Multi-event modeling of true reproductive states of individual female right whales provides new insights into their decline

Abstract

Abundance and population trends of Critically Endangered North Atlantic right whales (Eubalaena glacialis, NARW) have been estimated using mark-recapture analyses where an individual’s state is based upon set delineations of age, using historical estimates of age at first reproduction. Here we assigned individual females to states based upon their reproductive experience, rather than age. We developed a Bayesian mark-recapture-recovery model to investigate how survival, recapture, site-fidelity and dead-recovery probabilities vary for female NARW in different states, using data collected from 1977-2018. States were assigned as calves for individuals in their first year; pre-breeder for individuals greater than one year of age who had yet to produce a calf, or breeder if an individual had reproduced. A decline in abundance of female NARW was seen starting in 2014, with 185 females declining yearly to 142 by 2018. The largest decline was seen in breeding females, with 72 estimated to be alive at the beginning of 2018, while female pre-breeder abundance plateaued at around 70 between 2011- 2018. Females born from 2000 onwards had an average 4% (95% CI:0.03-0.06) chance of transitioning from pre-breeder to breeder, compared to 8% (95%CI:0.06-0.1) for females born prior. This reduction in transition rate from non-breeder to breeder for the current cohort resulted in breeding females declining to 51% of the female population by 2018. We show that a collapse in fecundity of breeding females, and the failure of pre-breeders to start breeding, is an important factor in understanding the current decline in abundance of the NARW.

A multistate capture-recapture model to estimate reproduction of North Atlantic right whales

“…We defined the following true reproductive states: 1 = alive and male; 2 = alive and female, nulliparous; 3 = alive and female, with calf; 4 = alive and female, resting from recent calf event; 5 = alive and female, waiting for next calf event; and 6 = dead. All females were either nulliparous [i.e., pre-breeders; Reed et al -Reed et al (2022)] or at some stage in the breeding cycle, acknowledging that females must rest for at least 1 year after weaning a calf before waiting to breed and birth another calf (Hamilton et al, 1998; Kraus and Rolland, 2007).…”

“…We defined the following true reproductive states: 1 = alive and male; 2 = alive and female, nulliparous; 3 = alive and female, with calf; 4 = alive and female, resting from recent calf event; 5 = alive and female, waiting for next calf event; and 6 = dead. All females were either nulliparous [i.e., pre-breeders;Reed et al -Reed et al (2022)] or at some stage in the breeding cycle, acknowledging that females must rest for at least 1 year after weaning a calf before waiting to breed and birth another calf (Hamilton et al, 1998;Kraus and Rolland, 2007) The mean age-specific survival probabilities for individuals younger than 4.5 years old were shared for males and females (e.g., s 1 ,…,s 4 ) until reaching an adult age when survival became sex specific (s F , s M ). The physiological demands of breeding warranted separate mean survival probabilities for females with a calf (s C ), for females resting from having recently weaned a calf (s R ), and for females waiting to breed (s F ).…”

The prelude to industrial whaling: identifying the targets of ancient European whaling using zooarchaeology and collagen mass-peptide fingerprinting

“…Open Sci. 10: 230741 the context of climate change [10] on the one hand, and by the increasingly precarious status of the small population of remaining North Atlantic right whales (Eubalaena glacialis) on the other [11].…”

Individual identification and photographic techniques in mammalian ecological and behavioural research—Part 2: Field studies and applications

“…As populations evolve over time, their size, composition and demographic structure may change (e.g., Holmes and York 2003;Wittemyer et al 2013) and so may the relationships between traits and fitness (e.g., Saether and Engen 2015;Wright et al 2019), which may in turn affect individual behaviour (e.g., Sapolsky and Share 2004;Ehlman et al 2022), pattern of social networks (e.g., Shizuka and Johnson 2020;Farine 2021), reproductive dynamics and survival (e.g., Cubaynes et al 2014;Reed et al 2022), thus affecting the populations' social and demographic trajectory. In other words, animal populations/communities undergo their own specific ecological and behavioural history that determines their prevalent socio-behavioural configuration and charts their socio-demographic future.…”