Data from: Spatial distribution of fishes in a Northwest Atlantic ecosystem in relation to risk of predation by a marine mammal

1. Numerous studies have shown that, at spatial scales of metres to
several kilometres, animals balance the trade-off between foraging success
and predation mortality by increasing their use of safer but less
profitable habitats as predation risk increases. However, it is less clear
whether prey respond similarly at the larger spatiotemporal scales of many
ecosystems. 2. We determine whether this behaviour is evident in a large
marine ecosystem, the southern Gulf of St. Lawrence (sGSL, 75 000 km2)
over a 42-year period. This ecosystem is characterized by a recent
increase in the abundance of a large marine predator, the grey seal
(Halichoerus grypus Fabricius), by more than an order of magnitude. 3. We
compared changes in spatial distribution over the 1971–2012 period between
important prey of grey seals (Atlantic cod, Gadus morhua L.; white hake,
Urophycis tenuis Mitchill; and thorny skate, Amblyraja radiata Donovan)
and non-prey fishes. Distribution was modelled using generalized additive
models incorporating spatially variable effects of predation risk, density
dependence and water temperature. 4. Distributions of cod, hake and skate
were strongly related to risk of predation by seals, with distribution
shifting into lower risk areas as predation risk increased. Non-prey
species did not show similar changes in habitat use. Spatial variation in
fish condition suggests that these low-risk areas are also less profitable
for cod and skate in terms of food availability. The effects of density
dependence and water temperature were also important in models, but did
not account for the changes in habitat use as the risk of predation
increased. 5. These results indicate that these fish are able to assess
and respond to spatial variation in predation risk at very large spatial
scales. They also suggest that non-consumptive ‘risk’ effects may be an
important component of the declines in productivity of seal prey in this
ecosystem, and of the indirect effects at lower trophic levels.