Research At French Frigate Shoals

 My plan was initially to post nice photos from French Frigate Shoals, and I will be doing more of that. However, I think it is important to give some background on the research that we are working on while here. The Hawaiian monk seal is federally listed as a critically endangered species; the population is roughly one thousand individuals. The Northwest Hawaiian Islands (NWHI) is habitat for the majority of the population, with French Frigate Shoals being the site of the largest breeding population.

Figure 1: Map of Hawaiian Archipelago. The area marked as the NWHI are part of the Papahanaumokuakea Marine National Monument (Baker et al. 2010). Please forgive my lack of diacritical usage, I haven't figured out how to do it on the blog writer.

The population at French Frigate Shoals, and in the NWHI as a whole is in steep decline. Although the main Hawaiian Island (MHI) population is currently increasing the overall population has declined by 4%/yr since 2008 when the population was estimated at 1,161 (Baker et al. 2010). In the NWHI the decline is driven by low pup and sub-adult survivability. The cause of high mortality amongst pups and sub-adults is multifaceted, although starvation is a large contributor.  Starvation seems counter intuitive on the surface because of the abundance of food in the NWHI, but competition with young seals by top predators such as Ulua, and sharks is thought to drive this mechanism.  Other factors include entrapment in marine debris, and shark predation. 
 

 

 Figure 2: Survivability curves for 6 NWHI populations represented by solid lines, and MHI population represented by the dotted line (Baker et al. 2010).

Figure 2 demonstrates that the vast majority of seals born in the NWHI do not survive to four years of age. This problem compounds survivability problems because the monk seals in the NWHI do not reach reproductive age until after the age of four.

 

 Figure 3: Female monk seal size by age.  FFS-French Frigate Shoals, LAY-Laysan Island, LIS-Lisianski Island, PMK-Pearl and Hermes Midway and Kure combined, MHI-Main Hawaiian Islands (Baker et al. 2010).

In the NWHI low sub-adult survivability (fig. 2) and a slow growth rate to sexual maturity (fig. 3) place the Hawaiian monk seal on the razors edge of extinction, and give little reassurance for the future of the species.  A tentative glimmer of hope for the population lies in increases in the NWHI at Laysan Island, and a general trend towards growth in the MHI. However, this view must be tempered with the reality that the population is extremely  similar genetically meaning that other factors, specifically disease, could quickly destroy all progress on these fronts.

 A yearling monk seal has lost the fat layer from mothers milk and must learn to forage well or starve.

 A monk seal pup with a fatal shark bite likely from a Galapagos shark. She died two days ago.

Baker J.D., Harting A.L., Wurth T.A., Johanos T.C. 2010. Dramatic shifts in Hawaiian monk seal distribution
predicted from divergent regional trends. Marine Mammal Science. DOI:10.1111/j.1748-7692.2010.00395.x

All photos by Darren Roberts. 

As a sidenote, I pulled strongly from one paper and personal knowledge due to lack of resources out here, as well as the fact that Baker et al. 2010 is up to date concerning a dynamic population.