Historically, populations were greatly reduced by feather and egg collecting in the late 1800s and early 1900s, and by high seas drift nets for squid and salmon that were active between 1978 and 1992. Prior to its closure, the high seas driftnet fishery killed over 17,500 P. immutabilis in 1990 alone (Johnson et al. 1993). Current key threats are being caught as bycatch in pelagic (Crowder and Myers 2002) and demersal longline fisheries (Stehn et al. 2001) in the North Pacific as well as in illegal high seas driftnet operations. Analyses in 2001 estimated that pelagic longliners in the North Pacific may kill 5,000-18,000 Laysan Albatross per year, with 8,000 thought the most likely figure, while demersal longline operations in the Bering Sea and Gulf of Alaska groundfish fisheries were estimated to kill c.715 birds per year (Crowder and Myers 2002). However, more recent estimates indicate a drastic reduction in bycatch from previous years (83 birds estimated taken in 2005) that is very likely attributable to the use of effective seabird avoidance measures (K. Rivera in litt. 2007). The bycatch rates in Japanese and Taiwanese pelagic longline fisheries in the North Pacific are still largely unknown. Other threats include organochlorine contamination, invasive species, plastic ingestion, lead poisoning, human disturbance and conflicts with aircraft (Harrison 1990, Ludwig et al. 1998, Finkelstein et al. 2003, Finkelstein 2006). Chicks with large volumes of proventricular plastic have been reported to have fledging weights significantly lower than chicks with low amounts of plastic, and there is some evidence to suggest it may have affected survival in 1986, when the volume of plastic ingestion was at its highest (Sievert and Sileo 2008). Oil pollution is no longer considered a likely threat (I. C. T. Nisbet in litt. 2010). Up to 10,000 chicks per year are potentially affected by lead poisoning from paint on buildings at Midway Atoll (Finkelstein 2006), and (7% of chicks on Sand Island fail to fledge from lead poisoning each year, with a predicted impact of 16% reduction in population size over the course of 50 years equating to 190,000 less birds, Finkelstein et al. 2010).. Avian pox virus affects chicks on Midway and the Main Hawaiian Islands where introduced mosquitoes are present, but studies on O'ahu colonies show that fledging success was not reduced (Young and VanderWerf 2008). Dogs kill adults and chicks on inhabited islands in Hawaii. Verbesina encelioides is an aggressive weed that degrades nesting habitat in the Northwestern Hawaiian Islands and introduced predators (notably the Polynesian Rat Rattus exulans [Jones et al. 2008]) are an issue for colonies in Mexico and on the Main Hawaiian Islands. In 2002, observations on Clarion Island, Mexico reported zero breeding success from the 46 nesting pairs, largely as a result of predation by several endemic species (eg. Clarion raven Corvus corax clarionensis and Clarion racer Masticophis anthonyi, Wanless et al. 2009). Observations from Guadalupe Island, Mexico, in December 2002 recorded 35 out of 490 adults killed by cats (7% of the total island breeding population that year, and 30% of the Punta Sur colony) (Keitt et al. 2006). Cats were also responsible for a tripling in nest failure rate at this colony (49%) compared with the nearby cat free Negro Islet colony (13%) (Keitt et al. 2006). Cat control around the colony from Jan-Mar 2003 removed 18 cats and curtailed adult mortality from cat predation, although cats continued to be seen around the colony after the breeding season ended (Keitt et al. 2006). It is likely that the population here had not experienced high levels of predation prior to 2002, as it would have been extirpated.
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