Demersal fish assemblages on seamounts exploited by fishing in the Azores (NE Atlantic)

Abstract

Seamount fish communities are susceptible to variations due to the oceanographic conditions and level of historical fishing effort. In the NE Atlantic, the Azores is considered an “oceanic seamount ecosystem area” because seamount concentration is high relative to other regions. Scientific information on seamounts in the Azores remains scarce and demersal fishery occurs mostly without any knowledge to endorse sustainable harvest strategies. To make available an important baseline information on dynamics of demersal fish populations inhabiting commercially exploited seamounts, the present study has as specific objectives to (a) describe the taxonomic composition of demersal fish assemblages on underwater mountains, (b) examine whether assemblages vary spatial and temporally, and (c) investigate what drives distributional patterns of species in terms of abundance and size composition. For this, three Azorean seamounts (Açores, Princesa Alice and Mar da Prata) exploited by bottom fishing were selected as case study areas. Data were obtained from scientific surveys and commercial fishery over the past c. 25 years. A total of 84 species from 45 families were identified. Sebastidae, Moridae, Sparidae and Centrophoridae were the most abundant families, mainly represented by Helicolenus dactylopterus, Mora moro, Pagellus bogaraveo and Deania profundorum, respectively. Fish assemblages were more distinguishable spatially than temporally. Depth was identified as the main factor responsible for these differences. The higher occurrence of shallow and intermediate (i.e., up to 600 m) habitats in Princesa Alice and Açores seems to favor the occurrence of a greater number of species and higher abundances in comparison to Mar da Prata. Phycis phycis, Pontinus kuhlii, H. dactylopterus, P. bogaraveo, Conger conger and M. moro were the species which primarily contributed to dissimilarities in assemblage structure among sample groups. Abundance indices and fish sizes showed a decreasing trend for many of these species, especially for those with sedentary behaviour inhabiting historically highly exploited seamount areas. These results highlighted the vulnerability of demersal fishes to the expansion of fishing effort in the offshore seamount areas. Spatial management of seamounts should be a priority being fish conservation balanced with strategies that support sustainable fisheries.

Contributions to Management Strategies in the NE Atlantic Regarding the Life History and Population Structure of a Key Deep-Sea Fish (Mora Moro)

“…Mora moro has been registered throughout the Azores on mud, sand, and rock bottoms at depths below 300 m. An increase in the occurrence and abundance of this species at depths between 800 and 1000 m reflected a spatial distribution restricted to seamounts, offshore banks, and island slopes, in which this depth range is mostly available. Variations in demersal fish abundance and distribution have frequently been associated with depth [48] or depth-related environmental factors (e.g., water temperature, oxygen saturation, and salinity) [49,50]. The inclusion of these physicochemical variables might improve habitat predictions, but they were not available at a fine-scale resolution and when derived from global data sets, may show low predictive power [51].…”

“…An increase in the mean L F in the catch was also observed during 2008-2014, and it may have been caused by larger individuals that became more available for fishing after a decrease in the abundance of medium-sized fishes. With the reorientation of the fleet to the MAR due to the implementation of fishing area restrictions [5,48], the relief in the fishing effort at the upper fringe of coastal habitats of the species allowed the populations to rebuild themselves to higher levels (see Figures 9 and 10). The exploitation rate (E) estimated for the most recent 2010-2016 period was below the optimum level of 0.5, and the fishing mortality (F) was lower than natural mortality (M), indicating that this species is currently not overexploited [43].…”

“…The exploitation rate (E) estimated for the most recent 2010-2016 period was below the optimum level of 0.5, and the fishing mortality (F) was lower than natural mortality (M), indicating that this species is currently not overexploited [43]. Recent studies in seamount areas have shown that the impacts of fishing on this stock are no longer pronounced because there is a fraction of the population that is not exploited and would be able to restore the levels of exploited stock by recruitment [48].…”

Population structure of the European conger Conger conger from the mid‐North Atlantic Ocean inferred from bathymetric distribution, length composition and movement patterns analyses

“…Fishing effect in the Azorean EEZ was evaluated based on the abundance and mean total length trends, which were similar and without large oscillations over time. However, recent analysis of fishing impacts on Azorean seamounts historically and intensively exploited by bottom longliners highlighted the species vulnerability to fishing by showing lower catches and smaller sizes than other seamount areas (Santos et al 2021).…”

Error Distribution Model to Standardize LPUE, CPUE and Survey-Derived Catch Rates of Target and Non-Target Species

“…In addition to being species that typify the depth-aligned demersal fish assemblage structure in the Azores [28][29][30][31], both the thornback ray and common mora are usually caught as by-catch of the Azorean hook-and-line fisheries targeting demersal fishes such as blackbelly rosefish H. dactylopterus, blackspot seabream Pagellus bogaraveo, and alfonsinos Beryx spp. [29,30,32,33].…”