Hydroacoustics to examine fish association with shallow offshore habitats in the Arabian Gulf

Abstract

In order to implement spatial fisheries management in the Arabian Gulf, a better understanding of the distribution of fish in relation to benthic habitats is required. To facilitate this, hydroacoustic fish surveys were conducted over oyster bed/reef ("shallow") and surrounding soft sediment ("deep") habitats in the offshore central Gulf, within Qatari waters. Transects at 'shallow' sites had significantly higher mean fish density and biomass. Mean target strength of individual fish was also significantly higher at 'shallow' sites. Fish positions in the water column were examined and overall there was a closer association with the seabed at the 'shallow' sites. Larger fish were found significantly closer to the seabed than smaller fish across all sites, but more so at 'shallow' sites than at 'deep' sites. Acoustic return from the seabed was extracted to provide information on the habitat type both using 'Sonar5' and 'Visual Habitat' software. The different site categories ('shallow' vs 'deep') were significantly different for all the measures of acoustic habitat. Fish density was significantly related to 'Visual Habitat' data, more so than depth alone. Our results show that fish distribution in the offshore Gulf is associated with complex, shallow oyster bed/reef habitats, and this is particularly the case for larger demersal fish that are commercially 2 exploited. The ability to characterise benthic habitats from acoustic fish survey data shows promise, with important time saving implications for the monitoring of marine environments and developing a spatial approach to fisheries management. This may include the identification of habitats with a relatively high density of larger fish for inclusion in candidate marine protected areas.

Decline in oyster populations in traditional fishing grounds; is habitat damage by static fishing gear a contributory factor in ecosystem degradation?

“…The majority of non-market species are integral components in maintaining the existence of commercial species firstly as part of a trophic chain and secondly by providing structural habitat (Cranfield et al, 2003). The importance of maintaining a complex benthic topography in the region was established during recent hydroacoustic surveys within fished hairãt which showed that the highest densities of high value commercial fish species were associated with the most complex topographical habitats, whereas sites with a featureless profile had low-density assemblages of low value fish (Egerton et al, 2018).…”

“…Intrinsic fish-habitat associations between the Qatari hairãt and a number of commercially important demersal species were recently confirmed in hydroacoustic surveys of sites which were once renowned as prolific during the pearl fishing epoch (Egerton et al, 2018) and wider habitat surveys (Walton et al 2017). Planning future management strategies for fish stocks should recognize the essential habitual niche of these fish, as many spend their entire life cycle associated with specific reefs (Egerton et al, 2018) while the Gargoor fleets consistently target traditional hairãt sites (Stamatopoulos and Abdallah, 2016).…”

“…The loss of ecosystem services (water column filtration, sediment stabilisation, substrate provision and benthic pelagic coupling) provided by a functional oyster hairãt can have drastic and rapid ecological effects, in regards to; water quality, benthic biodiversity and fish habitat which lead to decreases in reefassociated demersal fish (Bouma et al, 2009). Intrinsic fish-habitat associations between the Qatari hairãt and a number of commercially important demersal species were recently confirmed in hydroacoustic surveys of sites which were once renowned as prolific during the pearl fishing epoch (Egerton et al, 2018) and wider habitat surveys (Walton et al 2017). Planning future management strategies for fish stocks should recognize the essential habitual niche of these fish, as many spend their entire life cycle associated with specific reefs (Egerton et al, 2018) while the Gargoor fleets consistently target traditional hairãt sites (Stamatopoulos and Abdallah, 2016).…”

“…The location and areal extent of hairãt (4740.15 x 10 6 m 2 ) was predicted from depth-habitat relationships (Walton et al, 2017;Egerton et al, 2018) and calculated using Arc GIS © software and bathymetry data from the NOAA National Center for Environmental Information. All mapping was to a resolution of one minute.…”

The world is their oyster: Differences in epibiota on sympatric populations of native Ostrea edulis and non-native Crassostrea gigas (Magallana gigas) oysters

“…Newman et al, (2015) showed that the more complex a reef surface the greater the associated richness. Egerton et al, (2018) Osmundea pinnatifida which contributed 47% of the differences between the oysters.…”