Underwater Video Surveys Research Articles

Baited Remote Underwater Video surveys undercount sharks at high densities: insights from full-spherical camera technologies

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 585:113-121 (2017) - DOI: https://doi.org/10.3354/meps12395 Baited Remote Underwater Video surveys undercount sharks at high densities: insights from full-spherical camera technologies James P. Kilfoil1,*, Aaron J. Wirsing2, Matthew D. Campbell3, Jeremy J. Kiszka1, Kirk R. Gastrich1, Michael R. Heithaus1, Yuying Zhang1, Mark E. Bond1 1Department of Biological Sciences, Florida International University, North Miami, FL 33181, USA 2School of Environmental and Forest Sciences, University of Washington, Seattle, WA 98195, USA 3National Marine Fisheries Service, Southeast Fisheries Science Center, Mississippi Laboratories, Pascagoula, MS 39567, USA *Corresponding author: jkilf001@fiu.edu ABSTRACT: Video surveys are an essential tool for monitoring marine communities. Their use to study elasmobranch populations has dramatically increased over the last decade. However, the restricted field-of-view (FOV) of traditional cameras in these surveys may bias abundance estimates in a number of ways, including saturation at high densities and low detection probability for rare or cryptic species. This study investigated these potential biases using newly developed full-spherical (FS) camera technology. A comparison of 35 Baited Remote Underwater Video surveys (BRUVs), using both FS and traditional cameras, was conducted from July to August 2016 in shallow waters (0.4 to 8.5 m) of Tetiaroa, French Polynesia. Both blacktip reef Carcharhinus melanopterus and sicklefin lemon sharks Negaprion acutidens were quantified from traditional cameras using MaxN and MeanCount methods. These estimates were then regressed against FS cameras counts, which were assumed to more accurately represent site abundance, to test for gear saturation. Detection probabilities of the traditional and FS cameras were assessed using a Bayesian binomial model, with uninformed-uniform priors. Results indicated a significant effect of gear saturation for standard BRUVs as counts on FS cameras increased, regardless of the metric used. Furthermore, traditional cameras had a significantly lower detection probability (mean ± 2 SD: 69.88 ± 0.008%) than FS cameras (81.20 ± 0.007%). Our findings show that traditional cameras are unlikely to adequately discriminate differences in shark relative abundance at high densities. Therefore, standard BRUV techniques that use restricted FOV cameras are likely limited in their ability to provide accurate information to managers once populations have reached particular thresholds of abundance. KEY WORDS: 360° cameras · Detectability · Elasmobranchs · Monitoring · Video surveys Full text in pdf format Supplementary material PreviousNextCite this article as: Kilfoil JP, Wirsing AJ, Campbell MD, Kiszka JJ and others (2017) Baited Remote Underwater Video surveys undercount sharks at high densities: insights from full-spherical camera technologies. Mar Ecol Prog Ser 585:113-121. https://doi.org/10.3354/meps12395 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 585. Online publication date: December 22, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

The effect of artificial light on the community structure of reef-associated fishes at oil and gas platforms in the northern Gulf of Mexico

The northern Gulf of Mexico (GOM) contains almost 2300 oil and gas platforms. While some of these platforms are actively lit, allowing for normal working conditions throughout the night, many are unlit, illuminated only by small navigation beacons to warn vessels of their presence. In addition to producing oil and gas, these structures inadvertently serve as artificial reef habitat for a variety of GOM fish and invertebrate species. Though many fish species have been reported aggregating near these structures, this study is the first to examine changes in fish community structure in response to the structures’ artificial light regimes. Baited remote underwater video (BRUV) surveys were conducted at two lit and three unlit oil and gas platforms off the coast of Louisiana to examine the effect of platform artificial lighting on fish community structure during the day, at night, and during crepuscular periods. Seventeen recreationally harvested species were observed, with red snapper (Lutjanus campechanus) being the most abundant. Statistical analysis indicated that fish community varied significantly with depth, season, type, and season by type interactions. More fish were seen at lit platforms than at unlit platforms, with the majority of individuals identified near the surface. While fish abundance at the surface remained high during the day, the numbers declined at night. This suggests that though fishes are attracted to the vertical relief of the structure, they may be avoiding the artificial light field at the surface either to escape nocturnal predation or to forage away from the platform.

Are trawl marks a good indicator of trawling pressure in muddy sand fishing grounds?

The development of the vessel monitoring system (VMS) in the recent years has offered high-resolution data to map the distribution and intensity of fishing activities and contributed to enhancing the potential identification of fishing impacts. However, impacts could vary at very small scale and the resolution of VMS data might not be fine enough. Other proxy could be used, such as trawl marks visible on the seabed observed by underwater video or side-scan sonar to evaluate small-scale trawling effort. In the Bay of Biscay, an underwater video survey of the Nephrops norvegicus fishing ground was conducted and provided environmental characteristics such as depth and number of trawl marks at 152 transects. The relevance of observed trawl marks as a small-scale proxy of trawling effort was tested depending on the sediment type. The model showed a significant positive relation between density of marks and trawling effort for all sediments together but a different relation for each sediment type. Considering each sediment type separately, the unexpected high number of marks observed on sands could be linked with cohesive interactions between calcium carbonates particles while the low number of marks on fine lithoclastic muds could be due to sediment reworking and bioturbation. We conclude that the impact of trawling on the seabed varies with the type of sediments, hydrodynamic parameters, bioturbation and trawling intensity, leading to a very complex relationship. Trawl marks observed on video footage thus could be used as a proxy of trawling effort among the same type of sediment and not for fine lithoclastic muds.

Juvenile gadoid habitat and ontogenetic shift observations using stereo-video baited cameras

Understanding habitat variables affecting species distribution and survival is essential to their protection. This is especially important in areas where anthropogenic pressures can have a significant direct impact on not only the survival of the species but also damage their habitat. The Firth of Clyde, southwestern Scotland, was an important commercial fishing area for a variety demersal fish species up until 1973. However, stocks have since declined to near-zero despite fisheries measures put in place to aid recovery. Here we report on Stereo Baited Remote Underwater Video (SBRUV) surveys in the Firth of Clyde between June and September in 2013 and 2014 to determine the habitat of juvenile Atlantic cod Gadus morhua, haddock Melanogrammus aeglefinus, and whiting Merlangius merlangus. Habitat predictor variables explored included substratum type, depth, wave fetch, and bentho-demersal species diversity. G. morhua were most abundant in shallow, sheltered areas composed of gravel-pebble containing maerl. Ontogenetic shifts and density dependence were also observed. M. aeglefinus, and M. merlangus predominated over deeper sand and mud. Relative abundances of all three species were positively related to bentho-demersal diversity. This work demonstrates the potential of SBRUV as a non-destructive survey tool under northern-temperate conditions. Our results indicate that spatial conservation measures to benefit demersal fish should be advised by patterns of bentho-demersal diversity as well as physical substratum types.

Spatial Distribution of Reef Fish Species along the Southeast US Atlantic Coast Inferred from Underwater Video Survey Data.

Marine fish abundance and distribution often varies across spatial scales for a variety of reasons, and this variability has significant ecological and management consequences. We quantified the distribution of reef-associated fish species along the southeast United States Atlantic coast using underwater video survey samples (N = 4,855 in 2011–2014) to elucidate variability within species across space, depths, and habitats, as well as describe broad-scale patterns in species richness. Thirty-two species were seen at least 10 times on video, and the most commonly observed species were red porgy (Pagrus pagrus; 41.4% of videos), gray triggerfish (Balistes capriscus; 31.0%), black sea bass (Centropristis striata; 29.1%), vermilion snapper (Rhomboplites aurorubens; 27.7%), and red snapper (Lutjanus campechanus; 22.6%). Using generalized additive models, we found that most species were non-randomly distributed across space, depths, and habitats. Most rare species were observed along the continental shelf break, except for goliath grouper (Epinephelus itajara), which was found on the continental shelf in Florida and Georgia. We also observed higher numbers of species in shelf-break habitats from southern North Carolina to Georgia, and fewer in shallower water and at the northern and southern ends of the southeast United States Atlantic coast. Our study provides the first broad-scale description of the spatial distribution of reef fish in the region to be based on fishery-independent data, reinforces the utility of underwater video to survey reef fish, and can help improve the management of reef fish in the SEUS, for example, by improving indices of abundance.

Susceptibility of coral assemblages to successive bleaching events at Moorea, French Polynesia

In 2002, bleaching was reported throughout many Indo-Pacific coral-reef regions, including French Polynesia. Bleaching occurred again in French Polynesia in 2003, providing an opportunity to compare the effects of successive bleaching events on coral susceptibility. During 2002 and 2003, underwater video surveys were completed in stations at four depths (lagoon: 0–2, 2–4m; outer reef slope: 6–8, 12–14m) at two locations on the northern and north-western coast of Moorea (Society Archipelago) to compare the cover of healthy-appearing, the cover of partially bleached and the cover of fully bleached coral. Bleaching patterns were genus specific and differences in susceptibility among major genera were generally consistent between 2002 and 2003, with Acropora showing the greatest susceptibility. Some genera exhibited substantial spatial variability in bleaching susceptibility between years (e.g. Pocillopora, Montipora); however, this variability was significant only for fully bleached and partially bleached Acropora. Multivariate analyses showed that spatial patterns in the proportion of healthy-appearing coral were similar over time within the assemblages, whereas the cover of partially bleached and the cover of fully bleached coral were more variable among depths and locations. This variability has important implications for assessing changes to coral community structure over time and for estimating coral-reef resistance and resilience to future bleaching disturbance.

Investigating acoustic diversity of fish aggregations in coral reef ecosystems from multifrequency fishery sonar surveys

Remote species classification using fisheries acoustic techniques in coral reef ecosystems remains one of the greatest hurdles in developing informative metrics and indicators required for ecosystem management. We reviewed long-term marine ecosystem acoustic surveys that have been carried out in the US Caribbean covering various coral reef habitat types and evaluated metrics that may be helpful in classifying multifrequency acoustic signatures of fish aggregations to taxonomic groups. We found that the energetic properties across frequencies, in particular the mean and the maximum volume backscattering coefficient, provided the majority of the discriminating power in separating schools and aggregations into distinct groups. To a lesser extent, school shape and geometry helped isolate a distinctive group of reef fishes based on shoaling behaviour. Schools and aggregations were clustered into five distinct groups. The use of underwater video surveys from a Remote Operating Vehicle (ROV) conducted in the proximity of the acoustic observations allowed us to associate the clusters with broad categories of species groups such as large predators, including fishery important species to small forage fishes. The remote classification methods described here are an important step toward improving marine ecosystem acoustics for the study and management of coral reef fish communities.

Generalizing visual fast count estimators for underwater video surveys

A generalized Visual Fast Count (GVFC) method of moments estimator is proposed for estimating epifaunal species abundance from underwater video survey transects. This formalises and provides a statistical framework for previous ad‐hoc Visual Fast Count methods. For a single transect, we derive the expected value of the naive GVFC estimator and use this to create the method of moments estimator, which has reduced bias. A maximum likelihood estimator for multiple transects is derived. For illustration, our methods are applied to a series of video trawls at Folkestone Pomerania in the Dover Straits, UK. Although our methods have been developed for marine applications, they could also be applied to some terrestrial transect surveys.

三峡蓄水以来葛洲坝下中华鲟产卵场河床质特征变化

PDF HTML阅读 XML下载 导出引用 引用提醒 三峡蓄水以来葛洲坝下中华鲟产卵场河床质特征变化 DOI: 10.5846/stxb201306141703 作者: 作者单位: 中国水产科学研究院长江水产研究所,中国水产科学研究院长江水产研究所,中国水产科学研究院长江水产研究所,中国水产科学研究院长江水产研究所,中国水产科学研究院长江水产研究所,中国水产科学研究院长江水产研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然基金青年科学基金项目(31202003); 公益性农业行业专项(201203086) Changes of bottom substrate characteristics in spawning ground of chinese sturgeon downstream the gezhouba dam from impounding of three gorge reservoir Author: Affiliation: Yangtze River Fisheries Research Institute, Chinese Academy of Fishery Sciences,Yangtze River Fisheries Research Institute, Chinese Academy of Fishery Sciences,,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:中华鲟是国家一级保护水生动物,是产底层产粘性卵鱼类。河床质构成了中华鲟受精卵和早期胚胎发育的物理环境,其变化可能直接影响中华鲟自然繁殖的规模和效果。基于水声学和水下视频技术对葛洲坝下现存唯一已知中华鲟自然产卵场的河床质特征进行了连续观测,对三峡水库蓄水以来中华鲟自然产卵场的河床质特征变化进行了研究。水声学分析结果显示,2004-2012年间,中华鲟产卵场区域内河床硬度未有明显变化,但粗糙度显著增加 (P < 0.05)。对产卵位点的河床质特征分析表明,下产卵区的硬度增加(2012年显著高于2008和2004年 (P < 0.05)),上产卵区硬度呈明显下降趋势(2004年显著高于2008和2012年(P < 0.05));上产卵区的河床粗糙度均呈不显著上升趋势(P > 0.05);下产卵场区的河床粗糙度呈显著上升趋势(P < 0.05)。水下视频观测结果显示,三峡蓄水导致的水体含沙量明显减少,对河床的冲刷日益明显,表现在产卵场江段沉积细砂和粗砂区域面积显著减少,河床卵石缝隙充塞度明显下降 (P < 0.05)。下产卵区在2007-2012年视频观察过程中发现河床卵石缝隙充分暴露,几乎没有任何细砂或粗砂填充,与上产卵区河床卵石缝隙充塞度特征明显不同。长期观测表明,2004-2012年期间中华鲟自然产卵位点发生了明显的改变,2004-2007年均发生在下产卵区,而2008-2012年均发生在上产卵区,自然繁殖规模和效果也明显下降。综合分析显示,中华鲟产卵场河床质特征的变化可能是导致中华鲟自然产卵位点的改变和迁移的原因,进而影响中华鲟自然产卵场的繁殖适合度,影响中华鲟自然繁殖的规模和效果。对三峡蓄水清水下泄的生态影响评估以及中华鲟自然产卵场的改良或修复有重要借鉴意义。 Abstract:Since 2010, the Chinese sturgeon Acipenser sinensis, one of the first-class national protected animals in China, has been classified as Critically Endangered in the IUCN Red List of Threatened Species. The last spawning ground of the Chinese sturgeon is located just downstream from the Gezhouba dam(GZD) after its construction, and thus, it is critical to retain the availability of the spawning ground for the sustainability of the species. The riverbed substrate and its surrounding microhabitat supply an environment for survival and development of the embryos of the Chinese sturgeon, and so chronic change to riverbed characteristics could have significant consequences on the reproductive success of the Chinese sturgeon. Based on long-term investigation of the ecological factors linked with natural spawning and especially observation of the spawning substrate characteristics over the last 8 years, the arrangement and structure of the bottom substrate of the spawning ground have been greatly changed from impounding of water in the Three Gorge Reservoir (TGR). At the same time, the critically important spawning sites as well as the spawning scale have also changed with spawning events occurring at spawning sites downstream (SSD) from 2004 to 2007 and spawning sites upstream (SSU) from 2008 to 2012. The ecological effects of the bottom substrate on spawning success and embryo development of the Chinese sturgeon are still not well documented. To study the effects of bottom substrate characteristics linked to impounding of water in the TGR, acoustic surveys with a scientific echo-sounder (2004-2012) and underwater video surveys (2007-2012) were conducted in the 6 km reaches of the Yangtze river just downstream from GZD including the last spawning ground of the Chinese sturgeon. The echo-sounder surveys showed that great changes in bottom hardness (as seen in the 1st part of the 1st Bottom Echo from start to peak of the echogram) and roughness (as seen in the 2nd part of the 1st Bottom Echo from the peak to the end of the echogram) have occurred in the spawning ground. Even though bottom hardness did not change significantly over the whole spawning ground (P > 0.05), bottom hardness in the SSD in 2012 was significantly higher than that in 2008 and 2004 (P < 0.05), while at same time, bottom hardness in the SSU in 2008 and 2012 was significantly lower than in 2004 (P < 0.05). Bottom roughness over the whole spawning ground and in the SSD increased significantly from 2004 to 2012 (P < 0.05), while no significant changes were found in the SSU.Underwater video surveys showed that with the erosion by the cleaner water impounded in the TGR, the coarse and fine sand that could be observed in the spawning ground in 2008 had almost completely disappeared in 2012 and the embeddedness (a term describing the degree to which river bottom gravel, cobbles and boulders were covered or had settled into the coarse and fine sand of the river bottom as obervered from the underwater video surveys) in the whole study area had decreased dramatically (P < 0.05). The embeddedness in the SSD and SSU was about the same in 2008 and 2012, respectively. Particular note was that the embeddedness in the SSD from 2007 to 2012 was almost zero, which meant there was no coarse or fine sand embedded on the bottom and this represented a significantly lower embeddedness than that in the SSU in 2008 and 2012.Combining the changes in riverbed characteristics with the displacement of the critical spawning site of the Chinese sturgeon, we found that where spawning occurred was in areas with moderate bottom hardness, roughness and embeddedness. We can conclude that the changes in riverbed characteristics have possibly caused the positional changes of the critical spawning sites of Chinese sturgeon. The changes in bottom characteristics of the spawning ground may have also caused a degradation in suitability of the bottom substrate for spawning and consequently may have contributed to the habitat loss of the spawning ground. However, further proof is required in future studies, which will thoroughly evaluate the ecological effects of the erosion by the clean water from the TGR and help for outline the necessary steps to be taken to rehabilitate the spawning ground of the Chinese sturgeon. 参考文献 相似文献 引证文献

Do agonistic behaviours bias baited remote underwater video surveys of fish?

AbstractMarine environments require monitoring to determine the effects of impacts such as climate change, coastal development and pollution and also to assess the effectiveness of conservation measures. Marine protected areas (MPAs) are being established globally and require periodic monitoring to determine whether their objectives are being met. Baited underwater video systems are becoming a popular method for monitoring change within protected fish populations, because they are less damaging to habitats than bottom trawling and allow for more statistical powerful comparisons to determine spatial and temporal patterns in the relative abundances, lengths and biomass of demersal and pelagic fishes. However, much remains uncertain about how interactions between the fish and bait and between the fish themselves affect the results obtained. Agonistic behaviours are frequently observed around the bait of the camera and potentially bias fish density estimates by altering the number and size classes seen at cameras. Here we counted the number of agonistic behaviours between pink snappers (Pagrus auratus), the size of fish involved and whether the fish left the field of view following such behaviours. The study consisted of 20 baited underwater video deployments inside a New Zealand marine reserve and 20 in adjacent open areas. We observed a significant relationship between the peak number of fish observed at the camera and the total number of agonistic behaviours, as well as the number of both aggressor and subordinate fish leaving the camera field of view following interactions. The slope of the latter relationship and thus the absolute numbers of fish leaving were higher for subordinate fish. As subordinates were significantly smaller than aggressors, the apparent size frequency distribution is likely skewed away from smaller size classes. The staying time of the fish and thus the maximum number of fish present at the camera will be reduced by agonistic behaviours and the absolute magnitude of this effect appears to be greater at high fish densities. Our results suggest that an overall effect of these phenomena is to underestimate the differences in abundance between MPAs and open areas, but also to overestimate differences in average size.

Examining the utility of alternative video monitoring metrics for indexing reef fish abundance

Underwater video has become an important tool for monitoring reef fish populations worldwide because it is nonextractive and not strongly selective. A variety of approaches have been developed to enumerate fish on videos, but to our knowledge these metrics have not been tested to determine if they are proportional to true abundance. We compared the most commonly used metric, MaxN (i.e., the maximum number of fish in a single frame during the viewing interval), to a newly developed metric, MeanCount (i.e., the mean number of fish observed in a series of snapshots over a viewing interval), using simulations, a laboratory experiment, and an empirical study. MaxN was nonlinearly related to true abundance using all three approaches, providing increasingly dampened estimates of abundance with increasing true abundance (i.e., hyperstability). Therefore, MaxN may result in positively biased indices of abundance for declining fish stocks or negatively biased abundance indices when fish stocks are increasing. Alternatively, MeanCount was generally linearly related to true abundance and its variability was similar to MaxN, suggesting that MeanCount can be useful for indexing abundance of fish in underwater video surveys.

Application of baited remote underwater video surveys to quantify spatial distribution of elasmobranchs at an ecosystem scale

Understanding the distribution of mobile species across broad spatial scales and a variety of habitat types is essential in developing sound conservation strategies. The applicability of baited remote under-water video station (BRUVS) to determine the distribution of elasmobranchs at broad spatial scales (12° latitude) and across a range of habitat types was assessed. Shark-like batoids within the Great Barrier Reef Marine Park (GBRMP) were chosen as a case study, given the conservation concern surrounding these species, limited knowledge of their spatial ecology and their exposure to fishing. Rhynchobatus spp. (88.9%), were most frequently observed followed by Rhina ancylostoma (7.1%) and Glaucostegus typus (3.9%). Shark-like batoids were observed across a wide depth range (10.4–87.5m), showing highest affinity for 30–40m. The main predictors of Rhynchobatus spp. presence in the GBRMP were location, substrate type and season with individuals more commonly observed during winter and autumn in regions with substrates dominated by mud or gravel. There was no difference in the proportion of BRUVS in which shark-like batoids were observed between fished and unfished marine park zones. Surveys with BRUVS offer a standardized, non-extractive technique for quantifying the spatial distribution of mobile species that are difficult to sample using conventional techniques across broad spatial scales. Information generated using BRUVS may be useful in helping design improved conservation strategies for rare or threatened elasmobranchs.

A comparison of inshore marine soundscapes

Sound travels well through water and is capable of conveying information to any listener on both the presence of particular organisms and the quality of the environment. Many marine organisms use sounds to navigate, forage and communicate, while different marine habitats often have their own acoustical characteristics. However, there are still large gaps in our knowledge of marine soundscapes, particularly in regard to their spatial patterns. The goal of this research was to investigate passive acoustic monitoring as an ecological survey technique. The specific objectives were to compare soundscapes between and within benthic habitats and to evaluate the influence of different environmental factors. Acoustic recordings were made in Lough Hyne, Ireland during May 2012, following a nested design in three benthic habitats; Mud, Gravel and Cliff. Three patches of each habitat were selected using hydro-acoustic and underwater video surveys and within each patch five different sites were monitored (n=45). A nested analysis of variance (ANOVA) showed that acoustic profiles differed significantly within but not between habitats, although unique acoustic signatures existed over different spatial ranges, illustrating a degree of stability at local patch level. A distinct peak (2–4kHz) in acoustic complexity was observed in all habitat patches but one, and was caused by the presence of transient broadband pulses or snaps. These snaps were attributed to the presence of snapping shrimp (family Alpheidae), found at a particular location within the lough. Other distinctive sounds of suspected biological origin were identified in particular habitat patches (Cliff and Gravel) and suggested the presence of habitat related biophonies. Soundscape signatures of different patches were strongly correlated with proximity to the source of the high-energy snaps, indicating that location was more important than habitat in determining soundscape characteristics. Other environmental factors such as bottom type and depth were less important. It is evident that acoustical sources of high energy and broadband properties have pervasive effects over considerable distances (up to 1km). The acoustic characteristics of a habitat patch were greatly influenced by extraneous sounds, in this case from a biological source. The high acoustic connectedness of marine habitats underlines the need for evaluating the impact of anthropogenic activities, particularly for ecosystems with unique biophonies in need of protection. There is potential for developing passive acoustic monitoring as a principal method for surveying marine habitats and observing local processes at different spatial and temporal scales.

Tidal currents, sampling effort and baited remote underwater video (BRUV) surveys: Are we drawing the right conclusions?

Estuaries are hydrographically dynamic environments, and such variability can affect the distribution and abundance of estuarine fish. Baited remote underwater video (BRUV) can be used to quantify estuarine species, but BRUV-derived data may be confounded by variable bait plume area and the associated effect on relative sampling effort. This study investigated the potential effects of current velocity on estuarine fish abundance data, and whether associated changes in bait plume size are important for benthic BRUV surveys in estuaries. BRUV sampling was conducted across two zones in two adjacent estuaries, and current velocity measured with a drogue during each BRUV deployment. Current velocity ranged from 0.02 to 0.65ms−1, resulting in potential bait plume areas that varied by orders of magnitude. The maximum number of each species (MaxN) was processed to produce a standardised (by bait plume area) and unstandardised multivariate species data set. The two data sets, whilst developed from identical video footage, yielded contrasting results. Unstandardised data was more variable, but produced a stronger correlation between abiotic variables and community structure. In addition, repeated sampling at some sites revealed significant temporal variance in community structure when data was standardised by bait plume area. Variability in sampling effort resulting from variable current velocity and associated bait plume area may confound interpretation of BRUV data.

Counting crayfish: active searching and baited cameras trump conventional hoop netting in detecting Euastacus armatus

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 19:39-45 (2012) - DOI: https://doi.org/10.3354/esr00460 Counting crayfish: active searching and baited cameras trump conventional hoop netting in detecting Euastacus armatus Christopher J. Fulton1,*, Danswell Starrs1, Monica P. Ruibal1, Brendan C. Ebner2 1Evolution, Ecology & Genetics, Research School of Biology, The Australian National University, Canberra, ACT 2601, Australia 2Tropical Landscapes Joint Venture, CSIRO Ecosystem Sciences & TropWATER, James Cook University, PO Box 780, Atherton, QLD 4883, Australia *Email: christopher.fulton@anu.edu.au ABSTRACT: Accurate distribution and abundance estimates for rare and endangered species are necessary to ascertain extinction threats and take appropriate conservation measures. Traditional capture-based methods are imperfect for surveying elusive species such as freshwater crayfish in upland streams. We compared estimates of Murray River crayfish Euastacus armatus abundance made via direct visual assessments by snorkel, against baited remote underwater video surveys (BRUVS) and traditional hoop netting conducted in 2 montane river systems. Similar total abundances were recorded via visual survey and BRUVS across 4 sites within 1 river system where E. armatus was relatively common. In contrast, markedly lower values were obtained at these sites via conventional hoop netting methods. In another stream where E. armatus is particularly rare, the only detection of this species was via BRUVS. Average catch per unit effort (CPUE) was highest from active visual surveys (2.99 ind. h−1), followed by BRUVS (0.63) and hoop netting (0.13). Extremely low sampling efficiency from hoop netting was attributed to the short time periods crayfish attended baits (mean ± SE, 387 ± 209 s) relative to the rate of net retrieval (hourly). We conclude that in systems of adequate water clarity, visual surveys and BRUVS provide reliable, non-invasive methods for estimating freshwater crayfish abundance and hold promise particularly for research and monitoring of threatened Euastacus species. KEY WORDS: Visual census · Trapping · Monitoring · Sample estimates · Parastacidae · Rarity Full text in pdf format PreviousNextCite this article as: Fulton CJ, Starrs D, Ruibal MP, Ebner BC (2012) Counting crayfish: active searching and baited cameras trump conventional hoop netting in detecting Euastacus armatus . Endang Species Res 19:39-45. https://doi.org/10.3354/esr00460 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 19, No. 1. Online publication date: November 07, 2012 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2012 Inter-Research.

Reef Sharks Exhibit Site-Fidelity and Higher Relative Abundance in Marine Reserves on the Mesoamerican Barrier Reef

Carcharhinid sharks can make up a large fraction of the top predators inhabiting tropical marine ecosystems and have declined in many regions due to intense fishing pressure. There is some support for the hypothesis that carcharhinid species that complete their life-cycle within coral reef ecosystems, hereafter referred to as “reef sharks”, are more abundant inside no-take marine reserves due to a reduction in fishing pressure (i.e., they benefit from marine reserves). Key predictions of this hypothesis are that (a) individual reef sharks exhibit high site-fidelity to these protected areas and (b) their relative abundance will generally be higher in these areas compared to fished reefs. To test this hypothesis for the first time in Caribbean coral reef ecosystems we combined acoustic monitoring and baited remote underwater video (BRUV) surveys to measure reef shark site-fidelity and relative abundance, respectively. We focused on the Caribbean reef shark (Carcharhinus perezi), the most common reef shark in the Western Atlantic, at Glover's Reef Marine Reserve (GRMR), Belize. Acoustically tagged sharks (N = 34) were detected throughout the year at this location and exhibited strong site-fidelity. Shark presence or absence on 200 BRUVs deployed at GRMR and three other sites (another reserve site and two fished reefs) showed that the factor “marine reserve” had a significant positive effect on reef shark presence. We rejected environmental factors or site-environment interactions as predominant drivers of this pattern. These results are consistent with the hypothesis that marine reserves can benefit reef shark populations and we suggest new hypotheses to determine the underlying mechanism(s) involved: reduced fishing mortality or enhanced prey availability.

Bottom substrate attributes relative to bedform morphology of spawning site of Chinese sturgeon Acipenser sinensis below the Gezhouba dam

Characteristics of bottom substrates have caused wide concernas to their importance for sturgeon spawning ground requirements. Substrate requirements for spawning of Chinese sturgeon Acipenser sinensis have not yet been well studied because of the difficulties in investigating on a large and fast flowing river such as the Yangtze River. During 2007 and 2008, the underwater video surveys on the present spawning ground of A. sinensis were successfully conducted. Two kinds of substrates were documented: one stable infrastructure consisting of large boulders and cobbles mixed with pebbles and gravels, the other comprise sediments in transportation, especially coarse and fine sands. The large boulders (size range 20–50 cm), cobbles and pebbles (size range 10–20 cm), pebbles or gravels are estimated to account for 50, 30, 20% of the available substrates of the infrastructure on spawning ground according to our underwater video survey points, respectively. The transporting sands can be observed in most area, while the river sand embedded or covered the large structural compounds just occur in certain area and the substrate where spawning occurs annually and occasionally were similarly ‘clean’ of fine sediment. The eggs (embryos) of Chinese sturgeon have been observed ‘hiding’ in or adhering to the interstitial spaces between the clean large materials e.g. boulders, cobbles and pebbles during the 2007/2008 study period. Therefore the degree of cover of the larger particles by sand (embeddedness), which will directly affect the spawning habitat and subsequently influence survival of the new hatched larvae, were assessed by determining the topographic data in relation to water velocity. The multivariable correlation analysis and binary logistic regression analysis showed that the comparably topographic characteristics which had been confirmed to be suitable at the historic and present spawning sites would eventually contribute to the substrate deposition. The embeddedness of the sediment are obviously lower in shallow water with higher water velocity than in the deeper water with slower water current (P < 0.01) and the sites where the embryo occur can be predicted with the three physical variables: embeddedness of the sediment, water velocity and river bottom elevation. The bedform morphology with an adverse slope (channel slope adverse to the bottom elevation grads) formed by larger blocks of substrate, will improve the water turbulence at high current to carry the suspended or embedded fine sediments away from the spawning site and (in turn) provide enough interstitial spaces for effective egg deposition and incubation. Therefore the substrate requirements for the spawning habitat of Chinese sturgeon should be described and assessed more than just rocky and gravelly substrate, taking the embeddedness of sediment in well consider. The concepts of detailed description of the substrate requirements and their relationship with the overall bedform morphology has been shown to be essential to provide benefit for the rehabilitation of the spawning ground while fostering the conservation of the endangered species.

Validating the use of baited remote underwater video surveys for assessing the diversity, distribution and abundance of sharks in the Bahamas

Baited remote underwater video surveys (BRUVS) are a novel, non-invasive method of generating relative abundance indices for a number of marine species, including sharks. This tech- nique has become increasingly prevalent in shark ecology literature, but has yet to be formally vali- dated against more traditional shark survey methods. BRUVS and longline surveys were conducted over 4 seasons from summer 2008 to spring 2009, in 3 habitat zones in the waters off Cape Eleuthera, The Bahamas. By the end of the project, both techniques generated similar values of species richness; however, longline surveys reached these values faster and with fewer replicates than BRUVS. Over- all there was a significant positive correlation of relative abundance between the 2 survey tech- niques, but when analysed on a species-by-species basis, correlations were not statistically signifi- cant for the less abundant species. This suggests a threshold level of abundance, below which relative abundance estimates generated by the different survey techniques do not agree. In addition, this study identified shortcomings in the ability of BRUVS to accurately identify the species, size and sex of individuals captured on video due to the variable behaviour of the sharks in front of the cam- era; however, technological improvements incorporated into contemporary studies are identified which might improve data quality. BRUVS offer a non-invasive alternative to longline surveys for monitoring broad trends in the relative abundance of sharks, although in the format tested in this study they may lack the resolution required to approach finer scale, intra-species studies.

An inexpensive system for underwater video surveys of demersal fishes

A system for visual surveys of bottom fishes, assembled from readily available components, is described. A camera and a depth sounder transducer are mounted on a towed body. The camera captures the images, and the depth sounder measures the distance between the camera and the bottom. A video recorder is used to record the data—the video channel for the image, and the audio channel for distance information, which is dictated from the depth sounder display into a microphone. A relationship between distance and magnification is used to estimate the width of the survey path and the size of surveyed objects. A comparison of round goby ( Apollonia melanostoma) density estimated by repeated seining and use of the underwater visual apparatus showed that the smallest individuals are underrepresented by the visual assessment, but the visual method detects about 85% of the 50 mm TL or larger gobies.

Characteristics of Marine Aggregates in Shallow-water Ecosystems: Implications for Disease Ecology

Marine aggregates were evaluated for their potential role in the ecology of aquatic pathogens using underwater video surveys coupled with direct collection of aggregates in modified settling cones. Six locations, two each in New York, Connecticut, and Massachusetts, were surveyed over 8 months to explore differences in the characteristics of aggregates found in habitats populated by clams (Mercenaria mercenaria) and oysters (Crassostrea virginica). Microaggregate ( 500 μm) concentrations, but peak concentrations of macroaggregates and microaggregates, mean size of particles, and volume fraction of aggregated material varied among the six shallow-water habitats. Concentrations (colony-forming units per ml) of total heterotrophic bacteria (THB) and total mesophilic pathogenic bacteria (MPB) from samples of aggregates were significantly different among the four locations bordering Long Island Sound (LIS). The highest concentrations and enrichment factors in aggregates were observed in August for THB and in June for MPB. Significant correlations were detected for salinity and the concentrations and enrichment factors of THB in aggregates and for the concentrations and percentages of MPB in seawater samples. Significant correlations were also detected for temperature and the concentrations of MPB in aggregates and the enrichment factors for THB and MPB (marginal significance). Bacterial species identified in association with aggregates included: Vibrio cholerea, V. parahaemolyticus, V. vulnificus, V. alginolyticus, Aeromonas hydrophila, Pseudomonas aeruginosa, Escherichia coli, and Mycobacteria sp. These results have important implications for the way in which aquatic pathogens are collected, quantified, and monitored for risk-based surveillance in shallow-water ecosystems.