Fishery Discards Impact on Seabird Movement Patterns at Regional Scales

Human fishing activities are negatively altering marine ecosystems in many ways [1, 2], but scavenging animals such as seabirds are taking advantage of such activities by exploiting fishery discards [3-5]. Despite the well-known impact of fisheries on seabird population dynamics [6-10], little is known about how discard availability affects seabird movement patterns. Using scenarios with and without trawling activity, we present evidence that fisheries modify the natural way in which two Mediterranean seabirds explore the seascape to look for resources during the breeding season. Based on satellite tracking data and a mathematical framework to quantify anomalous diffusion phenomena, we show how the interplay between traveling distances and pause periods contributes to the spatial spreading of the seabirds at regional scales (i.e., 10-250 km). When trawlers operate, seabirds show exponentially distributed traveling distances and a strong site fidelity to certain foraging areas, the whole foraging process being subdiffusive. In the absence of trawling activity, the site fidelity increases, but the whole movement pattern appears dominated by rare but very large traveling distances, making foraging a superdiffusive process. Our results demonstrate human involvement on landscape-level behavioral ecology and provide a new ecosystemic approach in the study of fishery-seabird interactions.

[1]  H. Higuchi,et al.  Foraging of royal albatrosses, Diomedea epomophora, from the Otago Peninsula and its relationships to fisheries , 2005 .

[2]  M. Shlesinger,et al.  Beyond Brownian motion , 1996 .

[3]  David Grémillet,et al.  A junk-food hypothesis for gannets feeding on fishery waste , 2008, Proceedings of the Royal Society B: Biological Sciences.

[4]  Henri Weimerskirch,et al.  Are seabirds foraging for unpredictable resources , 2007 .

[5]  F. Mainardi,et al.  The fundamental solution of the space-time fractional diffusion equation , 2007, cond-mat/0702419.

[6]  Roger Pradel,et al.  Influence of food availability on demography and local population dynamics in a long-lived seabird , 2004, Proceedings of the Royal Society of London. Series B: Biological Sciences.

[7]  P. Pepin,et al.  The effects of short space and time scale current variability on the predictability of passive ichthyoplankton distributions: an analysis based on HF radar observations , 2002 .

[8]  D. Oro,et al.  Oceanographic habitat of an endangered Mediterranean procellariiform: implications for marine protected areas. , 2006, Ecological applications : a publication of the Ecological Society of America.

[9]  P. E. Kopp,et al.  Superspreading and the effect of individual variation on disease emergence , 2005, Nature.

[10]  Sophie Bertrand,et al.  Scale-invariant movements of fishermen: the same foraging strategy as natural predators. , 2007, Ecological applications : a publication of the Ecological Society of America.

[11]  Benjamin M. Bolker,et al.  Ecological Models and Data in R , 2008 .

[12]  Mark E. J. Newman,et al.  Power-Law Distributions in Empirical Data , 2007, SIAM Rev..

[13]  B. Rodríguez,et al.  Combining vessel-based surveys and tracking data to identify key marine areas for seabirds , 2009 .

[14]  Henri Weimerskirch,et al.  Does Prey Capture Induce Area‐Restricted Search? A Fine‐Scale Study Using GPS in a Marine Predator, the Wandering Albatross , 2007, The American Naturalist.

[15]  David R. Anderson,et al.  Model selection and multimodel inference : a practical information-theoretic approach , 2003 .

[16]  J. M. Arcos,et al.  Geographical patterns of seabird attendance to a research trawler along the Iberian Mediterranean coast , 2003 .

[17]  M. Shlesinger Mathematical physics: Search research , 2006, Nature.

[18]  R. Pradel,et al.  Density-dependent parameters and demographic equilibrium in open populations , 2007 .

[19]  G. Viswanathan,et al.  Lévy flights and superdiffusion in the context of biological encounters and random searches , 2008 .

[20]  Zumofen,et al.  Laminar-localized-phase coexistence in dynamical systems. , 1995, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics.

[21]  D. Oro,et al.  Significance of fisheries discards for a threatened Mediterranean seabird, the Balearic shearwater Puffinus mauretanicus , 2002 .

[22]  Robert W. Furness,et al.  Impacts of fisheries on seabird communities , 2003 .

[23]  H. Stanley,et al.  Optimizing the success of random searches , 1999, Nature.

[24]  Theunis Piersma,et al.  Shellfish Dredging Pushes a Flexible Avian Top Predator out of a Marine Protected Area , 2006, PLoS biology.

[25]  T. Geisel,et al.  The scaling laws of human travel , 2006, Nature.

[26]  D. Oro,et al.  Influence of trawling activity on the breeding ecology of a threatened seabird, Audouin\'s gull Larus audouinii , 1996 .

[27]  R. Furness,et al.  Influence of management practices and of scavenging seabirds on availability of fisheries discards to benthic scavengers , 2007 .

[28]  D. Pauly,et al.  Fishing down marine food webs , 1998, Science.

[29]  J. Klafter,et al.  The random walk's guide to anomalous diffusion: a fractional dynamics approach , 2000 .

[30]  M. Bhaskara Rao,et al.  Model Selection and Inference , 2000, Technometrics.

[31]  Stuart Bearhop,et al.  Changes in fisheries discard rates and seabird communities , 2004, Nature.

[32]  Simon Benhamou,et al.  How many animals really do the Lévy walk? , 2008, Ecology.

[33]  Andy Reynolds,et al.  How many animals really do the Lévy walk? Comment. , 2008, Ecology.

[34]  Germinal Cocho,et al.  Scale-free foraging by primates emerges from their interaction with a complex environment , 2006, Proceedings of the Royal Society B: Biological Sciences.

[35]  Frederic Bartumeus,et al.  Fractal reorientation clocks: Linking animal behavior to statistical patterns of search , 2008, Proceedings of the National Academy of Sciences.

[36]  P. Turchin Quantitative analysis of movement : measuring and modeling population redistribution in animals and plants , 1998 .

[37]  H. Weimerskirch,et al.  Natural and experimental changes in chick provisioning in a long-lived seabird, the Antarctic Prion , 1999 .

[38]  R. Hilborn,et al.  The Ecological Detective: Confronting Models with Data , 1997 .

[39]  L. Prior,et al.  Ecological Models and Data in R , 2011 .

[40]  T. Piersma,et al.  Proceedings of the 22nd International Ornithological Congress , 1999 .

[41]  F. Bartumeus,et al.  Optimal search behavior and classic foraging theory , 2009 .

[42]  Sophie Bertrand,et al.  Lévy trajectories of Peruvian purse-seiners as an indicator of the spatial distribution of anchovy ( Engraulis ringens ) , 2005 .

[43]  R. Freckleton,et al.  The Ecological Detective: Confronting Models with Data , 1999 .

[44]  A. M. Edwards,et al.  Revisiting Lévy flight search patterns of wandering albatrosses, bumblebees and deer , 2007, Nature.

[45]  Alexei Vazquez,et al.  Diffusion regimes in Lévy flights with trapping , 1999 .

[46]  M. Shlesinger,et al.  Stochastic pathway to anomalous diffusion. , 1987, Physical review. A, General physics.

[47]  D. Oro,et al.  Fisheries Ecosystem Impacts and Management in the Mediterranean: Seabirds Point of View , 2007 .

[48]  J. Manuel,et al.  Foraging Ecology of Seabirds at Sea: Significance of Commercial Fisheries in the NW Mediterranean. , 2001 .

[49]  Frederic Bartumeus,et al.  LÉVY PROCESSES IN ANIMAL MOVEMENT: AN EVOLUTIONARY HYPOTHESIS , 2007 .

[50]  D. Oro,et al.  Activity patterns and foraging behaviour of Audouin's gulls in the Ebro Delta, NW Mediterranean , 2004 .

[51]  Frederic Bartumeus,et al.  ANIMAL SEARCH STRATEGIES: A QUANTITATIVE RANDOM‐WALK ANALYSIS , 2005 .

[52]  H. Weimerskirch How can a pelagic seabird provision its chick when relying on a distant food resource? Cyclic attendance at the colony, foraging decision and body condition in sooty shearwaters , 1998 .

[53]  D. Oro,et al.  Diet and adult time budgets of Audouin's Gull Larus audouinii in response to changes in commercial fisheries , 2008 .

[54]  S. L. Lima,et al.  Towards a behavioral ecology of ecological landscapes. , 1996, Trends in ecology & evolution.

[55]  Small pelagic fish, trawling discards and breeding performance of the critically endangered Balearic shearwater : improving conservation diagnosis , 2006 .

[56]  M. Coll,et al.  Food-web dynamics in the South Catalan Sea ecosystem (NW Mediterranean) for 1978-2003 , 2008 .

[57]  Nicolas E. Humphries,et al.  Scaling laws of marine predator search behaviour , 2008, Nature.