Body condition of gray whales (Eschrichtius robustus) feeding on the Pacific Coast reflects local and basin-wide environmental drivers

Abstract

A small subset of the Eastern North Pacific gray whale population does not make the full migration from wintering grounds in Mexico to feeding grounds in the Bering, Chukchi and Beaufort seas and instead feed along the Pacific Coast between northern California and northern British Columbia – this group is known as the Pacific Coast Feeding Group (PCFG). We evaluated the body condition of PCFG whales observed in northern Washington and along Vancouver Island to evaluate how body condition of gray whales changes within and between years. We found that PCFG gray whales improve body condition through the feeding season and at varying rates by year and that they have variability in their body condition at the start and end of each feeding season. The inclusion of environmental factors, particularly the Pacific Decadal Oscillation (lagged two years) and September kelp canopy cover along the Washington coast (lagged one year), drastically improved the ability of a multiple regression model to predict average whale body condition for a given year as compared to models without environmental factors included. A comparison of our findings to a previously published study on body condition of gray whales at Sakhalin Island, Russia highlight the differences of life history strategy between a group of whales with a long migration (Sakhalin whales) and those with a short migration. Whales feeding at Sakhalin Island gain body condition quicker and more predictably to a good body condition by the end of the feeding season than the whales we studied in the PCFG. Photogrammetry may be an effective method for monitoring the effects of climate change on PCFG gray whales.

Naturally stressed? Glucocorticoid profiles in blubber of blue and gray whales in response to life history parameters

“…(Figure 5A). This was expected as low concentrations of blubber cortisol can be an indication of good nutritional status and lactating females are commonly observed in poorer conditions than other females on the feeding grounds (Akmajian et al, 2021; Bradford et al, 2012). As body condition studies show, our finding of elevated mean cortisol concentrations in lactating females may indicate that this group is in a low nutritional state.…”

“…The metabolic costs of fasting and migration may explain the higher corticosterone concentrations found in gray whales sampled in the first phase of their feeding season (from March to June) compared to those sampled between September to November (Figure 6). Lower corticosterone concentrations later in the feeding season may reflect improved body conditions observed in this species, particularly in whales from the Pacific Coast Feeding Ggroup (PCFG; Akmajian et al, 2021). Additional studies looking at GC concentrations and body conditions could help better understand the relationships between blubber glucocorticoids and food abundance in blubber tissue.…”

“…Nevertheless, our results shows that GC hormone profiles change in response to naturally occurring "stressors" such as maturity, pregnancy, and lactation, and they support the validity and feasibility of using hormones as biomarkers for metabolic status of blue and gray whales. When combined with existing photogrammetry or any visual assessment of body condition (Akmajian et al, 2021;Christiansen et al, 2021) such data can provide a robust and comprehensive tool to assess and monitor the metabolic health and well-being of these species. from stranded blue and gray whales.…”

Blue Whale Body Condition Assessed Over a 14-Year Period in the NE Pacific: Annual Variation and Connection to Measures of Ocean Productivity

“…Body condition is commonly used to assess the health of individuals in both terrestrial and aquatic ecosystems (Lockyer et al, 1985;Lockyer, 1986;Batzli and Esseks, 1992;Pettis et al, 2004;Konishi, 2006;Acevedo-Whitehouse and Duffus, 2009;Bradford et al, 2012;Williams et al, 2013;Braithwaite et al, 2015;Soledade Lemos et al, 2020;Akmajian et al, 2021;Rasmussen et al, 2021). Body condition studies are important to gauge the health of recovering populations of animals and the environment as a whole (Williams et al, 2013).…”

“…Alternatively, the use of photographic data has been developed as a low cost, easy to implement, and non-invasive way to monitor whale health. Qualitative visual body condition assessments of target areas make this methodology valuable for long-term studies (Pettis et al, 2004;Bradford et al, 2012;Akmajian et al, 2021). Photographic studies show temporal trends in the body condition of baleen whales over years for species such as North Atlantic right whales (Eubalaena glacialis) (Pettis et al, 2004), and gray whales (Eschrichtius robustus) (Bradford et al, 2012;Soledade Lemos et al, 2020;Akmajian et al, 2021).…”