The Marine Mammal Commission has regularly requested that the NMFS prohibit the lobster fishery near French Frigate Shoals and other major monk seal colonies as a precautionary measure until sufficient studies can be carried out on the commercial lobster fishery's impact on monk seals, not only through the lobster catch but also through the fishery's bycatch of octopuses, crabs and small reef fish which are all components of the monk seal diet. It is thought that one of the reasons for the general decline in monk seal numbers before the 1980s may have been disturbance caused by military and coastguard activities resulting in the abandonment of good quality pupping areas and of pups by their mothers. Hawaiian monk seals are generally very sensitive to disturbance and steps have now been taken to eliminate this problem. The entanglement of Hawaiian monk seals in marine debris may also be a major cause of death, particularly of young seals which are far more prone to entanglement. A survey which took place at French Frigate Shoals during the winter of 1996-1997 estimated that the area contained more than 29,000 net fragments in waters less than 10m deep, mostly trawl webbing transported to the area from outside the Hawaiian islands by ocean currents.
Scientists frequently remove dangerous marine debris from beaches and disentangle seals.
Since 1982 at least 66 seals have died or disappeared after being mobbed. Two adult males that had been particularly aggressive towards pups at French Frigate Shoals were captured and relocated in 1998. In recent years an increase in the occurrence of shark predation on monk seals has also been observed, mostly by Galapagos sharks. The lack of genetic diversity caused by the decline in population numbers may also compromise the future survival of the species, as may threats such as pollution. Biotoxin poisoning was implicated in a mass mortality of monk seals at Laysan Island in 1978.