BIO358 1st Edition Lecture 26 Outline of Last Lecture I Deep Diving Mammals and Sonar Outline of Current Lecture I What does the sea otter population look like what did it used to look like II Demographic alternative explanations for population declines III Killer whale hypothesis evidence to back it up Current Lecture 1998 Science Jim Estes unusual and novel relationship b t killer whales and sea otters 2003 national academy of sciences relationship result of industrial whaling Aleutian Islands part of Alaska abundance of marmam biodiversity fur seals phocids walruses cetaceans whales Site of high exploitation Late 1700 s mid 1800 s Russian hunting US Purchased Alaska and hunting pressure increased Early 1900 s northern fur seals and sea otters on brink of extinction 1911 earliest international wildlife conservation treaty fur seal treaty protected otters too Early 1770 s 1 some areas recovered to near maximum 2 some areas growing rapidly but not fully recovered 3 some areas sea otters are still absent Jim Estes 30 years spent studying sea otter ecology Areas with recovered sea otter populations there was dense rich productive kelp forest These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Ecology sea otters eat urchins urchins eat kelp 3 trophic level system In regions of the Aleutians with sea otters sea urchins kept in check that result in healthy lush kelp forests with high species diversity When sea otters are removed from the system urchins eat kelp to the sea floor low species diversity SEA OTTERS ARE APEX PREDATORS species whose effects cascade across successively lower trophic levels 1991 1 sea otter abundance was declining 2 first observed killer whale attack on a sea otter never seen in 3000 survey days Continued to see populations declining Hypothesis decline in Enhydra lutris eaten by killer whales decline in population of otters Demographic explanations 1 reduced fertility No change in pup rates survivability to weaning between stable regions and declining populations Nope 2 Redistribution No evidence from surveys or tagged animals immigration emigration NOPE 3 increased mortality likely but no evidence of disease pollutions toxins starvation and NO carcasses KILLER WHALE HYPOTHESIS LOOKING GOOD How to test this 1 Statistical approach if killer whale attacks were constant what s the probability that you wouldn t see it before 1991 0 006 percent chance of missing it you would have seen it suggests killer whales eating sea otters is a recent event 2 Metabolic approach how many killer whales would be required to account for the missing sea otters energetic cost and value 1 how much energy does a killer whale need Williams estimated field metabolic rate for killer whales 2 how much energy does a sea otter provide Used stranded sea otters to measure the caloric value of dead sea otters Female whale 3 5 otters per day Male whale 5 7 otters per day of killer whales eating 3 7 otters day over 6 years 40 000 missing otters how many killer whales are eating otters 3 7 whales If 4 killer whales ate nothing but otters for 6 years they would eat 40 000 sea otters Plausible hypothesis Unbelievably low number Natural experiment Kuluk bay vs Clam lagoon drop in Kuluk no drop in Clam Lagoon whale inaccessible evidence for killer whale hypothesis but WHY What happened in the 1990s sea otters ARE NOT the preferred diet of killer whales preferred cetaceans large whales pinnipeds larger and blubber fatter 1 pinniped populations also steeply declining eg Steller s sea lions 75 reduction in s N fur seal and phocids also decreased in s 2 killer whales switch prey base from pinnipeds to sea otters because pinnipeds were disappearing What is causing the decline in pinnipeds in the N Pacific Controversial hypothesis of Estes et al 1998 due to abundance and diversity of prey fish due to overfishing Alaska is the largest ground fish fishery in the US Pollock increased from 30 70 of the commercial harvest 1 7 billion pounds in the 1990 s WE ARE OUTCOMPETING THEM FOR THEIR FOOD Sequential mega faunal collapse in the N Pacifici Ocean Killer whales used to eat whales whales gone whaling killer whales ate pinnipeds pinnipeds dying out whales eat otters Evidence 1 Many large whales removed from N Pacific Pattern to loss of species great whales decrease harbor seals decrease fur seals decrease Stellar s sea lion decline sea otters decline cascading effect of killer whale predation it changed its prey base Hypothesis killer whale predation driving sequential decline VERY PLAUSIBLE What we did out in the open ocean changed a COASTAL ecosystem changing it from a 3 level trophic system to a 4 level system these estimations would have NEVER BEEN MADE WITHOUT LONG TERM STUDIES THEY ARE IMPORTANT