Beluga whale (Delphinapterus leucas) acoustic foraging behavior and applications for long term monitoring

Abstract

Cook Inlet, Alaska, is home to an endangered and declining population of 279 belugas (Delphinapterus leucas). Recovery efforts highlight a paucity of basic ecological knowledge, impeding the correct assessment of threats and the development of recovery actions. In particular, information on diet and foraging habitat is very limited for this population. Passive acoustic monitoring has proven to be an efficient approach to monitor beluga distribution and seasonal occurrence. Identifying acoustic foraging behavior could help address the current gap in information on diet and foraging habitat. To address this conservation challenge, eight belugas from a comparative, healthy population in Bristol Bay, Alaska, were instrumented with a multi-sensor tag (DTAG), a satellite tag, and a stomach temperature transmitter in August 2014 and May 2016. DTAG deployments provided 129.6 hours of data including foraging and social behavioral states. A total of 68 echolocation click trains ending in terminal buzzes were identified during successful prey chasing and capture, as well as during social interactions. Of these, 37 click trains were successfully processed to measure inter-click intervals (ICI) and ICI trend in their buzzing section. Terminal buzzes with short ICI (minimum ICI <8.98 ms) and consistently decreasing ICI trend (ICI increment range <1.49 ms) were exclusively associated with feeding behavior. This dual metric was applied to acoustic data from one acoustic mooring within the Cook Inlet beluga critical habitat as an example of the application of detecting feeding in long-term passive acoustic monitoring data. This approach allowed description of the relationship between beluga presence, feeding occurrence, and the timing of spawning runs by different species of anadromous fish. Results reflected a clear preference for the Susitna River delta during eulachon (Thaleichthys pacificus), Chinook (Oncorhynchus tshawytscha), pink (Oncorhynchus gorbuscha), and coho (Oncorhynchus kisutch) salmon spawning run periods, with increased feeding occurrence at the peak of the Chinook and pink salmon runs.

Cetacean Sociality, Reproduction, and Conservation

“…Among a wide range of environmental covariates, an index of prey biomass (including several species of salmon as well as eulachon (Thaleichthys pacificus)) was positively correlated with fecundity and older calf survival. Fecundity and older calf survival were also positively correlated with the returning run size of Chinook salmon in the Susitna River, an important foraging habitat for the Cook Inlet whales (Castellote et al 2021). Most of the life history parameters were at their lowest value in 2011, at the start of the recent decline in beluga whale abundance, with 2011 and 2012 representing the two lowest years for fecundity.…”

Possible occurrence of contact calls in all‐male groups of free‐ranging beluga whales

“…The low vocalization rate, averaging 0.2 calls per whale per minute, is comparable with that reported for male herds from the Svalbard population (Karlsen et al, 2002) and differs considerably from those in mixed‐age and ‐sex beluga groups in other areas of the White Sea, where average vocalization rates were an order of magnitude higher (Belikov & Bel'kovich, 2003; Panova et al, 2012). Wild belugas are known to decrease their vocal activity as an anti‐predator response to nearby killer whales (Fish & Vania, 1971) or during foraging (Alekseeva et al, 2013; Castellote et al, 2021). Predation by killer whales is thought to be an important factor affecting Svalbard belugas' behavior, including their acoustic signalization (Lydersen & Kovacs, 2021).…”

Postmortem pathology investigation of the wounds from invasive tagging in belugas (Delphinapterus leucas) from Cook Inlet and Bristol Bay, Alaska

“…The beluga tagged in Bristol Bay (DLBB16‐06) was instrumented with a spider‐legs tag (model SPLASH10‐L‐280B, Wildlife Computers) that included sensors for pressure (for depth), light level, submersion (wet/dry), ambient temperature, and also received transmissions from a stomach temperature transmitter (Andrews, 1998; Castellote et al, 2021) that was placed into the forestomach during the handling process. This spider‐legs tag (Figure 2c) included only two stainless steel cables that exited on each of the long sides of the tag, and the ends of the cables attached to one end of the two 9.5 mm diameter nylon rods that were implanted with the aid of a coring cannula (also 9.5 mm outer diameter).…”

“…An expanded program of capture-release of Bristol Bay belugas for the primary purpose of gathering health and behavioral data for comparison with Cook Inlet belugas began in 2012, and since then another 55 whales were processed over six field seasons. Although the electronic tags, especially the satellite-linked tags (hereafter referred to as satellite tags), applied to Cook Inlet and Bristol Bay belugas have provided data critical to conservation efforts (e.g., Castellote et al, 2021;Citta et al, 2016;Ezer et al, 2008Ezer et al, , 2013Hobbs et al, 2005), there has been no systematic examination of the potential effects of invasive tags on the tagged whales.…”