No 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.

Environmental variables are often the primary drivers of species' distributions as they define their niche. However, individuals, or groups of individuals, may sometimes adopt a limited range within this larger suitable habitat as a result of social and cultural processes. This is the case for Eastern Caribbean sperm whales. While environmental variables are reasonably successful in describing the general distribution of sperm whales in the region, individuals from different cultural groups have distinct distributions around the Lesser Antilles islands. Using data collected over 2 years of dedicated surveys in the Eastern Caribbean, we conducted habitat modeling and habitat suitability analyses to investigate the mechanisms responsible for such fine‐scale distribution patterns. Vocal clan‐specific models were dramatically more successful at predicting distribution than general species models, showing how a failure to incorporate social factors can impede accurate predictions. Habitat variation between islands did not explain vocal clan distributions, suggesting that cultural group segregation in the Eastern Caribbean sperm whale is driven by traditions of site/island fidelity (most likely maintained through conformism and homophily) rather than habitat type specialization. Our results provide evidence for the key role of cultural knowledge in shaping habitat use of sperm whales within suitable environmental conditions and highlight the importance of cultural factors in shaping sperm whale ecology. We recommend that social and cultural information be incorporated into conservation and management as culture can segregate populations on fine spatial scales in the absence of environmental variability.

Sperm whales have occupied the waters off the Galápagos Islands, Ecuador, for at least the past 200 years. During the 19th century, they were the target of intensive whaling that severely depleted the population. In recent times, after commercial whaling ended, sperm whales in the region remain vulnerable to multiple threats, especially potential entanglement in fishing gear, which may hinder their ability to recover from the whaling era. As a highly mobile, long‐lived species, long‐term analysis of the habitat use of sperm whales is necessary to establish effective conservation and management strategies. Here, contemporary (1985–2014) and historical (1830–1850) sperm whale habitat use off the Galápagos Islands was analysed and contrasted to the extent of the Galápagos Marine Reserve (GMR). Contemporary habitat use and its variability over time were modelled as a function of geographic, oceanographic, and topographic variables using generalized additive models. The fine‐scale habitat (<50 km) used by sperm whales was associated with topographic (i.e. depth and slope) and oceanographic characteristics (i.e. relative sea surface temperature and standard deviation of sea surface temperature), but these preferences varied over time. While historical and contemporary data indicate that sperm whale habitat primarily occurred within the boundaries of the GMR, in recent years, whales were found up to 30.1% of the time outside the GMR, potentially overlapping with commercial fisheries operating in the area. The dynamic nature of the relationship of this nomadic species with its habitat highlights the need of large‐scale conservation efforts across the Eastern Tropical Pacific region, including the wide‐scale enforcement of regulations requiring the use of Automatic Identification System in fishing vessels, the promotion of on‐board fisheries observer programmes, the development of adaptive management strategies, and international collaboration to identify and mitigate threats.

Southern Pacific humpback whales (Megaptera novaeangliae) breed in subtropical and tropical waters off Peru in the south to Nicaragua in the north. The effect of warming oceans on humpback whale distribution in breeding areas remains unclear. We modeled the spatial distribution of humpback whales off the coast of Ecuador in relation to environmental variables. We analyzed the temporal variability in humpback whale sighting rates (animals/hour) in a subtropical (Manabí, 1996–1999) and tropical (Esmeraldas, 2001–2019) breeding ground. At the regional scale, we found humpback whale presence was more likely in shallow waters over the continental shelf. Esmeraldas and Manabí breeding grounds are core wintering habitats with most humpback whale sightings along Ecuador. Within breeding grounds, individual sighting rates varied between and within years and in relation to local sea surface temperature anomalies (SSTa). More animals were sighted in years with cooler waters in the Esmeraldas breeding ground, while the opposite was true in Manabí. Our findings suggest that during ENSO conditions, humpback whales may reach their temperature niche limit in the warm tropical waters near Esmeraldas, while during La Niña conditions, cooler areas such as Peru and Manabi become less suitable, and whales move further north.