Great Shearwater(puffinus Gravis) Mortality Events Along the Eastern Coast of the United States

Abstract

The Great Shearwater (Puffinus gravis) is an abundant pelagic seabird that undertakes transequatorial migrations between the North and South Atlantic Ocean. This species is a useful indicator of large-scale alterations in marine dynamics due to its wide geographic range, long-distance migrations, and relative abundance. From 1993 to 2011, 12 separate mortality events, with 4,961 Great Shearwaters recovered, were documented along the eastern coast of the United States. Of these, seven events (n=4,885) occurred in the Southeast (SE) and five (n=76) in the Northeast (NE) United States. The cause of death was determined either by necropsy (n=60) or external examination (n=4,901). All Great Shearwaters stranded along the SE United States were emaciated while 58% were emaciated in the NE United States. No plastic was observed in Great Shearwaters in the SE US (n=27), but the gastrointestinal tract of 82% (n=27) of all stranded birds along the NE United States had at least one plastic bead. There was no evidence of infectious disease or heavy metals in stranded Great Shearwaters examined (n=14, from the 2005 SE event). Stable isotope analysis of feathers (n=9, from a 2007 SE event) suggests dietary differences between emaciated stranded birds and live-caught healthy birds. The temporal distribution of stranding detections suggests a general increase in the number of observed Great Shearwater strandings over the past two decades. From 1993 to 2000 there were a total of three mortality events with 296 individual Great Shearwaters. However, there was a threefold increase in the number of mortality events from 2001 to 2011 (nine events involving 4,665 individuals). The causes of this apparent increase in strandings are unknown but may be due to an increase in reporting effort over the past two decades combined with changing oceanographic conditions in the South Atlantic Ocean, leading to large-scale mortality of emaciated Great Shearwaters along the east coast of the United States.

A long-term retrospective study on rehabilitation of seabirds in Gran Canaria Island, Spain (2003-2013)

“…Emaciation was associated with several Great Shearwater ( Ardenna gravis ) mortality events along the Eastern coast of the United States [15] and stranded seabirds along the German North Sea coast [13]. Within the group of seabirds admitted due to other causes, the prevalence of infectious/parasitic disease was very low in our study (0.15%).…”

“…Few studies on causes of morbidity or mortality of seabirds covered more than one decade [13,15,26–28]. While most studies only cover a short period of time, the present retrospective study included data for a long period (11 years), providing a longer term view of causes of admission as they shift over time.…”

“…References on the final dispositions of seabird rehabilitation are scarce because most surveys usually have been focused on the causes of mortality [13,15,24,26,27]. In addition, a comparative analysis between studies of the final dispositions of seabirds in wildlife centers is difficult due to the heterogeneity of the surveys [14,17,18].…”

Stable Isotope Analyses of Multiple Tissues of Great Shearwaters (Ardenna Gravis) Reveals Long-Term Dietary Stability, Short-Term Changes in Diet, and Can be Used as a Tool to Monitor Food Webs

“…This is a large expanse of water and therefore we chose the great shearwater (Ardenna gravis) as our indicator species for several reasons: Great shearwaters captured off Cape Cod and in Massachusetts Bay travel widely, averaging 515 km per week, but appear to spend most of their time in the Gulf of Maine before beginning their migration south in August and September [32,33]. They feed on a wide range of prey species and as top marine predators, great shearwaters are sensitive to changes in their prey populations, such as sand lance, herring, and mackerel [34][35][36], as well as abiotic factors such as currents, surface temperature, and salinity [28,36,37]. Great shearwater populations have experienced mass mortality events of emaciated birds, the causes of which are currently unknown, suggesting their sensitivity as bioindicators of important ecological events that bear further investigation [37,38].…”

“…They feed on a wide range of prey species and as top marine predators, great shearwaters are sensitive to changes in their prey populations, such as sand lance, herring, and mackerel [34][35][36], as well as abiotic factors such as currents, surface temperature, and salinity [28,36,37]. Great shearwater populations have experienced mass mortality events of emaciated birds, the causes of which are currently unknown, suggesting their sensitivity as bioindicators of important ecological events that bear further investigation [37,38]. However, there are inevitably tradeoffs when selecting an indicator species.…”