Galápagos sperm whales (Physeter macrocephalus): waxing and waning over three decades

Abstract

While population sizes and structures naturally fluctuate over time, rapid within-generation changes are usually driven by shifts in habitat quality and (or) abrupt mortality. We evaluate how sperm whales (Physeter macrocephalus L., 1758 = Physeter catodon L., 1758) responded to the dynamic habit off the Galápagos Islands over 30 years, relating it to variation in prey availability and whaling operations in the tropical Pacific. In the 1980s, males and females were commonly sighted foraging and socializing in the northwest of the archipelago. Sightings decreased during the 1990s; by the 2000s, they became very rare: occasional single foraging males were sighted and females abandoned the archipelago. In the 2010s, whales return to the southern waters, in large groups with apparently more breeding males and calves. The waxing and waning of Galápagos sperm whales are likely caused by environmental shifts together with ripple effects of whaling. Their patchy prey are influenced by variation in sea temperature and productivity, which drives movements of whales in and out of the archipelago. Whaling may have aggravated these movements by leaving an attractive surplus of prey in coastal waters depleted of whales. These findings highlight the magnitude of spatiotemporal scales used by sperm whales and the consequent challenges of assessing population dynamics of long-lived, mobile pelagic species.

Multi‐state open robust design applied to opportunistic data reveals dynamics of wide‐ranging taxa: the sperm whale case

“…, Cantor et al. ). Other factors may influence the movement dynamics of sperm whales over periods of days to weeks, including occasional presence and harassment by adult males attempting to mate (Sundaresan et al.…”

“…The distribution of sperm whales in the Azores is strongly correlated with primary productivity, suggesting that prey availability is an important driver of local movements and habitat use (Tobeña et al 2016). The displacement of sperm whales from the study area may be a direct response to changes in food resources, feeding success, or be mediated by increased density and intraspecific competition (Whitehead and Rendell 2004, Whitehead et al 2008, Cantor et al 2017. Other factors may influence the movement dynamics of sperm whales over periods of days to weeks, including occasional presence and harassment by adult males attempting to mate (Sundaresan et al 2007, Craig et al 2014 or repeated disturbance from whale-watching boats (Gordon and Steiner 1992, Magalhães et al 2002, Christiansen et al 2013).…”

Oceanic islands and climate: using a multi-criteria model of drivers of change to select key conservation areas in Galapagos

“…The marine life of the Galapagos Islands has been commercially exploited since the late eighteenth century, marked with the hunting of Galapagos fur seals (Arctocephalus galapagoensis) (Townsend 1934), and local sperm whales (Physeter macrocephalus), which have never recovered from whaling activities (Cantor et al 2017;Whitehead et al 1997). Finfish fisheries in the Galapagos date back to the early nineteenth century (Castrejón 2011) and commercial fisheries were permanently established in 1945, where the main target species was the Galapagos grouper (Mycteroperca olfax), or locally referred to as bacalao (Schiller et al 2014).…”

“…Habitats included areas of (1) sea cucumber and lobster catches (Buglass et al 2017;Bustamante et al 2000;Toral-Granda and Martínez 2005;Wolff et al 2011), (2) shark nurseries (Llerena et al 2015), ( 3) corals (Glynn et al 2018), and (4) whale shark habitat (Hearn et al 2016). For density and distributions of predators (PD), we included (1) endemism and richness of sharks (Acuña-Marrero et al 2018;Hearn et al 2014), (2) sperm whale densities (Cantor et al 2017), (3) tiger shark densities (Acuña-Marrero et al 2017), and (4) hammerhead shark densities (Hearn et al 2010;Peñaherrera-Palma et al 2017). Polygons for each habitat and predators' density/distributions were scored with 1 whenever each was present.…”

Historical and contemporary habitat use of sperm whales around the Galápagos Archipelago: Implications for conservation

“…While during the 1980s sperm whales were found throughout the study area over a wide range of oceanographic conditions, their distribution shifted northward to the shallow and steep waters of the Marchena Channel in the 1990s, and in the 2010s it shifted southward of the islands, where bottom topography is deeper and flatter. Likewise, the probability of encountering whales also varied across decades, with more likely whale sightings in the 1980s than the 1990s and 2010s (Cantor et al, 2017). Decadal shifts in habitat use were also apparent in the 1800s; while in the 1830s sperm whales occurred west and south of the Archipelago, in the 1840s sperm whale sightings were also common in the northern Marchena Channel.…”