DOI 10.1186/s40462-020-00230-w Background
Aggregation sites represent important sources of environmental heterogeneity and can modify the movement behavior of animals. When these sites are artificially established through anthropogenic actions, the consequent alterations to animal movements may impact their ecology with potential implications for their fitness. Floating objects represent important sources of habitat heterogeneity for tropical tunas, beneath which these species naturally aggregate in large numbers. Man-made floating objects, called Fish Aggregating Devices (FAD), are used by fishers on a massive scale to facilitate fishing operations. In addition to the direct impacts that fishing with FADs has on tuna populations, assessing the effects of increasing the numbers of FADs on the ecology of tuna is key for generating sound management and conservation measures.
Methods
This study investigates the effects of increasing numbers of FADs (aggregation sites) on the movements of tunas, through the comparison of electronic tagging data recorded from 146 individuals tunas (yellowfin tuna, Thunnus albacares, and skipjack tuna, Katsuwonus pelamis) tagged in three instrumented anchored FAD arrays (Mauritius, Oahu-Hawaii and Maldives), that differed according to their distances among neighboring FADs. The effect of increasing inter-FAD distances is studied considering a set of indices (residence times at FADs and absence (travel) times between two visits at FADs) and their trends.
Results
When inter-FAD distances decrease, tuna visit more FADs (higher connectivity between FADs), spend less time travelling between FADs and more time associated with them. The trends observed for the absence (travel) times appear to be compatible with a random-search component in the movement behaviour of tunas. Conversely, FAD residence times showed opposite trends, which could be a result of social behavior and/or prey availability.
Conclusion
Our results provide the first evidence of changes in tuna associative behavior for increasing FAD densities. More generally, they highlight the need for comparing animal movements in heterogeneous habitats in order to improve understanding of the impacts of anthropogenic habitat modifications on the ecology of wild animals.
Acoustic tagging, Associative behavior, Density of floating objects, Movement behavior, Tropical tuna
| File | Pages | Size | Access | |
|---|---|---|---|---|
Publisher's official version | 10 | 1 Mo | ||
Additional file 1. Number of tuna tagged per tuna size for each FAD arrays and tuna species. | - | 181 Ko | ||
Additional file 2. Number of tuna tagged in each FAD array per species and size category. | - | 14 Ko | ||
Additional file 3. Number of tuna, number of CRTs, CATreturn(s) and CATdiff(s) for the full observation time and for only the first 38 days of observation. | - | 15 Ko | ||
Additional file 4. Random-walk model. | - | 667 Ko | ||
Additional file 5. Number of CRT (NCRT), CATdiff (NCATdiff) and CATreturn (NCATreturn) per individuals for each AFAD array and each specie-size category. YFT-70 (A, D and G), YFT-50 (B, E and H) and | - | 242 Ko |
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