Over the past few years humpback whale sightings have really increased. The North Pacific Humpback whale population has seen significant recovery following near decimation by commercial whaling. Protected since 1966, the population has grown from a low of 1,300 back up to historic levels of 20,000 plus (Ford, 2014). Summer feeding grounds that were purged of humpback whales by whalers in the 1950s have gradually been recolonized. One of the areas that has seen an impressive comeback is the Salish Sea, with the largest concentration of humpbacks found in the Strait of Juan de Fuca. From a single female (Figure 1) first documented in the summer of 1997 (“Big Mama (aka Mamma, Momma)”, n.d.), the number of humpbacks using the area has steadily grown. In 2015, the number of individuals surged from 80 or so the previous year to estimates of up to 200 (Bathe and Zeidler, 2016). Since then the number has remained high, though varies from year to year and throughout the feeding season (Figure 2). With a sizable population of humpback whales, evidently here to stay, comes a wealth of new observations to be made, as well as new challenges.
Humpback whales, like all baleen whales, do not live in stable family groups (pods), but they are known to be social. At their feeding grounds, both long- and short-term associations have been documented (e.g. Weinrich and Kuhlberg, 1991; Weinrich et al. 2006; Ziegesar et al. preprint). Unlike other baleen whales, they are generalist feeders, with prey ranging from forage fish like herring and sand lance, to krill and other plankton (Ford, 2014). Humpback whales have been documented using a variety of feeding techniques depending on the prey targeted, the prey density, and the feeding strategies known to the individual or group (e.g. Weinrich et al.1992; Hain et al.1995, McMillan et al. 2019). As a commercial whale watching boat captain for over 15 years, I have spent hundreds of hours observing whales. The influx of humpback whales in recent years has led to observations of feeding behaviours I have not seen previously: paired lunge feeding and loosely co-ordinated aggregates, both described below.
For the first behaviour, pairs and occasionally groups of three whales would go for a long dive together, presumably deep. Their return to the surface was preceded by a large bubble of air, then all animals would lunge toward the surface at an angle. This is in contrast to the well-known phenomena of bubble net feeding exhibited by Humpback whales in Alaska and Northern BC. In bubble net feeding, groups of humpbacks lunge vertically out of the water, consuming prey concentrated by a “net” of bubbles created by one member of the group. The “loose aggregate” behaviour is more common. Groups of 20 or more whales are found spread out over a few nautical miles. They do not lunge at the surface but seem to be feeding at depth. The aggregates form and then disperse, lasting for 20 minutes to several hours. Sometimes the whales seem to go on deep dives collectively, despite being spread out. While these behaviours are undoubtedly linked to prey distribution and abundance, researchers do not know how they find their prey, or even what their prey is in the Strait of Juan de Fuca (Reidy, 2019). There seems to also be a social component to their behaviour. To learn more I contacted Rhonda Reidy, a PhD candidate at the University of Victoria, studying humpback whale foraging in Juan de Fuca Strait.
As it turns out, feeding in pairs and trios is not uncommon amongst humpback whales. As for the aggregates, Reidy noted that humpbacks may possibly communicate over miles. This may shed some light on the formation and dispersal of the aggregates - the whales may be communicating the location of prey patches to each other. Reidy also cautioned that most studies of humpback whale feeding behaviour are based on surface observations, offering a very limited perspective on diet.
The recovery of humpback whales is certainly a story of resilience in nature. Humans did very little to facilitate the recovery of the whales other than stop killing them. The stepwise jump in numbers in the Salish Sea in 2015 begs the question of where those whales were feeding previously, and why did they not return to that feeding area? The return of humpback whales to historic population levels (as well as increases in some other species like seals and Bigg’s killer whales; Ford 2014) is interesting considering that important stocks such as herring and salmon are well below historic levels (McKechnie et al. 2014, Price et al. 2008). One can’t help but feel that the marine ecosystem is out of equilibrium. We don’t have data to fully appreciate what the ecosystem was like prior to intensive fishing and whaling, or consequently to appreciate effects of the removal of all those fish and whales. Reidy (2019) predicts the return of the humpbacks and other marine predators will have significant consequences for fisheries. Nichol et al. (2017) expect impacts on nearshore and continental shelf ecosystems. Whales, quite simply, eat a lot. But their impact is more complex than just making a dent in food webs. Roman et al. (2014) describe whales as “ecosystem engineers” whose role in nutrient cycling via defecation can enhance productivity in areas where they congregate.
Finally, while the return of humpbacks is certainly something to celebrate, it does bring a number of issues as we strive to co-habitate with them. The Strait of Juan de Fuca is a busy shipping route. Noise pollution is a particular concern these days with container ships identified as the major noise makers in the region (Basset et al. 2012). While casual surface observations reveal no changes in whale behaviour from shipping in the Strait of Juan de Fuca, Blair et al. (2016) documented subsurface behavioural changes in tagged humpback whales. Collisions with vessels and entanglement in fishing gear are more concrete examples of whale-human conflicts. Fisheries and Oceans Canada (2013) identifies these threats to individual humpbacks as “moderate”. Typically large vessel strikes are more likely to be fatal to whales than collisions with smaller boats. In a whale-small boat collision in Haida Gwaii a man was badly injured, the fate of the whale uncertain (Baker, 2016). In response to the increased potential for interaction between boats and whales the Marine Education and Research Society (MERS) began a boater education campaign “See a blow, go slow”. Posters have been distributed to marinas and fuel docks around BC (Figure 3). Hopefully with more research, education, and adaptive management practices, humans and humpback whales can successfully share the waters.
References
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