Abstract
The aggregation of wild fish around fish farms is spatially and temporally variable in terms of species composition and structure. In general, temporal variability has been less well studied than the spatial aspect of these aggregations. We analyzed temporal variability at differ- ent scales following a hierarchical sampling design, with year, season and time of day as the main factors, with the levels of the latter factor corresponding with feeding intensity at the farm. Envi- ronmental and production variables were considered, such as water temperature, photoperiod, feed supplied, number of stocked fish and stocked biomass. Dominant fish species were analyzed separately to determine possible segregation processes. The most relevant sources of variation in abundance and assemblage structure were seasonal changes among years and hourly changes with different feeding intensities between seasons. Feed supplied was the production variable that best explained the temporal pattern with respect to abundance, and this variable, combined with hours of daylight, determined the assemblage structure. Liza ramada and Sarpa salpa domi- nated the assemblage in winter and were always aggregated around the farm. Boops boops, Ob - lada melanura and Sardinella aurita dominated the assemblage in spring, summer and autumn, showing a marked seasonal pattern. These 3 species, although present around the farm most of the year, displayed periods of distinct maximum abundance corresponding to their reproductive period. This study emphasizes the importance of determining the temporal patterns in abundance of dominant species in order to better understand the interaction between fish farming and wild fish assemblages, and to ascertain the contribution of wild fish to the recycling of aquaculture- derived wastes.
Highlights
In marine cage fish farming, some resources are shared between wild biota and the reared animals, generating interactions between components of the natural and farmed environments
This study emphasizes the importance of determining the temporal patterns in abundance of dominant species in order to better understand the interaction between fish farming and wild fish assemblages, and to ascertain the contribution of wild fish to the recycling of aquaculturederived wastes
Our goals were to determine how some key driving environmental and husbandry variables influenced the temporal variability of the wild fish assemblage aggregated around a fish farm at different scales, and to examine the segregation of dominant fish species over time
Summary
In marine cage fish farming, some resources are shared between wild biota and the reared animals, generating interactions between components of the natural and farmed environments. The effects of fish farm wastes on the distribution and physiology of wild fish remain unclear (Uglem et al 2014) This aggregation phenomenon has been described as being analogous to the functioning of a large fish aggregating device (FAD) (Dempster et al 2002). In the Mediterranean, wild fish aggregations around fish farms exhibit spatial and temporal variations in their composition and structure (Dempster et al 2002, 2005, Valle et al 2007, Fernandez-Jover et al 2008, Segvić Bubić et al 2011, Bacher et al 2012, 2015). None of these studies have incorporated both long and short temporal scales or their interactions
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