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Marine litter in the upper São Vicente submarine canyon (SW Portugal): Abundance, distribution, composition and fauna interactions
Marine Pollution Bulletin xxx (2015) xxx–xxx
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Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Marine litter in the upper São Vicente submarine canyon (SW Portugal): Abundance, distribution, composition and fauna interactions Frederico Oliveira a,⇑, Pedro Monteiro a, Luis Bentes a, Nuno Sales Henriques a, Ricardo Aguilar b, Jorge M.S. Gonçalves a a b
Centre of Marine Sciences, CCMAR, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal OCEANA, Plaza España, Leganitos, 47, 28013 Madrid, Spain
a r t i c l e
i n f o
Article history: Received 17 March 2015 Revised 18 May 2015 Accepted 21 May 2015 Available online xxxx Keywords: S. Vicente Canyon ROV Litter Fishing gear Hook-and-line
a b s t r a c t Marine litter has become a worldwide environmental problem, tainting all ocean habitats. The abundance, distribution and composition of litter and its interactions with fauna were evaluated in the upper S. Vicente canyon using video images from 3 remote operated vehicle exploratory dives. Litter was present in all dives and the abundance was as high as 3.31 items 100 m1. Mean abundance of litter over rock bottom was higher than on soft substrate. Mean litter abundance was slightly higher than reported for other canyons on the Portuguese margin, but lower in comparison to more urbanized coastal areas of the world. Lost fishing gear was the prevalent type of litter, indicating that the majority of litter originates from maritime sources, mainly fishing activity. Physical contact with sessile fauna and entanglement of specimens were the major impacts of lost fishing gear. Based on the importance of this region for the local fishermen, litter abundance is expected to increase. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Marine litter has become ubiquitous in all oceans. From the most remote and inaccessible regions of the planet (e.g. Ryan and Moloney, 1993; Benton, 1995; Convey et al., 2002; Bergmann and Klages, 2012) to more common recreational beaches (e.g. Moore et al., 2001; Nagelkerken et al., 2001; Oigman-Pszczol and Creed, 2007; Ariza et al., 2008; Corcoran et al., 2009) marine litter has been accounted in all types, shapes and sizes. Marine litter composition is highly variable, ranging from microscopic plastic particles and fibers (Thompson et al., 2004; Martins and Sobral, 2011; Frias et al., 2014) to more visible items such as boat wrecks (Galgani et al., 1996), oil drums (Watters et al., 2010; Ramirez-Llodra et al., 2011; Schlining et al., 2013) and even radioactive waste containers (Calmet, 1989; Thiel, 2003). Nevertheless plastic, mainly due to its everyday use and high durability, is typically the major constituent of litter found in the marine environment, even in the deep sea (Galgani et al., 1996, 2000; Ryan et al., 2009; Schlining et al., 2013). Though strong currents and winds may transport litter, particularly the more buoyant, far away from its original source, marine
⇑ Corresponding author. E-mail address: [email protected] (F. Oliveira).
litter will eventually sink to amass in the deep sea. Accumulation occurs in areas of complex geomorphology and where hydrodynamic conditions are more favorable, such is the case of submarine canyons (Galgani et al., 1995, 1996, 2000; Mordecai et al., 2011; Schlining et al., 2013; Pham et al., 2014a). Submarine canyons often act as natural traps, deposits and transport pathways of particles from the shelf to the abyssal plains (Granata et al., 1999; Oliveira et al., 2007; Turchetto et al., 2007) and this same role as been described for marine litter (Galgani et al., 1996; Ramirez-Llodra et al., 2011; Schlining et al., 2013). In the Iberian west coast several major submarine canyons cut across the continental margin: the Mugía, Arosa, Porto, Aveiro, Lisboa, Setúbal, and S. Vicente Canyons (Peliz and Fiúza, 1999). The submarine canyons located off the north-western section of the Portuguese coast have been the subject of research in past years, with research programmes and multidisciplinary projects: OMEX II (1997–2000), EUROSTRATAFORM (van Weering and Weaver, 2007), HERMES (Weaver and Gunn, 2009) and HERMIONE (Weaver et al., 2009) focusing on oceanography, geology and biology of these ecosystems. Under the scope of these later projects, abundance and distribution of marine litter was also studied by Mordecai et al. (2011). Information regarding the canyons located in the south and south-western portions of the Portuguese margin is more limited, and the few studies conducted in the area focus primarily on geology.
http://dx.doi.org/10.1016/j.marpolbul.2015.05.060 0025-326X/Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Oliveira, F., et al. Marine litter in the upper São Vicente submarine canyon (SW Portugal): Abundance, distribution, composition and fauna interactions. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.060
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F. Oliveira et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
Using underwater video records taken during exploratory surveys, the present study aims to quantify the abundance, distribution and composition of marine litter across the upper section of São Vicente canyon, and describe visible effects of marine litter on the surrounding fauna. 2. Material and methods 2.1. Study area The study area is located in the southwest coast of Portugal, a mesotidal moderately exposed Atlantic coast (Monteiro et al., in press) with a narrow and steep continental shelf (Peliz and Fiúza, 1999; Relvas and Barton, 2002) and a gentle slope (Alves et al., 2003). The São Vicente submarine canyon, with its head scarp at 70 m below sea level, is one of the major geomorphological features incising this section of the continental shelf and slope (Terrinha et al., 2009). Located approximately 12 km offshore mainland Portugal (Fig. 1), the canyon is shaped as a wide, 120 km long corridor following a NE–SW orientation, aligned with the Odemira–Ávila fault, connecting the Alentejo margin to the Horseshoe Abyssal Plain (Alves et al., 2003; Terrinha et al., 2009). 2.1.1. Oceanography The ocean circulation patterns in the region are complex and seasonal. Relvas et al. (2007) gives a detailed description of the different mechanisms and interactions affecting the local oceanography. In brief: during the winter season, starting in September– October, dominant winds are mainly westerly and southerly. Slope circulation is typically dominated by a poleward current (transporting warm and saline water), until the spring transition in April–May, when the northerly winds prevail. This current does not influence the shelf except during particular events. According to Relvas and Barton (2002), coastal circulation depends on wind stress and the pressure gradient along the shore, and their relationship determines the direction and strength of the circulation. Wind-induced upwelling conditions in late spring are observed episodically when favorable winds occur (Peliz and Fiúza, 1999; Relvas et al., 2007).
2.1.2. Sources of land based litter – urban centers and rivers Most of the land section of the southwest Portuguese coast was designated Protected Landscape in 1988, and in 1995, a Natural Park was created (Parque Natural do Sudoeste Alentejano e Costa Vicentina), including a 2 km wide marine strip along its entire length (Castro and Cruz, 2009). Relatively far from major urban centers and with a small resident population concentrated in small towns and villages, low anthropogenic impacts are expected in the area, with minor levels of sewage and agricultural run-off being the major sources of land based pollution in the adjacent coastal waters. The São Vicente submarine canyon is not fed by any major river course and along the coastline the fresh water inputs are limited to small rivers and streams. 2.1.3. Sources of marine based litter – fishing and other maritime activities Off the southwest coast of Portugal there are important fishing grounds for local artisanal and industrial fleets operating different metiers targeting several species: surface and deep water longlines, purse-seine, gill nets, trammel nets, pots and traps, finfish and crustacean bottom trawls (Erzini et al., 1996; Gonçalves and Erzini, 1998; Galhardo et al., 2006; Campos et al., 2007; Coelho and Erzini, 2008). This area is also part of important maritime corridors linking the Mediterranean and North Africa to Northern Europe. Since 2008, a Vessel Traffic Service (VTS) system has been monitoring the maritime traffic to 50 miles offshore mainland Portugal with an average of 800 vessels being tracked daily (MAMAOT, 2012). Taking as a reference the year 2010, the VTS system registered 11.3 thousand merchant ships crossing the Portuguese waters (MAMAOT, 2012). 2.2. Survey The analysis of litter abundance and composition in the upper São Vicente submarine canyon was based on three exploratory remote operated vehicle (ROV) dives performed in June 2011 by the NGO Oceana (Fig. 1). The ROV platform, a Saab Seaeye Falcon DR rated 1000 m, was equipped with two forward facing color
Fig. 1. Location of the dive transects in S. Vicente canyon (SW coast of Portugal). Red lines correspond to the track of each dive performed during the survey. Isobaths represent 50 m depth intervals. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Please cite this article in press as: Oliveira, F., et al. Marine litter in the upper São Vicente submarine canyon (SW Portugal): Abundance, distribution, composition and fauna interactions. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.060
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cameras. The primary camera (standard definition: 480 TV lines, 0.2 lux) fixed to a tilt mount was continuously recorded. The secondary camera (high definition: 1080i) mounted under the first, was equipped with zoom and would allow real-time observation. Transects were performed at constant speed of 0.2/0.3 knots and whenever possible maintaining 50 cm or less above ground. The navigation data were acquired from the Ultra Short BaseLine (USBL) system (Linkquest TN1510AH with accuracy up to 0.25°) and included date, local time, latitude and longitude. All navigation track data were post-processed and smoothed with moving average. 2.2.1. Video analysis Each dive was considered a single continuous transect. ROV maneuvres that caused loss of bottom image were considered off-bottom events and the correspondent track segments were excluded from the total transect length and additional analysis. The video recordings collected during the ROV dives were annotated thoroughly for the presence of marine litter, litter/fauna interactions, as well as the dominant type of bottom. Video annotation was performed using the COVER software (Customizable Observation Video Image Recorder, v0.7.2; Carré, 2010). Observed litter items were classified according to their characteristics in the following categories: ‘Fishing line’, ‘Net’, ‘Fishing rope’, ‘Glass’, ‘Ceramics’, ‘Metal’ and ‘Plastic’. While most of the modern fishing gear is made of plastic (Brown and Macfadyen, 2007), we considered these items as different categories following Pham et al. (2014a) rationale: ‘‘because of our knowledge on its source and social implications and the particular impacts of this type of litter, such as ghost fishing and entanglement’’. Classified litter items were then categorized regarding their visible impact on the surrounding fauna as: ‘No effect’, ‘Contact’, ‘Entangling’, ‘Smothering’ and ‘Shelter/Substrate’. 2.2.2. Abundance and distribution of marine litter Since the purpose of Oceana’s ROV dives were mainly a documentation of the faunal communities, the ROV lacked scaling systems on which we could accurately determine the area sampled. Therefore, and given the nature of the transects, we did not calculate densities and instead recorded occurrences along the ROV track. The number of items recorded on each dive would later be divided by the respective track length as a measure of abundance that could be comparable with other studies (items 100 m1). Additionally, using GIS software, it was possible to georeference each occurrence of litter across the ocean floor. Because of the nature of the data collected (few replicates and non-normally distributed data), the non-parametric Wilcoxon test was used to evaluate differences in abundance of litter items distributed along the different types of bottom.
3. Results 3.1. Abundance, distribution and composition of marine litter The transect durations and video records (Table 1), ranged from 210 min at SVC1 (transect length: 3439 m) to 173 min at SVC3
(transect length: 1936 m). Additional material included 329 HD short video segments ranging from 5 s. to 9 min. A total of 115 litter items were observed in the video records from the three dives performed in the surveyed area. The observed marine litter had an erratic distribution along the ROV track and in only one occasion we found a small aggregation of litter (4 items in total), with plastic bags entangled in a lost fishing net. Overall, lost fishing gear (ropes, lines and nets) accounted for the vast majority of litter items present on the seafloor in all stations surveyed, with fishing ropes (40.0%) and lines (37.4%) being the main component of litter. Lost fishing nets represented 11.3% of the observed litter while Glass, Ceramics, Metal and Plastic were less frequent, and combined represented only 11.3% of the total items recorded (Fig. 2). The video records from the shallower station showed the highest abundance of litter. Despite being the shortest transect, in SVC3 station we found 55.7% of all litter items observed and of these, 97% were fishing related (60 items). Lost fishing gear were a less dominant component of litter at the other two stations surveyed but still represented 81% at SVC2 (25 items) and 75% at SVC1 (15 items). Plastic, in the form of plastic bags, was more abundant at SVC2, the deepest station, where 83% (5 items) of all plastic items were observed. Abundance of marine litter ranged from 0.58 items 100 m1 at SVC1 to 3.30 items 100 m1 at SVC3 (Table 1), with a mean (±st.dev.) abundance of 1.67 (±1.44) items 100 m1 considering the three transects. The ROV transects were not focused on any particular type of substrate. The video analysis showed that, in total, a slight higher proportion of soft sediment was surveyed (54.4%). Yet, litter items were more commonly found on rock substrate (80.87% of all items). Track segments over rocky substrate showed a higher mean abundance of litter (2.89 ± 2.22 items 100 m1) compared to segments over soft sediment (0.49 ± 0.15 items 100 m1). This was particularly evident at SVC3 and SVC2, while at SVC1 litter abundance across the different types of sediment was more even (Table 2). However, some components of litter were present in higher numbers over soft sediment, like plastic bags and glass. The abundance of litter items over both types of substrate was not considered significantly different (Wilcoxon test: W = 8, p-value = 0.2).
3.2. Fauna/marine litter interaction Of the total items, 31.0% had no visible impact on the adjacent fauna and were coiled up (fishing lines), stretched across the seafloor (fishing ropes and nets) or entangled in other litter (plastic) (Fig. 3A). In 35.3% of the items observed, no actual damage was perceived despite the items being in physical contact with sessile fauna (mainly Porifera: Geodia sp., Asconema setubalense) (Fig. 3B). Nevertheless, 31.1% of the items caused direct impact, either entangling fauna (27.6% – lines, ropes and nets) or covering portions of the rocky reef (3.5% – nets). Coiled up fishing lines were the primary source of entanglement (Table 3), particularly for tridimensional complex or branching fauna such as the Echinodermata: Astrospartus mediterraneus, Centrostephanus longispinus, Cidaris cidaris, Leptometra cf. celtica or the Cnidaria: Eunicella sp., Antipathella subpinnata, Corallium rubrum, Dendrophyllia cornigera
Table 1 Summary of the remote operated vehicle (ROV) dive transects. Transect length was calculated using ROV tracks excluding off-bottom events. Dive station SVC1 SVC2 SVC3
Latitude 0
Longitude 00
37°06 05.09 N 37°020 29.7400 N 36°590 44.2400 N
0
00
009°07 98.64 W 009°060 76.3100 W 009°060 06.2100 W
Video length (min)
Transect length (m)
Depth interval (m)
Litter items
Litter abundance (items 100 m1)
210 175 173
3439 2738 1936
480–108 553–268 204–93
20 31 64
0.58 1.13 3.31
Please cite this article in press as: Oliveira, F., et al. Marine litter in the upper São Vicente submarine canyon (SW Portugal): Abundance, distribution, composition and fauna interactions. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.060
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F. Oliveira et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
seafloor habitats off California (0–38 items 100 m1) (Watters et al., 2010). The research on marine litter distribution has pointed out that oceanography and geomorphology are the main factors influencing the general distribution of litter in the marine environment (Galgani et al., 1996, 2000; Schlining et al., 2013; Pham et al., 2014a). In our survey the proportion of litter that might have been originated in other areas and transported by currents, such as plastic bags, was very low. We assume that most of the items observed, particularly hook-and-line equipment, were more likely to be lost in the location where they were found. It was evident, however, that the bottom features played an important role in the litter distribution. Complex relief terrain, rocky outcrops, boulders and depressions constitute physical obstacles in the seafloor that favor accumulation (Galgani et al., 1996; Schlining et al., 2013). In the S. Vicente canyon, litter items were more commonly observed over rocky substrates. Mean values of litter abundance on rock were almost six times higher than in the soft sediment. This pattern has already been described by other authors. For instance, in a submersible dive performed in the Planier canyon, Galgani et al. (1996) reported that more than 50% of the observed litter was pilled near rocks. Bauer et al. (2008) and Watters et al. (2010) also observed in their studied regions, a disproportionate occurrence of litter in rock compared to soft sediment. Given its complexity, rock substrate provides numerous places for fishing gear and other litter to become snagged and trapped. Rock habitats support dense aggregations of tridimensional complex sessile fauna (e.g. corals, gorgonians, hydrozoans, bryozoans, sponges), increasing the probability for litter entanglement (Bauer et al., 2008). Furthermore, rocky habitats are associated with several important commercial fish species and consequently are more likely to be targeted by fishermen (Chiappone et al., 2005; Bauer et al., 2008; Angiolillo et al., 2015). As shown by Bauer et al. (2008), the distribution of litter may be influenced by other factors like the levels of activity in a certain area. These authors, while evaluating the incidence of marine litter in a Marine Sanctuary, reported a strong link between boat density and litter abundance and distribution. Similar results were observed in our study, where the highest abundance of litter was recorded in the shallower transect, which is located in the vicinity of what is known among local fisherman as the ‘‘Sagres Bank’’, a common fishing ground were higher fishing activity takes place. The studies of Galgani et al. (1996, 2000), Pham et al. (2014a), Schlining et al. (2013) have demonstrated that the composition of the litter on the seabed is a clue to the litter sources impacting a particular region. In the west Portuguese margin (e.g. Lisboa, Cascais and Setúbal), Mordecai et al. (2011) found that litter composition is dominated by plastic, ranging from 30% at Setúbal to 86% at Lisboa, which the authors attributed to land based sources. Similar results were reported by Galgani et al. (1996) for four
Fig. 2. Components of marine litter (%) found in the sampled stations on the upper S. Vicente canyon. In parenthesis is the total number of litter items.
(Fig. 3C and D). In contrast, only 2.5% of the litter observed was used as shelter (glass bottle) or hard substrate (broken ceramic vase – Fig. 3E), including a net that simultaneously entangled Ophiuroidea on one side while providing a fixation point for hundreds of Leptometra celtica on the other (Fig. 3F).
4. Discussion 4.1. Abundance, distribution and composition of marine litter Video records of the upper S. Vicente canyon revealed the existence of litter in all three stations surveyed. Compared with other canyons in the West Portuguese margin, the upper S. Vicente canyon had a slight higher abundance of litter (1.67 ± 1.44 items 100 m1). Mordecai et al. (2011) reported abundances ranging from 0.083 items 100 m1 in the Nazaré canyon up to 1.32 items 100 m1 in the Lisbon canyon. While our observations may indicate that the S. Vicente canyon is more impacted by human activity, these results can also be influenced by the different depths sampled and the distance to the coast. While our study was limited to the upper canyon (93–553 m depth) approximately 12–17 km from the coast, Mordecai et al. (2011) explored locations as deep as 4574 m and as far as 138 km offshore. Surveys at deeper locations should be conducted to address the issue of how abundant litter is further down the S. Vicente canyon. Marine litter was also more abundant in the upper S. Vicente canyon than what was described for Condor Seamount (0.3 items 100 m1) (Pham et al., 2013) or Gorringe Bank (max. 0.4 items 100 m1) (Vieira et al., in press), more remote locations but where, similarly, fishing gear comprises the majority of litter documented. Nevertheless, mean abundance of litter in the seafloor at S. Vicente was less than the levels reported in other regions of the world, particularly near highly developed and populated coasts, like the canyons off the French Mediterranean coast (0.35–11.23 items 100 m1) (Galgani et al., 1996) or in the deep
Table 2 Abundance of marine litter relative to the type of bottom at each of the stations surveyed. In parenthesis is the proportion of transect with the respective substrate type. Dive station
SVC1
SVC2
SVC3
Substrate type
Rock (51)
Soft sediment (49)
Rock (26)
Soft sediment (74)
Rock (63)
Soft sediment (37)
Litter items Fishing line Net Fishing rope Glass Ceramics Metal Plastic
4 – 2 1 – 1 1
6 1 2 2 – – –
11 1 9 – 1 – 1
– 1 3 – – – 4
21 10 29 – 1 – –
1 – 1 1 – – –
Total
9
11
23
8
61
3
Abundance (items 100 m1)
0.51
0.66
3.25
0.40
4.91
0.41
Please cite this article in press as: Oliveira, F., et al. Marine litter in the upper São Vicente submarine canyon (SW Portugal): Abundance, distribution, composition and fauna interactions. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.060
F. Oliveira et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
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Fig. 3. Marine litter and fauna interactions. (A) Fishing ropes stretched on the seafloor; (B) coiled fishing line in contact with the glass sponge Asconema setubalense showing minor signs of damage on the opposite side; (C) fishing lines entangled in the black coral Antipathella subpinnata; (D) Astrospartus mediterraneus entangled in coiled fishing lines; (E) sponge using a broken ceramic vase as substrate; and (F) accumulation of feather stars Leptometra cf. celtica in the head rope of a lost net.
Table 3 Components of marine litter in number according to their interaction with adjacent fauna. Litter items
No effect
Contact
Entangling
Smothering
Shelter/substrate
Fishing line Net Fishing rope Glass Ceramics Metal Plastic
9
12
22
–
–
1 15
1 28
7 3
4 –
1 –
3 1 1 6
– – – –
– – – –
– – – –
1 1 – –
Total
36
41
32
4
3
canyons located in the French Mediterranean coast (e.g. Cassidaigne, Paillon, Var and Planier), where plastic comprised more than 70% of all litter items encountered. A common feature of all these canyons is the link to densely populated and industrialized areas and major rivers. Far from dense urban centers, in the Nazaré canyon, litter composition was more similar to our results with higher proportions of maritime sourced litter, even though fishing gear only represented 37% of the total litter reported (Mordecai et al., 2011). In our survey, plastic as well as other typically land sourced materials, made up a very small proportion of the total litter. Taking this into account, we suggest that there is little influence of land based litter in this region despite its proximity to the coast. The vast majority of the litter documented is clearly originated from maritime activities. Based on our observations, we can conclude that fishing is the main source of marine litter impacting this particular region. These findings are in agreement
with several studies conducted elsewhere, where commercial or recreational fishing is a key activity and where litter composition is typically dominated by derelict fishing gear (Galgani et al., 2000; Chiappone et al., 2002, 2005; Lee et al., 2006; Bauer et al., 2008; Watters et al., 2010; Pham et al., 2013; Smith and Edgar, 2014; Vieira et al., in press; Angiolillo et al., 2015).
4.2. Fauna/marine litter interaction The main components of the litter found in our survey, appear to be originated from hook-and-line operations (fishing ropes: main lines; fishing lines: snoods). The issue of abandoned, lost or otherwise discarded fishing gear (ALDFG) in the hook-and-line fisheries has been reviewed by Macfadyen et al. (2009). Ghost fishing in the hook-and-line fishery is considered of less concern, because once lost, the gear loses its efficiency in a relative short time (Brown and Macfadyen, 2007). However, this gear may persist in the marine environment and entanglement is considered the major impact. Entanglement of fauna in fishing gear may lead to a series of traumatic effects ranging from abrasion, wounds that lead to infection, starvation, impaired mobility and heightened risk of predation, and in worse cases amputation, strangulation and eventually death (Laist, 1997; Chiappone et al., 2005; Criddle et al., 2009; Gregory, 2009). During our survey in the St. Vincent canyon we did not find evidences of ghost fishing in any of the lost fishing gears observed. Smothering was a rare event caused by small portions of lost nets and physical contact with sessile fauna and entanglement of specimens were the major impacts of ALDFG in the seafloor. While physical contact of the fishing gear with sessile fauna did not cause any visible damage, the long term effect of lines and ropes constant rasping may eventually lead to breakage of ramifications, skin abrasion, open wounds, epibiosis and
Please cite this article in press as: Oliveira, F., et al. Marine litter in the upper São Vicente submarine canyon (SW Portugal): Abundance, distribution, composition and fauna interactions. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.060
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infection. Because of their morphology, gorgonians, erect sponges, corals and colonial zoanthids might be more susceptible to this kind of damage, as observed by Angiolillo et al. (2015). In contrast, entanglement on derelict fishing gear has been reported to cause severe damage in corals, gorgonians and sponges (Bavestrello et al., 1997; Chiappone et al., 2002; Yoshikawa and Asoh, 2004; Pham et al., 2013). In our observations, gorgonians and corals (Octocorallia and Hexacorallia) were also common entangled species, and some showed evident signs of tissue damage and epibiosis of fouling organisms. Yoshikawa and Asoh (2004) suggested that once a coral becomes entangled in a fishing line, there is a high probability of mortality of the colony. Other entangled fauna present in our study, like the Echinodermata, may become entangled on their own while moving on the seafloor or scavenging for food, but since they are mobile it is plausible that they might be able to escape with only minor distress. The impact of the hook-and-line fishery is generally perceived as having less damaging effects in the environment when compared with other fishing methodologies, such as trawls, nets, traps and pots (George et al., 2007; Macfadyen et al., 2009; Puig et al., 2012; Pham et al., 2014b). In fact, in a scuba survey conducted in the Florida Keys National Marine Sanctuary, Chiappone et al. (2005) concluded that while lost hook-and-line gear is widespread in the region, the damage to shallow reef sessile invertebrates is considered minor (affecting less than 0.5% of total densities). Yet, the cumulative effects of this gear over time might be more harmful, mainly because of its extensive use, often extremely long configuration and low cost (Macfadyen et al., 2009). For example, in the south coast of Portugal, commercial longliners may fish a long-line with 900–8000 hooks spaced 1.5–3.0 m apart depending on the size of the fishing vessel (Gonçalves, 2000; Erzini et al., 2001; Coelho and Erzini, 2008). Also, as discussed earlier, the hook-and-line fishery generally operates in high relief terrain, increasing the probability of impact on slow growth, sensitive sessile fauna that use hard substrate as habitat (Watters et al., 2010; Schlining et al., 2013). Some types of litter may however provide suitable substrate for some species (Katsanevakis et al., 2007; Watters et al., 2010; Mordecai et al., 2011; Gomes-Pereira et al., 2012; Schlining et al., 2013; Angiolillo et al., 2015). In our study, we observed a net stretched over soft bottom that provided a fixation point for an unusual concentration of the feather star Leptometra cf. celtica. Slightly above the seafloor these filter feeder organisms were apparently in a advantageous position to gather food from the bottom currents. Over time, the natural processes of colonization of lost fishing gear may also reduce its impact on the seafloor. Some authors have stated that, at some extent, this type of litter might be integrated into the habitat. Lost hook-and-line can be overgrown by Porifera (Chiappone et al., 2002, 2005) and even ‘ghost’ gill and trammel nets and traps can be heavily colonized by algae and invertebrates in less than one year (Erzini et al., 1997, 2008), eventually becoming incorporated into the reef. The São Vicente canyon and adjacent area are important fishing grounds for both artisanal and commercial fishing fleets. Our observations suggest that this activity is the main contributor of litter impacting this region. Because the majority of the modern fishing gear is made of highly durable synthetic materials, if lost, it will persist in the environment for many years, in particular in the deep sea where it is protected from degradation processes. Unless appropriate measures are set to prevent or avoid gear loss, such as those recommended by Macfadyen et al. (2009), the abundance of this type of litter in the region is only likely to increase. All EU member states are required to take action to achieve good environmental status (GES) for the marine environment by 2020, under the Marine Strategy Framework Directive (2008/56/EC) (MSFD). The data presented here will contribute to
a better evaluation of the reference ecological status at national level, since mapping the distribution and identifying the composition and sources of marine litter is one of the criteria (10.1.2), under the Descriptor 10, for determining GES of European marine waters. Acknowledgements This work was carried out under the OCEANA Ranger Expedition 2011 – Heading Toward Seamounts and by the MeshAtlantic project – Mapping Atlantic Area seabed habitats for better marine management, www.meshatlantic.eu (UE–ERDF ‘Atlantic Area 2007-2013’ program). References Alves, T.M., Gawthorpe, R.L., Hunt, D.W., Monteiro, J.H., 2003. Cenozoic tectonosedimentary evolution of the western Iberian margin. Mar. Geol. 195, 75–108. Angiolillo, M., Lorenzo, B., Farcomeni, A., Bo, M., Bavestrello, G., Santangelo, G., Cau, A., Mastascusa, V., Cau, A., Sacco, F., Canese, S., 2015. Distribution and assessment of marine debris in the deep Tyrrhenian Sea (NW Mediterranean Sea, Italy). Mar. Pollut. Bull. 92, 149–159. 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Marine litter in the upper São Vicente submarine canyon (SW Portugal): Abundance, distribution, composition and fauna interactions Frederico Oliveira a,⇑, Pedro Monteiro a, Luis Bentes a, Nuno Sales Henriques a, Ricardo Aguilar b, Jorge M.S. Gonçalves a a b
Centre of Marine Sciences, CCMAR, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal OCEANA, Plaza España, Leganitos, 47, 28013 Madrid, Spain
a r t i c l e
i n f o
Article history: Received 17 March 2015 Revised 18 May 2015 Accepted 21 May 2015 Available online xxxx Keywords: S. Vicente Canyon ROV Litter Fishing gear Hook-and-line
a b s t r a c t Marine litter has become a worldwide environmental problem, tainting all ocean habitats. The abundance, distribution and composition of litter and its interactions with fauna were evaluated in the upper S. Vicente canyon using video images from 3 remote operated vehicle exploratory dives. Litter was present in all dives and the abundance was as high as 3.31 items 100 m1. Mean abundance of litter over rock bottom was higher than on soft substrate. Mean litter abundance was slightly higher than reported for other canyons on the Portuguese margin, but lower in comparison to more urbanized coastal areas of the world. Lost fishing gear was the prevalent type of litter, indicating that the majority of litter originates from maritime sources, mainly fishing activity. Physical contact with sessile fauna and entanglement of specimens were the major impacts of lost fishing gear. Based on the importance of this region for the local fishermen, litter abundance is expected to increase. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Marine litter has become ubiquitous in all oceans. From the most remote and inaccessible regions of the planet (e.g. Ryan and Moloney, 1993; Benton, 1995; Convey et al., 2002; Bergmann and Klages, 2012) to more common recreational beaches (e.g. Moore et al., 2001; Nagelkerken et al., 2001; Oigman-Pszczol and Creed, 2007; Ariza et al., 2008; Corcoran et al., 2009) marine litter has been accounted in all types, shapes and sizes. Marine litter composition is highly variable, ranging from microscopic plastic particles and fibers (Thompson et al., 2004; Martins and Sobral, 2011; Frias et al., 2014) to more visible items such as boat wrecks (Galgani et al., 1996), oil drums (Watters et al., 2010; Ramirez-Llodra et al., 2011; Schlining et al., 2013) and even radioactive waste containers (Calmet, 1989; Thiel, 2003). Nevertheless plastic, mainly due to its everyday use and high durability, is typically the major constituent of litter found in the marine environment, even in the deep sea (Galgani et al., 1996, 2000; Ryan et al., 2009; Schlining et al., 2013). Though strong currents and winds may transport litter, particularly the more buoyant, far away from its original source, marine
⇑ Corresponding author. E-mail address: [email protected] (F. Oliveira).
litter will eventually sink to amass in the deep sea. Accumulation occurs in areas of complex geomorphology and where hydrodynamic conditions are more favorable, such is the case of submarine canyons (Galgani et al., 1995, 1996, 2000; Mordecai et al., 2011; Schlining et al., 2013; Pham et al., 2014a). Submarine canyons often act as natural traps, deposits and transport pathways of particles from the shelf to the abyssal plains (Granata et al., 1999; Oliveira et al., 2007; Turchetto et al., 2007) and this same role as been described for marine litter (Galgani et al., 1996; Ramirez-Llodra et al., 2011; Schlining et al., 2013). In the Iberian west coast several major submarine canyons cut across the continental margin: the Mugía, Arosa, Porto, Aveiro, Lisboa, Setúbal, and S. Vicente Canyons (Peliz and Fiúza, 1999). The submarine canyons located off the north-western section of the Portuguese coast have been the subject of research in past years, with research programmes and multidisciplinary projects: OMEX II (1997–2000), EUROSTRATAFORM (van Weering and Weaver, 2007), HERMES (Weaver and Gunn, 2009) and HERMIONE (Weaver et al., 2009) focusing on oceanography, geology and biology of these ecosystems. Under the scope of these later projects, abundance and distribution of marine litter was also studied by Mordecai et al. (2011). Information regarding the canyons located in the south and south-western portions of the Portuguese margin is more limited, and the few studies conducted in the area focus primarily on geology.
http://dx.doi.org/10.1016/j.marpolbul.2015.05.060 0025-326X/Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Oliveira, F., et al. Marine litter in the upper São Vicente submarine canyon (SW Portugal): Abundance, distribution, composition and fauna interactions. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.060
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Using underwater video records taken during exploratory surveys, the present study aims to quantify the abundance, distribution and composition of marine litter across the upper section of São Vicente canyon, and describe visible effects of marine litter on the surrounding fauna. 2. Material and methods 2.1. Study area The study area is located in the southwest coast of Portugal, a mesotidal moderately exposed Atlantic coast (Monteiro et al., in press) with a narrow and steep continental shelf (Peliz and Fiúza, 1999; Relvas and Barton, 2002) and a gentle slope (Alves et al., 2003). The São Vicente submarine canyon, with its head scarp at 70 m below sea level, is one of the major geomorphological features incising this section of the continental shelf and slope (Terrinha et al., 2009). Located approximately 12 km offshore mainland Portugal (Fig. 1), the canyon is shaped as a wide, 120 km long corridor following a NE–SW orientation, aligned with the Odemira–Ávila fault, connecting the Alentejo margin to the Horseshoe Abyssal Plain (Alves et al., 2003; Terrinha et al., 2009). 2.1.1. Oceanography The ocean circulation patterns in the region are complex and seasonal. Relvas et al. (2007) gives a detailed description of the different mechanisms and interactions affecting the local oceanography. In brief: during the winter season, starting in September– October, dominant winds are mainly westerly and southerly. Slope circulation is typically dominated by a poleward current (transporting warm and saline water), until the spring transition in April–May, when the northerly winds prevail. This current does not influence the shelf except during particular events. According to Relvas and Barton (2002), coastal circulation depends on wind stress and the pressure gradient along the shore, and their relationship determines the direction and strength of the circulation. Wind-induced upwelling conditions in late spring are observed episodically when favorable winds occur (Peliz and Fiúza, 1999; Relvas et al., 2007).
2.1.2. Sources of land based litter – urban centers and rivers Most of the land section of the southwest Portuguese coast was designated Protected Landscape in 1988, and in 1995, a Natural Park was created (Parque Natural do Sudoeste Alentejano e Costa Vicentina), including a 2 km wide marine strip along its entire length (Castro and Cruz, 2009). Relatively far from major urban centers and with a small resident population concentrated in small towns and villages, low anthropogenic impacts are expected in the area, with minor levels of sewage and agricultural run-off being the major sources of land based pollution in the adjacent coastal waters. The São Vicente submarine canyon is not fed by any major river course and along the coastline the fresh water inputs are limited to small rivers and streams. 2.1.3. Sources of marine based litter – fishing and other maritime activities Off the southwest coast of Portugal there are important fishing grounds for local artisanal and industrial fleets operating different metiers targeting several species: surface and deep water longlines, purse-seine, gill nets, trammel nets, pots and traps, finfish and crustacean bottom trawls (Erzini et al., 1996; Gonçalves and Erzini, 1998; Galhardo et al., 2006; Campos et al., 2007; Coelho and Erzini, 2008). This area is also part of important maritime corridors linking the Mediterranean and North Africa to Northern Europe. Since 2008, a Vessel Traffic Service (VTS) system has been monitoring the maritime traffic to 50 miles offshore mainland Portugal with an average of 800 vessels being tracked daily (MAMAOT, 2012). Taking as a reference the year 2010, the VTS system registered 11.3 thousand merchant ships crossing the Portuguese waters (MAMAOT, 2012). 2.2. Survey The analysis of litter abundance and composition in the upper São Vicente submarine canyon was based on three exploratory remote operated vehicle (ROV) dives performed in June 2011 by the NGO Oceana (Fig. 1). The ROV platform, a Saab Seaeye Falcon DR rated 1000 m, was equipped with two forward facing color
Fig. 1. Location of the dive transects in S. Vicente canyon (SW coast of Portugal). Red lines correspond to the track of each dive performed during the survey. Isobaths represent 50 m depth intervals. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Please cite this article in press as: Oliveira, F., et al. Marine litter in the upper São Vicente submarine canyon (SW Portugal): Abundance, distribution, composition and fauna interactions. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.060
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cameras. The primary camera (standard definition: 480 TV lines, 0.2 lux) fixed to a tilt mount was continuously recorded. The secondary camera (high definition: 1080i) mounted under the first, was equipped with zoom and would allow real-time observation. Transects were performed at constant speed of 0.2/0.3 knots and whenever possible maintaining 50 cm or less above ground. The navigation data were acquired from the Ultra Short BaseLine (USBL) system (Linkquest TN1510AH with accuracy up to 0.25°) and included date, local time, latitude and longitude. All navigation track data were post-processed and smoothed with moving average. 2.2.1. Video analysis Each dive was considered a single continuous transect. ROV maneuvres that caused loss of bottom image were considered off-bottom events and the correspondent track segments were excluded from the total transect length and additional analysis. The video recordings collected during the ROV dives were annotated thoroughly for the presence of marine litter, litter/fauna interactions, as well as the dominant type of bottom. Video annotation was performed using the COVER software (Customizable Observation Video Image Recorder, v0.7.2; Carré, 2010). Observed litter items were classified according to their characteristics in the following categories: ‘Fishing line’, ‘Net’, ‘Fishing rope’, ‘Glass’, ‘Ceramics’, ‘Metal’ and ‘Plastic’. While most of the modern fishing gear is made of plastic (Brown and Macfadyen, 2007), we considered these items as different categories following Pham et al. (2014a) rationale: ‘‘because of our knowledge on its source and social implications and the particular impacts of this type of litter, such as ghost fishing and entanglement’’. Classified litter items were then categorized regarding their visible impact on the surrounding fauna as: ‘No effect’, ‘Contact’, ‘Entangling’, ‘Smothering’ and ‘Shelter/Substrate’. 2.2.2. Abundance and distribution of marine litter Since the purpose of Oceana’s ROV dives were mainly a documentation of the faunal communities, the ROV lacked scaling systems on which we could accurately determine the area sampled. Therefore, and given the nature of the transects, we did not calculate densities and instead recorded occurrences along the ROV track. The number of items recorded on each dive would later be divided by the respective track length as a measure of abundance that could be comparable with other studies (items 100 m1). Additionally, using GIS software, it was possible to georeference each occurrence of litter across the ocean floor. Because of the nature of the data collected (few replicates and non-normally distributed data), the non-parametric Wilcoxon test was used to evaluate differences in abundance of litter items distributed along the different types of bottom.
3. Results 3.1. Abundance, distribution and composition of marine litter The transect durations and video records (Table 1), ranged from 210 min at SVC1 (transect length: 3439 m) to 173 min at SVC3
(transect length: 1936 m). Additional material included 329 HD short video segments ranging from 5 s. to 9 min. A total of 115 litter items were observed in the video records from the three dives performed in the surveyed area. The observed marine litter had an erratic distribution along the ROV track and in only one occasion we found a small aggregation of litter (4 items in total), with plastic bags entangled in a lost fishing net. Overall, lost fishing gear (ropes, lines and nets) accounted for the vast majority of litter items present on the seafloor in all stations surveyed, with fishing ropes (40.0%) and lines (37.4%) being the main component of litter. Lost fishing nets represented 11.3% of the observed litter while Glass, Ceramics, Metal and Plastic were less frequent, and combined represented only 11.3% of the total items recorded (Fig. 2). The video records from the shallower station showed the highest abundance of litter. Despite being the shortest transect, in SVC3 station we found 55.7% of all litter items observed and of these, 97% were fishing related (60 items). Lost fishing gear were a less dominant component of litter at the other two stations surveyed but still represented 81% at SVC2 (25 items) and 75% at SVC1 (15 items). Plastic, in the form of plastic bags, was more abundant at SVC2, the deepest station, where 83% (5 items) of all plastic items were observed. Abundance of marine litter ranged from 0.58 items 100 m1 at SVC1 to 3.30 items 100 m1 at SVC3 (Table 1), with a mean (±st.dev.) abundance of 1.67 (±1.44) items 100 m1 considering the three transects. The ROV transects were not focused on any particular type of substrate. The video analysis showed that, in total, a slight higher proportion of soft sediment was surveyed (54.4%). Yet, litter items were more commonly found on rock substrate (80.87% of all items). Track segments over rocky substrate showed a higher mean abundance of litter (2.89 ± 2.22 items 100 m1) compared to segments over soft sediment (0.49 ± 0.15 items 100 m1). This was particularly evident at SVC3 and SVC2, while at SVC1 litter abundance across the different types of sediment was more even (Table 2). However, some components of litter were present in higher numbers over soft sediment, like plastic bags and glass. The abundance of litter items over both types of substrate was not considered significantly different (Wilcoxon test: W = 8, p-value = 0.2).
3.2. Fauna/marine litter interaction Of the total items, 31.0% had no visible impact on the adjacent fauna and were coiled up (fishing lines), stretched across the seafloor (fishing ropes and nets) or entangled in other litter (plastic) (Fig. 3A). In 35.3% of the items observed, no actual damage was perceived despite the items being in physical contact with sessile fauna (mainly Porifera: Geodia sp., Asconema setubalense) (Fig. 3B). Nevertheless, 31.1% of the items caused direct impact, either entangling fauna (27.6% – lines, ropes and nets) or covering portions of the rocky reef (3.5% – nets). Coiled up fishing lines were the primary source of entanglement (Table 3), particularly for tridimensional complex or branching fauna such as the Echinodermata: Astrospartus mediterraneus, Centrostephanus longispinus, Cidaris cidaris, Leptometra cf. celtica or the Cnidaria: Eunicella sp., Antipathella subpinnata, Corallium rubrum, Dendrophyllia cornigera
Table 1 Summary of the remote operated vehicle (ROV) dive transects. Transect length was calculated using ROV tracks excluding off-bottom events. Dive station SVC1 SVC2 SVC3
Latitude 0
Longitude 00
37°06 05.09 N 37°020 29.7400 N 36°590 44.2400 N
0
00
009°07 98.64 W 009°060 76.3100 W 009°060 06.2100 W
Video length (min)
Transect length (m)
Depth interval (m)
Litter items
Litter abundance (items 100 m1)
210 175 173
3439 2738 1936
480–108 553–268 204–93
20 31 64
0.58 1.13 3.31
Please cite this article in press as: Oliveira, F., et al. Marine litter in the upper São Vicente submarine canyon (SW Portugal): Abundance, distribution, composition and fauna interactions. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.060
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seafloor habitats off California (0–38 items 100 m1) (Watters et al., 2010). The research on marine litter distribution has pointed out that oceanography and geomorphology are the main factors influencing the general distribution of litter in the marine environment (Galgani et al., 1996, 2000; Schlining et al., 2013; Pham et al., 2014a). In our survey the proportion of litter that might have been originated in other areas and transported by currents, such as plastic bags, was very low. We assume that most of the items observed, particularly hook-and-line equipment, were more likely to be lost in the location where they were found. It was evident, however, that the bottom features played an important role in the litter distribution. Complex relief terrain, rocky outcrops, boulders and depressions constitute physical obstacles in the seafloor that favor accumulation (Galgani et al., 1996; Schlining et al., 2013). In the S. Vicente canyon, litter items were more commonly observed over rocky substrates. Mean values of litter abundance on rock were almost six times higher than in the soft sediment. This pattern has already been described by other authors. For instance, in a submersible dive performed in the Planier canyon, Galgani et al. (1996) reported that more than 50% of the observed litter was pilled near rocks. Bauer et al. (2008) and Watters et al. (2010) also observed in their studied regions, a disproportionate occurrence of litter in rock compared to soft sediment. Given its complexity, rock substrate provides numerous places for fishing gear and other litter to become snagged and trapped. Rock habitats support dense aggregations of tridimensional complex sessile fauna (e.g. corals, gorgonians, hydrozoans, bryozoans, sponges), increasing the probability for litter entanglement (Bauer et al., 2008). Furthermore, rocky habitats are associated with several important commercial fish species and consequently are more likely to be targeted by fishermen (Chiappone et al., 2005; Bauer et al., 2008; Angiolillo et al., 2015). As shown by Bauer et al. (2008), the distribution of litter may be influenced by other factors like the levels of activity in a certain area. These authors, while evaluating the incidence of marine litter in a Marine Sanctuary, reported a strong link between boat density and litter abundance and distribution. Similar results were observed in our study, where the highest abundance of litter was recorded in the shallower transect, which is located in the vicinity of what is known among local fisherman as the ‘‘Sagres Bank’’, a common fishing ground were higher fishing activity takes place. The studies of Galgani et al. (1996, 2000), Pham et al. (2014a), Schlining et al. (2013) have demonstrated that the composition of the litter on the seabed is a clue to the litter sources impacting a particular region. In the west Portuguese margin (e.g. Lisboa, Cascais and Setúbal), Mordecai et al. (2011) found that litter composition is dominated by plastic, ranging from 30% at Setúbal to 86% at Lisboa, which the authors attributed to land based sources. Similar results were reported by Galgani et al. (1996) for four
Fig. 2. Components of marine litter (%) found in the sampled stations on the upper S. Vicente canyon. In parenthesis is the total number of litter items.
(Fig. 3C and D). In contrast, only 2.5% of the litter observed was used as shelter (glass bottle) or hard substrate (broken ceramic vase – Fig. 3E), including a net that simultaneously entangled Ophiuroidea on one side while providing a fixation point for hundreds of Leptometra celtica on the other (Fig. 3F).
4. Discussion 4.1. Abundance, distribution and composition of marine litter Video records of the upper S. Vicente canyon revealed the existence of litter in all three stations surveyed. Compared with other canyons in the West Portuguese margin, the upper S. Vicente canyon had a slight higher abundance of litter (1.67 ± 1.44 items 100 m1). Mordecai et al. (2011) reported abundances ranging from 0.083 items 100 m1 in the Nazaré canyon up to 1.32 items 100 m1 in the Lisbon canyon. While our observations may indicate that the S. Vicente canyon is more impacted by human activity, these results can also be influenced by the different depths sampled and the distance to the coast. While our study was limited to the upper canyon (93–553 m depth) approximately 12–17 km from the coast, Mordecai et al. (2011) explored locations as deep as 4574 m and as far as 138 km offshore. Surveys at deeper locations should be conducted to address the issue of how abundant litter is further down the S. Vicente canyon. Marine litter was also more abundant in the upper S. Vicente canyon than what was described for Condor Seamount (0.3 items 100 m1) (Pham et al., 2013) or Gorringe Bank (max. 0.4 items 100 m1) (Vieira et al., in press), more remote locations but where, similarly, fishing gear comprises the majority of litter documented. Nevertheless, mean abundance of litter in the seafloor at S. Vicente was less than the levels reported in other regions of the world, particularly near highly developed and populated coasts, like the canyons off the French Mediterranean coast (0.35–11.23 items 100 m1) (Galgani et al., 1996) or in the deep
Table 2 Abundance of marine litter relative to the type of bottom at each of the stations surveyed. In parenthesis is the proportion of transect with the respective substrate type. Dive station
SVC1
SVC2
SVC3
Substrate type
Rock (51)
Soft sediment (49)
Rock (26)
Soft sediment (74)
Rock (63)
Soft sediment (37)
Litter items Fishing line Net Fishing rope Glass Ceramics Metal Plastic
4 – 2 1 – 1 1
6 1 2 2 – – –
11 1 9 – 1 – 1
– 1 3 – – – 4
21 10 29 – 1 – –
1 – 1 1 – – –
Total
9
11
23
8
61
3
Abundance (items 100 m1)
0.51
0.66
3.25
0.40
4.91
0.41
Please cite this article in press as: Oliveira, F., et al. Marine litter in the upper São Vicente submarine canyon (SW Portugal): Abundance, distribution, composition and fauna interactions. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.060
F. Oliveira et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
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Fig. 3. Marine litter and fauna interactions. (A) Fishing ropes stretched on the seafloor; (B) coiled fishing line in contact with the glass sponge Asconema setubalense showing minor signs of damage on the opposite side; (C) fishing lines entangled in the black coral Antipathella subpinnata; (D) Astrospartus mediterraneus entangled in coiled fishing lines; (E) sponge using a broken ceramic vase as substrate; and (F) accumulation of feather stars Leptometra cf. celtica in the head rope of a lost net.
Table 3 Components of marine litter in number according to their interaction with adjacent fauna. Litter items
No effect
Contact
Entangling
Smothering
Shelter/substrate
Fishing line Net Fishing rope Glass Ceramics Metal Plastic
9
12
22
–
–
1 15
1 28
7 3
4 –
1 –
3 1 1 6
– – – –
– – – –
– – – –
1 1 – –
Total
36
41
32
4
3
canyons located in the French Mediterranean coast (e.g. Cassidaigne, Paillon, Var and Planier), where plastic comprised more than 70% of all litter items encountered. A common feature of all these canyons is the link to densely populated and industrialized areas and major rivers. Far from dense urban centers, in the Nazaré canyon, litter composition was more similar to our results with higher proportions of maritime sourced litter, even though fishing gear only represented 37% of the total litter reported (Mordecai et al., 2011). In our survey, plastic as well as other typically land sourced materials, made up a very small proportion of the total litter. Taking this into account, we suggest that there is little influence of land based litter in this region despite its proximity to the coast. The vast majority of the litter documented is clearly originated from maritime activities. Based on our observations, we can conclude that fishing is the main source of marine litter impacting this particular region. These findings are in agreement
with several studies conducted elsewhere, where commercial or recreational fishing is a key activity and where litter composition is typically dominated by derelict fishing gear (Galgani et al., 2000; Chiappone et al., 2002, 2005; Lee et al., 2006; Bauer et al., 2008; Watters et al., 2010; Pham et al., 2013; Smith and Edgar, 2014; Vieira et al., in press; Angiolillo et al., 2015).
4.2. Fauna/marine litter interaction The main components of the litter found in our survey, appear to be originated from hook-and-line operations (fishing ropes: main lines; fishing lines: snoods). The issue of abandoned, lost or otherwise discarded fishing gear (ALDFG) in the hook-and-line fisheries has been reviewed by Macfadyen et al. (2009). Ghost fishing in the hook-and-line fishery is considered of less concern, because once lost, the gear loses its efficiency in a relative short time (Brown and Macfadyen, 2007). However, this gear may persist in the marine environment and entanglement is considered the major impact. Entanglement of fauna in fishing gear may lead to a series of traumatic effects ranging from abrasion, wounds that lead to infection, starvation, impaired mobility and heightened risk of predation, and in worse cases amputation, strangulation and eventually death (Laist, 1997; Chiappone et al., 2005; Criddle et al., 2009; Gregory, 2009). During our survey in the St. Vincent canyon we did not find evidences of ghost fishing in any of the lost fishing gears observed. Smothering was a rare event caused by small portions of lost nets and physical contact with sessile fauna and entanglement of specimens were the major impacts of ALDFG in the seafloor. While physical contact of the fishing gear with sessile fauna did not cause any visible damage, the long term effect of lines and ropes constant rasping may eventually lead to breakage of ramifications, skin abrasion, open wounds, epibiosis and
Please cite this article in press as: Oliveira, F., et al. Marine litter in the upper São Vicente submarine canyon (SW Portugal): Abundance, distribution, composition and fauna interactions. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.060
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infection. Because of their morphology, gorgonians, erect sponges, corals and colonial zoanthids might be more susceptible to this kind of damage, as observed by Angiolillo et al. (2015). In contrast, entanglement on derelict fishing gear has been reported to cause severe damage in corals, gorgonians and sponges (Bavestrello et al., 1997; Chiappone et al., 2002; Yoshikawa and Asoh, 2004; Pham et al., 2013). In our observations, gorgonians and corals (Octocorallia and Hexacorallia) were also common entangled species, and some showed evident signs of tissue damage and epibiosis of fouling organisms. Yoshikawa and Asoh (2004) suggested that once a coral becomes entangled in a fishing line, there is a high probability of mortality of the colony. Other entangled fauna present in our study, like the Echinodermata, may become entangled on their own while moving on the seafloor or scavenging for food, but since they are mobile it is plausible that they might be able to escape with only minor distress. The impact of the hook-and-line fishery is generally perceived as having less damaging effects in the environment when compared with other fishing methodologies, such as trawls, nets, traps and pots (George et al., 2007; Macfadyen et al., 2009; Puig et al., 2012; Pham et al., 2014b). In fact, in a scuba survey conducted in the Florida Keys National Marine Sanctuary, Chiappone et al. (2005) concluded that while lost hook-and-line gear is widespread in the region, the damage to shallow reef sessile invertebrates is considered minor (affecting less than 0.5% of total densities). Yet, the cumulative effects of this gear over time might be more harmful, mainly because of its extensive use, often extremely long configuration and low cost (Macfadyen et al., 2009). For example, in the south coast of Portugal, commercial longliners may fish a long-line with 900–8000 hooks spaced 1.5–3.0 m apart depending on the size of the fishing vessel (Gonçalves, 2000; Erzini et al., 2001; Coelho and Erzini, 2008). Also, as discussed earlier, the hook-and-line fishery generally operates in high relief terrain, increasing the probability of impact on slow growth, sensitive sessile fauna that use hard substrate as habitat (Watters et al., 2010; Schlining et al., 2013). Some types of litter may however provide suitable substrate for some species (Katsanevakis et al., 2007; Watters et al., 2010; Mordecai et al., 2011; Gomes-Pereira et al., 2012; Schlining et al., 2013; Angiolillo et al., 2015). In our study, we observed a net stretched over soft bottom that provided a fixation point for an unusual concentration of the feather star Leptometra cf. celtica. Slightly above the seafloor these filter feeder organisms were apparently in a advantageous position to gather food from the bottom currents. Over time, the natural processes of colonization of lost fishing gear may also reduce its impact on the seafloor. Some authors have stated that, at some extent, this type of litter might be integrated into the habitat. Lost hook-and-line can be overgrown by Porifera (Chiappone et al., 2002, 2005) and even ‘ghost’ gill and trammel nets and traps can be heavily colonized by algae and invertebrates in less than one year (Erzini et al., 1997, 2008), eventually becoming incorporated into the reef. The São Vicente canyon and adjacent area are important fishing grounds for both artisanal and commercial fishing fleets. Our observations suggest that this activity is the main contributor of litter impacting this region. Because the majority of the modern fishing gear is made of highly durable synthetic materials, if lost, it will persist in the environment for many years, in particular in the deep sea where it is protected from degradation processes. Unless appropriate measures are set to prevent or avoid gear loss, such as those recommended by Macfadyen et al. (2009), the abundance of this type of litter in the region is only likely to increase. All EU member states are required to take action to achieve good environmental status (GES) for the marine environment by 2020, under the Marine Strategy Framework Directive (2008/56/EC) (MSFD). The data presented here will contribute to
a better evaluation of the reference ecological status at national level, since mapping the distribution and identifying the composition and sources of marine litter is one of the criteria (10.1.2), under the Descriptor 10, for determining GES of European marine waters. Acknowledgements This work was carried out under the OCEANA Ranger Expedition 2011 – Heading Toward Seamounts and by the MeshAtlantic project – Mapping Atlantic Area seabed habitats for better marine management, www.meshatlantic.eu (UE–ERDF ‘Atlantic Area 2007-2013’ program). References Alves, T.M., Gawthorpe, R.L., Hunt, D.W., Monteiro, J.H., 2003. Cenozoic tectonosedimentary evolution of the western Iberian margin. Mar. Geol. 195, 75–108. Angiolillo, M., Lorenzo, B., Farcomeni, A., Bo, M., Bavestrello, G., Santangelo, G., Cau, A., Mastascusa, V., Cau, A., Sacco, F., Canese, S., 2015. Distribution and assessment of marine debris in the deep Tyrrhenian Sea (NW Mediterranean Sea, Italy). Mar. Pollut. Bull. 92, 149–159. Ariza, E., Sardé, R., Jiménez, J., Mora, J., Ávila, C., 2008. Beyond performance assessment measurements for beach management: application to Spanish Mediterranean beaches. Coast. Manage. 36, 47–66. Bauer, L.J., Kendall, M.S., Jeffrey, C.F.G., 2008. Incidence of marine debris and its relationships with benthic features in Gray’s Reef National Marine Sanctuary, Southeast USA. Mar. Pollut. Bull. 56, 402–413. Bavestrello, G., Cerrano, C., Zanzi, D., Cattaneo-Vietti, R., 1997. Damage by fishing activities to the gorgonian coral Paramuricea clavata in the Ligurian Sea. Aquat. Conserv.: Mar. Freshwater Ecosyst. 7, 253–262. Benton, T.G., 1995. From castaways to throwaways: marine litter in the Pitcairn Islands. Biol. J. Linn. Soc. 56, 415–422. Bergmann, M., Klages, M., 2012. Increase of litter at the Arctic deep-sea observatory HAUSGARTEN. Mar. Pollut. Bull. 64, 2734–2741. Brown, J., Macfadyen, G., 2007. Ghost fishing in European waters: impacts and management responses. Mar. Pol. 31 (4), 488–504. Calmet, C., 1989. Ocean Disposal of Radioactive Waste: Status Report. IAEA Bulletin, 4/1989.
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Please cite this article in press as: Oliveira, F., et al. Marine litter in the upper São Vicente submarine canyon (SW Portugal): Abundance, distribution, composition and fauna interactions. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.060