Shark Predation on Hawaiian Monk Seals - Pacific Islands Fisheries ...

Figure 3.--Number of pups born at FFS between 1984 and 2008.
FFS was once the most populous site with more than 400 individuals residing there in the late
1980s; however, the estimated number in 2006 was only 189 seals (NMFS, unpubl. data). The
primary factors in the FFS subpopulation’s decline have been poor juvenile survival
exacerbated by lower reproductive rates. Survival of preweaned and recently weaned pups to
age 1 at FFS was historically higher than in recent years, declining from about 95% in the late
1980s to less than 75% in 7 of the last 8 years (Baker, 2008; Harting et al., in prep.). The
prolonged period of low juvenile survival at FFS has produced an anomalous age structure.
Many of the reproductive females at FFS are now at an advanced age and are entering the
phase of reduced fecundity, with few younger females to replenish the breeding population.
Consequently, the number of pups born at FFS has declined from approximately 120 in the late
1980s to only 34 in 2009 (NMFS, unpubl. data). Population projections using a dedicated
stochastic simulation model predict a steady decline at FFS over the next 25 to 50 years based
on an assumption that current demographic rates and conditions are representative of those that
will occur over the lifetime period of the simulation (Harting, 2002).
Beginning in 1997, a marked increase in shark predation on preweaned monk seal pups at FFS
occurred (Hawn, 2000; Hayes, 2002; NMFS, 2003; NMFS, 2004; NMFS, 2005) (Fig. 4). At
Trig and Whaleskate Islands, the number of predation mortalities from sharks (including both
confirmed and inferred losses, defined in Appendix C) peaked between 1997 and 1999.
Additional pups were permanently maimed by severe shark bites that likely reduced the seals’
ability to dive, forage and reproduce (Fig. 4).
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