BIO358 1st Edition Lecture 26Outline 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 declinesIII. Killer whale hypothesis – evidence to back it upCurrent 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 whalingAleutian 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 wouldhave 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 WITHOUTLONG-TERM STUDIES – THEY ARE