Data from: Robust estimates of a high Ne/N ratio in a top marine predator, southern bluefin tuna

Genetic studies of several marine species with high fecundity have
produced “tiny” estimates (≤10−3) of the ratio of effective population
size (Ne) to adult census size (N), suggesting that even very large
populations might be at genetic risk. A recent study using close-kin
mark-recapture methods estimated adult abundance at N ≈ 2 × 106 for
southern bluefin tuna (SBT), a highly fecund top predator that supports a
lucrative (~$1 billion/year) fishery. We used the same genetic and life
history data (almost 13,000 fish collected over 5 years) to generate
genetic and demographic estimates of Ne per generation and Nb (effective
number of breeders) per year and the Ne/N ratio. Demographic estimates,
which accounted for age-specific vital rates, skip breeding, variation in
fecundity at age, and persistent individual differences in reproductive
success, suggest that Ne/N is >0.1 and perhaps about 0.5. The
genetic estimates supported this conclusion. Simulations using true Ne = 5
× 105 (Ne/N = 0.25) produced results statistically consistent with the
empirical genetic estimates, whereas simulations using Ne = 2 × 104 (Ne/N
= 0.01) did not. Our results show that robust estimates of Ne and Ne/N can
be obtained for large populations, provided sufficiently large numbers of
individuals and genetic markers are used and temporal replication (here, 5
years of adult and juvenile samples) is sufficient to provide a
distribution of estimates. The high estimated Ne/N ratio in SBT is
encouraging and suggests that the species will not be compromised by a
lack of genetic diversity in responding to environmental change and
harvest.