Stable Isotope Analysis of Specimens of Opportunity Reveals Ocean-Scale Site Fidelity in an Elusive Whale Species

Abstract

Elusive wildlife are challenging to study, manage, or conserve, as the difficulty of obtaining specimens or conducting direct observations leads to major data deficiencies. Specimens of opportunity, such as salvaged carcasses or museum specimens, are a valuable source of fundamental biological and ecological information on data-deficient, elusive species, increasing knowledge of biodiversity, habitat and range, and population structure. Stable isotope analysis is a powerful indirect tool that can be used to infer foraging behavior and habitat use retrospectively from archived specimens. Beaked whales are a speciose group of cetaceans that are challenging to study in situ, and although Sowerby's beaked whale (Mesoplodon bidens) was discovered >200 years ago, little is known about its biology. We measured δ13C and δ15N stable isotope composition in bone, muscle, and skin tissue from 102 Sowerby's beaked whale specimens of opportunity collected throughout the North Atlantic Ocean to infer movement ecology and spatial population structure. Median δ13C and δ15N values in Sowerby's beaked whale bone, muscle, and skin tissues significantly differed between whales sampled from the east and west North Atlantic Ocean. Quadratic discriminant analysis that simultaneously considered δ13C and δ15N values correctly assigned >85% of the specimens to their collection region for all tissue types. These findings demonstrate Sowerby's beaked whale exhibits both short- and long-term site fidelity to the region from which the specimens were collected, suggest that this species is composed of two or more populations or exhibits a metapopulation structure, and have implications for conservation and management policy. Stable isotope analysis of specimens of opportunity proved a highly successful means of generating new spatial ecology data for this elusive species and is a method that can be effectively applied to other elusive species.

Playing “hide and seek” with the Mediterranean monk seal: a citizen science dataset reveals its distribution from molecular traces (eDNA)

“…Conservation biology hinges upon understanding the distribution and abundance of threatened species in order to draw appropriate conservation measures. However, assessing the distribution of elusive and endangered species is still challenging due to the difficulty of conducting direct observations, which are not numerous and are scattered over a large time frame, making classical survey methods of little use 1 and resulting in a major lack of data 2 . This is particularly evident for the Mediterranean Sea, which is widely recognized as an important hotspot for marine biodiversity 3 , yet whose critical habitats for endangered species still need to be identified for conservation purposes 4 – 7 .…”

Sowerby’s Beaked Whales (Mesoplodon bidens) in the Skagerrak and Adjacent Waters: Historical Records and Recent Post-Mortem Findings

“…Important summer areas have been identified using bottom-mounted autonomous acoustic recorders. Possible calving areas have been described off Western Ireland [11,55,56] and stabile isotope analysis suggests that there may be several populations of SBWs [3,4]. Efforts to study live and dead SBWs in proximity to the Skagerrak basin would provide additional insights into SBWs in the Northeastern Atlantic.…”

“…Our data support previous findings that SBWs mainly prey on fish and adds data on prey species within Scandinavian waters in proximity to the Skagerrak basin. Previous analysis of stable isotopes proposes that there are differences in foraging and feeding behaviour between SBWs in the eastern and western Atlantic [4], but exactly how their diets differ is not fully understood. More information on prey items from each region and SBW foraging behaviour is vital to learn more about this elusive species, and thus be able to provide conservation recommendations where needed.…”

“…Sowerby's beaked whales (Mesoplodon bidens (Sowerby, 1804), SBW) have the most northerly range of Mesoplodon beaked whale species in the Atlantic Ocean, but their distribution, biology and threats are not fully understood [1,2]. Recent studies have found morphological differences between SBWs from the western and eastern North Atlantic, suggesting a metapopulation structure or several populations within the species [3,4]. Thus, intra-species differences regarding their ecology, behaviour or migrations may exist.…”

Strandings of a neonate and a pregnant Sowerby's beaked whale (Mesoplodon bidens(Sowerby, 1804)) in Ireland

“…This species is currently classed as least concern under the International Union for Conservation of Nature (IUCN) red list (Pitman & Brownell Jr., 2020). The population in the eastern Atlantic was estimated to comprise 3518 individuals using aerial survey data (CV = 0.43%, 95% CI 1570–7883; Rogan et al ., 2017) while stable isotope evidence from stranded specimens has indicated local site fidelity of whales within the west and east North Atlantic, which suggests the potential for different populations (Smith et al ., 2021).…”