Evaluation of the 2012 "True Puffin" mortality event, as observed along the coastline of northern California, Oregon, and Washington

Eric McKane Page

The Northeastern Pacific Ocean's near-shore ecosystem is influenced by a wide variety of physical and biological variables that make it well-suited to support a vibrant and diverse food web comprised of invertebrates, fish, marine mammals, and seabirds. Some of the most abundant seabirds in this ecosystem are in the family Alcidae in the order Charadriiformes, and are commonly referred to as alcids. Of these, perhaps none are so widely recognized as the puffins, including Tufted Puffins and Horned Puffins; and also, their name notwithstanding, Rhinoceros Auklets. These three species are commonly referred to collectively as "true puffins". In the months of January, February, and March of 2012, citizen scientists in the Coastal Observation and Seabird Survey Team (COASST) organization observed and documented a dramatic increase in the number of "true puffin" carcasses being deposited on the coastline of Northern California, Oregon, and Washington. When this mortality event reached its conclusion in late March, a total of 1,029 "true puffin" carcasses had beached, approximately sixteen times the average for the months of January, February, and March in the years leading up to the mortality event. This study describes alternate hypotheses for this mortality event, including a v "true puffin" population wintering anomalously close to the coastline and/or anomalously strong onshore winds, both of which have the potential to increase carcass beaching rates without actually increasing the mortality rate. Alternate hypotheses that do involve increased mortality rates include anomalously severe winter storminess indices, an anomalously high number of first-year juvenile "true puffins" in the population accounted for by an unusually successful breeding season in 2011, and a suppression of the forage fish population that comprises the bulk of "true puffin" diets. All of these hypotheses, with the exception of the latter involving a suppressed forage fish population, are examined and found to be implausible. The suppressed forage fish population, while not being categorically accepted, would appear to offer the most likely explanation for the mortality event, and is the hypothesis best supported by this study and by the necropsies conducted on the beached "true puffin" carcasses.

Evaluation of the 2012 "True Puffin" mortality event, as observed along the coastline of northern California, Oregon, and Washington

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