, on their breeding grounds, southern right whale (Eubalaena australis) mother-calf pairs primarily reside in very shallow water of 5-10 m depth close to shore, in close proximity to or in the surf zone (Payne, 1986).…”

Distribution of breeding humpback whale habitats and overlap with cumulative anthropogenic impacts in the Eastern Tropical Atlantic

“…Previous studies have observed humpback whales in warm waters between 21°C and 28°C, including Silver Bank (West Indies), Antongil Bay (Madagascar), the Great Barrier Reef, and Hawai'i (Ersts & Rosenbaum, ; Johnston, Chapla, Williams, & Mattila, ; Rasmussen et al, ; Smith et al, ; Whitehead & Moore, ). A majority of humpbacks were observed in shallow waters less than 30 m in depth in Antongil Bay, between 15 and 60 m in the West Indies, 30–58 m in the Great Barrier Reef, and between 40 and 80 m in Hawai'i (Ersts & Rosenbaum, ; Pack et al, ; Smith et al, ; Whitehead & Moore, ). Depth may have an impact on different breeding behaviours, such as needing deeper waters for mating displays or shallower waters for young calves (Ersts & Rosenbaum, ).…”

From land and sea, long‐term data reveal persistent humpback whale (Megaptera novaeangliae) breeding habitat in New Caledonia

“…Habitat models suggest a preference for nearshore shallow waters in accordance with other humpback whale breeding grounds around the world (Bortolotto, Danilewicz, Hammond, Thomas, & Zerbini, 2017;Cartwright et al, 2012;Lindsay et al, 2016;Martins et al, 2001;Oviedo & Solís, 2008;Smith et al, 2012;Trudelle et al, 2018 (Mercado III & Frazer, 1999), hence potentially constraining the spatial distribution of singing males. Rugged (Pack et al, 2017) and/or shallow habitats (Mercado & Frazer, 1999), such as that of the South Lagoon reef complexes, could be less suitable for acoustic communication, and therefore less attractive for singers and their audience. Based on these distributional preferences, the Merlet integral reserve (IUCN category Ia) was rarely used by humpback whales in the New Caledonia South Lagoon.…”