Reef fishes' trophodynamic between trawled and non-trawled environments

FUNES M; GALVAN DE

Viña del Mar

Congreso; IsoEcol2018; 2018

Universidad Andrés Bello

Temperate reefs fishes from western Patagonia are long living animals, with low energy budget and high site fidelity. They present complex reproduction strategies and low reproduction potential, which make them particularly vulnerable to local impacts. Trawl fisheries impact the environment by removing target animals, producing discards and scrapping the sea bottom: factors that can alter the availability of different prey. We studied the trophodynamic of two reef fishes of Western Patagonia: Argentine sandperch; Pseudopercis semifasciata and Argentine seabass; Acanthistius patachonicus. Previous studies suggested that the seabass feeds more on soft bottoms preys and less on water column preys than the sandperch. Also, a broader diet and foraging range was descripted for the sandperch. Diet features were compared between trawled and non-trawled areas using stable isotope analysis of C and N along an overlapping size range. At trawled areas, isotopic niches were wider (area Ps: 0.34, area Ap: 0.64) and overlapped more (0.1) than at non-trawled areas (area Ps: 0.32, area Ap: 0.11; niche overlap: 0.04). Trends along body sizes were non-significant for the seabass (p>0.05). The sandperch showed significant trends of δ13C values vs size only at trawled areas (p= 0.004), while trends of δ15N values vs size were significant only at non-trawled areas (p= 0.005). The seabass expanded its trophic diversity at trawled areas, which could be a consequence of an increased availability of soft bottom preys by surface scrapping and/or the usage of discards. Regarding the sandperch, trophic level was expected to increase as they become bigger. This predicton was met at non-trawled areas, while at the trawled site, diets were relatively constant through sizes. Trends in δ13C values vs size could also be reflecting the availability of more benthic preys on impacted environments. Finally, fishes at trawled areas seem to have more similar diet showing less niche partitioning. This is one of a few cases where theoretical changes on trophic features between trawl and non-trawled environments were actually found, and the differences in trophodynamic features between species sets a good scenario to capture its complexity.