An experimental evaluation of the short-term effects of trawling on infaunal assemblages of the coast off southern Brazil

Abstract

Bottom trawling is a large-scale fishing activity along the Brazilian coast, but its effects on benthic infauna are still poorly known. This is the first experimental evaluation of benthic responses to bottom trawling along the Brazilian coast. We tested the effects of trawling on macroinfaunal assemblages on the inner continental shelf off Paraná (southern Brazil) by using a sampling design with adjacent trawl and control areas. We hypothesized that if trawl fishing has a negative effect then we should expect lower numbers of species and lower benthic densities after an experimental trawling. Sampling was conducted at adjacent sites within each area to minimize confounding due to spatial variation. Five sites were sampled at a control, and five at an experimental area for infaunal and sedimentological variables. Sampling was carried out just before and one hour after experimental trawling. Multidimensional scaling followed by a PERMANOVA did not show any clear variation tendencies in the structure of the benthic assemblages in the impacted area before and after trawling. However, variance analysis showed a significant and unexpected increase in infaunal total density, in the density of the numerically dominant species (except for the polychaetes Capitella sp. and Loandalia tricuspis) and in species richness in the experimental area. Conversely, no significant variations were recorded in the control area. We suggest that the overall increase in benthic density after a disturbance is correlated with the reworking of the sediment matrix and benefits the suspension-feeders after sediment resuspension.

Response of benthic fauna to experimental bottom fishing: A global meta‐analysis

“…Areas were defined as undisturbed, if they were known from fisheries‐enforcement data to have been subjected to no or negligible fishing activity for at least 10 years prior to the fishing experiment, or were known to have remained unimpacted because they were in marine‐protected areas or protected by seabed obstructions (Brown, Finney, & Hills, ; Pranovi, Raicevich, Libralato, Ponte, & Giovanardi, ). Areas were described as previously disturbed when subject to fishing disturbance in the last 10 years prior to the study (Castaldelli et al., ; Prantoni, Lana, Sandrini‐Neto, Filho, & deOliveira, ). To test for any effects of environmental factors that influence the growth rates, and hence recovery rates, of individuals and populations, we considered primary production (PP, mg C m −2 day −1 ) at each study site, as estimated from the vertically generalised productivity model (Behrenfeld & Falkowski, ); particulate organic carbon flux to depth (POC flux, g C org m −2 year −1 , Lutz, Caldeira, Dunbar, & Behrenfeld, ); mean sea bottom temperature (SBT, °C) calculated from monthly mean bottom temperature for 2009–2011 all sourced from the MyOcean product “GLOBAL‐REANALYSIS‐PHYS‐001‐009”; mean water depth (Depth, m) from GEBCO if not reported in the original study, and “biogenic (%),” “gravel (%),” “sand (%)” and “mud (%)” as continuous variables extracted from source papers or from dbSEABED (http://instaar.colorado.edu/~jenkinsc/dbseabed/, Jenkins, ) when data were not provided in the articles.…”

“…Areas were defined as undisturbed, if they were known from fisheries-enforcement data to have been subjected to no or negligible fishing activity for at least 10 years prior to the fishing experiment, or were known to have remained unimpacted because they were in marine-protected areas or protected by seabed obstructions (Brown, Finney, & Hills, 2005;Pranovi, Raicevich, Libralato, Ponte, & Giovanardi, 2005). Areas were described as previously disturbed when subject to fishing disturbance in the last 10 years prior to the study (Castaldelli et al, 2003;Prantoni, Lana, Sandrini-Neto, Filho, & deOliveira, 2013). To test for any effects of environmental factors that influence the growth rates, and hence recovery rates, of individuals and populations, we considered primary production (PP, mg C m −2 day −1 ) at each study site, as estimated from the vertically generalised productivity model (Behrenfeld & Falkowski, 1997) Mud was chosen over sand as it correlates less than sand with gravel (Table SI7.5).…”

Determination of functional structure of soft-bottom marine macrobenthic communities of the Samsun Shelf Area using biological traits analysis

“…Jennings and Kaiser (1998) found that biogenic habitats and mud sediments are less exposed to natural disturbance caused by wave movements and bottom currents, and are generally more affected by fisheries, resulting in long-term ecosystem changes. On the contrary, Prantoni et al (2013) and Sciberras et al (2013) reported that soft-bottom habitats are highly exposed to natural physical disturbance and are usually less affected by fisheries. Tillin et al (2006) showed that there is no clear change in the functional community composition between localities in the Dogger Bank (North Sea) area exposed to different levels of trawling intensity.…”

Composition, density, and shell use of hermit crabs (Crustacea: Paguroidea) from subtidal boulder fields in southeastern Brazil

“…Except by the latter study, where animals were manually captured along a perpendicular transects to the water line, all the other studies used material obtained by a shrimp fishery boat equipped with double-rig nets used for trawling, a method which is frequently used in Brazilian fishery of penaeid shrimps in coastal waters (Castilho et al, 2008;Prantoni et al, 2013). This method is efficient, but also significantly impacts the bottom community (Pauly et al, 2002;Worm & Lenihan, 2014), because it generates a series of direct and indirect impacts, especially due to its low selectivity (Kaiser & Spencer, 1996;Rumohr & Kujawski, 2000;Worm & Lenihan, 2014).…”