Fin whales of the Great Bear Rainforest: Balaenoptera physalus velifera in a Canadian Pacific fjord system

Abstract

Fin whales (Balaenoptera physalus) are widely considered an offshore and oceanic species, but certain populations also use coastal areas and semi-enclosed seas. Based upon fifteen years of study, we report that Canadian Pacific fin whales (B. p. velifera) have returned to the Kitimat Fjord System (KFS) in the Great Bear Rainforest, and have established a seasonally resident population in its intracoastal waters. This is the only fjord system along this coast or elsewhere in which fin whales are known to occur regularly with strong site fidelity. The KFS was also the only Canadian Pacific fjord system in which fin whales were commonly found and killed during commercial whaling, pointing to its long-term importance. Traditional knowledge, whaling records, and citizen science databases suggest that fin whales were extirpated from this area prior to their return in 2005-2006. Visual surveys and mark-recapture analysis documented their repopulation of the area, with 100-120 whales using the fjord system in recent years, as well as the establishment of a seasonally resident population with annual return rates higher than 70%. Line transect surveys identified the central and outer channels of the KFS as the primary fin whale habitat, with the greatest densities occurring in Squally Channel and Caamaño Sound. Fin whales were observed in the KFS in most months of the year. Vessel- and shore-based surveys (27,311 km and 6,572 hours of effort, respectively) indicated regular fin whale presence (2,542 detections), including mother-calf pairs, from June to October and peak abundance in late August-early September. Seasonal patterns were variable year-to-year, and several lines of evidence indicated that fin whales arrived and departed from the KFS repeatedly throughout the summer and fall. Additionally, we report on the population's social network and morphometrics. These findings offer insights into the dynamics of population recovery in an area where several marine shipping projects are proposed. The fin whales of the Great Bear Rainforest represent a rare exception to general patterns in this species' natural history, and we highlight the importance of their conservation.

Fig 1. Study area.

(A) The Kitimat Fjord System in mainland British Columbia, Canada. Blue dashed line indicates current marine traffic routes; red line indicates new routes that have been proposed for shipping projects based in the port of Kitimat (see text). (B–E) Sightings of fin whales within the Kitimat Fjord System since 1994. Only sightings whose geographic positions are known or estimated are shown here. Survey effort for B-C are provided in S1 Fig in S1 File. In D, sightings data are supplied by the BC Cetacean Sightings Network; these sightings are opportunistic and not connected for effort.

Fig 2. Fin whale detection history.

History of documentation of fin whales in the Kitimat Fjord System. (A) Reported kills from the whaling records, not corrected for effort; (B) sightings reported to the BC Cetacean Sightings Network, not corrected for effort; (C) effort-corrected encounter rates (fin whales detected per kilometer of track line surveyed) for three boat-based research platforms, 2004–2015 (note different y-axis scales); (D) effort-corrected detection rates (fin whales detected per hour of scan effort) of fin whales from three shore-based research stations, 2010–2019. Note that shore-based detection rates are for demonstration purposes only; they were not used to assess annual trends in relative abundance.

Fig 3. Population trends.

Results of photo-identification mark-recapture abundance estimation using POPAN models (black, with 95% confidence intervals), displayed alongside catalog size (grey). A. Annual abundance; B. Population.

Fig 4. Site fidelity.

Annual rate of return (recaptures from any previous year) for whales with dorsal distinctiveness score of 2–3 (black, solid line) and 1 (grey, dashed line). Distinctiveness scores (1 = Extremely distinctive, 2 = adequately distinctive; 3 = indistinct and difficult to identify) are displayed separately to assess for the influence of distinctiveness on perceived rates of return (see main text for further details).

Fig 5. Fin whale distribution.

Effort-corrected encounter rates of fin whales in the Kitimat Fjord System, for (A–B) surveys along planned routes, 2005–2014 (see S1 Fig in S1 File for effort), and (C) line transect sampling, 2013–2015 (see S1 Fig in S1 File for effort). In A and B, rates are binned spatially using the blocking from Keen et al. (2017). In C, binning was based upon the strata used in density estimation (S6 Table in S1 File). The color scale in each map is scaled by the maximum observed by the respective research platform. Pink coloration indicates no survey effort.

Fig 6. Fin whale seasonality.

Seasonality of fin whale occurrence in the Kitimat Fjord System. (A) Monthly distribution of kills during local whaling, 1927–1966, not corrected for effort. (B) Monthly distribution of sightings reported to the BC Cetacean Sightings Network, 1994–2019 (“certain” reports only), not corrected for effort. (C–E) Effort-corrected encounter rates (whales detected per km transited) in two-week calendar bins, scaled by the maximum observed during surveys along planned sourtes by the Gitga’at Guardian Watchmen (2005–2018) and aboard RV Elemiah (2006–2016) and during line transect sampling aboard RV Bangarang (2013–2015). (F–H) Effort-corrected detection rates from shore-based observation platforms in the fjord system’s outer waters of Caamano Sound (2010, 2011, 2014, 2019), central waters in south Gil Basin (2011–2016), and Squally Channel further inland (2017–2019). Shore-based detection rates (whales detected per hour of scan effort) were scaled by the maximum observed in each year then averaged across years for each two-week calendar bin. Grey vertical bars indicate standard error about the mean (black dot).

Fig 7. Stomach contents.

Presence of euphausiids in the stomachs of fin whales caught by Coal Harbour whalers within the KFS, 1954–1966 (n = 44 inspected stomachs).

Fig 8. Historical comparison of body dimensions.

Lengths of fin whales killed within the Kitimat Fjord System (n = 54) between 1927 and 1966 (histogram; light grey = males; dark grey = females) compared to the whales in the KFS measured remotely by UAS in 2019 (red dots) and published lengths (left to right: mean lengths in BC whaling database (dots, Gregr et al. 2000); length at sexual maturity (dashed lines, Mizroch et al. 1984); average adult length for the North Pacific subspecies (dots, Aguilar 2009); and maximum recorded length in BC whaling database (Gregr et al. 2000).