Population trends for humpback whales (Megaptera novaeangliae) foraging in the Francisco Coloane Coastal-Marine Protected Area, Magellan Strait, Chile Marine Mammal Science, 2019, 20pp.
Cole Monnahan, Jorge Acevedo, Noble Hendrix, Scott Gende, Anelio Aguayo-Lobo, Francisco Martinez
In 2003 a feeding aggregation of southeastern Pacific humpback whales
(Megaptera novaeangliae) was reported in the Magellan Strait. While Chile
established its first marine national park in the Strait to protect humpback
whale habitat, fatal ship strikes remain a concern because of overlap with
a busy shipping lane. To better understand population risk, we estimated
abundance and survival for this population using Bayesian robust-design
mark-recapture models fit to photographic data from 2004 to 2016. Overall,
the model estimated a total of 204 whales (95% CI: 199Ã¢â‚¬â€œ210) during
the last 12 yr, and 93 (95% CI: 86Ã¢â‚¬â€œ100) in the 2016/2017 austral summer.
The population grew at 2.3% (CI: 2.1%Ã¢â‚¬â€œ3.1%), an annual increase of two
whales. Annual survival (including calves) was estimated at 0.892 (CI:
0.871Ã¢â‚¬â€œ0.910). Our results corroborate a persistent feeding population, but
one that is increasing relatively slowly. Owing to its vulnerability stemming
from its small size, coupled with significant overlap with a busy shipping
lane, we argue this subpopulation is at significant risk from ship strikes
and may be one of the few populations where anthropogenic mortalities
could regulate population dynamics. We therefore encourage continued
monitoring via photographic mark-resighting surveys, and analyses explicitly
investigating potential population-level ship strike effects.