Baited Remote Underwater Video (BRUV) survey of elasmobranchs on Bonaire s reef

Transcription

1 Baited Remote Underwater Video (BRUV) survey of elasmobranchs on Bonaire s reef Name: Nijs Ruijs, Hogeschool Zeeland Date: Supervisors: Martin de Graaf 1

2 Table of contents: 1. Introduction Materials and method Study area Baited remote underwater video Citizen science project Results BRUV Citizen science project Discussion Acknowledgement 18 Appendix 1 Bibliography.19 Appendix 2 Material list for a sample day.21 Appendix 3 Sample plan..23 2

3 1. Introduction: Elasmobranchs are of critical importance to our oceans seas. Elasmobranchs, Alpha predators, are predators locating at the top of a food chain. These predators contribute to an ecological balance in the marine environment by consuming dead and weaker organisms in the food chain from the same or lower trophic levels (Techera and Klein, 2016). Their importance in the organisation, stability, and biodiversity in the Caribbean has been emphasized in a study by Rezende et al. (2009). Elasmobranchs are considered natural regulators of piscivore biomass on Caribbean reefs (Chapman et al, 2006). Over the past decades the elasmobranch populations have declined drastically worldwide due to their depleting food sources through overfishing and bycatch in commercial fisheries (Aires-da-Silva and Gallucci, 2007; Myers et al., 2007; Herndon, 2010; Branch et al., 2010; Cosandey-Godin and Morgan, 2011). The combination of high fishing pressure and K- selected life-history characteristics, e.g. slow growth, late maturity and low fecundity, make elasmobranchs extremely vulnerable to overexploitation and inhibit the recovery potential of impacted populations (Stevens et al. 2000). Critical habitat loss, particularly in continental and insular shelves of tropical and subtropical regions, has also impacted elasmobranch species (Dulvy et al. 2014). Human pressures in coastal zones have most likely caused the near absence of most species of reef sharks in the Wider Caribbean Region (Ward-Paige et al. 2010). The removal of large predators like sharks can disrupt the balance of marine food webs and cause large scale ecological changes (Heithaus et al. 2008, 2010, 2012). A key ambition of the Dutch Caribbean Nature Policy Plan , is the effective implementation of elasmobranch protection. Based on reports by the Western Central Atlantic Fishery Commission (WECAFC) supported by local diver and anecdotal accounts, the situation in the Dutch Caribbean is no different (Debrot and Criens, 2005). It appears that throughout the wider Caribbean, elasmobranch populations decline when human population density increases (Stallings, 2009). This is mainly through the deterioration and decline of important elasmobranch habitats including habitats of juvenile elasmobranchs in coastal waters (Fowler et al., 2005). The current status of elasmobranch populations in the Gulf of Mexico and the Caribbean remains generally poorly known (Fowler et al. 2005). There is no data available on population status, distribution and abundance of elasmobranchs in the Dutch Caribbean. The aim of the project is to conduct a base-line survey to describe the current elasmobranch diversity, distribution and relative abundance on inshore reefs (<50 m depth) within the territorial waters of Bonaire. The standardized BRUV base-line survey will serve as a reference point to evaluate the performance of future management actions on elasmobranchs populations. Furthermore, the base-line survey may identify elasmobranch hot spots and this information may be used for the design of future reserves to improve protection. Besides the BRUV survey, a citizen science project is developed in cooperation with three dive centres: Bas Tol, East coast diving and Carib Inn. Where Carib inn only goes diving at the West coast, while Bas Tol and East coast only go diving at the East coast of Bonaire. 3

4 This goal will be reached by answering the following research question : What is the current diversity and distribution of elasmobranch on the coastal reefs (<40m depth) of Bonaire? 4

5 2. Materials and methods 2.1 Study area This study was conducted between September 2016 and December 2016 on Bonaire. The sea along the coast of Bonaire, including Lac Bay and Klein Bonaire, till a depth of 60m belong to Bonaire National Marine park. The total area is approximately hectare. The Bonaire National Marine Park contains of a variety of marine habitats for elasmobranchs including coral reef, seagrass, sand and mangroves. The Bonaire Marine National Marine Park is separated in different management zones (figure 2) West Coast No Diving Zone (WCNDZ), West Coast No Fishing Zone (WCNFZ), West Coast General Use Zone, East Coast General Use Zone, Lac Bay General Use Zone. Since the West coast general use is so spread out over Bonaire it is split in 3 sub zones, South West coast and North West coast and Klein Bonaire. North West coast is further divided in North West Coast 1-2 Figure 2: Management zones Standardized-BRUV survey. More data is obtained by a citizen science project with professional dive guides. It has proven to be a cost effective and robust method to collect shark distribution and abundance data (Vianna et al. 2014). This project is in cooperation with 3 dive centres, Bas Tol, East coast diving and Carib Inn. 5

6 2.2 Baited remote underwater video: The Baited Remote Underwater Video (BRUV) survey was conducted with 3 single camera collapsible systems, each unit consists one GoPro video camera (details type camera). BRUVs were deployed during daylight hours between 9:00 AM and 5:00 PM and were retrieved after 90 minutes. A distance of 500 m was maintained between simultaneous deployments to reduce overlap of bait odour plumes (Willis & Babcock, 2000, Harvey et al., 2007, Heagney et al., 2007).. The bait bag was positioned 60cm in front of the camera (figure 3). Mainly 1 kg of tuna (Thunnus sp.) was used. Area Zone Drops at 40m depth Drops at 10m depth West Coast South General use Klein Bonaire General use North General use No Diving No Fishing Lac Bay General use East Coast General use Table 1: Original sampling plan The BRUVs are deployed at the top of the drop-off (10m) and at the bottom of the reef (40m). When bottom of the reefs are deeper than 40m, BRUVs will not be deployed since the GoPro s housing can t cope with the pressure. The BRUVs deploying at 10m depth are pointing slightly downwards and the BRUVs at 40m depth on the bottom of the reef are pointing forward (figure 4). Figure 3: A Baited Remote Underwater Video. Figure 4: Cross-section of a reef with the position of a BRUV displayed. 6

7 A total of 110 standardized-bruv deployments were executed for the baseline survey in Bonaire. To conduct an extensive baseline survey deployments were distributed over depths of 10m and 40m at every management zone. Since all life-stages of the most common elasmobranch species on Bonaire, Caribbean reef shark (Carcharhinus perezii), are in this depth range (Bond et al, 2012). Beforehand it was not known where the habitat types are found, and by this the deployments were not distributed over the habitat types but management zones. The video footage was analysed by counting the number of individuals at a frame where the maximum number is seen of the whole footage (MaxN), in this way recurring individuals were excluded. Habitat types in this survey were categorized in subgroups to derive data of elasmobranch species on habitat types. After the BRUV had reached the bottom an image of the video was used to determine the habitat type at a deployment. Within the habitat types the amount of complexity is determined additionally. The habitat complexity is a 6-point scale, from bare substratum till extreme complexity. However, the category extreme complexity is never determined. Figure 5: 6-point scale about the habitat complexity described by Polunin and Roberts (1993). 7

8 2.3 Citizen science Citizen science project using observations by professional dive guides has proven to be a cost effective and robust method to collect elasmobranch distribution and abundance data (Vianna et al. 2014). A citizen science project was developed in cooperation with three dive centres: Bas Tol, East coast diving and Carib Inn. For each dive, dive guides recorded date, location and if elasmobranch species were observed they recorded number and species. In addition to distribution and diversity data, these initiatives ensure local participation to the research. 8

9 Number of deployment per habitat type 3. Results 3.1 BRUV In total, 103 BRUV deployments were conducted stratified based on habitat, management zone (general use, no diving, no fishing) and wave exposure (sheltered west coast, exposed east coast). The frequency of the determined habitats are seen below, where: management zone 0 is West Coast General use zone, management zone 1 is West coast no fishing zone, management zone 2 is West Coast no diving zone, management zone 3 is Klein Bonaire, management zone 4 is East coast, and management zone 5 is Lac Bay. Frequency of habitat types Management zone coral reef macroalgae seagrass sand Figure 6: Frequency of habitat types. From all deployments 4 elasmobranch species were recorded over different samples. The Caribbean reef shark (C. perezi) (figure 7) was both the most abundant shark species as well as elasmobranch species, it was observed 11 times. The other shark species is the Great hammerhead shark (S. mokarran) (figure 8), which was observed just once. The Spotted eagle ray (A. narinari) (figure 9) is the most abundant ray species and was recorded 5 times. The Southern stingray (D. americana) (figure 10) was observed 4 times. In total 21 individuals were observed over 16 deployments, the geographical distribution of the elasmobranch species is shown in figure 11. Figure 7: Caribbean reef shark (C. perezi) 9

10 Figure 8: Greater hamerhead (S. mokarran). Figure 9: Spotted eagle ray (A. narinari). Figure 10: Southern stingray (D. americana). 10

11 Figure 11: Species composition. 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Shark (n=4) Ray (n=2) Shark (n=8) Ray (n=7) Shallow Shallow Deep Deep Caribbean Reef Shark Great Hammerhead Spotted Eagle Ray Stingray Figure 12: Distribution of the species composition over deep and shallow deployments. 11

12 Figure 13: Geographical distribution of elasmobranch species on Bonaire. 3.2 Citizen science Over 429 observations the cooperating dive guides recorded 356 (83.0%) Spotted eagle rays, which is the most abundant elasmobranch species. The second most abundant elasmobranch species is the Southern stingray, 64 (14.9%) Southern stingrays were recorded. The third most dominant elasmobranch species is the Nurse shark (G. cirratum), it was recorded 60 times (14.0%). At 75 different sites 5 (1.2%) Manta rays (M. birostris) and 2 (0.5%) Caribbean reef sharks were recorded. A Bull shark (C. leucas) was recorded just once (0.2%). In total 488 elasmobranchs were recorded in 429 observations, thus at every observations 1.1 individuals were recorded. The species composition of each month is illustrated in figure 14. In figure 15 the average number recorded elasmobranch per dive per month is shown distributed over the East coast and West coast. The species composition recorded by professional dive guides at the West coast is shown in figure 16 and at the East coast in figure 17. Although the first observations of December are included in figure 14 the data is excluded from the other graphs, because the cooperating dive guides ended recording on the 5th of December. The data from December was to less to add it to the graph, nevertheless, no elasmobranchs were recorded in this month. The relative numbers of recorded Elasmobranchs are used to compare the data with the other months, because each month has different number of observations and in this way it can be analysed. 12

13 AVG NUMBER PER DIVE Recorded Elasmobranchs over total observations per month (%) July August September October November Bull shark Caribbean reef shark Nurse shark Spotted eagle ray Southern stingray Manta ray Figure 14: Recorded Elasmobranchs per month over total observations per month. The absolute numbers of recorded individuals per month are at the end of the bars. 4,5 4 3,5 3 2,5 2 1,5 1 0,5 0 JUL A U G SEP OCT NOV EC shark EC ray WC shark WC Ray Figure 15: Average number recorded elasmobranchs per dive distributed over the East Coast (EC) and West Coast (WC). 13

14 100% 90% 80% 70% 60% 50% 40% 30% 20% Manta ray Stingray Spotted Eagle Ray Bull shark Nurse shark Caribbean Reef Shark 10% 0% Shark (n=4) Ray (n=56) Figure 16: species composition recorded by dive guides at the West coast of Bonaire. 100% 90% 80% 70% 60% 50% 40% 30% Manta ray Stingray Spotted Eagle Ray Nurse shark 20% 10% 0% Shark (n=59) Ray (n=369) Figure 17: Species composition recorded by dive guides at the East coast of Bonaire. 14

15 4. Discussion In this survey data was collected using the standardized-bruv method. Advantages are, for instance sampling with a non-invasive method, causes minimal damage to the benthic environment and it is not size-selective like traditional capture method where hook or mesh size are influential (Cappo et al., 2006). In addition, results can be compared with other regions because same methods have been used to perform surveys in other parts of the Dutch Caribbean. From the surveys on the Northern Dutch Caribbean islands, like St. Maarten, Saba, Saba bank, and St. Eustatius, it can be concluded that the elasmobranch abundance is lower on Bonaire. For instance, the Saba bank is much more abundance with elasmobranchs then Bonaire, where from 85 elasmobranch observations 41 Nurse sharks and 36 Caribbean reef sharks were recorded (Stoffers, T., 2014). On St. Maarten 109 elasmobranch observations were performed where a total of 37 sharks were recorded (Kramer, O., Odinga, J., 2015). The West coast of Bonaire is the civilized area, where most boat activity, commercial and touristic fisheries occur. This is because the West coast is sheltered and the East coast is exposed, so there is wave activity. At the West coast, divers can therefore enter the water their self, instead of only go diving with professional dive guides. At the East coast this is not the case, divers only go diving with professional dive guides. This makes the diving activity at the East coast less. Additionally, only commercial fisheries occur at the East coast. In other words, the human pressure along the West coast is much higher than along the East coast. This taken in mind, the East coast was assumed to be more abundance. Even though, more deployments are performed in the sheltered zone more sharks are recorded in the exposed area, close to the East coast (most northern point and most southern point of Bonaire) (figure 13) However, along the West coast more rays are recorded. This could be through the higher number of deployments at the West coast than at the East coast. When you add the data from the citizen science project to this assumption, it can be approved, since the average numbers of EC shark and EC ray are significant higher than WC shark and WC ray (figure 15). Furthermore, the number of elasmobranchs recorded by professional dive guides at the East coast is higher with almost a factor 10. Professional dive guides go to dive sites, where they know that they can show their group nice coral reefs, many fish, turtles, and maybe even sharks and rays. At the East coast, for instance, the dive centre East coast dive only took observations at 2 dive sites. At these dive sites East coast diving recorded many sharks and a lot of rays. Additionally, dive centre Bas Tol has mainly done observations at 1 dive site where he recorded a lot of sharks and rays. Although it is data from 3 dive sites, it is very useful to confirm the assumed distribution and diversity of elasmobranch species. For example, the citizen science project showed that Nurse sharks are found on Bonaire, even though the BRUV survey did not record any. In this way the citizen science project is very useful to obtain data about the diversity and distribution of elasmobranch species. Furthermore, a high number of observations are obtained in a short period, which could never be reached conducting the BRUV survey, because it would be too time-consuming and therefore too expensive. 15

16 Factors that could influence the data: Firstly, mainly samples are taken at the West coast where recreational diving activities are very abundance. Divers, which are observed during recording time could have an negative influence by avoiding that particular area. Best data to cover up this finding are the deployments ZES1, ZES2, ZED1, ZED2 and ZED3, illustrated in figure 10. At all deployments Caribbean reef sharks were observed, except for ZES1. On the footage of ZES1 divers were observed. Secondly, the short timeframe this survey is performed. Day variability of reef fish assemblages are not accounted, which may influence the diversity and abundance of Elasmobranchs (Bird et al., 2012) and effect the spatial distribution. Furthermore, temporal aspects such as migrations of species are not taken into account since this survey is only performed during a half year period. Habitat types and complexity were not known before performing this survey, which made the deployments not distributed equally over the habitat types and complexity, but management zones. In addition, not all deployments have been executed because of lack in resources by STINAPA and weather conditions. Vessels and rangers of STINAPA could not always be working on this survey, since they had other tasks to do that were more important at that time, for instance, damage monitoring after the hurricane Matthew. Figure 18: 4 deployments where sharks were observed. At deployment ZES1 divers were observed. 16

17 5. Acknowledgement: I would like to thank Dr. Martin de Graaf and Caren Eckrich for their guidance during this internship and, of course, for making it possible to gain fieldwork experience on a tropical island. Special thanks go to the rangers of STINAPA and Ludson and Ludi, as they all were the muscle men and driving force behind the fieldwork. Furthermore, I would like to thank Twan Stoffers for his training and advice concerning the application of the BRUV methodology. Finally, all other staff members of STINAPA deserve credit for the hospitality and kindness during my office days at STINAPA headquarters. 17

18 Appendix 1 Bibliography: Afonso, A.S., Andrada, H.A., Hazin, F.H.V., (2014). Structure and Dynamics of the shark assemblage off Recife, Northeastern Brazil. PLOS ONE, volume 9. Aires-da Silva, A.M. and Gallucci, V. (2007). Demographic and risk analyses applied to management and conservation of the blue shark (Prionace glauca) in the North Atlantic Ocean. Marine and Freshwater Research, volume 58, Albins, M. A. and Hixon M.A. (2008). Invasive Indo Pacific lionfish Pterois volitans reduce recruitment of Atlantic coral reef fishes. Marine Ecology Progress Series, 367, Arias-Gonzalez, J. E., Gonzalez Gandara C., (2011). Predicted impact of the invasive lionfish Pterois volitans on the food web of a Caribbean coral reef. Environmental Research, 111(7), Beek Van I.J.M., Debrot, A.O., Walker, P.A., Kinga, I., (2014). Shark protection plan for the Dutch Caribbean EEZ. Birt, M.J., Harvey, E.S., &Langlois, T.J. (2012). Within and between day variability in temperate reef fish assemblages: Learned response to baited video. Journal of Experimental Marine Biology and Ecology, , Bond, M.E., Babcock, E.A., Pikitch, E.K., Abercrombie, D.L., Lamb, N.F., Chapman, D.D., (2012). Reef sharks exhibit site-fidelity and higher relative abundance in marine reserves on the Mesoamerican Barrier Reef. PLOS ONE, volume 7. Bonfil, R., (1996). Status of shark resources in the Southern Gulf of Mexico and Caribbean: implications for management. Elsevier, Fisheries research 29, Branch, T. A., Watson, R., Fulton, E. A., Jennings, S., McGilliard, C. R., Pablico, G. T. and Tracey, S. R. (2010). The trophic fingerprint of marine fisheries. Nature, 468, Brooks, E.J., Sloman, K.A., Sims, D.W., Danylchuk, A.J., (2011). Validating the use of baited remote underwater video surveys for assessing the diversity, distribution and abundance of sharks in the Bahamas. Endangered species research, volume 13: Brooks, E.J., Sims, K.A., Danylchuk, A.j., Sloman, K.A., (2012). Seasonal abundance, philopatry and demographic structure of Caribbean reef shark (carcharhinus perezi) assemblages in the North-East Exuma Sound, The Bahamas. Cappo, M., E. Harvey, and M. Shortis. (2006). Counting and measuring fish with baited video thecniques- an overview. Chapman, D.D., Pikitch, E.K., (2006). Marine parks need sharks? Science, 312(5773), Cosandey-Godin, A. and Morgan, A. (2011). Fisheries Bycatch of Sharks: Options for Mitigation. Ocean Science Division, Pew Environment Group, Washington DC. Fowler, S. L., Cavanagh, R. D., Camhi, M., Burgess, G. H., Cailliet, G. M., Fordham, S. V., Simpfendorfer, C. A. and Musick, J. A. (2005). Sharks, rays and chimaeras: The status of the Chondrichthyan fishes. National Wildlife (Vol. 14, p. 461). 18

19 Garla, R.C., Chapman, D.D., Shivji, M.S., Wetherbee, B.M., Amorim, A.F., (2006). Habitat of juvenile Caribbean reef sharks, Carcharhinus perezi, at two oceanic insular marine protected areas in the Southwestern Atlantic Ocean: Fernando de Noronha Archipelago and Atol das Rocas, Brazil. Elsevier, Fisheries research 81, Herndon, A., Gallucci, V.F., DeMaster, D., and Burke, W. (2010). The case for an international commission for the conservation and management of sharks (ICCMS). Marine Policy, 34, Kramer, O., & Odinga, J. (2015). Baited Remote Underwater stereo Video (stereo-bruv) survey as a basis for elasmobranch conservation and management on Sint Maarten, Dutch Caribbean. Van Hall Larenstein University of Applied Sciences Kuijk, V.T. (2013). The effect of marine reserve zones and habitat types on the structure of tropical reefsfish assemblages around St. Eustatius. Wageningen University, Aquaculture and fisheries group. Myers, R. A., Baum, J. K., Shepherd, T. D., Powers, S. P. and Peterson, C. H. (2007). Cascading effects of the loss of apex predatory sharks from a coastal ocean. Science (New York, N.Y.), 315, Rezende, E.L., E.M. Albert, (2009). Compartments in a marine food web associated with phylogeny, body mass, and habitat structure. Ecology Letters, 12(8), Stallings, C.D. (2009). Fishery Independent Data Reveal Negative Effect of Human Population Density on Caribbean Predatory Fish Communities. PLOS ONE, 4(5). Stoffers, T. (2014). Fish assemblages on the Saba bank (Dutch Caribbean): the effect of habitat, depth and fisheries. Wageningen University, Aquaculture and fisheries group. Tavares, R., (2009). Fishery biology of the Caribbean reef sharks, Carcharhinus perezi (poey, 1876), in a Caribbean insular platform: Los Roques Archipleago National Park, Venezuela. Pan-American Journal of Aquatic Sciences, 4(4): Techera, E.J. and Klein, N. (2010). Fragmented governance: Reconciling legal strategies for shark conservation and management. Marine Policy, volume 35, White, J., Simpfendorfer, C.A., Tobin, A.J., Heupel, M.R. (2013). Application of baited remote underwater video surveys to quantify spatial distribution of elasmobranchs at an ecosystem scale. Journal of Experimental Marine Biology and Ecology, Volume 488, Ward-Paige, C.A., Mora, C., Lotze, HK., Pattengil-Semmens, C., McClenachan, L., Arias-Castro, E., Myers, R.A., (2010). Large-Scale Absence of sharks on reefs in the Greater-Carribean: A footprint of human pressures. PLOS one, Volume 5. 19

20 Appendix 2 - Materials list for a sampling day: Materials Extra description Check 3x GoPro Hero 1x GoPro Hero 4 Silver standerd (Incl. bacpac and extra battery) 5x Sandisk micro sdcard 20

21 3x BRUVs (incl. 3x baitholders, 3x rope and 3x buoys) 3x PVC pipe and 6x tie-rips Baits Notebook and pencil Snorkeling gear GPS For the connection of the baitholders and BRUVs Leftovers of fish from fishermen are used as bait Mask, fins and snorkel 21

22 Appendix 3 Sampling plan: Figure 19: Management zones of Bonaire Figure 20: Klein Bonaire (KB) 22

23 Figure 21: South West coast (SW) Figure 22: West coast no fishing zone 1 (WC1) 23

24 Figure 23: West coast no fishing zone 2 (WC2) Figure 24: North West coast 1 (NW1) 24

25 Figure 25: 16: West North coast West no coast diving 1 (NW1) zone (WN) Figure 26: North West coast 2 (NW2) 25

26 Figure 27: West coast no diving zone (WN) Figure 28: North West coast 2 (NW2) 26

27 Figure 29: East coast (SE) Figure 30: East coast (SE) 27