Consequences of alternative functional response formulations in models exploring whale-fishery interactions

• Published in: Marine Mammal Science
• Main Authors: Mackinson, S, Blanchard, JL, Pinnegar, JK, Scott, R
• Format: Article in Journal/Newspaper
• Language: English
• Published: Soc Marine Mammalogy 2003
• Subjects: Biological Sciences; Ecology; Community Ecology; minke whale
• Online Access: https://doi.org/10.1111/j.1748-7692.2003.tb01123.x; http://ecite.utas.edu.au/100515

We evaluated the utility of Ecosim for exploring interactions between cetaceanpredators, their prey, and fisheries. We formulated six Ecosim parameterizations,representing alternative hypotheses of feeding interactions (functional response)between cetaceans and their main fish prey, and examined differences in thepredicted responses to simulated harvesting regimes for minke whales and theirprey. Regardless of the type of function response formulated, intense fishing on themain fish prey of minke whales had a longer-lasting negative impact on minkewhales than when minke whale biomass was removed directly by harvesting.Consumption rate, biomass, feeding time and mortality of minke whales were allsensitive to the type of functional response specified. Inclusion of handling timelimited minke whales consumption at high prey densities and predicted higherconsumption at low prey densities; features characteristic of a type II functionalresponse. Predicted decline and recovery rates of minke whales were slower thanwhen consumption rates were not limited. Addition of foraging time adjustmentsresulted in more conservative estimates of decline and recovery. However,when other mortality was linked to time spent foraging, exposure to highermortality at low prey densities, and reduced mortality at high prey densities resultedin dramatic differences in predicted biomass trajectory. Sensitivity to the othermortality assumption is important for cetaceans whose predation mortality is onlya small proportion of total mortality. Differences in the feeding and biomassdynamics were also observed when prey availability to predators was representedby changes in prey vulnerability, confirming earlier reports that Ecosim predictionsare sensitive to this parameter.