The DEPONS project Disturbance Effects on the Harbour Porpoise Population in the North Sea

Transcription

1 The DEPONS project Disturbance Effects on the Harbour Porpoise Population in the North Sea Jacob Nabe-Nielsen, Aarhus University ASCOBANS meeting Wilhelmshaven, 20 June 2017 Modelling cumulative effects of human pressures Harbour porpoise (Phocoena phocoena) populations are influenced multiple types of anthropogenic disturbances, bycatch etc. Objective of DEPONS: develop data-driven model for assessing population effects of wind-farm construction. 1

2 Structure of the DEPONS model The DEPONS model is agent-based: simulates movements, birth and death of individual animals. The population carrying capacity emerges from competition for a dynamic food resource. Noise causes animals to forage less efficiently. Data on movement, reactions to noise and food distribution were collected as part of the DEPONS project. Structure of the DEPONS model Mechanisms in DEPONS resemble those in PCAD, but model structure is different. Population Consequences of Acoustic Disturbance (PCAD) Not used in DEPONS population effects emerge from reduced foraging. National Research Council (USA) (2005) 2

3 % Collection of movement data Natural movements were recorded using satellite tags, FastLoc GPS tags and dead reckoning. Porpoises were entrapped in pound nets along the coasts of Denmark and caught actively by Rømø in the Wadden Sea. Observed fine-scale movements CRW!"#$!"$$!#$ $ #$ "$$ "#$ Turning angle &'$($)*+,-',!$(./# Spatial memory One daily position 9!"#$!"$$!#$ $ #$ "$$ "#$ % " Distance (m) per 30-min Skagen (tagging site) &'$($$")+,-',$(#.0! % $ #$$ "$$$ $ )$$ 0$$ 1$$ 8$$ "$$$ ")$$ " Denmark! %!" 3

4 Modelling fine-scale movements Satiation memory and spatial memory decay calibrated to obtain realistic fine-scale movements. Kernel home ranges Tagged animals Residence time (days) Simulated fine-scale movements Simulated (no land) Tagged animals Simulated Nabe-Nielsen et al. 2013, Oikos Modelling large-scale movements Dispersal: move towards the most profitable area ever visited. Random turns after each dispersal step. Calibrated to yield realistic home range sizes. Skagen (tagging site) Denmark 4

5 Modelling food distribution Food availability based on porpoise survey data. North Sea Porpoise distribution: Gilles et al., 2016, Ecosphere Modelling food distribution Food in patches. Food recovers after being depleted by a porpoise. 20 km DanTysk wind farm Denmark Germany Porpoise distribution: Gilles et al., 2016, Ecosphere 5

6 Modelling energetics and life history Porpoises use energy when moving; decreased survival. Porpoises obtain energy from patches they encounter. Life history traits (birth, lactation etc.) included. survival (S p ) S e xe x= β= x= β=0.4 x= β= Porpoise energy E level (E p ) Nabe-Nielsen et al. 2014, Ecol. Modelling Modelling energetics and life history Porpoises use energy when moving; decreased survival. Porpoises obtain energy from patches they encounter. Life history traits (birth, lactation etc.) included. 6

7 Modelling behavioural response to noise Sound level, assuming spherical spreading Modelling behavioural response to noise RT = Threshold for when porpoises start responding to noise. c = Deterrence coefficient, determines strength of deterrence 7

8 Modelling behavioural response to noise Random walk component Spatial memory Deterrence component V* = V S + V R + V D V* = move for animals that are exposed to noise Modelling behavioural response to noise V* = V S + V R + V D 8

9 Modelling behavioural response to noise V* = V S + V R + V D Modelling behavioural response to noise V* = V S + V R + V D 9

10 Modelling behavioural response to noise V* = V S + V R + V D Calibrating response to noise Data on porpoise densities collected during construction of the Gemini wind farm. NL Germany Source level = 234 db SEL Distance from piling [m] 10

11 Calibrating response to noise Recovery at different distances from piling Minimize difference between obs. and simulated Movement by pile-driving Simulated response to continuous pile driving. 8.9 km 11

12 Importance of spatial distribution of noise AU Scenario based on EU 2020 target: 3900 turbines (23 GW); randomly distributed at 15 40m depth. UNIVERSITY Impacts of bycatch and pingers Spatially explicit simulation of gillnet fisheries in inner Danish waters. Use of pingers to prevent bycatch in gillnets. van Beest et al. 2017, Ecosphere 12

13 Impacts of bycatch and pingers Negative population impacts of mitigating bycatch with pingers exceed those of bycatch. Combination of closed areas and pingers worked. Population size (N agents) Baseline (no fishing) 1.2 % bycatch per year Use of pingers; no bycatch 100 Baseline Bycatch contemporary Bycatch worst-case Pinger use only Simulation year van Beest et al. 2017, Ecosphere Conclusions and perspectives The DEPONS model is data driven; animal movements and response to noise are as observed in nature. Population effects emerge from the same principles as in nature. The model is spatially explicit; effects of disturbances vary among areas and depend on disturbance history etc. The model is free, open source, easy to use and can be extended to assess cumulative impacts of various kinds of anthropogenic disturbances, bycatch etc. 13

14 References Gilles, A., Viquerat, S., Becker, E.A., Forney, K.A., Geelhoed, S.C. V., Haelters, J., Nabe-Nielsen, J., Scheidat, M., Siebert, U., Sveegaard, S., van Beest, F.M., van Bemmelen, R. & Aarts, G. (2016) Seasonal habitat-based density models for a marine top predator, the harbor porpoise, in a dynamic environment. Ecosphere, 7, e Nabe-Nielsen, J., Tougaard, J., Teilmann, J., Lucke, K. & Forchhammer, M.C. (2013) How a simple adaptive foraging strategy can lead to emergent home ranges and increased food intake. Oikos, 122, Nabe-Nielsen, J., Sibly, R.M., Tougaard, J., Teilmann, J. & Sveegaard, S. (2014) Effects of noise and bycatch on a Danish harbour porpoise population. Ecological Modelling, 272, NRC (2005) Marine Mammal Populations and Ocean Noise: Determining When Noise Causes Biologically Significant Effects. Committee on Characterizing Biologically Significant Marine Mammal Behavior, National Research Council. van Beest, F.M., Kindt-Larsen, L., Bastardie, F., Bartolino, V. & Nabe-Nielsen, J. (2017) Predicting the population-level impact of mitigating harbor porpoise bycatch with pingers and time-area fishing closures. Ecosphere, 8, e