Quantifying the effects of prey abundance on killer whale reproduction

Abstract

Summary 1.Management decisions for threatened and endangered species require risks to be identified and prioritized, based on the degree to which they influence population dynamics. The potential for recovery of small populations at risk may be determined by multiple factors, including intrinsic population characteristics (inbreeding, sex ratios) and extrinsic variables (prey availability, disease, human disturbance). Using Bayesian statistical methods, the impact of each of these risk factors on demographic rates can be quantified and assigned probabilities to express uncertainty. 2.We assessed the impact of a wide range of factors on the fecundity of two threatened populations of killer whales Orcinus orca , specifically whether killer whale production is limited by availability of Chinook salmon Oncorhynchus tshawytscha . Additional variables included anthropogenic factors, climate variables, temporal effects, and population variables (population size, number of males, female age). 3. Our results indicate that killer whale fecundity is highly correlated with the abundance of Chinook salmon. For example, the probability of a female calving differed by 50% between years of low salmon abundance and high salmon abundance. Weak evidence exists for linking fecundity to other variables, such as sea surface temperature. 4. There was strong data support for reproductive senescence in female killer whales. This pattern of rapid maturity and gradual decline of fecundity with age commonly seen in terrestrial mammals has been documented in few marine mammal species. Maximum production for this species occurs between ages 20-22, and reproductive performance declines gradually to menopause over a period of 25 years. 5. Synthesis and applications . Our results provide strong evidence for reproductive senescence in killer whales, and more importantly, that killer whale fecundity is strongly tied to the abundance of Chinook salmon, a species that is susceptible to environmental variation and has high commercial value to fisheries. This strong predator-prey relationship highlights the importance of understanding which salmon populations overlap with killer whales seasonally and spatially, so that those salmon populations important as prey for killer whales can be identified and targeted for conservation efforts.

Ecological Knowledge, Leadership, and the Evolution of Menopause in Killer Whales

“…Second, that leadership by postreproductively aged females is especially prominent in difficult years when salmon abundance is low. This finding is critical because salmon abundance drives both mortality and reproductive success in resident killer whales [9,10]. Third, females are more likely to lead their sons compared to their daughters, supporting predictions of recent models [5] of the evolution of menopause based on kinship dynamics.…”

Quantifying injury to common bottlenose dolphins from the Deepwater Horizon oil spill using an age-, sex- and class-structured population model

“…However, it should be noted that due to the logistical difficulty of observing births for cetaceans, and the fact that the highest risk of mortality occurs during the neonatal period (Stolen & Barlow 2003, Mann & Watson-Capps 2005, estimates of fecundity or birth rate likely integrate early calf (neonatal) survival rate to some degree. N onetheless, relationships among prey abundance, body condition, and fecundity (which may include some aspect of calf survival) have been documented for cetaceans (Ward et al 2009, Williams et al 2013, Meyer-Gutbrod et al 2015, suggesting a process by which DD responses in fecundity could occur. Specifically in bottlenose dolphins, shorter birth intervals were noted in a population from the US Atlantic coast following a significant depletion from a morbillivirus outbreak (Thayer 2008), and increases in calf/group ratios were documented in the years following a major hurricane in the northern Gulf of Mexico, presumably in response to increased prey availability following fishery closures or potential calf losses during the hurricane (Miller et al 2010).…”

Stable isotopes of captive cetaceans (killer whales and bottlenose dolphins)

“…S1, Table S1), we found only six control studies on marine mammals [pinnipeds (Hobson et al, 1996;Kurle, 2002;Lesage et al, 2002;Zhao et al, 2006) and sirenians (Ames et al, 1996; Alves-Stanley and Worthy, 2009)], but none on cetaceans. Therefore, there is an urgent need to estimate isotopic discrimination and turnover for these taxa, because studies investigating the feeding ecology of cetaceans, especially those that are declining or are susceptible to the activities of commercial fisheries (DeMaster et al, 2001;Lewison et al, 2004;Ward et al, 2009), will probably continue to increase in the coming years (supplementary material Fig. S1, Table S1).…”