DOI: 10.5061/dryad.cc2fqz6fd
title: Northeast Atlantic species distribution shifts over the last two decades

description: Marine species are widely shifting their distributions in response to
 global changes, and it is commonly expected they will move northward and
 to greater depths to reach cooler, less disturbed habitats. However, local
 manifestations of global changes, anthropogenic pressures, and species
 characteristics may lead to unanticipated and varied responses by
 individual species. In this regard, the Celtic-Biscay Shelf is a
 particularly interesting study system because it has historically been
 heavily fished and occurs at the interface between two distinct
 biogeographic provinces, its community is thus comprised of species with
 diverse thermal preferenda. In the context of rapidly warming temperatures
 and intense fishery exploitation, we investigated the distribution shifts
 of 93 taxa (65 Actinopteri, 10 Elasmobranchii, 11 Cephalopoda, 5
 Malacostraca, and 2 Bivalvia), which were sampled annually from 1997 to
 2020 during a scientific bottom trawl survey. We used a set of 11
 complementary spatial indices to quantify taxon distribution shifts over
 time. Then, we explored the relative effect of taxon abundance, fishing
 pressure, and climatic conditions on taxon’s distribution shift when a
 significant shift was detected. We observed that 56% of the taxa
 significantly shifted. Not all taxa will necessarily shift northward and
 to deeper areas, as is often expected. Two opposite patterns were
 identified: taxa either moving deeper and to the southeast, or moving
 closer to the surface and to the northwest. The main explanatory factors
 were climate change (short- and long-term temperatures) and taxon
 abundance. Fishing pressure was the third, but still significant,
 explanatory factor of taxa of greater commercial importance. Our research
 highlights that taxa are displaying complex distribution shifts in
 response to the combined anthropogenic disturbances and underscores the
 need to conduct regional studies to better understand these responses at
 the ecosystem scale to develop more suitable management plans and
 policies.
description: This dataset was collected during the scientific bottom trawl
 survey EVHOE (Evaluation of fishing resources of Western Europe; EVHOE
 cruise, R/V Thalassa, IFREMER, DOI: 10.18142/8)
 carried out between October and December from 1997 to 2020 along the
 Celtic-Biscay Shelf.
description: # Northeast Atlantic species distribution shifts over the last two decades
 [https://doi.org/10.5061/dryad.cc2fqz6fd](https://doi.org/10.5061/dryad.cc2fqz6fd) Raw data of this study comes from the scientific bottom trawl survey EVHOE (Evaluation of fishing resources of Western Europe; EVHOE cruise, R/V Thalassa, IFREMER, DOI: 10.18142/8) carried out between October and December from 1997 to 2020 along the Celtic-Biscay Shelf (CBS). The latter occurs at the interface between the Celtic Sea (CS) and the Bay of Biscay (BoB). EVHOE relies on a stratified random sampling design in which 119 to 158 stations were sampled annually. The EVHOE survey is funded through the European Union Data Collection Framework. At each station, specimens were collected using a 36/47 GOV bottom trawl (opening width: 20 m; height: 4 m; mesh size: 20 mm) operated for 30 min at a towing speed of 4 knots. Once on board, species were identified to the finest possible taxonomic scale. Due to variation in taxonomic resolution, some species were assigned to a coarser taxonomic level, hereafter named “taxon” and “taxa”. We excluded the 2017 dataset, as an incident of boat engine failure prevented completion of the sampling campaign. To reduce potential bias due to the sampling method, we only retained the Taxon with a reliable temporal and spatial coverage. We selected Taxon collected during at least 80% of the studied years and at 5% or more of the sampling stations within a given year. This selection was adapted for the analysis of temporal shifts in taxon distribution but not for the exploration of invasive species income. The dataset contains tables summarizing the Taxon characteristics, Taxon populations annual spatial indices, explanatory variables, and models results of Taxon distribution shift analysis and the explanatory variables influencing distribution shifts. Please read the paper or contact the authors for more details. ## Description of the data and file structure * 1_Taxa_population_guilds | **Column** | **Explanation** | | :-------------------- | :--------------------------------------------------------------------------------- | | taxa\_code | EVHOE survey Taxon code | | common\_name | Taxon common name | | name\_latin | Taxon latin name | | distri | Taxon population distribution according to presence-absence data | | pop\_nb | Taxon population number identified in the area according to presence-absence data | | class | Taxonomic class | | position\_guild | Taxon vertical distribution guild (pelagic, demersal, benthic swimmer, or benthic) | | biogeographic\_guild | Taxon biogeographic guild (Atlantic, boreal, or Lusitanian) | | rel\_com\_imp | Taxon relative commercial importance (lesser or greater commercial importance) | | lat\_min\_biblio | Minimum latitude recorded for this Taxon in the literature | | lat\_max\_biblio | Maximum latitude recorded for this Taxon in the literature | | ref\_range\_lat\_data | Reference for the minimum and maximum latitudes | distribution_final : CBS = 1 population distributed in the CBS area, CS = 1 population distributed in the CS area, BoB = 1 population distributed in the BoB area, CS_BoB = 2 populations (1 in CS and 1 in BoB) Based on information from the scientific literature, FishBase, and ICES, each taxon was assigned to a biogeographic guild (Atlantic, boreal, or Lusitanian) and a vertical distribution guild (pelagic, demersal, benthic swimmer, or benthic). Two benthic guilds were defined according to Taxon swimming capacity: the benthic swimmer Taxon were Actinopteri, Elasmobranchii, and Cephalopoda and the benthic Taxon were Malacostraca and Bivalvia. We calculated each taxon’s relative commercial importance using ICES mean catches in FAO divisions 27.7 g-h and 27.8 a-b, corresponding to the Celtic Sea and the Bay of Biscay delineated in our study, respectively, between 2006 and 2019 (source: Eurostat/ICES compilation of catch data and statistics, ICES 2021, Copenhagen). On the basis of this information, Taxon were considered to be of lesser commercial importance (mean catch for taxon &lt; 0.25 quantile of the distribution of mean catches for all taxa) or of greater commercial importance (mean catch for taxon ≥ 0.25 quantile of the distribution of mean catches for all taxa). * 2_Spatial_index_abun_biomass Annual spatial index calculated for each Taxon population. | **Column** | **Explanation** | | :---------------- | :------------------------------------------------------------------------ | | year | year | | taxa\_code | EVHOE survey Taxon code | | distri | Taxon population distribution according to presence-absence data | | sub\_pop | Taxon population when two populations were identified in the studied area | | long\_CG | Taxon population longitude center of gravity | | long\_q5 | Taxon population longitude quantile 0.05 = western limit | | long\_q95 | Taxon population longitude quantile 0.95 = eastern limit | | lat\_CG | Taxon population latitude center of gravity | | lat\_q5 | Taxon population latitude quantile 0.05 = southern limit | | lat\_q95 | Taxon population latitude quantile 0.95 = northern limit | | depth\_CG | Taxon population depth center of gravity | | depth\_q5 | Taxon population depth quantile 0.05 = lower limit | | depth\_q95 | Taxon population depth quantile 0.95 = upper limit | | I | Taxon population inertia | | PA | Taxon population positive area | | abun\_IA | Taxon population relative abundance index | | biomass\_tons\_IA | Taxon population biomass index | A relative abundance index was used as a descriptor of population status (Hutchings & Baum, 2005). To account for the randomly stratified sampling design, we calculated taxon relative abundance index as the number of individuals of a given taxon elevated to the surface area (in square nautical miles) of the CS , BoB or CBS depending on the delineation of the populations within the distribution zones (Mahé & Poulard, 2005). The biomass index estimated using EVHOE data is used to calculate a harvest rate and to quantofy the influence of fishing pressure on Taxon distribution shifts. * 3_Model_results_temporal_change_analysis Results of GLM and GLS models for the analysis of Taxon significant distribution shift during the studied period. | **Column** | **Explanation** | | :------------- | :------------------------------------------------------------------------ | | taxa\_code | EVHOE survey Taxon code | | distri | Taxon population distribution according to presence-absence data | | sub\_pop | Taxon population when two populations were identified in the studied area | | "index"\_p | P value of the statistical analysis | | "index"\_slope | Slope estimated by the model | | "index"\_test | Model used for the analysis of temporal changes of the index (GLM or GLS) | "index" are either lat, long, depth (CG, q5, and q95), I or PA. * 4_Significant_temporal_change_interpreted Significant results of GLM and GLS models for the analysis of Taxon distribution shift during the studied period and their shifting direction. | **Column** | **Explanation** | | :------------ | :------------------------------------------------------------------------ | | taxa\_code | EVHOE survey Taxon code | | distri | Taxon population distribution according to presence-absence data | | sub\_pop | Taxon population when two populations were identified in the studied area | | spatial index | Spatial index | | p\_value | Significant p value (alpha ≤ 0.05) | | slope | Slope estimated by the model | | test | Model used for the analysis of temporal changes of the index (GLM or GLS) | | moving | Shifting direction | * 5_Climate_explanatory_variables | **Column** | **Explanation** | | :----------- | :------------------------------------------------------------------------------------------- | | year | Year | | annual\_AMO | Annual Atlantic Multidecadal Oscillation index | | winter\_NAO | Winter North Atlantic Oscillation (December of the previous year to March of the focal year) | | BT\_ano\_CS | Bottom temperature anomalies in the Celtic Sea | | BT\_ano\_BoB | Bottom temperature anomalies in the Bay of Biscay | | BT\_ano\_CBS | Bottom temperature anomalies in the Celtic-Biscay Shelf | * 6_Taxon_population_relative_F | **Column** | **Explanation** | | :---------------- | :------------------------------------------------------------------------ | | taxa\_code | EVHOE survey Taxon code | | distri | Taxon population distribution according to presence-absence data | | sub\_pop | Taxon population when two populations were identified in the studied area | | year | Year | | biomass\_tons\_IA | Taxon population biomass index | | catches\_fao | Catches reported by the FAO | | relative\_F | Fishing pressure index | To quantify fishing pressure, we estimated a harvest rate as the ratio between nominal catches (sources: Eurostat/ICES compilation of catch data and statistics - ICES 2011 & 2021, Copenhagen) and the biomass estimated during EVHOE (within the CS, BoB, and CBS). We decided against using fishing mortality (e.g., ICES analytical assessment) as a proxy for fishing pressure because both analytical stock assessments are lacking for most of the studied taxa and EVHOE’s survey area did not entirely match up with ICES fish stock delineations. * 7_Relative_importance_of_explanatory_variables The relative importance (i.e., the cumulative AICc weight) of each explanatory variable was calculated by summing Akaike weights across all models that included the explanatory variable (Table S2; Burnham & Anderson, 2002; Arnold, 2010). | **Column** | **Explanation** | | :------------ | :------------------------------------------------------------------------ | | taxa\_code | EVHOE survey Taxon code | | distri | Taxon population distribution according to presence-absence data | | sub\_pop | Taxon population when two populations were identified in the studied area | | spatial index | Spatial index | | moving | Shifting direction | | abun\_IA | Relative importance of abundance | | relative\_F | Relative importance of fishing pressure | | annual\_AMO | Relative importance of annual AMO | | winter\_NAO | Relative importance of winter NAO | | BT\_ano | Relative importance of bottom temperature anomalies | * 8_Model_average_estimates_of_explanatory_variables The variables’ estimates and 80% confidence intervals were obtained by computing the average model using all the models (Arnold, 2010). | **Column** | **Explanation** | | :------------ | :------------------------------------------------------------------------ | | taxa\_code | EVHOE survey Taxon code | | distri | Taxon population distribution according to presence-absence data | | sub\_pop | Taxon population when two populations were identified in the studied area | | spatial index | Spatial index | | moving | Shifting direction | | abun\_IA | Abundance estimate | | relative\_F | Fishing pressure estimate | | annual\_AMO | Annual AMO estimate | | winter\_NAO | Winter NAO estimate | | BT\_ano | Bottom temperature anomalies estimate | ## Sharing/Access information Data was derived from the following sources: * EVHOE survey data are available at [https://www.seanoe.org/data/00688/80041/](https://www.seanoe.org/data/00688/80041/) * NAO data are available at [https://www.ncdc.noaa.gov/teleconnections/nao/](https://www.ncdc.noaa.gov/teleconnections/nao/) * AMO data are available at [https://psl.noaa.gov/data/timeseries/AMO/](https://psl.noaa.gov/data/timeseries/AMO/) * The monthly aggregated bottom temperatures were provided by the Atlantic Margin Model FOAM (Forecasting Ocean Assimilation Model). The data had a horizontal resolution of 7 km (0.111 × 0.067°) and covered the period from 1997 to 2020 (UK Met Office Operational Suite, [http://marine.copernicus.eu/).](http://marine.copernicus.eu/\).) * Taxon’s relative commercial importance was estimated using ICES mean catches in FAO divisions 27.7 g-h and 27.8 a-b, corresponding to the Celtic Sea and the Bay of Biscay delineated in our study, respectively, between 2006 and 2019 (source: Eurostat/ICES compilation of catch data and statistics, ICES 2021, Copenhagen). * Fishing pressure was estimated with a harvest rate as the ratio between nominal catches (sources: Eurostat/ICES compilation of catch data and statistics - ICES 2011 & 2021, Copenhagen) and the biomass estimated during EVHOE (within the CS, BoB, and CBS).