Assessing cetacean surveys throughout the Mediterranean Sea: a gap analysis in environmental space

Laura Mannocci ,Philip S Hammond ,Giancarlo Lauriano ,Caterina Maria Fortuna ,Tim Lewis ,Carla A Chicote ,Manel Gazo ,Simone Panigada ,Aviad Scheinin ,Nathalie Di‐Méglio ,Jason J Roberts ,Tilen Genov ,Patrick N Halpin ,Giuseppe Notarbartolo Di Sciara ,Draško Holcer ,Vincent Ridoux ,Mohamed Nejmeddine Bradaï ,Léa David ,Matthieu Authier ,Kristin Kaschner ,Ana Cañadas ,Adriana Vella ,Juan Antonio Raga ,D Kerem ,Alexandros Frantzis ,Oliver Boisseau ,Janis Vella

doi:10.1038/s41598-018-19842-9

Abstract

Heterogeneous data collection in the marine environment has led to large gaps in our knowledge of marine species distributions. To fill these gaps, models calibrated on existing data may be used to predict species distributions in unsampled areas, given that available data are sufficiently representative. Our objective was to evaluate the feasibility of mapping cetacean densities across the entire Mediterranean Sea using models calibrated on available survey data and various environmental covariates. We aggregated 302,481 km of line transect survey effort conducted in the Mediterranean Sea within the past 20 years by many organisations. Survey coverage was highly heterogeneous geographically and seasonally: large data gaps were present in the eastern and southern Mediterranean and in non-summer months. We mapped the extent of interpolation versus extrapolation and the proportion of data nearby in environmental space when models calibrated on existing survey data were used for prediction across the entire Mediterranean Sea. Using model predictions to map cetacean densities in the eastern and southern Mediterranean, characterised by warmer, less productive waters, and more intense eddy activity, would lead to potentially unreliable extrapolations. We stress the need for systematic surveys of cetaceans in these environmentally unique Mediterranean waters, particularly in non-summer months.

Highlights

Heterogeneous data collection in the marine environment has led to large gaps in our knowledge of marine species distributions
We mapped the extent of interpolation versus extrapolation and the proportion of data nearby in environmental space when models calibrated on existing survey data were used for prediction across the entire Mediterranean Sea
It is critical to assess the coverage of datasets in environmental space to evaluate the extent of extrapolation when a species distribution models (SDMs) calibrated on existing data is used for prediction across a study region

Summary

Introduction

Heterogeneous data collection in the marine environment has led to large gaps in our knowledge of marine species distributions. Our objective was to evaluate the feasibility of mapping cetacean densities across the entire Mediterranean Sea using models calibrated on available survey data and various environmental covariates. A global gap analysis of line transect surveys used to derive abundance estimates and habitat-based density models of cetaceans has revealed large geographic gaps in the Southern Hemisphere and seasonal gaps in non-summer months[8]. The manmade Suez Canal, which exposes the Mediterranean Sea to the distinct fauna of the Red Sea, caused the former to become the globally most invaded marine ecosystem[21], augmenting and hastening biodiversity shifts Despite these marked anthropogenic pressures, the collection of systematic data to assess marine animal abundances and responses to these stressors has been heterogeneous throughout the Mediterranean Sea, reflecting the uneven distribution of funding for population monitoring[22]. The wide range of some cetaceans across the Mediterranean Sea (e.g., fin whale and sperm whale27–29), combined with their vulnerability to the multiple anthropogenic pressures[30,31,32,33], stress the need to develop predictive models to map their densities throughout the Mediterranean Sea

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Discussion

Conclusion