Long-term changes in the diversity, abundance and size composition of deep sea demersal teleosts from the Azores assessed through surveys and commercial landings

Abstract

To obtain important baseline information about population dynamics and to provide valuable insights about the possible effects of artisanal fishing on the demersal fish community, this study had three specific objectives: (1) to update the annotated list of demersal teleost species occurring in the Azores (mid-North Atlantic); (2) to describe their depth distribution and related fishery information; and (3) to evaluate annual changes in their observed abundance and length composition. To do this, a time series with about 25 years of scientific data from the commercial fishery and surveys was analyzed. The demersal teleost community was represented by 213 species, predominantly deep-water species, reflecting the main marine habitat in the Azores region. Fishery takes place mainly in the intermediate strata (200–600 m), where the most commercially important species occur. No changing in the fork length (LF) distribution toward small individuals caused by size-selective fishing was detected in this study. The high variability observed in the LF data indicates the need for more accurate studies considering alternative statistical analyses (e.g., generalised linear models) to examine the possible factors (e.g. depth coverage, gear configuration, soak time, and fishing area) that cause this variability. On the other hand, the abundance indices of some commercially important species appear to have declined (Phycis phycis, Pontinus kuhlii, Conger conger, Beryx splendens and B. decadactylus), while others appear to be more stable (Helicolenus dactylopterus) or even increasing (Mora moro). Although the available data are insufficient for a formal assessment on the status of exploited populations, the long-term analysis of commercial landings and survey data was used as a basis to assess deep sea demersal teleost fisheries of the Azores, under a precautionary approach.

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

“…The most abundant fish orders found on the studied seamounts (i.e., Perciformes, Gadiformes and Squaliformes) were in reasonable agreement with demersal communities described in neighboring areas of the Azores (e.g., Menezes et al., 2009; Santos, Novoa‐Pabon, et al, 2020; Santos, Silva, et al, 2019) and other NE Atlantic archipelagic regions such as Madeira (e.g., Menezes, 2003; Menezes et al., 2009), Canaries (e.g. Uiblein et al, 1996) and Cape Verde (e.g., Menezes et al., 2015; Monteiro et al., 2008).…”

“…Uiblein et al, 1996) and Cape Verde (e.g., Menezes et al., 2015; Monteiro et al., 2008). At family level, we recorded a common pattern of dominance by typical deep‐sea families such as Sebastidae (rockfishes), Moridae (cods), Centrophoridae (gulper sharks) (e.g., Menezes et al., 2006, 2015; Santos, Silva, et al, 2019). Species inhabiting the Azorean seamounts (e.g., Aphanopus carbo, Conger conger, Helicolenus dactylopterus, Pontinus kuhlii, Mora moro ) were also present on other NE Atlantic underwater mountains (e.g., Christiansen et al., 2015; Menezes & Giacomello, 2013; Menezes et al., 2009; Uiblein et al, 1996), supporting a “stepping stone” hypothesis of historical dispersion and colonization for some species (Lloris et al., 1991).…”

“…(2006) and Pinho and Menezes (2006). Years were aggregated into four groups according to regulations that had significant impact on fishing operation in the Azorean area (Santos, Novoa‐Pabon, et al, 2020; Santos, Silva, et al, 2019): 1995–2001 (a) comprised the beginning of the surveys until the instauration of the Ordinance n° 101/2002 (Açores, 2002), which introduces a restricted area of 3 NM around the islands for longline fishing; 2002–2009 (b) from the application of the Ordinance n° 101/2002 until the instauration of the Ordinance n° 48/2010 (Açores, 2010), which closes the Condor bank to the demersal deep‐sea fishery; 2010–2011 (c) from the application of the Ordinance n° 48/2010 until the instauration of the Ordinance n° 50/2012 (Açores, 2012), which expands the restricted area for longline fishing from 3 NM to 6 NM; 2012–2018 (d) from the application of the Ordinance n° 50/2012 until the last year surveyed.…”

“…Fishing is the main activity at sea in the Azores archipelago and demersal fishery is the most important one in weight (Pinho & Menezes, 2006). Historically, Azorean demersal fishery has taken place along the slopes of the islands, but this behavior has changed towards seamounts due to fleet modernization and fishing area restrictions (Diogo et al., 2015; Santos et al., 2019b). Despite its essentially small‐scale characteristics (the Azorean demersal fleet is predominantly composed by small vessels, <12 m length; Silva & Pinho, 2007), the expansion of this bottom fishing towards seamount areas is worrisome.…”

Population structure and movement patterns of blackbelly rosefish in the NE Atlantic Ocean (Azores archipelago)

“…The demersal fishing fleet consists mainly of small‐scale vessels (< 12 m in length with limited autonomy: Carvalho, Edwards‐Jones, & Isidro, ) equipped with handlines and bottom longlines. Blackbelly rosefish is one of the species targeted by the Azorean bottom longline fleet, with an average of 270 t landed annually in the last five years (Santos, Silva, Novoa‐Pabon, Silva, & Pinho, ). Fisheries take place without a complete knowledge on stock structure and level of exploitation.…”