Population size, survival and reproductive rates of northern Norwegian killer whales (<i>Orcinus orca</i>) in 1986–2003

Kuningas, Sanna; Similä, Tiu; Hammond, Philip S.

doi:10.1017/s0025315413000933

Cited by 42 publications

(52 citation statements)

References 66 publications

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“…This high survival rate for adult female is expected for long‐lived mammals, for example in other populations of bottlenose dolphin: 0.96 in Scotland (95% CI 0.94–0.98, Arso Civil et al, ) and 0.94 in New Zealand (95% CI: 0.92–0.95, Currey et al, ). These rates are comparable to other CR studies on small cetaceans: orca (0.98, SE 0.01, Kuningas, Similä, & Hammond, ), and Indo‐Pacific bottlenose dolphin (0.93, 95% CI 0.88–0.96, Dulau, Estrade, & Fayan, ). We did not detect any effect of current reproduction status on survival probability.…”

Section: Discussionsupporting

confidence: 85%

Joint estimation of survival and breeding probability in female dolphins and calves with uncertainty in state assignment

Couet

Gally

Canonne

et al. 2019

Ecology and Evolution

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While the population growth rate in long‐lived species is highly sensitive to adult survival, reproduction can also significantly drive population dynamics. Reproductive parameters can be challenging to estimate as breeders and nonbreeders may vary in resighting probability and reproductive status may be difficult to assess. We extended capture–recapture (CR) models previously fitted for data on other long‐lived marine mammals to estimate demographic parameters while accounting for detection heterogeneity between individuals and state uncertainty regarding reproductive status. We applied this model to data on 106 adult female bottlenose dolphins observed over 13 years. The detection probability differed depending on breeding status. Concerning state uncertainty, offspring were not always sighted with their mother, and older calves were easier to detect than young‐of‐the‐year (YOY), respectively, 0.79 (95% CI 0.59–0.90) and 0.58 (95% CI 0.46–0.68). This possibly led to inaccurate reproductive status assignment of females. Adult female survival probability was high (0.97 CI 95% 0.96–0.98) and did not differ according to breeding status. Young‐of‐the‐year and 1‐year‐old calves had a significantly higher survival rate than 2‐year‐old (respectively, 0.66 CI 95% 0.50–0.78 and 0.45 CI 95% 0.29–0.61). This reduced survival is probably related to weaning, a period during which young are exposed to more risks since they lose protection and feeding from the mother. The probability of having a new YOY was high for breeding females that had raised a calf to the age of 3 or lost a 2‐year‐old calf (0.71, CI 95% 0.45–0.88). Yet, this probability was much lower for nonbreeding females and breeding females that had lost a YOY or a 1‐year‐old calf (0.33, 95% CI 0.26–0.42). The multievent CR framework we used is highly flexible and could be easily modified for other study questions or taxa (marine or terrestrial) aimed at modeling reproductive parameters.

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Section: Discussionsupporting

confidence: 85%

Joint estimation of survival and breeding probability in female dolphins and calves with uncertainty in state assignment

Couet

Gally

Canonne

et al. 2019

Ecology and Evolution

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“…This catalogue consisted of photographs taken in northern Norway in the former NSS herring wintering ground in Tysfjord-Ofotfjord-Vestfjord from 1986 to 2003 (work of Similä and colleagues mentioned in [36]).…”

Section: Methodsmentioning

confidence: 99%

First longitudinal study of seal-feeding killer whales (Orcinus orca) in Norwegian coastal waters

Jourdain¹,

Vongraven

Bisther³

et al. 2017

PLoS ONE

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Killer whales (Orcinus orca) have been documented preying on either fish or marine mammals in several regions, suggesting that this odontocete species has the ability to specialize on different types of prey. Off Norway, killer whales have been shown to rely on the Atlantic herring (Clupea harengus) as a main prey resource. Infrequent observations have revealed seals as an additional component of their diet, yet the extent of predation on marine mammals has remained largely unknown. Here, we present the findings of 29 years of photographic and observational data on seal-feeding killer whale groups identified in Norwegian coastal waters. Four groups have been observed preying and feeding on seals over several years, taking both harbor (Phoca vitulina) and grey (Halichoerus grypus) seals. These stable groups are shown to adopt small group sizes, were typically observed in near-shore areas and were not encountered on herring wintering grounds. Behavioral and social traits adopted by these groups are similar to those of pinniped-feeding killer whales from other regions. The potential ecological reasons and the extent of such prey specializations are discussed.

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“…Estimates of the abundance (N), number of deaths (D), recruits (R) and population growth rate (l) for each year 1993 -2010. The average intercalf interval is approximately 6 years in other killer whale populations (Olesiuk et al, 1990;Kuningas et al, 2013). Fearnbach et al, 2012).…”

Section: R E S U L T Smentioning

confidence: 99%

Using opportunistic photo-identifications to detect a population decline of killer whales (Orcinus orca) in British and Irish waters

Beck

Foote

Kötter³

et al. 2013

J. Mar. Biol. Ass.

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An assemblage of killer whales that has been sighted in waters off the west coast of the British Isles and Ireland has previously been shown to be isolated from other North Atlantic killer whale communities based on association patterns. By applying a Bayesian formulation of the Jolly -Seber mark-recapture model to the photo-identification data compiled from opportunistic photographic encounters with this population of killer whales, we show that such sparse and opportunistically-collected data can still be valuable in estimating population dynamics of small, wide-ranging groups. Good quality photo-identification data was collected from 32 encounters over 19 years. Despite a cumulative total of 77 identifications from these encounters, just ten individuals were identified and the remaining 67 identifications were re-sights of these ten animals. There was no detected recruitment through births during the study and, as a result, the population appears to be in a slight decline. The demography of the population was highly skewed towards older individuals and had an unusually high ratio of adult males, and we suggest that demographic stochasticity due to a small population size may be further impacting the population growth rate. We recommend that this population be managed as a separate conservation unit from neighbouring killer whale populations.

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Population size, survival and reproductive rates of northern Norwegian killer whales (Orcinus orca) in 1986–2003

Cited by 42 publications

References 66 publications

Joint estimation of survival and breeding probability in female dolphins and calves with uncertainty in state assignment

Joint estimation of survival and breeding probability in female dolphins and calves with uncertainty in state assignment

First longitudinal study of seal-feeding killer whales (Orcinus orca) in Norwegian coastal waters

Using opportunistic photo-identifications to detect a population decline of killer whales (Orcinus orca) in British and Irish waters

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