Bald Eagle (Haliaeetus leucocephalus) Targeting Forage Fish in Open Water

Tom Okey observed:

I was watching a Bald Eagle (Haliaeetus leucocephalus) perched atop a cement outfall mound just offshore (east) of Island View Beach, and just north of the parking lots, at about 7:30 am. The eagle was staring East or ENE when it suddenly flew in that direction very low over the surface of Haro Strait (about as close as a brown pelican does) for about 200-300 meters. It then grabbed into the water with its talons, as if to catch a salmon. When it appeared to emerge empty handed, I initially thought it missed an adult salmon, but as I followed it back to its perch with my Bushnell 8x42 binoculars I realized that it was carrying a single very small silvery fish (i.e. a forage fish) in its talons. It then appeared to manipulate the fish with its beak, and I didn't see the fish after that.

The Eagle was either watching for signs of fish on the surface, or it was watching the gulls or other birds indicate the locations of forage fish. This barnacle-covered exposed perch was only about a meter above the water at the time (the low tide of 1.5 m was at 7:26 am during the observation). I was observing from the sandy intertidal strand ~150 m south of that perch (distance estimated post hoc using Google Earth).

It was a sunny morning, and many species were feeding on forage fish at this location including 14 Great Blue Herons feeding in the shallow tidal lagoons (~5-10 cm deep), groups of gulls offshore at about the distance the eagle flew (with one group of gulls in a feeding frenzy), and a variety of other bird species resting on the water.

Bald Eagles are known to feed on spawning Pacific herring as well as Eulachon and Pacific Sand Lance when these forage fishes are on the beach, or in very shallow water at the mouths of rivers or in estuaries (Armstrong 1995) in addition to targeting adult salmon, other large fishes, and other prey such as birds and mammals. However, I am not aware of any previous documented observations of Bald Eagles targeting and capturing forage-sized fish in open water the same way they catch adult salmon.

This observation begs the question of whether such (inefficient) open water targeting of forage fish by eagles indicates the scarsity of returning adult salmon, which are at low numbers in 2018 potentially due in part to lingering effects of the warm water anomaly in the North Pacific of 2013-2016. The urgency of this issue of low salmon returns is illustrated by the recent closing of recreational salmon fishing in nearby areas. This feeding pattern of Bald Eagles might be another indicator of low salmon returns.

I saw a river otter (Lontra canadensis) in the surf zone (with small wind-wave-surf from the East) during the evening of this morning observation. I also observed small group of 2 or 3 harbour porpoise (Phocoena phocoena) and a harbour seal (Phoca vitulina) during he morning of 22 June at the same time as the Bald Eagle sighting on 21 June--in the same area that the eagle captured the single tiny fish. This bird and marine mammal activity indicated the availability of forage fish, whether they are herring, other forage fish, or salmon smolts.

Also during the same morning of the present eagle observation (21 June) at approximately the same time Julian Gan and David Costalago of the Hakai Institute took the following video ~10 m offshore of the northern tip of Sonora Island about 250 km to the northwest, which David shared on Twitter:

May this video of 3520 pink, chum, sockeye and herring serve as a summary of yesterday's #salmon sampling with @jclgan et al. @HakaiInstitute. Now off for a (likely) very nice day of #sockeye tagging. pic.twitter.com/6WmAocLZt6

— David Costalago (@nauplius97) June 21, 2018

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Julian Gan and David Costalago clarified that:

Most fish captured in this net sample were pink salmon (Oncorhynchus gorbuscha) and chum salmon (O. keta). The proportion of pink:chum was about 2:1. Sockeye salmon (O. nerka) comprised less than 1% of the total catch. They suggested these proportions were typical of this time of the year.

Additional comment from Tom Okey:

Referring to this net sample of fish does not imply that the forage-sized fish in the Haro Strait where the present observation was made is similar to the species composition described by that sample 250 km to the northwest in the Discovery Islands, just north of Strait of Georgia proper. It simply illustrates that there is high forage fish activity in both areas (salmon fry off Sonora Island).

Literature Cited

Armstrong, R.H., 1995. The importance of fish to bald eagles in southeast Alaska: a review. In Proceedings of the Bald Eagle Symposium

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