SIO 133 Marine Mammal Popula4on Dynamics John Hildebrand, Scripps Inst. Oceanography, UCSD
Popula4on Dynamics Study fundamental life history characteris4cs such as birth and death rates Age Distribu4on Marine Mammals are K- selected - Large bodies - Long Lifespan - Low mortality for Adults r- selected = black r = reproduc4on K- selected = colored K = carrying capacity r- Selected is result random removal e.g. by preda4on
Sperm Whale Stranding Data Evan and Hindell, J. Zoo. Lond. (2004) 263, 237-250 Three Groups of Stranded Sperm Whales Feb 1998 86 individuals mostly Female North and west coasts of Tasmania Age determined from the number of den4nal growth layers Ages of females from 0.75 to 64 years, Majority (77%) aged between 20 and 45 years.
Sperm Whale Stranding and Whaling Data Evan and Hindell, J. Zoo. Lond. (2004) 263, 237-250 Stranding Survival Rate Whaling in Japanese Waters Stranding data bias Lack of Males Too Few Young Tooth wear underes4mate age Whaling data bias Selected for Large Bodies Few Old due to Fisheries Catch
Measuring Popula4on Growth Life history data: Age of sexual maturity, birth rate, juvenile and adult survival rate maximum age Few es4mates of marine mammal popula4on growth using life history data. Hindrance is lack of direct data on survival rates. Mark- recapture studies of survival or fecundity: Killer, humpback, gray, bowhead, and right whales California and Steller sea lions Boelenose and Hector s dolphins Polar bear Manatee
Measuring Popula4on Growth: Right Whales Photo iden4fica4on 1980 to 1997 372 individuals = 141 females, 143 males. Popula4on growth rate = 1% CI =[1.00, 1.02] ESTIMATING POPULATION PROJECTION MATRICES FROM MULTI- STAGE MARK RECAPTURE DATA FUJIWARA1 AND CASWELL Ecology, 83(12), 2002, pp. 3257 3265
Rates of Popula4on Increase Important Parameters: age at which females start reproducing, number of years between births how many years a female will live and reproduce, For Marine Mammals: many years to reach sexual maturity long gesta4on periods max one young a year many species once every several years (What is max growth rate assuming no twins?)
Taxonomic Differences Pop Growth Life history strategies: Sea Oeers Fast Growth: 17 20% per year Pinnipeds may Reproduce Annually 8-13% for otariids (e.g. Northern fur seals) 6-13% for phocids (e.g. Hawaiian monk seals) A puzzling species is the Steller sea lion, observed Increase only about 3% per year
Taxonomic Differences Pop Growth Life history strategies: Mys4cetes Slow Growth Rates: 4 to 10%, perhaps higher ( Best, 1993 ) Bowhead whales 3 4% capable 4 5% max Gray whales 5 7%. Southern right whales 7% per year Humpback whales 7 10% per year or higher Blue and fin whales, imprecise but 4 8%
Taxonomic Differences Pop Growth Life history strategies: Manatees max popula4on rate 7% Dugongs 5 6% per year Odontocetes Very Low Rates 2 3% killer whales most species maximum rate 4% Harbor porpoise, may have higher rates
Measuring Popula4on Abundance Popula4on abundance es4mates Surveys or counts Line- transect sampling Point- transect sampling Mark- recapture Acous4c cue coun4ng Trends Repeated over several years to get trend (%/year) 10 or more years required to measure growth rates. Es4mates so imprecise that it may be difficult to determine trends in abundance ( Taylor et al., 2007)
Mark- Recapture: Photo Iden4fica4on Method for estimating abundance and other parameters based on ratios of marked to unmarked individuals. Allows for assessments of population size, rates of survival, recruitment and growth rate. Characterize vital trends in marine mammal populations over time for application to management and conservation regimes. 1981 # 254 1984 # 254 1997 # 254
Survey 1 Survey 2: M = 12 C = 15 R = 4
Mark- Recapture Equa4on Peterson- Lincoln Es4mator: Closed Popula4on: 2 surveys Marked animals in 1 st sample (M) estimated Number of individuals in population (N) = Marked animals Recaptured in 2 nd sample (R) number Captured in 2 nd sample (C) 12 = 4 N = 45 N 15