Population growth is limited by nutritional impacts on pregnancy success in endangered Southern Resident killer whales (Orcinus orca)

Abstract

The Southern Resident killer whale population (Orcinus orca) was listed as endangered in 2005 and shows little sign of recovery. These fish eating whales feed primarily on endangered Chinook salmon. Population growth is constrained by low offspring production for the number of reproductive females in the population. Lack of prey, increased toxins and vessel disturbance have been listed as potential causes of the whale’s decline, but partitioning these pressures has been difficult. We validated and applied temporal measures of progesterone and testosterone metabolites to assess occurrence, stage and health of pregnancy from genotyped killer whale feces collected using detection dogs. Thyroid and glucocorticoid hormone metabolites were measured from these same samples to assess physiological stress. These methods enabled us to assess pregnancy occurrence and failure as well as how pregnancy success was temporally impacted by nutritional and other stressors, between 2008 and 2014. Up to 69% of all detectable pregnancies were unsuccessful; of these, up to 33% failed relatively late in gestation or immediately post-partum, when the cost is especially high. Low availability of Chinook salmon appears to be an important stressor among these fish-eating whales as well as a significant cause of late pregnancy failure, including unobserved perinatal loss. However, release of lipophilic toxicants during fat metabolism in the nutritionally deprived animals may also provide a contributor to these cumulative effects. Results point to the importance of promoting Chinook salmon recovery to enhance population growth of Southern Resident killer whales. The physiological measures used in this study can also be used to monitor the success of actions aimed at promoting adaptive management of this important apex predator to the Pacific Northwest.

Effect of age, sex, and season on the variation in blood analytes of a clinically normal ex situ population of killer whales (Orcinus orca)

“…RIs are also used for population health investigations. Wild killer whale populations are exposed to stressors such as food limitations and the persistent presence of organochlorines, which are suspected of being immunomodulatory . The availability of established RIs for killer whales and an understanding of the variables affected by physiologic stimuli will be necessary for investigations into the impact of these stressors on killer whales.…”

Inbreeding in an endangered killer whale population

“…We also only had the opportunity to sample observed animals. The rate of fetal loss has been estimated to be >50% in this population (Wasser et al ., ), and inbreeding depression could be expressed as fetal loss.…”

The coast-wide collapse in marine survival of west coast Chinook and steelhead: slow-moving catastrophe or deeper failure?

“…Wasser et al [48] cite this blanket statement: “Anadromous salmonids ( Oncorhynchus sp. ), which hatch in fresh water, migrate to the ocean, and then return to their natal waterways to breed, are threatened primarily by habitat loss from dams and overfishing (SOS 2011)” (Lines 98-101 of the SI).…”

“…These region-specific issues cannot possibly be the drivers of the continental-scale response that we document and to further delay not only increases the threat to salmon, but to those species that rely on them, such as southern resident killer whales. Wasser et al [48] state that “ Low availability of Chinook salmon appears to be an important stressor among these fish-eating whales as well as a significant cause of late pregnancy failure, including unobserved perinatal loss… Results point to the importance of promoting Chinook salmon recovery to enhance population growth of Southern Resident killer whales. ” There are many real consequences to ineffective policy responses—lost time, inability to boost salmon abundances (for both human and non-human salmon predators alike), and elevated costs for many other industries.…”

“…Given the massive investment in restoration and monitoring activities for Pacific salmon, the development of correct conservation analyses and policy planning is critical. Over $1 Billion is now spent annually in the continental United States alone on freshwater habitat restoration [146, 147], and there is great pressure to remove or modify hydropower dams in the Columbia River basin to rebuild salmon runs to historical levels of abundance and productivity and more recently to help endangered orca populations [48]. Within the Columbia River, the total cost of recent conservation efforts reaches or exceeds ca.…”