Inter-individual differences in contamination profiles as tracer of social group association in stranded sperm whales

Abstract

Ecological and physiological factors lead to different contamination patterns in individual marine mammals. The objective of the present study was to assess whether variations in contamination profiles are indicative of social structures of young male sperm whales as they might reflect a variation in feeding preferences and/or in utilized feeding grounds. We used a total of 61 variables associated with organic compounds and trace element concentrations measured in muscle, liver, kidney and blubber gained from 24 sperm whales that stranded in the North Sea in January and February 2016. Combining contaminant and genetic data, there is evidence for at least two cohorts with different origin among these stranded sperm whales; one from the Canary Island region and one from the northern part of the Atlantic. While genetic data unravel relatedness and kinship, contamination data integrate over areas, where animals occured during their lifetime. Especially in long-lived animals with a large migratory potential, as sperm whales, contamination data may carry highly relevant information about aggregation through time and space.

Long-term associations among male sperm whales (Physeter macrocephalus)

“…Autenrieth et al’s [ 15 ] genetic analysis suggested that the 27 male sperm whales that stranded together in the North Sea were not maternally related individuals but instead included assemblages of individuals from different natal geographic regions. Schnitzler et al [ 16 ] also reported evidence for at least two cohorts with different origins among 24 of these males based on contaminant and genetic analyses. Considering the long calving intervals of individual females (every 4~6 years) [ 13 , 17 ] and the size of female family units (~10; [ 6 ]), it would be almost impossible to form an all-male group consisting of more than very few related males of approximately the same age.…”

Beached bachelors: An extensive study on the largest recorded sperm whale Physeter macrocephalus mortality event in the North Sea

“…Levels of a range of contaminants were determined, but were not considered to be of significance in terms of causality of the mortality event (details in [ 60 ]). Data on contaminant profiles together with genetic data gave evidence for at least two cohorts among the stranded sperm whales with different origins; one from the Canary Islands and one from the northern part of the Atlantic [ 59 , 60 ].…”

“…Levels of a range of contaminants were determined, but were not considered to be of significance in terms of causality of the mortality event (details in [ 60 ]). Data on contaminant profiles together with genetic data gave evidence for at least two cohorts among the stranded sperm whales with different origins; one from the Canary Islands and one from the northern part of the Atlantic [ 59 , 60 ]. The genetic diversity was comparable to the genetic diversity in sperm whales from the entire Atlantic Ocean and males did not comprise maternally related individuals within this stranding event, but assemblages of individuals from different geographic regions [ 59 ].…”

“…[ 20 ]). Levels of a range of potential contaminants were determined in samples collected from sperm whales in this study, but were not deemed to be of significance in terms of direct causality of the stranding event [ 60 ].…”

“…Maternal relatedness and the putative origin was investigated by studying genetic diversity of 27 of the stranded sperm whales (details in [ 59 ]). Among 24 of these individuals, contamination profiles as an indication of social structures were also investigated (details in [ 60 ]).…”