Behavior and bioenergetics of gray whales on their breeding ground.

Written by Aude Pacini

Last February, I was part of a collaborative project between MMRP (led by Dr Lars Bejder), AMRU (led by Dr Fredrik Christiansen) and the Laguna San Ignacio Ecosystem Science Program (led by Dr Jorge Urbán R. and Dr Steven Swartz). The main goal of this project is to obtain information about the behavior and bioenergetics of gray whales (Eschrichtius robustus) mother/calf pairs. The multi-year project relies on a combination of technologies such as Unoccupied Aerial Vehicles (UAVs) and archival tags. In this blog, I will mainly focus on our tagging efforts.

The Laguna San Ignacio Ecosystem Science Program (LSIESP) was created in 2007 by Dr Steven Swartz, Mary Lou Jones and Dr Jorge Urbán, Dr Alejandro Gómez-Gallardo. LSIESP is a program that aims to enhance the conservation of the the San Ignacio lagoon which is part of the UNESCO World Heritage Site: “Whale Sanctuary of El Vizcanio." (Figure 1)

Figure 1. Map of San Ignacio lagoon. The shaded area is where whale-watching is legal.

Lars Bejder, Pernille Sorensen from Aarhus University and myself went to San Ignacio lagoon in Baja California for two weeks in February 2018 to collect data. We joined the LSIESP team which included scientists from the Universitad Autonoma de Baja California Sur, AMRU and UCSD.

The field site was in the desert and researchers were housed next to the many visitors of the lagoon who hoped to meet gray whales (Figure 2). Because of the remoteness of this field site, there was no running water and electricity was provided by wind and solar power.

Figure 2. The Kuyimita camp site.

The goal of this project is to quantify the basic behavior and bioenergetics of mother/calf pairs using non-invasive archival tags called Dtags (Figure 3). These tags collect acoustic, pressure and acceleration data that provide information on respiration rate and fluke stroke. Energetic expenditure associated in behavior such as resting, traveling, and nursing can then be quantified in both mothers and calves. Think of an activity tracker similar to the ones people commonly use but for whales !

Figure 3. Dtag deployement on a gray whale adult female.

Dr Sergio Martínez Aguilar was our captain and his knowledge of gray whale behavior proved to be extremely valuable. We deployed 11 tags on mother/calf pairs and successfully obtained over 70 hours of acoustic, accelerometer and pressure data (Figure 4). We also followed some groups to obtain behavioral observations and photo ID.

Fabien Vivier (a current PhD student at MMRP) flew UAVs above the tagged whales. This helped us validate the behavioral data we collected on the tags.

Figure 4. Mother/calf pair with Dtag on both individuals

Once a tag was deployed, it typically stayed on an animal for more than five hours and we tracked it using VHF signals emitted by the tag (Figure 5). Tags would generally come off when whales rubbed against each other, or automatically with the pre-programmed release mechanism. The next day, we would look for the tag and retrieve the data.

Figure 5. Tracking the VHF signal of the tag at sunset.

We are now analyzing the data to look at energy expenditures of these animals looking at resting, nursing/suckling, traveling and other behaviors. Results will be compared to activity budgets associated with migration along the Pacific coast and in Alaska, where gray whales feed in the summer. Results will inform management agencies of the energetic requirements associated with undisturbed activities and the potential costs of human activities such as underwater noise pollution, whale watching or oil exploration.

Permits:

This work was conducted under Permit # SGPA/DGVS/000531/18 and is in compliance with UH IACUC procedures. Special thanks to the volunteers at LSIESP and all the staff at Kuyimata. Photo credits: Aude Pacini, Fabien Vivier, Sergio Martínez Aguilar.