DOI: 10.5061/dryad.h9w0vt4rb
title: Food chain without giants: Modelling the trophic impact of bowhead whaling on little auk populations in the Atlantic Arctic

description: In the Atlantic Arctic, bowhead whales (Balaena mysticetus) were nearly
 exterminated by European whalers between the 17th and 19th centuries. The
 collapse of the East Greenland-Svalbard-Barents Sea population, from an
 estimated 50,000 to a few hundred individuals, drastically reduced
 predation on mesozooplankton. Here, we tested the hypothesis that this
 event strongly favoured the demography of the little auk (Alle alle), a
 zooplanktivorous feeder competitor of bowhead whales, and the most
 abundant seabird in the Arctic. To reconstruct pre-whaling little auk
 abundance, we modelled trophic niche overlap between the two species using
 deterministic simulations of mesozooplankton spatial distribution. We
 estimated a 70% increase in Northeast Atlantic Arctic little auk
 populations following bowhead whaling, from 2.8 million to 4.8 million
 breeding pairs. While corresponding to a major population increase, this
 is far less than predicted by previous studies. Our study illustrates a
 trophic shift resulting from the near extirpation of a marine megafauna
 species, and the methodological framework we developed opens up new
 opportunities for marine trophic modelling.
description: # **Food chain without giants: Modelling the trophic impact of bowhead
 whaling on little auk populations in the Atlantic Arctic**
 [https://doi.org/10.5061/dryad.h9w0vt4rb](https://doi.org/10.5061/dryad.h9w0vt4rb) You will find here the dataset related to the paper "Food chain without giants: Modelling the trophic impact of bowhead whaling on little auk populations in the Atlantic Arctic". This dataset contains **four main files** : * PCBM_Results_10000rep_2024-05-14.txt : The main output of the model * sf_surfacewhaleauk_depth : The shapefile of the study area * coast.txt : A latitude/longitude file to identify coast lines * Food chain of giants_main script.R : Main script  ## Description of main output dataframe (PCBM\_Results\_10000rep\_2024-05-14.txt) This dataframe contains the modelling output of each of the 10,000 Monte-Carlo repetitions. Titles are in French, with the following translation for abbreviations : * eff = number of individuals/breeding couple * bal = bowhead whale * mer = little auk * act = 21st century (current) * hist = 17th century (historical) * biom = Mesozooplankton biomass (expressed in tonnes) * taux/prop = ratio * conso / nonconso = consumed/not consumed * acces = accessible * aire = foraging area * chevauchement = overlap * poids = weight of each foraging factor * densite = density **Here is a brief summary of column structure :** * Column 6 contains the main result = abundance of pre-whaling little auk populations. * Columns 9 to 26 contain parameter values resulting from random draws for each Monte-Carlo repetition * Columns 27 to 50 contain the main outputs for biomass consumption for both period of time and for both species * Columns 51 to 78 contain various indicators computed with model outputs * Columns 79 to 87 contain mesozooplankton biomass distribution among the different foraging areas * Columns 88 to 159 contain detailed estimations of mesozooplankton biomass distribution among the different stratum (0.20m; 20.50m; 50.200m) and the different seafloor depth (20; 50; 100; 200; 6,000) **Variables per column (Col) correspond to :** * Col 1: Number of EGSB adult bowhead whales in the 21st century * Col 2: Number of EGSB adult bowhead whales in the 17th century * Col 3: Number of adult little auks in the 21st century * Col 4: Number of little auk breeding pairs in the 21st century * Col 5: Number of juvenile little auks in the 21st century - Col 6: Number of adult little auks in the 17th century - Col 7: Number of little auk breeding pairs in the 17th century - Col 8: Number of juvenile little auks in the 17th century - Col 9: Length of little auk breeding season (days) - Col 10: Mean mesozoopkankton biomass simulated per cubic meter of water in the whole bowhead whale foraging area in the strata 0-200m (g/m2) - Col 11: Ratio Production to Biomass as drawn by Monte-Carlo simulation - Col 12: Proportion of annual secondary production achieved during the study period (%) - Col 13: Proportion of copepods within mesozooplankton biomass (%) - Col 14-16: Proportion (%) of the total mesozooplankton biomass in the water column within each stratum -  Col 17: Daily mesozooplankton food requirements by an adult bowhead whale, averaged over one year (t.ww.day-1 with ww=wet weight and t=tonne) - Col 18: Multiplication factor of bowhead whale food requirements during summer - Col 19: Critical mesozooplankton biomass density threshold for bowhead whale foraging (g.m-3)  - Col 20: Daily mesozooplankton food requirements by an adult little auk (g.ww.day-1 with ww=wet weight) - Col 21: Mesozooplankton food requirements for a juvenile little auk between hatching and fledging (g.ww.) - Col 22: Critical mesozooplankton biomass density threshold for little auk foraging (g.m-3) - Col 23: Capture requirements of mesozooplankton individuals during subwater foraging by little auks (ind.s-1) - Col 24: Mean wet weight of mesozooplankton individuals captured by little auks (mg.ww.) - Col 25: Diving speed during foraging by little auks (m.s-1) - Col 26: Foraging area around the beak from which little auks fully extract mesozooplankton biomass (m²) - Col 27 and 28: Total mesozooplankton biomass consumed by EGSB bowhead whale population in the 17th and 21st centuries (tonnes) - Col 29, 30 and 31: Total mesozooplankton biomass accessible to EGSB bowhead whale population in the 17th and 21st centuries (tonnes) - Col 32: Total mesozooplankton biomass not accessible to EGSB bowhead whale population (tonnes) - Col 33 and 68: Total mesozooplankton biomass within the EGSB bowhead whale foraging area (tonnes) - Col 24 to 38: Share (%) of mesozooplankton biomass (accessible or total) eaten by bowhead whales in the 17th and 21st centuries  * Col 39 and 40: Total mesozooplankton biomass consumed by the little auk population in the 17th and 21st centuries (tonnes) - Col 41 to 47: Total mesozooplankton biomass accessible to the little auk population in the 17th and 21st centuries and eaten by whales (*consobal*) or not eaten by whales (*nonconsobal*)* *(tonnes) - Col 48: Total mesozooplankton biomass not accessible to the little auk population (tonnes) - Col 49 and 50: Total mesozooplankton biomass within the little auk whale foraging area in the 17th and 21st centuries (tonnes) - Col 51 to 58: Share of accessible/total/within little auk foraging area that is consumed or accessible to little auks in the 17th and 21st centuries (%) - Col 59 to 62: Percentage of overlap by one species over the other's trophic niche (%) in the 17th and 21st centuries (tonnes) - Col 65 to 67: Weights (%) of the geography, depth and biomass threshold criteria in the difference in biomass accessibility between bowhead whales and little auks - Col 69: Mean mesozooplankton density in the study area (g.m-3) - Col 70: Percentage of water volume within study area that contains mesozooplankton patches (%) - Col 71 and 72: Total mesozooplankton biomass within patches (tonnes) and percentage relatively to total biomass (%) - Col 73 to 75: Total mesozooplankton biomass within each strata (0-20m, 20-50m, 50-200m)  (tonnes) - Col 76 to 78: Mean density of mesozooplankton biomass within each strata (g.m-3) - Col 79 to 82: Mesozooplankton biomass accessible to EGSB bowhead whales in subsets of the foraging area (Kara sea, Barents sea, Greenland sea, Arctic bassin) (tonnes) - Col 83 to 87: Mesozooplankton biomass accessible to little auks in subsets of the foraging area (East Greenland, Svalbard, Novaya Zemlya, Jan Mayen, Franz Joseph) (tonnes) - Col 88 to 195 contain the detailed estimations of mesozooplankton biomass (tonnes) generated by the model with the following characteristics :  * species : 'bal' (bowhead whale) or 'mer' (little auk) * centuries: 'hist' (17th century) or 'act' (21st century) * status: 'conso' (consumed), 'acces' (accessible to), 'nonconso' (accessible and not consumed), 'nonacces' (not accessible to) * ocean strata (0.20m; 20.50m; 50.200m) * seafloor depth (20; 50; 100; 200; 6,000) ## Description of shapefile (sf\_surfacewhaleauk\_depth) This shapefile contains geographical information (CRS = ESRI:102016 - North Pole Aziumthal Equidistant) about the 22,225 cells of 400 km² (20 x 20km) covering the study area :  * Percentage (%) of the cell's surface within the four sea regions (Kara, Arctic, Barents, Greenland) and within the five little auk foraging areas (East Greenland, Svalbard, Novaya Zemlya, Jan Mayen, Franz Joseph) [NA equals to 0, meaning that the cell is completely outside of these areas] * Mean seafloor depth (meters) from the  General Bathymetric Chart of the Oceans [cells with NA are cells unreported in GEBCO and therefore excluded from the analysis] ## Description of coast.txt This dataset contains the geographical information (lon = longitude, lat = latitude) to draw the coast lines and plot the copepod biomass estimation data from Drago et al. (2022) (see link below).  ## Description of R script The R script contains all the details necessary to follow the modelling steps described in the methods section of the article, aiming at estimating the pre-whaling little auk in the Atlantic Arctic.  It starts with the Monte-Carlo simulations and ends with the final dataframe (PCBM_Results_XXXXXrep_XXXX-XX-XX.txt). All required packages are listed. All data needed to run the script are to be downladed here and using the github link below.  ## Sharing/Access information Simulations of the global distribution of copepod biomass from Drago et al., 2022 used as inputs in the model are available at [https://github.com/dlaetitia/Global_zooplankton_biomass_distribution.git](https://github.com/dlaetitia/Global_zooplankton_biomass_distribution.git). ## Code/Software The model was created using R version 4.2.2