Farallon Islands

Rabbit Cave /  by Michael Johns

We monitor the breeding population of Rhinoceros auklets on the Farallones by checking artificial wooden nest boxes distributed across the island. These boxes are visited on a regular basis to note which ones contain an active breeding pair, whether those pairs are successful at hatching an egg, and ultimately how many pairs end up fledging a chick; giving us an estimate of the annual breeding success for this species. In addition to the nest boxes, we also monitor breeding activity in Rabbit Cave, a large vestige of the islands geologic past that acts as a kind of massive burrow for Rhinoceros auklets. The entrance to Rabbit Cave starts out as a narrow crawl space that opens up into a cavernous amphitheatre at the back. 

Landscape of a Year /  by Michael Johns

Animals tend to be fairly predictable in their reproductive timing and migration patterns. The figure above depicts a series of density curves, with peaks and troughs corresponding to the average timing of key biological events for a select number of marine species that are monitored on or from Southeast Farallon Island.

Pinnipeds, a taxonomic group that includes seals and sea lions, are found hauled out on the island year round, with peak pupping events occurring in the summer. Northern fur seals, which have made an astounding recovery on the Farallones following the days of the Russian Fur Trade, remain at sea for several months of the year and are only seen in force from summer to late fall. Whales are also visible from the island year round. Gray whale numbers peak in January as they migrate south to their breeding grounds off Baja California Mexico, and again in March during a northward migration back to their feeding grounds in Alaska. Humpback and blue whales are most abundant in the productive summer months, where they are seen gorging themselves on krill and schooling fish. For seabirds, breeding occurs only in the summer months, with the exception of the ashy storm-petrel which extends chick rearing well into October. Three distinct peaks represent the timing of egg laying, hatching, and chick fledging. 

The study of seasonal life-history patterns is called phenology, and it can tell us a lot about the stability of a system. As I mentioned, animals tend to be fairly predictable in their phenology. Individuals cue in on environment and biological signals, so shifts in the timing of reproduction or migration can indicate changes in environmental condition, food availability, or the health of a population. For species found on the Farallones, the major cause for concern in the face of a warming ocean is the availability of key prey items, namely krill, which sustain the rich biodiversity in this region. A mismatch between the timing of krill and the timing of reproduction for seabirds can lead to major declines in breeding success, and subsequent declines in population numbers. 

Data courtesy of a partnership between Point Blue Conservation Science and the USFWS. The plot was created in R with the ggplot2 and ggridges packages. 

Sei Whales Off The Farallones /  by Michael Johns

In addition to daily opportunistic sightings, we conduct standard 1-hour whale watches from atop Lighthouse Hill to document the timing and abundance of Cetaceans around the Farallon Islands. These data are useful in particular for showing where whales are in relation to shipping lanes leading into San Francisco Bay, to better inform mitigation measures aimed at reducing the number of ship strikes.

On one particular whale watch, during an exceptionally calm day, I came across a feeding flock of 6 black-footed albatross and several dozen pink-footed shearwaters. I considered the possibility that this flock was associated with killer whales, since albatross have been known to scavenge on orca kills, and killer whales had been reported in recent days just south of us in Monterey Bay. Sure enough, after watching for a few minutes a tall black dorsal fin came into view, followed by two smaller fins. A pod of transient killer whales that were feeding on some unknown pinniped at the surface. After radioing the sighting to the rest of the crew, everyone made it up to the lighthouse for a look before they eventually departed to the west. 

After the killer whales had left we decided to keep looking around for other sightings. Within minutes a blue whale surfaced right next to the East Landing mooring ball, in water probably half as deep as the length of the animal itself. As if that wasn't good enough, someone pointed out a small pod of whales swimming toward the island. They were all dark baleen whales with a visible blow, six of them traveling in tight formation towards an islet we call Sugar Loaf. Initially, I assumed perhaps it was a group of minke whales, clumping together in response to a pod of their natural predators nearby. The shape of their rostrums, size, behavior, and blow were all wrong though, and as they got closer we couldn't see an signs of white patches indicative of minkes on their pec fins. They were too small to be fin or blue whales, too big to be minkes, and definitely not a toothed whale. The only other obvious possibility for this part of the world is the sei whale, a species of rorqual found in temperate waters worldwide, but generally seen much further offshore and rarely sighted off California. 

To put this sighting into context, only 17 sei whales have ever been seen on the Farallones since 1987, and generally the sightings consisted of a solitary individual. Not only did this group contain a Farallon record breaking 6 animals, but they swam close enough to the island for us to get excellent looks for a prolonged period of time, and even photos of the event (of which my favorite is of a western gull pondering whether it can eat one of the whales). Truly a rare and amazing sight. 

Photos taken through Point Blue Conservation Science | USFWS

Relative Size /  by Michael Johns

Probably the most important question in the conservation work that we do, and the most popular question people have about the Farallones, is the population size of the various seabird species on the island. The answer, such as roughly 250,000 murres, 20,000 auklets, and 500 puffins, may not be fully appreciated when taken at face value. The figure above is an attempt to put these numbers into context by representing each population as a collection of boxes, where the area of each box is scaled in proportion to the other boxes. With this visualization, you can see just how abundant Common Murres are in relation to Pigeon Guillemots or Tufted Puffins. With continued monitoring and management, hopefully all of these boxes will continue to grow in size.

Data courtesy of a partnership between Point Blue Conservation Science and the USFWS. The plot is called a "Treemap", created in R with the ggplot2 and treemapify packages.