Spatio-temporal patterns in fin whale Balaenoptera physalus habitat use in the northern Gulf of St. Lawrence

Abstract

Significant ecosystem changes in the Gulf of St. Lawrence (GSL) have had farreaching effects at all trophic levels. The abundance of fin whales (Balaenoptera physalus) has declined significantly in the northern GSL over the past decade. This study aimed to test the hypothesis that the observed decline was correlated to changing environmental conditions. Cetacean sighting data from 292 surveys, resulting in 2986 fin whale encounters from 2007 to 2013, were used to fit two separate generalised additive models in terms of (1) bathymetric and oceanographic variables (the proxy model) and (2) modelled krill biomass (the prey model). The concept of "handling time" was introduced to correct for time off search effort, applicable to other studies relying on opportunistically sampled data. While a positive correlation between krill biomass and fin whale numbers was found, the performance of the proxy model (24.2 % deviance explained) was overall better than the prey model (11.8 %). Annual predictive maps derived from the final proxy model highlighted two key areas with recurrently high relative fin whale abundance and a significant overlap with shipping lanes. While both models provided evidence for an annual decline in relative fin whale abundance, static bathymetric features were the most important predictors of habitat use and no correlation between dynamic variables and the decline was found. High resolution prey data and a better understanding of the feeding ecology of fin whales are proposed to further investigate the predator-prey relationship and decline of fin whales in the GSL.

Predicting suitable coastal habitat for sei whales, southern right whales and dolphins around the Falkland Islands

“…Therefore, sightings will be recorded both in key foraging habitats and in less optimal areas through which the animals are simply transiting, potentially affecting the predictive power of the model. Nevertheless, the final GAM models for sei whales and SEI–BAL explained 35–39% of the total deviance, which is similar to other studies modelling balaenopterids on their feeding grounds, for example fin whales in the Gulf of St. Lawrence (23.7%: [ 13 ]), Antarctic minke whales in the Southern Ocean (25.3%: [ 39 ]), and sei whales in the North Pacific (44.9%: [ 40 ]).…”

“…There may be other important explanatory variables influencing the distribution of cetaceans in this study that were not incorporated as PVs, in particular direct measures of prey distribution and abundance. Several studies have demonstrated that due to the mobility and spatial variability of cetacean prey species, it may be preferable to use environmental variables as proxies of their occurrence [ 13 , 38 ]. However, that relies upon having robust information regarding the PVs that may be governing those prey, and of the extent to which cetacean species specialise on particular prey species rather than switching between available prey [ 9 ].…”

“…However, inclusion of prey biomass data does not always result in better predictive performance for more generalist baleen whale species [e.g. 13 ].…”

“…sea surface temperature, chlorophyll, fronts) variables [7,8,[10][11][12]. Since cetacean distributions may primarily be driven by those of their prey, it is likely that such factors serve as proxies for spatio-temporal variation in prey density [13]; information on the latter is only rarely directly obtainable [14]. Geographical and environmental space can be treated as continuous or discrete among the different SDM methods [15].…”

Declining reproductive success in the Gulf of St. Lawrence’s humpback whales (Megaptera novaeangliae) reflects ecosystem shifts on their feeding grounds

“…The three North Atlantic Fisheries Organisation management divisions where biological environmental data were collected and collated by DFO and used here are indicated (4R, 4S, 4T). Figure adapted with permission from Schleimer et al, 2019 [Colour figure can be viewed at wileyonlinelibrary.com]…”