Ontogenetic and seasonal analysis of the diet and isotopic niche of humpback whales in the Magellan Strait, Chile

Abstract

The ecological niche is dynamic, since the position and width of the niche can vary at different spatial and temporal scales. We examined the trophic ecology of southeast Pacific humpback whales Megaptera novaeangliae in the Magellan Strait feeding area in 2011, 2012 and 2017, analyzing changes in diet and the width of the isotopic niche in relation to ontogeny and seasonality. The isotopic composition of carbon (δ13C) and nitrogen (δ15N) in whale skin and in putative prey species was analyzed. Bayesian mixing models were used to determine the diet, and the isotopic niche was estimated using the standard ellipse area. Differences were found between the diets of juveniles and adults; Fuegian sprat Sprattus fuegensis was consumed mostly by adult individuals. We found no differences in the diet or in the isotopic niche of humpback whales throughout the feeding season in all years. This study suggests that the differences in diet between age classes are influenced by the ability to find and capture prey, whereas seasonality does not influence the niche width of humpback whales in the Magellan Strait. Our results suggested that fluctuations in the abundance of prey populations could influence in the trophic niche dynamics of humpback whales in the Magellan Strait. In particular, a reduction in the availability of Fuegian sprat would mainly affect adult individuals, leading to a dietary switch and/or to an expansion of their feeding area.

A review of post-whaling abundance, trends, changes in distribution and migration patterns, and supplementary feeding of Southern Hemisphere humpback whales

“…Another investigation on feeding behaviour in the area has demonstrated the adoption of bubble-net feeding, some of which were single straight-line bubble curtains (Acevedo et al, 2011). Gibbons et al (2003) have indicated the presence of schooling fish as Fuegian sprat Sprattus fueguensis as potential prey, and more recently stable isotope analysis confirmed these to be the main food item of humpback whale individuals in the area (Haro et al, 2016), especially of adults in comparison with juveniles (Haro et al, 2021).…”

Whales and climate

“…Another investigation on feeding behaviour in the area has demonstrated the adoption of bubble-net feeding, some of which were single straight-line bubble curtains (Acevedo et al, 2011). Gibbons et al (2003) have indicated the presence of schooling fish as Fuegian sprat Sprattus fueguensis as potential prey, and more recently stable isotope analysis confirmed these to be the main food item of humpback whale individuals in the area (Haro et al, 2016), especially of adults in comparison with juveniles (Haro et al, 2021).…”

Approaching the Ecological Role of the Squat Lobster (Munida gregaria) and the Fuegian Sprat (Sprattus fuegensis) in the Francisco Coloane Marine Area (Magellan Strait, Chile) Using a Pelagic Food Web Model

“…The Francisco Coloane Marine Area in the Magellan Strait, which has a pelagic ecosystem with a high diversity of fauna, has recorded at least 14 species of marine mammals and 32 marine and/or coastal birds [35][36][37]; it is also a feeding area for Magellanic penguins (Spheniscus magellanicus), humpback whales (Megaptera novaeangliae), and sea lions [38]. Although these large predator populations are supported by species such as the squat lobster and Fuegian sprat [33,34,39,40], no information exists regarding the ecological role these crustaceans and fish play in the ecosystem and the impact that possible biomass changes in these species would have on the food web. According to the role previously indicated for Munida spp.…”

“…According to the role previously indicated for Munida spp. in southern coastal ecosystems and its importance in the diet of various species [26,27,33,40], we hypothesized that the squat lobster fulfills a role in connecting basal trophic level groups and higher trophic level groups in the study area. In accordance with previous reports on small pelagic fish in productive ecosystems and the fact that the Fuegian sprat has a role as both predator and prey in the fjord and channel system, we also hypothesized that the Fuegian sprat plays a role related to energy transfer in the Francisco Coloane ecosystem.…”