Critical Decline of the Eastern Caribbean Sperm Whale Population

Gero, Shane; Whitehead, Hal

doi:10.1371/journal.pone.0162019

Cited by 30 publications

(46 citation statements)

References 39 publications

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“…Our estimates are consistent with known adult survival rates of sperm whales in Southern Australia (Evans and Hindell ) and in the Eastern Caribbean (Gero and Whitehead ), and are considerably higher than those found in Japan, where the population is subject to significant mortality in fishing gear (Evans and Hindell ).…”

Section: Discussionsupporting

confidence: 88%

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

et al. 2019

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Capture–mark–recapture methods have been extensively used to estimate abundance, demography, and life history parameters of populations of several taxa. However, the high mobility of many species means that dedicated surveys are logistically complicated and expensive. Use of opportunistic data may be an alternative, if modeling takes into account the inevitable heterogeneity in capture probability from imperfect detection and incomplete sampling, which can produce significant bias in parameter estimates. Here, we compare covariate‐based open Jolly‐Seber models (POPAN) and multi‐state open robust design (MSORD) models to estimate demographic parameters of the sperm whale population summering in the Azores, from photo‐identification data collected opportunistically by whale‐watching operators and researchers. The structure of the MSORD also allows for extra information to be obtained, estimating temporary emigration and improving precision of estimated parameters. Estimates of survival from both POPAN and MSORD were high, constant, and very similar. The POPAN model, which partially accounted for heterogeneity in capture probabilities, estimated an unbiased super‐population of ~1470 whales, with annual abundance showing a positive trend from 351 individuals (95% CI: 234–526) in 2010 to 718 (95% CI: 477–1082) in 2015. In contrast, estimates of abundance from MSORD models that explicitly incorporated imperfect detection due to temporary emigration were less biased, more precise, and showed no trend over years, from 275 individuals (95% CI: 188–404) in 2014 to 367 (95% CI: 248–542) in 2012. The MSORD estimated short residence time and an even‐flow temporary emigration, meaning that the probability of whales emigrating from and immigrating to the area was equal. Our results illustrate how failure to account for transience and temporary emigration can lead to biased estimates and trends in abundance, compromising our ability to detect true population changes. MSORD models should improve inferences of population dynamics, especially when capture probability is low and highly variable, due to wide‐ranging behavior of individuals or to non‐standardized sampling. Therefore, these models should provide less biased estimates and more accurate assessments of uncertainty that can inform management and conservation measures.

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Section: Discussionsupporting

confidence: 88%

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

et al. 2019

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“…In sperm whales (Physeter macrocephalus), sociality was shown to be primarily driven and maintained by kinship selection and the alloparental care function provided by closely related adult females to calves within matrilineal females/immatures social units (80,81). The likely alteration of this female sociality caused by the rapid loss of individuals was proposed as one of the factors potentially contributing further to the decline of some populations (80,82,83). Female killer whales are also known to take care of their kin, protect them during attacks, transmit ecological knowledge like hunting techniques, and share prey with them (9,47,(84)(85)(86)(87).…”

Section: Discussionmentioning

confidence: 99%

Role of sociality in the response of killer whales to an additive mortality event

Busson

Authier

Barbraud

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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In highly social top predators, group living is an ecological strategy that enhances individual fitness, primarily through increased foraging success. Additive mortality events across multiple social groups in populations may affect the social structure, and therefore the fitness, of surviving individuals. This hypothesis was examined in a killer whale (Orcinus orca) population that experienced a 7-y period of severe additive mortality due to lethal interactions with illegal fishing vessels. Using both social and demographic analyses conducted on a unique long-term dataset encompassing periods before, during, and after this event, results indicated a decrease in both the number and the mean strength of associations of surviving individuals during the additive mortality period. A positive significant correlation between association strength and apparent survival suggested that the fitness of surviving individuals was impacted by the additive mortality event. After this event, individuals responded to the loss of relatives in their social groups by associating with a greater number of other social groups, likely to maintain a functional group size that maximized their foraging success. However, these associations were loose; individuals did not reassociate in highly stable social groups, and their survival remained low years after the mortality event. These findings demonstrate how the disruption of social structure in killer whales may lead to prolonged negative effects of demographic stress beyond an additive mortality event. More importantly, this study shows that sociality has a key role in the resilience of populations to humaninduced mortality; this has major implications for the conservation of highly social and long-lived species. sociality | survival | social structure | anthropogenic disturbances | killer whales

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“…Sperm whales are not considered rare, but have been depleted to approximately one‐third of their prewhaling population sizes and are protected by various national and international laws and treaties (e.g., the US Endangered Species Act, IUCN Red List, International Whaling Commission). Given evidence of population structure within and between ocean basins (Alexander et al., ; Engelhaupt et al., ; Lyrholm & Gyllensten, ; Mesnick et al., ), the likelihood that populations were unevenly depleted by whaling (Ivashchenko et al., ), and lack of information on population recovery globally, it is highly probable that some sperm whale populations are still endangered or at risk (Carroll, Hedley, Bannister, Ensor, & Harcourt, ; Gero & Whitehead, ; Notarbartolo‐Di‐Sciara, ). Our results provide support for current isolation of populations located in different ocean basins, with episodic dispersal of females restricted to only warm climate periods.…”

Section: Discussionmentioning

confidence: 99%

“…Whaling Commission). Given evidence of population structure within and between ocean basins (Alexander et al, 2016;Engelhaupt et al, 2009;Lyrholm & Gyllensten, 1998;Mesnick et al, 2011), the likelihood that populations were unevenly depleted by whaling (Ivashchenko et al, 2014), and lack of information on population recovery globally, it is highly probable that some sperm whale populations are still endangered or at risk (Carroll, Hedley, Bannister, Ensor, & Harcourt, 2014;Gero & Whitehead, 2016;Notarbartolo-Di-Sciara, 2014 Gendron, & Coakes, 2003;Pecl & Jackson, 2008). In particular, climate change can affect the Atlantic and Pacific oceans quite differently (Boyle & Keigwin, 1985;Cheng et al, 2009;Greene et al, 2008;Howard, 1997), which may explain the apparent refugial population of sperm whales in the Pacific Ocean during the last long glacial period.…”

Section: Discussionmentioning

confidence: 99%

Demography or selection on linked cultural traits or genes? Investigating the driver of low mtDNA diversity in the sperm whale using complementary mitochondrial and nuclear genome analyses

et al. 2018

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Mitochondrial DNA has been heavily utilized in phylogeography studies for several decades. However, underlying patterns of demography and phylogeography may be misrepresented due to coalescence stochasticity, selection, variation in mutation rates and cultural hitchhiking (linkage of genetic variation to culturally-transmitted traits affecting fitness). Cultural hitchhiking has been suggested as an explanation for low genetic diversity in species with strong social structures, counteracting even high mobility, abundance and limited barriers to dispersal. One such species is the sperm whale, which shows very limited phylogeographic structure and low mtDNA diversity despite a worldwide distribution and large population. Here, we use analyses of 175 globally distributed mitogenomes and three nuclear genomes to evaluate hypotheses of a population bottleneck/expansion vs. a selective sweep due to cultural hitchhiking or selection on mtDNA as the mechanism contributing to low worldwide mitochondrial diversity in sperm whales. In contrast to mtDNA control region (CR) data, mitogenome haplotypes are largely ocean-specific, with only one of 80 shared between the Atlantic and Pacific. Demographic analyses of nuclear genomes suggest low mtDNA diversity is consistent with a global reduction in population size that ended approximately 125,000 years ago, correlated with the Eemian interglacial. Phylogeographic analysis suggests that extant sperm whales descend from maternal lineages endemic to the Pacific during the period of reduced abundance and have subsequently colonized the Atlantic several times. Results highlight the apparent impact of past climate change, and suggest selection and hitchhiking are not the sole processes responsible for low mtDNA diversity in this highly social species.

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Critical Decline of the Eastern Caribbean Sperm Whale Population

Cited by 30 publications

References 39 publications

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

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

Role of sociality in the response of killer whales to an additive mortality event

Demography or selection on linked cultural traits or genes? Investigating the driver of low mtDNA diversity in the sperm whale using complementary mitochondrial and nuclear genome analyses

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