Acoustic mapping of fish aggregation areas to improve fisheries management in Las Perlas Archipelago, Pacific Panama

Ocean & Coastal Management 53 (2010) 615e623

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Acoustic mapping of fish aggregation areas to improve fisheries management in Las Perlas Archipelago, Pacific Panama Sarah J.M. Harper a,1, C. Richard Bates b, Hector M. Guzman c, James M. Mair a, * a

School of Life Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK Department of Earth Sciences, University of St Andrews, St Andrews KY16 9AL, UK c Smithsonian Tropical Research Institute, MRC 0580-08, Box 0843-03092, Panama b

a r t i c l e i n f o

a b s t r a c t

Article history: Available online 19 August 2010

The purpose of this study was to investigate, characterize and map areas of the seabed of Las Perlas Archipelago (LPA), Republic of Panama using swath-bathymetry acoustic sonar techniques and to assess these methods as tools for feeding information into management zoning policy. In 2007 the LPA was granted conservation protection under national legislation. However, detailed management plans are still pending. Seabed mapping plays a fundamental role in identifying areas which should be prioritized within the management framework. Visual representation of habitat maps provides an effective medium for involving stakeholders in a co-management arena. In this survey, acoustically mapped areas of the seabed were ground-truthed using a combination of benthic grab samples, drop-down video and diver observations. The resulting mapped areas were then incorporated into a Geographic Information System (GIS) for further analysis. The output was a physical characterization of the seabed at three locations selected for being areas of high rugosity (habitat complexity) and, therefore, their potential importance as valuable fish aggregation sites. The rocky reefs and rhodolith beds identified in this survey represent particularly important fish aggregation and nursery habitats which should be considered priorities for protection under the management plans. This survey demonstrated the use of acoustic techniques to spatially resolve topographic features and physical characteristics of the seabed, illustrating their potential value as tools for fisheries management and marine reserve zoning in Las Perlas Archipelago and elsewhere. Ó 2010 Elsevier Ltd. All rights reserved.

1. Introduction Increasing global concern over anthropogenic pressure on the marine environment has driven resource managers and policy makers to seek out applicable tools for designating and protecting threatened habitats. Effective ocean management requires a detailed understanding of the spatial distribution of species and habitats [1]. Until recently, knowledge of seafloor characteristics such as the location of small-scale geological features and the distribution of biotic habitats has been quite limited. Marine surveys have traditionally involved sampling at discrete locations and then extrapolating between sample points to map out the seafloor [2]. * Corresponding author. Centre for Marine Biodiversity and Biotechnology, School of Life Sciences, Heriot-Watt University, John Muir Building, Edinburgh, Scotland EH14 4AS, UK. Tel.: þ44 131 451 3314; fax: þ44 131 451 3009. E-mail address: [email protected] (J.M. Mair). 1 Permanent address: Fisheries Centre, Aquatic Ecosystems Research Laboratory (AERL), 2202 Main Mall, The University of British Columbia, Vancouver, BC, Canada. Tel.: þ1 604 822 2731. 0964-5691/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.ocecoaman.2010.07.001

While this method contributes to our understanding of the marine environment, it only provides a snapshot, covering but a fraction of the actual seafloor area. Advances in remote sensing are improving coverage by providing more detailed maps than were previously possible through traditional sampling methods [3]. Optical remote sensing is widely used as a tool for mapping coastal environments but can only capture the uppermost regions of the ocean [4,5]. Acoustic remote sensing is starting to fill this gap by allowing researchers to produce detailed habitat maps of deeper seafloor regions [6e8]. Modern multibeam bathymetric and sidescan sonar systems can be used to survey wide areas of the seafloor, thus mapping benthic communities and identifying vulnerable or sensitive habitats such as coral reefs [8e10]. As a management tool, habitat maps are fundamental for the designation of marine reserves and zoning within them. Mitigating the impacts of human activities and managing resources could be greatly improved through the use of such tools. Fisheries, for example, could be managed more effectively if key habitats could be easily identified, mapped and presented to policy makers [9,11].

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Fig. 1. Las Perlas Archipelago (Panama). Marine Special Management Zone boundary and the location of acoustic seabed surveys.

Fisheries play a fundamental role in the global economy while also acting as a primary food source for many coastal communities worldwide. As fish stocks become over-exploited, it is increasingly difficult to balance conservation objectives with social and economic imperatives [12]. Designating areas of the ocean as marine reserves is one important approach to fisheries management [13e15]. Marine reserve management measures often restrict certain activities while allowing others, e.g. tourism. In some cases, all resource extraction activities, including fishing, are prohibited within the boundaries of this category of protected area. Many scientific studies support this approach by demonstrating the benefit of no-take zones (NTZs) which have notable abundance and diversity inside marine reserves [16,17,15,18]. Marine reserves can act as important sources of larval production, providing benefit to fish stocks beyond reserve boundaries [16] and potentially increasing yield in adjacent fisheries [19,20]. It should not be forgotten, however, that the areas outside Marine Protected Areas (MPAs) can be seen to also have important overall ‘connectivity’ significance and be of regional conservation importance [21]. Nevertheless, marine reserves provide an effective framework for integrated management, encouraging local participation and comanagement opportunities [12].

Another approach is ecosystem-based fisheries management, which places greater emphasis on the effect of fisheries activities on habitats and on non-target species than a more traditional singlespecies approach to fisheries management [22]. This approach employs a multi-species model which can be used to evaluate various policy options and their implications at an ecosystem, rather than single species, level. These models are contingent upon understanding species and habitat interactions within an area. As a management strategy, utilization of such models is promising as their analysis can assist in the evaluation of various fishery policy options for their effectiveness in preventing fishery collapse and their acceptability by multiple stakeholders. Sound scientific knowledge is key in presenting any successful management strategy; however, meaningful stakeholder participation is also a requirement for effective policy implementation [23]. In May 2007 the Government of Panama designated the Las Perlas Archipelago (LPA) as a Marine Special Management Zone. Numerous recent studies have described the unique and sensitive habitats found within the archipelago, which provided the rationale for its designation. National legislation has established a framework for the protection and management of LPA by limiting activities such as commercial harvesting while continuing to allow

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artisanal fishing practices. With this framework in place, the next step is to develop detailed management plans for the area; plans which take into account both the species and the habitats found within LPA as well as the people who interact with them. Successful protection of the archipelago from loss of biodiversity and collapse of fish stocks will largely depend on the ability of resource managers and policy makers to effectively delineate zones within the LPA. This necessitates detailed knowledge of the biology and ecology of the area, participation by resource users and the political will to implement the necessary regulatory measures. Previous research initiatives and baseline studies in the LPA have focused on identifying particular species and habitats and assessing the biological diversity of the area [24e31]. Several of these studies were essential in developing the preliminary management framework for the LPA Special Management Zone. However there are still knowledge gaps that need to be filled in order to further delineate regulatory measures and develop an effective strategy for the sustainable management of the local resources. This study aimed to map major topographic features and habitat complexity in the deeper parts of the LPA, beyond the limits of satellite imagery, through the use of acoustic remote sensing [24] combined with traditional benthic survey methods. The information would then provide greater scientific evidence for the zoning of activities within the LPA Special Management Zone with particular attention on identifying the location of important fish aggregation sites. 2. Materials and methods 2.1. Survey area The LPA lies between 08 400 1900 N, 79 030 4900 W and 08 1104600 N, 78 460 3100 W within the Gulf of Panama, located 70 km southeast of Panama City. It includes over 250 basaltic rock islands and islets and represents the second largest archipelago in the Tropical Eastern Pacific (TEP) region [30]. The islands are surrounded by shallow continental shelf within the 50 m isobath. The seabed is composed of basalt, sandstone and calcareous sediments [32]. Between the 5th and 12th of May, 2008 the Smithsonian’s R/V Urraca research vessel was deployed to survey the seabed of the LPA. Three study areas were selected from within the boundary of the LPA Marine Special Management Zone, based on records and anecdotal evidence that these areas are used as fishing grounds. The three sites surveyed were Bajo Darwin, Roca Niagara and Roca Trollop (Bajo San Jose), each covering approximately 3 km2 of seabed (Fig. 1). The Bajo Darwin survey covered an area of 3 km2 with depths varying from 24 to 53 m. Roca Niagara covered an area of 2.6 km2 and had a depth range of 4e53 m. Roca Trollop covered an area of 3.4 km2 and varied from 3 to 27 m. 2.2. Acoustic survey An acoustic survey was carried out using an integrated system which captured bathymetry and sidescan images. Sidescan sonar systems work by emitting an acoustic signal that interacts with the seafloor and returns a signal which is interpreted based on its strength. The strength of the backscatter provides information on superficial features of the seabed (e.g. sand waves, rocky outcrops and biogenic structures) and characteristics of the sediment [3]. The interpretation of sidescan images normally involves the identification of acoustic classes based on the ground-truth data [33,34]. The SEA SonarPlus High Frequency system used in this survey consisted of a pair of underwater transducers fixed to the side of the vessel, approximately 2 m below the surface. The system was connected by cable to a shipboard recording device and computer

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for the acquisition, display and storage of data. The sonar frequency was set at 468 kHz with a swath width of 100 m to port and starboard. The average tow speed was 4 knots with signals being emitted at a minimum rate of 7 pings per second. Proprietary SEA software was used in the initial acquisition and processing of the bathymetric sidescan data. SEA Grid 2000 software together with Fledermaus software (IVS) was then used for further processing of the bathymetric data in order to produce a mosaic of depth (bathymetry) on a 2 m bin size. Water column and beam angle corrections for the amplitude (backscatter) data were made using SonarWiz Map (Chesapeake Inc.) with appropriate adjustments made to the images for color and contrast. The outputs were a georeferenced amplitude image (sidescan data) and the xeyez coordinates (bathymetric data) which were then imported into ArcGIS version 9.2 for further spatial analysis. Ground Control Points for geo-referencing were selected based on preliminary acoustic maps produced during the survey and these were then targeted to test the different types of acoustic seafloor condition. 2.3. Ground-truth surveys Sediment samples were collected from 28 stations across the three survey sites, using a Van Veen grab. Samples were processed according to standard methodology for Particle Size Analysis [35] and sediments were classified according to the median value of F ¼ log2 particle size (mm) and the Wentworth scale. Also calculated were the gravel, sand and silt/clay fractions as a percentage of the total sample weight. These were based on: gravel fraction (>2 mm); sand fraction (0.063e2 mm); and silt þ clay fraction (<0.063 mm). Drop-down video recordings were also collected at the sites to visualize the seafloor and assist in the classification of habitat types. Video scenes were reviewed and classified according to broad physical characteristics. The location and times of video tows were recorded and geo-referenced using a hand-held GPS. Depth measurements were taken from the vessels depth sounder and tidally corrected to give depth at chart datum. Divers surveyed two of the sites using video and stills-photography. The coordinates of these dives were recorded and the depths corrected for tidal state. These data were included in the overall habitat descriptions but only as qualitative evidence. 2.4. Data processing The acoustic data were processed with ArcGIS and extensions. A Digital Bathymetric Model (DBM) was created using a Triangulated Irregular Network (TIN) to represent the seafloor at each site. From the DBMs, secondary maps were created for slope and aspect. Slope, aspect and depth are useful in predicting the distribution of benthic communities [10]. The Benthic Terrain Modeler (BTM) extension for ArcGIS was used for further data analysis. The DBM was used to calculate the Bathymetric Position Index (BPI), which is an evaluation of the slope of each cell relative to neighboring cells (output cell size set at 2 m). BPI calculations were made at a broad and a fine scale in order to detect both large and smaller-scale topographic features [36]. Rugosity was calculated as a measure of topographic complexity using the BTM extension. The resulting classified maps were then incorporated into the analysis for delineating habitat boundaries. Using all the acoustic generated maps (DBM, BPI, rugosity and slope), physically and biologically (where possible), distinct areas of the seabed were identified by drawing separate polygons around zones with different patterns in the acoustic signature from the sidescan backscatter. This resulted in the creation of shapefiles for each habitat type which were then related back to the ground-truth

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Fig. 2. Bajo Darwin survey site (a) Bathymetry, (b) Sidescan sonar mosaic with ground-truth points, (c) Bathymetric Position Index classified into Zones, (d) Rugosity, (e) Habitat classification map.

data/seabed morphology, sediment type and conspicuous epifauna from drop-down video and diver surveys. As a final output, the three sites within the LPA were classified into broad habitat types. 3. Results 3.1. Bajo Darwin The bathymetry map of Bajo Darwin showed two seabed mounds or pinnacles about 50 m apart that rise steeply from about 52 m to approximately 24 m from the surface at their peak (Fig. 2a). Dropdown video and preliminary diver observations indicated a high biomass of large fish such as grouper (Epinephelus spp.), snapper

(Lutjanus spp.) and corvina (Cynoscium spp.) around the pinnacles as well as well-developed epifaunal communities including non reefbuilding scleractinian corals (Tubastrea, Cladopsammia), sponges and crustose coralline algae, but dominated by dense black corals (Antiphates, Myriopathes). The concentrated biomass was also observable from the acoustic data as backscatter within the water column (Fig. 3a). The area surrounding the rocky pinnacles and along the western margin of the surveyed area was relatively flat and dominated by unconsolidated sediment, predominantly sand and mud (Table 1). The sand and mud-dominated areas showed low acoustic reflectivity on the sidescan images compared to the darker pixilated areas of the seabed mounds (Fig. 2b). The classified bathymetric position index map identified distinct regions of shelf, slope, crest and

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Fig. 3. Sidescan sonar image of rocky-reef areas from (a) Bajo Darwin, and (b) Niagara survey sites showing the amplitude of backscatter through the water column. Darker patches within the water column interpreted as dense fish biomass.

depression (Fig. 2c). Rugosity, as expected, was found to be the highest around the two rocky outcrops and lowest in the mud/sanddominated areas (Fig. 2d). Fig. 2e presents a classification of the site into broad habitat types which were delineated by sidescan images, bathymetry, BPI and rugosity maps. The resulting map of the survey site was divided into three distinct regions representing: (1) the fine sedimentary (sand & mud) areas which were relatively flat, deeper shelf regions; (2) rocky-reef areas, which had areas of medium slope, medium rugosity values and high backscatter values (darker areas) in the sidescan images; (3) the seabed mounds (pinnacles) which had the highest habitat complexity based on both the high rugosity value

and the observations of diverse and abundant marine life from the ground-truth surveys. 3.2. Roca Niagara The bathymetry map of Roca Niagara showed an elongated area 0.5 km2, slightly north of the middle of the site, rising up from the seabed at around 35 m up to 4 m at the shallowest point (Fig. 4a). This shallow central region was characterized as mostly bedrock through interpretation of the strong acoustic return signal from the sidescan image (Fig. 4b) and further verified by the drop-down

Table 1 Particle size analysis of benthic grab samples taken from three sites around Las Perlas Archipelago. Median particle size, sorting and skewness calculated from cumulative size frequency curve and classified according to the Wentworth scale. Percentage content of gravel, sand and silt/clay is also displayed for each sample along with the depth (chart datum) at which the sample was taken and whether or not rhodoliths were present. Sand

Silt þ Clay

Rhodoliths

Depth (m)

0.00% 0.00% 1.62% 0.00% 0.00% 0.00% 0.00% 3.22%

92.07% 87.96% 89.18% 87.29% 88.87% 88.44% 93.70% 94.60%

7.93% 12.04% 9.21% 12.71% 11.13% 11.56% 6.30% 2.18%

No No No No No No No No

41 43 48 42 37 35 29 26

Very coarse sand Fine sand Fine sand Fine sand Coarse sand Very coarse sand Fine sand Fine sand Fine sand Fine sand Fine sand Very coarse sand

20.20% 1.69% 1.23% 4.27% 3.46% 21.85% 0.23% 0.00% 0.25% 1.25% 0.00% 15.12%

79.80% 96.34% 95.82% 91.51% 96.54% 78.15% 96.19% 97.40% 96.17% 91.32% 93.16% 84.83%

0.00% 1.98% 2.95% 4.22% 0.00% 0.00% 3.58% 2.60% 3.58% 7.43% 6.84% 0.05%

No No No No No No No No No No No No

18 40 38 38 21 19 33 42 45 49 48 30

Very coarse sand Coarse sand Coarse sand Very coarse sand Coarse sand Coarse sand Coarse sand Coarse sand

29.20% 5.51% 5.42% 34.61% 13.76% 5.32% 17.96% 22.34%

70.66% 94.21% 94.53% 65.39% 86.09% 94.68% 82.04% 77.36%

0.15% 0.28% 0.05% 0.00% 0.15% 0.00% 0.00% 0.30%

Yes Yes Yes No Yes Yes No Yes

17 17 20 16 21 22 18 15

Site

Sample

Median (phi)

Sorting

Skewness

Classification

Bajo Darwin

S4-1 S4-2 S4-3 S4-4 S4-5 S4-6 S4-7 S4-8

2.75 3 3 3.3 3.25 3 2.75 2.25

0.625 0.55 0.55 0.55 0.5 0.575 0.5 0.5

2.875 3.05 3.05 3.2 3.25 2.925 2.75 2.25

Fine sand Fine sand Fine sand Fine sand Fine sand Fine sand Fine sand Medium sand

Roca Niagara

S1-1 S1-2 S1-3 S1-4 S1-5 S1-6 S1-7 S1-8 S1-9 S1-10 S1-11 S1-12

0.25 2.75 2.9 3.2 0.75 0.25 3 3 2.75 2.75 3 0.25

0.875 0.5 0.45 0.55 0.625 0.625 0.5 0.5 0.5 0.65 0.625 0.625

0.125 2.85 2.95 3.05 0.875 0.375 3 3 2.75 2.85 2.875 0.125

Bajo Trollop

S3-1 S3-2 S3-3 S3-4 S3-5 S3-6 S3-7 S3-8

0.25 1 0.75 0 0.75 0.75 0.75 0.6

1.125 0.7 0.7 1.375 0.75 0.625 0.975 1.125

0.125 0.95 0.7 0.125 0.75 0.875 0.475 0.375

Gravel

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Fig. 4. Roca Niagara survey site. (a) bathymetry, (b) sidescan sonar mosaic with ground-truth points, (c) classified BPI, (d) rugosity, (e) habitat classification map.

video that showed rocky reef and boulder-dominated areas. Qualitative evidence of fish biomass was visible from the sidescan images of the water column. Fig. 3b shows a sidescan image from the northern part of the survey site approaching the reef, in which a pattern of strong acoustic returns is interpreted as shoals of fish. The grab samples from the central region of the site were dominated by coarse and very coarse sand, while the surrounding, deeper regions (below 35 m) were dominated by fine sand. The classified BPI map illustrated the topographic variation with distinct regions of steep slope (escarpment), crests and depressions interspersed with small patches of flat, shelf area (Fig. 4c). Rugosity was moderate to high in many of these areas, suggesting the presence of rocky or biogenic reef structures which were also

observed from the drop-down video (Fig. 4d). The final map shows the broad habitat classification with two distinct regions: (1) fine sediments of relatively flat shelf; (2) rocky-reef areas (Fig. 4e). 3.3. Roca Trollop The bathymetry map of Roca Trollop showed a 1.5 km2 shallow ridge approximately 13 m in depth, running the length of the site in a northwest to southeast orientation (Fig. 5a). The shallowest region (0.1 km2) is toward the southeast of the ridge where the depth is only 3 m. Diver observations of the site indicated high abundance and diversity of sessile organisms in certain areas, with numerous coral, fish and invertebrate species (sensu Guzman et al., 2008a) [30].

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Fig. 5. Bajo Trollop survey site (a) bathymetry, (b) sidescan sonar mosaic with ground-truth points, (c) classified BPI, (d) rugosity, (e) habitat classification map.

Broad sediment classifications identified this as a shell-sanddominated area from a benthic survey [31] conducted in 2003. This broad classification of the substrate was further defined by the ground-truth surveys during this study, which identified coarse and very coarse sand in all grab samples around this site. Also identified from the benthic grab samples and from the video and diver surveys was the presence of rhodolith (red coralline algae) beds covering extensive areas of the seabed (Table 1). From the sidescan images two acoustic classes were

distinguished, most probably representing differences in the returning signal from the rhodolith dominated seabed compared to either bedrock or the smooth, sand-dominated areas (Fig. 5b). The limited number of grab samples taken at this site made it difficult to correlate the acoustic signal to distinct sediment types. The classified BPI showed several broad crest features surrounded by shelf and a few open depressions (Fig. 5c). Rugosity values were lower here than in some of the other sites but the highest values for this site were located on the crest areas, which were most probably the

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rocky coral communities (Fig. 5d). The sidescan images revealed small seabed features in these areas of high rugosity which may be rocky-reef areas encrusted with soft corals. Fig. 5e illustrates the two main habitat regions that could be discriminated from the bathymetry and sidescan data. The two regions represent: (1) unconsolidated sediment/rhodolith beds; (2) rocky reef. 4. Discussion and conclusions This study revealed broad-scale topographic features within the three sites surveyed in Las Perlas Archipelago (LPA). Rocky reefs were identified in all three sites, some of which represented coral communities and economically important fish aggregation areas. Overall, sediment heterogeneity and topographic complexity were greatest at Roca Niagara and Roca Trollop, while Bajo Darwin had the highest measure of habitat complexity around the two topographic peaks. The acoustic survey revealed lower topographic complexity in some areas of Roca Trollop, but ground-truth data revealed smallscale features which may represent important larval fish habitat. The interpretation of the seabed surveys and subsequent identification of potentially important fish habitat was based on habitat complexity and the presence of particular seabed features. 4.1. Habitat complexity Complex habitats are often considered more valuable for conservation because of their increased surface area, food and shelter foster higher species diversity and richness [37]. Measuring rugosity over large spatial scales serves as a potentially valuable management tool and index of potential shelter for mobile (benthic and neritic) marine organisms [38]. Rugosity can be calculated post hoc by applying an algorithmic spatial analysis function to bathymetric data [36,39]. This method can be used over much broader areas, and was employed for this study. Rugosity measurements were presented as maps of the survey sites, which were then used to identify areas of potentially high biodiversity (sensu [36]). These were validated with ground-truth data added to assist in the identification of areas which may be important fish habitat. Previous studies, describing the relationship between fish diversity and habitat characteristics in coral reef communities [37,40] and rocky-reef systems [41,42], have demonstrated a positive relationship between habitat complexity and the abundance and diversity of fish species [26,43]. Benfield et al. [26] showed large scale features to be of greater importance in determining fish assemblages than small-scale features in areas of the LPA; however, small-scale features may also represent essential fish habitat for certain life-stages. Detecting smaller features from the acoustic data would require a finer survey resolution than was possible for this survey. Areas identified as rhodolith beds, for example, are smallscale features (<10 cm diameter) which may provide important topographic relief for fish in their early larval stages but were too small to be detected by the rugosity calculations in this survey. Although undetected by the rugosity maps, rhodolith fragments and beds were identified from ground-truth surveys at Roca Trollop, suggesting an important habitat function for fish at this site. 4.2. Seabed features Rhodoliths add structural complexity to habitats by providing microhabitats for organisms and result in increased biological diversity [44,45]. Rhodolith aggregations or ‘beds’ have been identified as important sites for recruitment and growth of certain commercially important bivalves [44]. Scallop and shrimp fishing often occur in rhodolith beds, suggesting that these habitats support high numbers of invertebrate species [44]. The absence of

large features in rhodolith beds is thought to explain the lack of adult fish in these habitats [44], although they may have a crucial role for larval/juvenile fish. The presence of rhodolith beds should therefore be considered an important habitat feature for an ecosystem-based approach to managing fisheries in the LPA. Indeed, the scallop fishery in LPA collapsed about 15 years ago without recovery [25] and with our survey managers may be able to manage this habitat to restore populations. Other features known for their structural complexity and role in providing microhabitats are coral reefs and communities [26]. Coral colonies have long been recognized as important habitat for fishes and invertebrates such as spiny lobsters, crabs and urchins [32]. Guzman et al. [30] identified areas of high coral abundance and diversity in the shallow regions of the LPA. The study found that coral communities had higher species diversity than the coral reefs in the archipelago. Several sites were described as having particularly rich coral communities such as Roca Trollop, a satellite area of the newly designated Special Management Zone. The bathymetric survey of Roca Trollop showed higher rugosity values in the shallow, rocky-reef areas. The ground-truth surveys revealed some of the deeper surrounding areas to be dominated by rhodoliths. These two features together suggest that Roca Trollop could represent valuable habitats for fish and invertebrate species at multiple life-history stages. The high-relief, topographic complexity of the coral communities and rocky reefs provide shelter, food and protection for adult fish while the smaller-scale features of the rhodolith beds provide habitat for larval organisms with reduced predation from large fish. 4.3. Fisheries and conservation management Although the three sites surveyed are now protected from commercial fishing activities (under National legislation designating 1688 km2 of marine protected area of Las Perlas ‘Special Management Zone’ e Law No. 18, May 31st 2007), artisanal and sport fisheries continue to occur in the area. The designation of the LPA as a protected area resulted in certain other fishing restrictions within its boundaries. Future, additional restrictions and zoning within the MPA will require that sensitive and vulnerable habitats be identified and spatially defined. In terms of prioritizing areas for conservation and management (e.g. marine reserves or no-take zones), areas with higher habitat complexity will most likely support a greater diversity and abundance of species. As a fisheries management tool this has important implications for the restriction of certain gear types and the exclusion of all fishing practices in areas that may support a particularly high diversity of fish species and/or act as important fish nursery habitat. Identifying conservation priorities requires detailed knowledge of the distribution of sensitive species and habitats, particularly in relation to potentially harmful anthropogenic activities (i.e. pollution, overfishing, coastal development) and threat of climate change [1]. The response of fish populations to intense fishing pressure will only be magnified by climate change and other anthropogenic stresses [12]. Reducing fishing pressure will enhance the ability of marine biota and fish stocks to adapt to changing environmental conditions [46]. An intrinsic buffering capacity is even more critical for small-scale fisheries which may be more affected by climatic shifts and human activities. Marine reserves may be the best means of protecting fish and other species against the negative effects of climate change, while also allowing artisanal fisherfolk to continue traditional harvesting practices which support small coastal communities. With an ever-increasing ability to acquire detailed information about the marine environment, the tools necessary for identifying vulnerable species and threatened habitats are now available in modern, cost-effective acoustic techniques.

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4.4. Conclusion There are numerous methodologies available for mapping seabed features in relation to assessing habitats and formulating fishery management plans. This survey demonstrated the use of acoustic techniques to spatially resolve topographic features and physical characteristics of the seabed over areas of Las Perlas Archipelago in the Gulf of Panama. It illustrated their potential value as tools for fisheries management and marine reserve zoning which could be of valuable potential when applied elsewhere.

Acknowledgements We thank the Government of Panama for providing permits to work and collect in the area. The authors would like to thank C. Guevara, R. Scott and the crew of R/V Urraca for assisting during the fieldwork. We thank our anonymous reviewer for comments on the manuscript. Funding for this study was partially provided by the Darwin Initiative, a programme of the UK government’s Department for Environment, Food and Rural Affairs (DEFRA), St Andrews University and Heriot-Watt University, UK and the Smithsonian Tropical Research Institute, Panama.

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