Cryptic Mortality from Fisheries Interactions

Large numbers of marine mammals die from fisheries interactions every year.  We know of those mortalities that are documented by fisherman, trained fisheries observers, electronic monitoring, disentanglement teams or stranding programs, but most mortalities go unnoticed. Dolphins and pinnipeds can fall out of nets or off hooks before fishermen or observers have a chance to record them.  Whales can swim away entangled in fishing gear only to die later.  Dead marine mammals at sea can sink or be scavenged, and strandings can go undiscovered.  Management agencies are forced to make decisions based on known human-caused mortalities even though they are well aware that those numbers are likely outnumbered by cryptic mortalities.  Published estimates of detected mortality as a percent of total mortality have ranged from zero to 30-35%, which suggests that cryptic mortality may account for anywhere from roughly two-thirds to 100% of total mortality.  I will review published models and estimates of cryptic mortality, identify the data needs for such analyses, discuss research gaps, and suggest advances that can be made.