How few whales were there after whaling?

Transcription

1 How few whales were there after whaling? Jennifer Jackson, Nathalie Patenaude, Emma Carroll and C. Scott Baker University of Auckland, New Zealand and Marine Mammal Institute, Oregon State University

2 so wide a chase, and so remorseless a havoc 19th century whaling first depleted right, gray, bowhead and sperm whales 1904 to 1982, more then 2,000,000 blue fin, humpback and sei whales killed in the Southern Hemisphere 1994 Soviet illegal whaling revealed 1982, International Whaling Commission agrees to moratorium, to take effect in 1986, and to undertake a Comprehensive Assessment of each whale stock to develop a Revised Management Procedure for future hunting 1987, Japan, Norway and Iceland initiate scientific whaling (courtesy of International Fund for Animal Welfare)

3 Reconstructing the recent historical abundance of whales Within IWC, Primary emphasis Current abundance Pre-exploitation abundance (assumed to be at K) Recovery to MSYL or about 54% of K Less emphasis The minimum size of the population - N min or the bottleneck The relationship of N min to variation in recovery of stocks Full ecological restoration

4 Population dynamic modeling and the IWC comprehensive assessment Hitting with fixed MSY Solves for K, assuming intrinsic rate of increase (r max ) and MSYL, using estimates of current abundance a catch history Typically calculated for small number of fixed parameter estimates, e.g., for southern rights high r max (7.5%) low struck and lost ratio (1.3x) Find N min from reconstructed trajectory e.g., southern rights as few as 60 mature females surviving in the year 1920 (the bottleneck ) all stocks combined Southern right whales (IWC2001 as adapted by Baker and Clapham 2004)

5 mtdna diversity, haplotype richness and N min(f) Genetic diversity is lost at a rate that is inversely proportional to the size of the population Loss of haplotype diversity (h) for maternally inherited mtdna is 4x more rapid than for nuclear DNA The number of surviving mtdna lineages (haplotype richness) must represent the absolute lower limit of recent historical population size for females, N min(f) mtdna also reflects maternal traditions, including fidelity to migratory destinations.

6 Comparing demographic and genetic approaches For K and N min P t+1 =P t +rp t (1-(P t /K) u )-C t P t = total population size in year t r = maximum growth rate K= pre-exploitation population size u = 2.39 (sets the MSYL = 0.6K) C t = known catches in year t For mtdna diversity haplotype richness h t+1 = h t (1-1/N ef ) h t haplotype diversity at time t t time given in generations N ef effective female population size at time t Southern right whale (IWC2001 as adapted by Baker and Clapham 2004)

7 Southern Right Whales, then ,000 on breeding grounds (IWC 2001) PACIFIC OCEAN CHILE/ PERU ATLANTIC OCEAN NAM MO INDIAN OCEAN PACIFIC OCEAN BREEDING GROUNDS ARG SBR TDC SAF CROZET ISLAND SWA SEA NZ (2) PRE-WHALING ANTARCTIC

8 Southern Right Whales, now 6,000-8,000 in 4 recovering populations PACIFIC OCEAN ATLANTIC OCEAN INDIAN OCEAN PACIFIC OCEAN ARG SAF SWA BREEDING GROUNDS NZ CURRENT

9 A revised assessment Bayesian framework allows for uncertainty in key parameters used in previous IWC assessment of southern right whales (IWC 2001) rates of increase; current abundance; catch records (struck and lost) Abundance 120, ,000 80,000 60,000 40,000 20,000 Struck and lost 2.4x r = 7.5% r = 4% r = 7.5% r = 10% Struck and lost 1.3x 5,000 4,000 3,000 2,000 1, N r = 4% r = 7.5% r = 10% Year

10 Estimating true Nmin A lower bound for the number of females at the time of a recent population bottleneck is the number of mtdna haplotypes, as defined by variation in a length of sequence, and counted in a contemporary sample. An improved estimate of true Nmin must correct for: Population sampling a Discovery Curve using rarefaction Sequence sampling an empirical approach Historical stochastic sampling pre-exploitation haplotype richness and frequencies number of females likely for surviving haplotypes Census size (for comparison to assessment) males:females (2x) mature:immature (2x)

11 Contemporary mtdna diversity of southern right whales Region n samples n haplotypes haplotype diversity h (SE) nucleotide diversity %(SE) Argentina South Africa Western Australia New Zealand (0.032) 2.82 (1.53) (0.029) 2.43 (1.30) (0.072) 2.35 (1.29) (0.042) 1.37 (0.78) Total θ = ( ) Using 275 bp of the control region Patenuade et al. (in press) J Heredity

12 Haplotype count ) Population sampling - the Discovery curve 54 haplotypes Clench equation Number of haplotypes = Sub-sample size ( x sample size) (1 + ( x sample size)

13 2) Sequence sampling - an empirical adjustment for New Zealand Position of Variable Site Haplotype BakHapA b C T T C G T T G T C T T T A G A C BakHapB+. C C T... A BakHapC. C... C C.. T C C. G A G T BakHapD T C.. A C C.. T C C.. A G. BakHapE T.... C C A. T C C. G A G. CarHapJ T. C.... A C.. C..... PorHap4.1.. C PorHap17. C..... A. T C C C G A G T 275 bp, 8 haplotypes Carroll et al., (in preparation)

14 2) Sequence sampling - an empirical adjustment for New Zealand Position of Variable Site Haplotype BakHapA b C T T C G T T G T C T T T A G A C C G C C A C T C G C BakHapB+. C C T... A T BakHapB'. C C T... A BakHapC. C... C C.. T C C. G A G T BakHapD T C.. A C C.. T C C.. A G. T C T. G T. T A BakHapE T.... C C A. T C C. G A G CarHapJ T. C.... A C.. C PorHap4.1.. C T.. C PorHap4.2.. C PorHap17. C..... A. T C C C G A G T A bp, 10 haplotypes suggesting a minimum upward adjustment of 25% Carroll et al., (in preparation)

15 3) Historical stochastic sampling - pre-exploitation haplotype richness 38 haplotypes θ = post-exploitation Frequency Insert distributions 150 neutral haplotypes θ = pre-exploitation Pre-exploitation frequencies based on current θ and assumption of neutrality. Haplotypes

16 Frequency Frequency ) Historical stochastic sampling - females likely for surviving haplotypes 46 females 79 females 114 females 56 females 115 females 150 pre-exploitation haplotypes 259 females 100 pre-exploitation haplotypes females Surviving haplotypes Likelihood from 10,000 resamples

17 A corrected Nmin 1. Current population sampling haplotypes 2. Sequence sampling haplotypes 3. Historical stochastic sampling 68 haplotypes 114 females (150 pre-ex haplotypes) 68 haplotypes 259 females (100 pre-ex haplotypes) 4. Demographic correction (4x) for Nmin(census) 114 females 456 census bottleneck 259 females 1,036 census bottleneck

18 Corrected Nmin and the IWC assessment Median trajectories (and 95% probability intervals) for the base case and high rmax are incompatible with Nmin Only the median trajectory for rmax = 4% is plausible Abundance N 1920 r = 4% r = 7.5% r = 10% Estimated Nmin(census) 1,036 (100 pre-exploitation) 456 (150 pre-exploitation) Year

19 HITTING current haplotype richness Driving the program BOTTLESIM with HITTER trajectories confirms that current haplotype richness is only plausible for low rmax 160 pre-ex haplotypes = 150 Number of haplotypes pre-ex haplotypes = x struck and lost 2.4x struck and lost r = 4% r = 7.5% r = 10% Year 68 haplotypes 54 haplotypes

20 Implications for conservation: variability in recovery (space and time) Incorporating genetic parameters into population dynamic models provides informative constraints (greater biological reality) Exploitation was intensive and bottleneck was severe, but demographically plausible scenarios favored by IWC are not consistent with surviving haplotype richness rmax is overestimated or non-linear potential ascertainment bias among stocks potential for Allee effect (depensation) at low abundance Variable rates of regional recovery require multi-stock (metapopulation) models potential for loss of maternal traditions and local extinction

21 Implications for management: time to recovery High rmax (10%) Base case rmax (7.5%) High struck and lost Low rmax (4%) 54% year to 95% (courtesy of International Fund for Animal Welfare) Time to hunt? Assuming rmax of 10%, the nominal level of recovery required for commercial whaling (54%) could be reached by the year 2013

22 With thanks to NZ Marsden Fund NZ Department of Conservation WWF New Zealand Whale and Dolphin Conservation Society Conservation Action Fund N Gales, S Childerhouse, A Rodrigo Marine Mammal Institute Oregon State University Jen Jackson Auckland Island Right Whale Project, Nick Gales, Nathalie Patenaude, Simon Childerhouse and Scott Baker 52 0 South, winter 1996