Summer 2013 was the first of the Bangarang Project’s three field seasons. We conducted 4 months of visual, acoustic, and oceanographic surveys in a broad transect (1,220 km2) of the northern fjords of the Gitga’at First Nation. The study area is a semi-enclosed fjordland, rendering it an ideal system for focused study.
Data were collected from the SV Bangarang, Eric’s 12m motorsailer, in close collaboration with the Gitga’at First Nation and the NPO North Coast Cetacean Society. Our crew of three researchers performed repeated circuits of the study area.
Within each circuit, at 24 systematically spaced stations, we performed casts of CTD, Secchi disk, and our cylindrical-conical plummet zooplankton net. The plankton net was equipped with a calibrated flowmeter in order to determine the actual volume of water sampled during each tow. Its samples were preserved in a buffered 5% formaldehyde-seawater solution.
While underway between stations, we conducted visual and acoustic transects designed to investigate the predator density found within the prey fields of each study block and then test how their overlap differs among blocks and throughout the season. A secondary objective is using these visual surveys to infer local predator population sizes for the study area as a whole.
1. Echosounder mapping
We record images of the prey field using a Syqwest Hydrobox dual-beam echosounder. These echograms provide a map of the ambient depth, distribution, and patchiness of prey in each block. This can then be compared to echograms recorded while with foraging whales. There is no published evidence that echosounder surveys disturb large whales, but to be overcautious we stop pinging in the presence of orca and whales that do not appear to be foraging.
2. Passive acoustic monitoring
An oil-filled hydrophone array was towed 100m behind the vessel during transects, and stored on a deck-mounted reel for efficient pay out and retrieval. The audio stream from this array is monitored live. These hydrophones are powered by an isolated battery to ensure uncorrupted acoustic signals at low frequencies, where fin whales vocalize.
3. Distance sampling
We conducted distance sampling according to the published standards (Buckland et al. 2001). Distances to sightings were estimated using binoculars with compass and reticles. When whales were within a feasible distance, I would break transect and take photo-ID, behavioral notes, breath intervals, and fecal samples. My team endeavored to disturb the whales as little as possible, and I would abandon encounters if I observed adverse reactions to our presence. Special focus was given to fin whales, the newest arrival species to the fjordland and the least studied.
4. Strip-width scans
To count seabirds, jumping salmon, and tidal features such as debris fields, we scanned a 150m fixed-width strip on both sides of the vessel. Our strip-width methodology was modeled after Tasker et al. (1984), Huff et al. (2006) and Ballance (2010), among others. In order to know whether a bird is within the 150m strip, my team used a novel handheld range finder design (adapted from Heineman 1981) for estimating distances in confined coastal habitats where the horizon is obscured.
This study design, when replicated multiple times per season for multiple seasons, will allow me to broadly characterize the dynamics of the Great Bear’s summer pelagic ecosystem. Results will be packaged in my dissertation but each chapter will be published in public-access scientific journals. This research will be used to make recommendations to policy makers, inform tanker management practices in the study area, and provide a model for similar research in other systems.