Spatial Scale, Means and Gradients of Hydrographic Variables Define Pelagic Seascapes of Bluefin and Bullet Tuna Spawning Distribution

Abstract

Seascape ecology is an emerging discipline focused on understanding how features of the marine habitat influence the spatial distribution of marine species. However, there is still a gap in the development of concepts and techniques for its application in the marine pelagic realm, where there are no clear boundaries delimitating habitats. Here we demonstrate that pelagic seascape metrics defined as a combination of hydrographic variables and their spatial gradients calculated at an appropriate spatial scale, improve our ability to model pelagic fish distribution. We apply the analysis to study the spawning locations of two tuna species: Atlantic bluefin and bullet tuna. These two species represent a gradient in life history strategies. Bluefin tuna has a large body size and is a long-distant migrant, while bullet tuna has a small body size and lives year-round in coastal waters within the Mediterranean Sea. The results show that the models performance incorporating the proposed seascape metrics increases significantly when compared with models that do not consider these metrics. This improvement is more important for Atlantic bluefin, whose spawning ecology is dependent on the local oceanographic scenario, than it is for bullet tuna, which is less influenced by the hydrographic conditions. Our study advances our understanding of how species perceive their habitat and confirms that the spatial scale at which the seascape metrics provide information is related to the spawning ecology and life history strategy of each species.

Continental‐scale hotspots of pelagic fish abundance inferred from commercial catch records

“…This may explain why temperature, kinetic energy, oxygen concentration and salinity are often seen as important predictors of biogeographical range but a mechanistic understanding of their influence is often missing in the literature. For example, the role of salinity, a consistently high‐scoring variable in all bioregions (Supporting Information Appendix S3, Table S4), in determining the occurrence of pelagic species, is particularly obscure albeit some evidence exists that haline fronts may be indirectly linked with reproductive success (e.g., Alvarez‐Berastegui et al, ), or prey density and therefore favourable foraging areas (e.g., Maury, Gascuel, Marsac, Fonteneau, & Rosa, ). Remotely sensed measurements of ocean colour and their derivatives, such as FCPI, are more readily interpretable, but may lack explanatory power (Supporting Information Appendix S3, Table S4) if the target organisms sit several trophic levels above primary producers (Grémillet et al, ), track productivity at depth by following the deep scattering layer or chlorophyll maxima and/or time lags occur between chlorophyll peaks and resource availability for consumers (Navarro et al, ).…”

Fisheries conservation on the high seas: linking conservation physiology and fisheries ecology for the management of large pelagic fishes

“…In contrast, the HBS approach directly incorporates data on oceanographic conditions, fisheries gear behaviour and the ecophysiology and behaviour of pelagic fishes ( Hinton and Nakano, 1996 ; Lynch et al ., 2012 ). Finally, although they are not strictly stock assessment models, the recent development of spatial ecosystem, species distribution and seascape spatial distribution models also show great potential to refine spatial understanding of fish behaviour, movements, and distribution ( Lehodey et al ., 2008 , 2015 ; Kearney and Porter, 2009 ; Alvarez-Berastegui et al ., 2014 ; Everson et al ., 2015 ).…”

Trophic Ecology of Atlantic Bluefin Tuna (Thunnusthynnus) Larvae from the Gulf of Mexico and NW Mediterranean Spawning Grounds: A Comparative Stable Isotope Study

“…The Balearic Sea is amongst the most important BFT spawning areas in the MED. The spawning grounds are strongly linked to the hydrographic features that characterize the Balearic Sea [ 11 ], [ 12 ], [ 24 ]. The area is under the influence of incoming Atlantic surface waters encountering resident surface water masses, which results in a complex hydrography characterized by frontal structures and associated mesoscales features, such as anticyclonic and cyclonic gyres [ 25 – 27 ].…”