Modeling the potential habitats of dusky, commons and bottlenose dolphins in the Humboldt Current System off Peru: The influence of non-El Niño vs. El Niño 1997-98 conditions and potential prey availability
Introduction
The marine ecosystem off the coast of Peru encompasses the north part of the Humboldt Current ecosystem and is recognized as one of the most productive upwelling systems in the world (Chávez et al., 2008). It is affected by inter-annual fluctuations between warm and cold conditions associated with El Niño-Southern Oscillation (ENSO). This ecosystem produces far more fish biomass (Peruvian anchovy Engraulis ringens) than other upwelling systems (Carr, 2001, Bakun and Weeks, 2008, Bertrand et al., 2010). This large concentration of pelagic fishes influences the patterns of abundance, spatial distribution and trophic ecology of a great diversity of top-level predators including pinnipeds and seabirds (Majluf, 1991, Jahncke et al., 2004, Passuni et al., 2016). Although cetaceans such as small delphinids are important top predators in marine ecosystems, the distributional aspects of these species remain unknown in the Humboldt Current ecosystem off Peru.
The distribution of delphinids is largely influenced by the distribution of their prey (Cockcroft and Peddemors, 1990, Sekiguchi et al., 1992, O’Donoghue et al., 2010), which often occupies highly productive areas such as upwelling zones (Findlay et al., 1992). Thus, oceanographic descriptors can be used as proxies for understanding the processes explaining the preference of cetaceans for certain habitats (Redfern et al., 2006, Ballance et al., 2006). Delphinids perform movements between the coast and oceanic zones and/or along coastlines at meso and macro spatial scales (Forney and Barlow, 1998). Although temporal habitat may overlap among some species during such movements, it seems that species avoid competition via differential habitat use and diet (Henderson et al., 2014). For instance, in the northeastern Pacific, the short-beaked common dolphin is not present in the northern California Current, where the Pacific white-sided dolphin (Lagenorhynchus obliquidens) seems to be much more adapted to prey on fish and squid (Pardo et al., 2015). In the Eastern Tropical Pacific, the spotted (Stenella attenuata) and spinner dolphins (Stenella longirostris) are associated with tropical surface waters while the striped (Stenella coeruleoalba) and common dolphins (Delphinus spp.) inhabit upwelling-modified waters (Au and Perryman, 1985, Reilly and Fiedler, 1994). Likewise, dolphin distributions could change at different temporal scales as a response to prevailing environmental variations, seasonally (Neumann, 2001, Würsig et al., 2007) or inter-annually during strong ENSO events (Fiedler and Reilly, 1994, Forney, 2000, Sánchez et al., 2000, Benson et al., 2002, Henderson et al., 2014).
In the Humboldt Current System off Peru, important insight has been gained into the causes of its high productivity, analyzing long-term time series of data on some of its components: phytoplankton (Echevin et al., 2008, Ochoa et al., 2010), zooplankton (Ayón et al., 2004, Ayón et al., 2008, Ayón et al., 2011, Bertrand et al., 2010, Bertrand et al., 2014), pelagic fish (Pauly et al., 1989, Ñiquen and Bouchon, 2004, Gutierrez et al., 2007, Espinoza and Bertrand, 2008, Yi et al., 2013, Bertrand et al., 2016), top predators such as seabirds and pinnipeds (Majluf and Trillmich, 1981, Majluf, 1991, Jahncke et al., 2004, Cárdenas-Alayza, 2012, Passuni et al., 2016, Barbraud et al., 2017) and oceanographic characteristics (Alheit and Ñiquen, 2004, Chávez et al., 2008, Swartzman et al., 2008, Bertrand et al., 2011). These data have been integrated into trophic models that include ENSO dynamics to elucidate the functional significance of this upwelling system (Tam et al., 2008, Taylor et al., 2008). Despite such advances in knowledge, the system remains a “puzzle” with some pieces unresolved (Cury et al., 1998, Taylor and Wolff, 2007). Small cetaceans such as delphinids are missing pieces of the puzzle.
Research on delphinids in Peru during recent decades has been mainly conducted by studying landed animals coming from direct hunting and by-catch in artisanal fisheries (Read et al., 1988, Van Waerebeek and Reyes, 1990, Van Waerebeek and Reyes, 1994, García-Godos et al., 2007, Alfaro-Shigueto et al., 2008, Mangel et al., 2010). Although some habitat characteristics, patterns of distribution and abundance have been inferred from such data, such inferences must be ground-truthed with information collected in situ.
Herein, maximum entropy models were developed with the aim of understanding the spatial-temporal patterns and potential habitat of long and short-beaked common (Delphinus capensis, Delphinus delphis), dusky (Lagenorhynchus obscurus) and bottlenose dolphins (Tursiops truncatus) in relation to oceanographic variables and the distribution of potential prey species as descriptors of their ecological niche in the Humboldt Current System off Peru. Since strong upwelling characterizes the neritic zone, and eddies and upwelling filaments enter the oceanic realm, we predicted that areas where such processes occur would influence the distribution of dolphins and their putative prey, thus creating spatial segregation of dolphins in the Peruvian marine ecosystem.
Section snippets
Sampling design
Sightings of common, dusky, and bottlenose dolphins were recorded along with oceanographic parameters during cruises conducted by the Instituto del Mar del Perú (IMARPE, Peruvian Sea Research Institute) for stock assessment of Peruvian anchovy (Engraulis ringens) throughout Peruvian territorial waters. Cruises were generally conducted during “March to April” and “August to November” from 1997 to 2014. The sampling design consisted of systematic navigation along parallel transects. Typically, a
Validation of Maxent models and the contribution of variables
AUC values showed adequate model performance for all delphinids and potential prey species (AUC > 0.7) except to short-beaked common dolphin (AUC = 0.665) and longnose anchovy (AUC = 0.687) during non-El Niño conditions. COR showed correlations > 0.17 for all delphinids except to short-beaked common dolphin (rpb = 0.074). The highest values were dusky dolphins (rpb = 0.304) and bottlenose dolphins (rpb = 0.212) for delphinids during non-El Niño conditions. Red squat lobster (rpb = 0.353) and
Modeling considerations
Before going into the ecological and oceanographic interpretations of our results it is important to mention that (i) maximum entropy models predict a potential distribution (potential habitat) and do not necessarily represent the magnitude of species abundance. (ii) Models for mesopelagic prey species (e.g. Panama lightfish and other myctophids) must be interpreted with caution since some of these species inhabit very deep waters and we used only sea surface information for correlations.
Acknowledgments
This project was conducted under a collaboration framework between Universidad de Antofagasta, Chile and IMARPE, Perú. M. Llapapasca is grateful to the program Magíster en Ecología de Sistemas Acuáticos of Universidad de Antofagasta for providing a scholarship and IMARPE (Dirección General de Investigaciones de Recursos Pelágicos and Dirección de Investigaciones Oceanográficas y Cambio Climático) for data used in this study. Special thanks to Nadia López, M. Rivadeneira and N. Marcel for
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