Habitat selection of Southern Right Whales (Eubalaena australis) in the breeding ground Península Valdés

Abstract

The Southern Right Whale (Eubalaena australis) was object of a commercial exploitation until the mid of the XX century, that brought this species to the brink of extinction. The species was protected globally in 1986 and since this moratorium entered into force, populations throughout the southern hemisphere have been recovering at an 8% annual rate. Even so, in Peninsula Valdés (Argentina) it has been observed that the growth rate is decreasing in recent years from near 7% in 2007 to a 0.06% for 2016. In this breeding ground also changes in distribution and group composition have been reported, with mother and calves remainingclose to the shore and solitary individuals relocating to deeper waters or to other coastal areas outsidePenínsula Valdés. We use SDMs to predict the SRW distribution in the Peninsula Valdés incorporatingenvironmental data and records collected by the CENPAT Marine Mammal Laboratory in four differentperiods: 1999-2000, 2004-2007, 2008-2012 and 2013-2016. Predictions maps were then used to assess ifthere was a shift of the SRW distribution in the Peninsula Valdés trough the time and if it was related topopulation growth. Roughness of the seabed, bathymetry and wave energy were used as potential predictorsfor selection of Southern Right Whales. Bayesian hierarchical spatial model (BHSM) were applied toidentify which environmental variables mostly affect their distribution in northern Patagonia and to predicttheir probability of occurrence in un-sampled locations.Among all the variables combination tested, the selected model included the roughness, wave energy andspatial effect, with bathymetry being highly correlated to roughness and hence was excluded from themodels. The selected model was then used to perform the analysis in each period. Overall, roughness showeda positive relationship with the SWR occurrence, preferring consolidated seabed. The wave energy showed anegative relationship with the SWR occurrence, indicating that whales prefer low wave energy areas.Looking at the magnitude of the estimated effects, it is suggested that wave energy is more relevant for theSWR occurrence than the roughness of the seabed.Along the examined periods, there is a tendency of SRW to restrict their distribution mainly to coastal areaswith consolidated seabed and low wave energy. This is explained by the fact that mothers with calvesreplaced other types of groups in the near shore strip. The results are congruent with a density-dependentprocess, in which the coastal breeding areas of Peninsula Valdes could be reaching their carrying capacity, soit is expected that in the coming years an increase in the number of mothers with young will be observed inother areas, such as the Bay of San Antonio in the Gulf San Matias.