Stereo-video Systems Research Articles

Length selectivity of commercial fish traps assessed from in situ comparisons with stereo-video: Is there evidence of sampling bias?

Stock assessments of tropical demersal teleost fisheries generally rely on fishery-dependent samples of age structure. Baited remote underwater stereo-video (stereo-BRUV) systems can provide fishery independent information on the biases and selectivity of particular fishing gears in relation to the length distribution of what is potentially available for capture. In the tropical demersal fishery off northwestern Australia the length distributions of 12 species sampled by standard commercial fish traps and stereo-BRUVs were compared using kernel density estimation techniques. We found no significant differences in the shape of the length distributions sampled by either method. However, the location (mean length) of the length distribution of seven of the 11 target species and the one bycatch species differed between the sampling methods. A family-specific trend was exhibited, likely due to the ambush behaviour of larger epinephelids in traps and the saturation of the field of view of stereo-BRUV by schools of smaller lutjanids. However, the difference in mean length was not biologically significant for these families. These results indicate that samples of target species derived from commercial trap catches are likely to provide representative and robust estimates of vital population statistics and life history parameters.

Depth Refuge and the Impacts of SCUBA Spearfishing on Coral Reef Fishes

In recent decades, spearfishing with SCUBA has emerged as an efficient method for targeting reef fish in deeper waters. However, deeper waters are increasingly recognised as a potential source of refuge that may help sustain fishery resources. We used a combination of historical catch data over a 20-year time period and fishery-independent surveys to investigate the effects of SCUBA spearfishing on coral reef fish populations in the southern Mariana Islands. Two jurisdictions were studied; Guam, where SCUBA spearfishing is practiced, and the nearby Commonwealth of Northern Mariana Islands (CNMI), where SCUBA spearfishing has been banned since 2003. Fishery-independent data were collected using baited remote underwater stereo-video systems (stereo-BRUVs) stratified by depth, marine protected area status and jurisdiction. Herbivores (primary consumers) dominated spearfishing catches, with parrotfish (scarines) and surgeonfish/unicornfish (acanthurids) the main groups harvested. However, the large, endangered humphead wrasse (Cheilinus undulatus) was the main species by weight landed by SCUBA spearfishers. SCUBA spearfishing was associated with declining size of scarines over time and catches shifting from a dominance of large parrotfishes to a mixed assemblage with increasing proportions of acanthurids. Comparisons between Guam and the nearby CNMI revealed differences in the assemblage of fished species and also greater size of scarines and acanthurids in deep water where SCUBA fishing is banned. These results suggest that SCUBA spearfishing impacts reef fish populations and that the restriction of this fishing method will ensure refuge for fish populations in deeper waters. We recommend a ban on SCUBA spearfishing to preserve or aid the recovery of large, functionally important coral reef species and to improve the sustainability of coral reef fisheries.

A little bait goes a long way: The influence of bait quantity on a temperate fish assemblage sampled using stereo-BRUVs

Baited remote underwater video systems are becoming a widely adopted tool for sampling fish assemblages. One of the outstanding knowledge gaps associated with this technique is the effect of different quantities of bait on the fish assemblages sampled. We investigated how different quantities of bait (0g, 200g, 1000g or 2000g of crushed pilchards, Sardinops sagax) influenced the relative abundance and species richness of a temperate, Western Australian reef fish assemblage sampled with baited remote underwater stereo-video systems (stereo-BRUVs). The presence of bait significantly increased the relative abundance and numbers of fish species sampled, with few differences between the three quantities of bait. Trends in fork length were identified between bait quantities for some species. For example, juvenile stage Coris auricularis (a protogynous labrid) were significantly larger in the unbaited treatment, whereas males of the same species were significantly smaller at unbaited treatments. This pattern was interpreted as being the result of intraspecific competition and the dominance of larger males in the presence of bait. When bait was present, fish were significantly closer to the stereo-BRUVs. However, there was again no difference between the three baited treatments.At this location in temperate Western Australia, stereo-BRUVs with 200g of bait are as effective at sampling the temperate reef fish assemblage as stereo-BRUVs set with greater quantities of bait. In our study, the numbers of high trophic level species recorded were low. In areas with abundant high trophic level fishes, such as tropical reef systems, greater quantities of bait may be required to prevent it being quickly depleted by intense feeding.

Presettlement schooling behaviour of a priacanthid, the Purplespotted Bigeye Priacanthus tayenus (Priacanthidae: Teleostei)

We report in situ behavioural observations of presettlement schooling in Priacanthus tayenus off Coral Bay, Western Australia collected using pelagic Baited Remote Underwater stereo-Video systems. Two groups of fish (8 and 9 individuals) were observed that aggregated into a single school. Mean total length was 24.1 mm (12.5–30.2 mm). The fish swam at a mean speed of 8.5 cm s−1 in a group spacing themselves more or less evenly at a distance of around one body length from the nearest neighbour within the school. P. tayenus appeared to be sometimes associated with juveniles of other species. The results presented here add to the limited, but growing body of literature on the schooling behaviour of the early pelagic stages of demersal fishes.

Using artificial illumination to survey nocturnal reef fish

Effects of three different light wavelengths (blue, red and white) were assessed on the composition, abundance and behaviour of nocturnal fish at the Houtman Abrolhos Islands, Western Australia. The effects of fishing were also considered by further examining the combined effects of lighting and fishing (open vs. closed areas). Data were collected using baited remote underwater stereo-video systems (stereo-BRUVs), which were equipped with red (620–630nm), white (550–560nm) or blue (450–465nm) lights. The total number of individuals, relative abundance of fish and assemblage composition differed under each lighting condition and fishing status. The greatest number of individuals was observed on samples illuminated by red lights (43% of all individuals surveyed). The species Apogon doederleini, Gymnothorax woodwardi, and Pempheris klunzingeri were each more abundant and spent longer in the field of view of the cameras using red lights. In contrast to white and blue light, the wavelength of red light is thought to be beyond the visual sensitivity of these fish species, and may not have affected their behaviour. The heavily targeted species, Pagrus auratus, were twice as abundant on stereo-BRUVs illuminated by blue lights and white lights than on red lights, but only in areas closed to fishing. This higher abundance on blue and white lights may have been due to the attraction of baitfish to these lights. In addition to the effects of lighting, clear effects of fishing were noted on nocturnal populations of P. auratus. Light wavelength can influence observations and measurements made of a nocturnal fish assemblage, and therefore careful consideration of choice of light wavelength should be made for nocturnal studies using artificial illumination on stereo-BRUVs.

Similarities between Line Fishing and Baited Stereo-Video Estimations of Length-Frequency: Novel Application of Kernel Density Estimates

Age structure data is essential for single species stock assessments but length-frequency data can provide complementary information. In south-western Australia, the majority of these data for exploited species are derived from line caught fish. However, baited remote underwater stereo-video systems (stereo-BRUVS) surveys have also been found to provide accurate length measurements. Given that line fishing tends to be biased towards larger fish, we predicted that, stereo-BRUVS would yield length-frequency data with a smaller mean length and skewed towards smaller fish than that collected by fisheries-independent line fishing. To assess the biases and selectivity of stereo-BRUVS and line fishing we compared the length-frequencies obtained for three commonly fished species, using a novel application of the Kernel Density Estimate (KDE) method and the established Kolmogorov–Smirnov (KS) test. The shape of the length-frequency distribution obtained for the labrid Choerodon rubescens by stereo-BRUVS and line fishing did not differ significantly, but, as predicted, the mean length estimated from stereo-BRUVS was 17% smaller. Contrary to our predictions, the mean length and shape of the length-frequency distribution for the epinephelid Epinephelides armatus did not differ significantly between line fishing and stereo-BRUVS. For the sparid Pagrus auratus, the length frequency distribution derived from the stereo-BRUVS method was bi-modal, while that from line fishing was uni-modal. However, the location of the first modal length class for P. auratus observed by each sampling method was similar. No differences were found between the results of the KS and KDE tests, however, KDE provided a data-driven method for approximating length-frequency data to a probability function and a useful way of describing and testing any differences between length-frequency samples. This study found the overall size selectivity of line fishing and stereo-BRUVS were unexpectedly similar.

Response of diurnal and nocturnal coral reef fish to protection from fishing: an assessment using baited remote underwater video

Diel variation is known to alter the composition and structure of reef fish assemblages. What is unknown is how nocturnal fish assemblages respond to closed fishery area management. Diurnal and nocturnal reef fish assemblages at the Houtman Abrolhos Islands, Western Australia, were studied using baited remote underwater stereo-video systems (stereo-BRUVs). Surveys were conducted during the day and at night (using blue illumination) from three sites inside and three sites outside a closed fishery area (CFA). The relative abundance of 116 fish species from 41 families was recorded. Significant changes were observed in fish assemblage structure from day to night (driven by high dispersion at night) and in areas open versus closed to fishing (driven by increased abundance within the CFA). The effect of protection from fishing was consistent for both diurnal and nocturnal fish assemblages. Closer examination of six targeted fish species showed that their response to diel changes and the absence of fishing pressure varied from species to species. The targeted fishes Pagrus auratus and Glaucosoma hebraicum were sampled during the day and at night with both species responding positively to protection from fishing. Results suggest that the inclusion of diurnal and nocturnal fish assemblage data will provide an improved ability to assess the effectiveness of closed fishery area management.

Bait Effects in Sampling Coral Reef Fish Assemblages with Stereo-BRUVs

Baited underwater video techniques are increasingly being utilised for assessing and monitoring demersal fishes because they are: 1) non extractive, 2) can be used to sample across multiple habitats and depths, 3) are cost effective, 4) sample a broader range of species than many other techniques, 5) and with greater statistical power. However, an examination of the literature demonstrates that a range of different bait types are being used. The use of different types of bait can create an additional source of variability in sampling programs. Coral reef fish assemblages at the Houtman Abrolhos Islands, Western Australia, were sampled using baited remote underwater stereo-video systems. One-hour stereo-video recordings were collected for four different bait treatments (pilchards, cat food, falafel mix and no bait (control)) from sites inside and outside a targeted fishery closure (TFC). In total, 5209 individuals from 132 fish species belonging to 41 families were recorded. There were significant differences in the fish assemblage structure and composition between baited and non-baited treatments (P<0.001), while no difference was observed with species richness. Samples baited with cat food and pilchards contained similar ingredients and were found to record similar components of the fish assemblage. There were no significant differences in the fish assemblages in areas open or closed to fishing, regardless of the bait used. Investigation of five targeted species indicated that the response to different types of bait was species-specific. For example, the relative abundance of Pagrus auratus was found to increase in areas protected from fishing, but only in samples baited with pilchards and cat food. The results indicate that the use of bait in conjunction with stereo-BRUVs is advantageous. On balance, the use of pilchards as a standardised bait for stereo-BRUVs deployments is justified for use along the mid-west coast of Western Australia.

Contrasting habitat use of diurnal and nocturnal fish assemblages in temperate Western Australia

This study examined the diversity and relative abundance of fish species in six coastal habitats during the day and at night. Habitats included seagrass beds, Ecklonia macroalgal beds, other macrophytes, deep reef, rhodolith beds and sand. Surveys were conducted using baited remote underwater stereo-video systems, which at night were equipped with either white or red lights. Three research questions were examined; 1) do fish assemblages sampled during the day differ to those sampled at night across six inshore and near shore marine habitats? 2) Are patterns of habitat associations displayed by diurnal fishes maintained at night? 3) Do stereo-BRUVs sample different fish assemblages when equipped with red versus white lights?Diurnal surveys sampled significantly greater species richness (66% greater) and numbers of individuals (92% more than red lights, 82% than white lights) than nocturnal surveys. Diurnal surveys also showed greater discrimination in the fish assemblages between the six habitats with replicate samples from a habitat clustered together. This clustering of replicate samples was reduced at night where a number of species of fish were seen in multiple habitats. Thirty-one percent of the species viewed at night were seen on multiple habitats, but only a single habitat during the day.Compared to red lights, white lights surveyed a greater number of individuals and species in rhodolith beds (94% more individuals and 63% more species) and over sand (94% more individuals, 83% more species). This was likely due to an attraction of fish to bait fish accumulating near the white light source, but not in the red light source. However, surveys of fish assemblages at night were deemed most effective when red lights were used, because this lighting type had an improved ability to statistically distinguish fish assemblages across the habitats surveyed. By conducting nocturnal survey studies researchers may obtain a more holistic understanding of habitat use by fish species and account for this usage in biodiversity and fisheries management plans.

Within and between day variability in temperate reef fish assemblages: Learned response to baited video

Many studies that test for spatial patterns in fish assemblages do not have temporal replication, and where they do, the scale of this replication is in the order of seasons or years. Rarely are patterns tested at the scale of days or time of day. As a result, any descriptions of spatial patterns are potentially confounded by within or between day variations, with differences between locations possibly due to the differences between times sampled. This study aimed to determine whether significant short-term temporal variability existed within and between days in a temperate, shallow-water reef fish assemblage in south-western Australia. Three sites were sampled at morning, midday and afternoon for five consecutive days using baited remote underwater stereo–video systems. Significant differences were detected in the fish assemblage at different times of the day with morning and midday assemblages different from afternoon assemblages. Differences were detected between days with a significant shift in the assemblage after day two. The use of bait in this study was thought to influence the behaviour of Pseudocaranx spp. which furthermore influenced sampling of the entire fish assemblage between days. This study shows that large scale monitoring and sampling programmes using baited cameras need to consider the possible influence of within and between day variability in their experimental designs and must carefully design sampling to test for spatial and temporal structures in fish assemblages.

Comparison of the relative efficiencies of stereo-BRUVs and traps for sampling tropical continental shelf demersal fishes

The sampling efficiencies of commercial standard fish traps and baited remote underwater stereo-video systems (stereo-BRUVs) were compared by examining the diversity and relative abundance of tropical demersal fish that each method sampled on the north-western shelf (40–60m) of Western Australia. Stereo-BRUVs recorded many more species (91 species from 32 families) than commercial fish traps (30 species and 15 families). Stereo-BRUVs also sampled many more individuals (mean 36.55±5.91 SE) than fish traps (mean 12.30±1.40 SE). This suggests stereo-BRUVs would be more capable of detecting changes in the relative abundance of species over time. Data from four commercially important species (Epinephelus bilobatus, Epinephelus multinotatus, Lethrinus punctulatus and Lutjanus russelli) revealed that stereo-BRUVs had much greater statistical power to detect change than an equivalent number of samples from fish traps. In contrast, fish traps had a greater statistical power to detect change for a fifth target species, Lutjanus sebae. For two commonly sampled species, Abalistes stellatus11Usage follows CAABcodes (Rees, A.J.J., Yearsley, G.K., Gowlett-Holmes, K. and Pogonoski, J. Codes for Australian Aquatic Biota (on-line version). CSIRO Marine and Atmospheric Research, World Wide Web electronic publication, 1999 onwards. Available at: http://www.cmar.csiro.au/caab/.). and Lethrinus punctulatus, stereo-BRUVs sampled a smaller mean length than fish traps while for a third species, Lutjanus sebae, stereo-BRUVs recorded a larger mean length. The length frequencies for these species were not significantly different between methods, although stereo-BRUVs sampled a much larger range of lengths than was captured in traps. This study demonstrates that stereo-BRUVs are potentially a much more powerful technique than fish traps for assessing species richness, relative abundance and size structure in multi-species fisheries in north-western Australia.

Declines in the abundance of coral trout ( Plectropomus leopardus) in areas closed to fishing at the Houtman Abrolhos Islands, Western Australia

This study aimed to assess temporal trends in the abundance and size of the tropical coral trout, Plectropomus leopardus (Lacepède, 1802), in areas open and closed to fishing at the Houtman Abrolhos Islands. Baited remote underwater stereo-video systems (stereo BRUVs) were used to conduct surveys from 2005 to 2009 from shallow and deep sites across four geographically-separated groups of islands. A total of 1542 P. leopardus were observed from 77% of stereo BRUV deployments with an average abundance of 2.35 ± 0.1 SE per deployment. The lengths of 1238 individuals were measured, with sizes ranging from 118.2 to 727 mm. At commencement of the study in 2005, there were 65% more P. leopardus in areas open vs. closed to fishing. From 2005 to 2009, however, abundances fell by 50% in areas closed to fishing, such that abundances were then similar between areas open and closed to fishing. Relative abundance changed very little in fished locations throughout the course of the study, despite the implementation of fisheries restrictions on other iconic species that may have increased fishing effort on P. leopardus. In areas closed to fishing 12–32% of P. leopardus measured over the five years of the study (average of 25%) were larger than the minimum legal size for retention of 450 mm total length. Much fewer were larger than legal size in areas open to fishing (6–15%, average of 11%). Illegal fishing is considered to be the primary cause of the decline in abundance of P. leopardus inside closed area boundaries.

Evidence of artisanal fishing impacts and depth refuge in assemblages of Fijian reef fish

Protection from fishing generally results in an increase in the abundance and biomass of species targeted by fisheries within marine reserve boundaries. Natural refuges such as depth may also protect such species, yet few studies in the Indo Pacific have investigated the effects of depth concomitant with marine reserves. We studied the effects of artisanal fishing and depth on reef fish assemblages in the Kubulau District of Vanua Levu Island, Fiji, using baited remote underwater stereo-video systems. Video samples were collected from shallow (5–8 m) and deep (25–30 m) sites inside and outside of a large old marine reserve (60.6 km2, 13 years old) and a small new marine reserve (4.25 km2, 4 years old). Species richness tended to be greater in the shallow waters of the large old reserve when compared to fished areas. In the deeper waters, species richness appeared to be comparable. The difference in shallow waters was driven by species targeted by fisheries, indicative of a depth refuge effect. In contrast, differences in the abundance composition of the fish assemblage existed between protected and fished areas for deep sites, but not shallow. Fish species targeted by local fisheries were 89% more abundant inside the large old reserve than surrounding fished areas, while non-targeted species were comparable. We observed no difference in the species richness or abundance of species targeted by fisheries inside and outside of the small new reserve. This study suggests that artisanal fishing impacts on the abundance and species richness of coral reef fish assemblages and effects of protection are more apparent with large reserves that have been established for a long period of time. Observed effects of protection also vary with depth, highlighting the importance of explicitly incorporating multiple depth strata in studies of marine reserves.

Large decline in the abundance of a targeted tropical lethrinid in areas open and closed to fishing

In Western Australia, one of the most important commercially and recreationally tar- geted, yet understudied fish species is the redthroat emperor Lethrinus miniatus. The present study aimed to compare the relative abundance and size of L. miniatus in areas open and closed to fishing at the Houtman Abrolhos Islands and to assess change in these populations over a 5 yr period. Baited remote underwater stereo-video systems (stereo BRUVs) were used to conduct the surveys from 2005 to 2009, which included different depths and locations across 4 geographically separated groups of islands. Data showed high spatial variability in the relative abundance of L. miniatus across depths, sites, and island group locations. In 2005 and 2006, L. miniatus were more abundant at depths of 22 to 26 m than in 8 to 12 m. At this time, individuals were also 1.3× more abundant and 10% larger in length in areas closed to fishing than in areas open to fishing. Starting in 2007, however, relative abundances of L. miniatus declined so markedly that in 2009 only 20% of the 2005 and 2006 numbers remained. This decline removed the disparity between depths, closed areas and fished locations. Unlike with relative abundance, L. miniatus remained consistently larger inside closed areas (mean 370 mm fork length) than in areas open to fishing (mean 350 mm). Of the 483 individuals measured across the 5 yr of the study, 98% were larger than the minimum legal size for retention, and therefore subject to harvest. Mean lengths increased each year, as the size structure of the population reflected an aging cohort. With declines in measured relative abundance in excess of 80% over the past 5 yr, the sustainability of L. miniatus assemblages at the Houtman Abrolhos Islands is in question.

Influence of Range, Angle of View, Image Resolution and Image Compression on Underwater Stereo-Video Measurements: High-Definition and Broadcast-Resolution Video Cameras Compared

AbstractAn investigation of how increasing the distance and angle to objects of interest affected the measurement accuracy and precision achievable with high-definition and medium-resolution PAL stereo-video systems was conducted. A test was also conducted to determine whether varying the compression of the imagery influenced measurement accuracy and precision. Measurements of five different lengths of PVC pipe (ranging from 51.5 to 3,001 mm) that represented the lengths of reef fishes routinely sampled with stereo-video were made at 1 m intervals out to the maximum visibility (9 m range) over three different angles (90°, 80° and 70°). High-definition stereo-video imagery was compressed at three different bit-rates. The results show that higher definition stereo-video imagery allows objects to be measured more accurately and precisely over greater ranges. When both ends of a target can be clearly seen in high-definition stereo-video imagery, the associated error is approximately 1% of the total length of the object. There was no deleterious effect on accuracy or precision from increasing the angle of view. Lower compression did not result in more accurate and precise length estimates. The configuration of a stereo-video system needs to match the task of a particular survey, as changes in the base separation and angle of convergence will affect the accuracy and precision of measurements. With full high-definition systems, smaller lengths (&lt;50 mm) of PVC could not be accurately measured at distances greater than 5 m whereas longer lengths (500‐3,001 mm) could be measured with acceptable accuracy and precision at 9 m.

Using Stereo-Video for Deep Water Benthic Habitat Surveys

Towed body systems of various configurations have been used for many years to map the seabed. Prior to the last several years, single video camera systems were widely used to gather qualitative data, or collect often low-accuracy quantitative data using laser dot patterns projected into the field of view. The introduction of stereo-video systems has enabled the capture of accurate and reliable spatial information with estimates of accuracy and precision. CSIRO has recently adopted stereo-video on a towed body system used for habitat mapping and biodiversity survey work in the deep ocean (100 to 2,000 m depths). This paper provides an overview of the research context, describes the towed body system, and reports on the addition of stereo-video to the system and the status of ongoing developments in the project. Applications of the system to managing marine biological resources are illustrated using examples from surveys undertaken recently off Southeast Australia.

A method for the possible species discrimination of juvenile gadoids by broad-bandwidth backscattering spectra vs. angle of incidence

AbstractLundgren, B., and Nielsen, J. R. 2008. A method for the possible species discrimination of juvenile gadoids by broad-bandwidth backscattering spectra vs. angle of incidence. – ICES Journal of Marine Science, 65: 581–593. Measurements were made of the broad-bandwidth (80–220 kHz) acoustic backscattering from free-swimming juvenile gadoids at various orientations and positions in an acoustic beam, under controlled conditions. The experimental apparatus consisted of a stereo-video camera system, a broad-bandwidth echosounder and echo-processor system, a narrowband 120 kHz split-beam echosounder, a large tank, and a fishnet cage. The net cage was centred on the acoustic beams and was virtually transparent, both acoustically and optically. Accurate three-dimensional positions and angular orientations of individual fish were estimated from stereo-images captured synchronously when broad-bandwidth echoes were received from passing fish. Fish positions were also estimated from data collected with a synchronized split-beam echosounder. Software was developed for image analysis and modelling, including calibration, alignment of acoustic and optical-reference frames, and automatic position-fitting of fish models to manually marked fix-points on fish images. The software also performs Fourier spectrum analysis and pulse-shape analysis of broad-bandwidth echoes. Therefore, several measurement series on free-swimming juvenile gadoids were evaluated. The method and data may be used to improve the acoustic identification of fish species and sizes, and thereby improve investigations of spatial prey–predator relationships, and the accuracy and efficiency of acoustic surveys.

Behaviour of temperate and sub-tropical reef fishes towards a stationary SCUBA diver

Using remote underwater stereo–video systems we examined fish behaviour towards a stationary SCUBA diver at temperate (Rottnest Island) and sub-tropical (Houtman Abrolhos Islands) reefs in Western Australia. Changes in species richness, relative abundance, fish length, and the mean distance of individual fish from stereo–video cameras, in the presence and absence of a SCUBA diver, were assessed to infer changes in behaviour. Results show that a stationary SCUBA diver may obtain accurate measures of species richness and of the composition of fish assemblages in an area. However, the usefulness of these measures to reflect changes in fish behaviour appears limited as responses of fish towards the stationary SCUBA diver were highly species specific. Several species differed in their mean relative abundance (Heterodontus portusjacksoni, Coris auricularis, Thalassoma lunare), length (Ophthalmolepsis lineolatus, C. auricularis), and the distance to which they would approach the stereo–video systems (Kyphosus sydneyanus, Scarus schlegeli) when a SCUBA diver was present. Here, species-specific changes in the behaviour of several common and abundant fish species towards a stationary SCUBA diver advises caution to avoid biases when interpreting results obtained by SCUBA divers.

Joint Prediction Algorithm and Architecture for Stereo Video Hybrid Coding Systems

3-D video will be the most prominent video technology in the next generation. Among the 3-D video technologies, stereo video systems are considered to be realized first in the near future. Stereo video systems require double bandwidth and more than twice the computational complexity relative to mono-video systems. Thus, an efficient coding scheme is necessary for transmitting stereo video. In this paper, a new structure of prediction core in stereo video coding systems is proposed from the algorithm level to the hardware architecture level. The joint prediction algorithm (JPA), which combines three prediction schemes, is proposed for high coding efficiency and low computational complexity. It makes the system outperform MPEG-4 temporal scalability and simple profile by 2-3 dB in rate-distortion performance. Besides, JPA also utilizes the characteristics of stereo video and successfully reduces about 80% computational complexity. Then, a new hardware architecture of the prediction core based on JPA and a modified hierarchical search block-matching algorithm is proposed. With a special data flow, no bubble cycles exist during the block-matching process. The proposed architecture also adopts the near-overlapped candidates reuse scheme to save the heavy burden of data access. Besides, both on-chip memory requirement and off-chip memory bandwidth can be reduced by the proposed new scheduling. Compared with the hardware requirement for the implementation of full search block-matching algorithm, only 11.5% on-chip SRAM and 3.3% processing elements are needed with a tiny PSNR drop, making it area-efficient while maintaining high stereo video quality and processing capability

Experimental Evaluation of Tracking Algorithms Used for the Determination of Fish Behavioral Statistics

The fine-scale swimming behavior of fish can now be studied because of the development of sophisticated measurement devices such as multibeam sonar and stereo video systems. However, even with these sensors, improved methods are still required to generate quality estimates of swimming speeds and turn rates. Biologists have commonly relied on pointwise differentiation of noisy position measurements while engineers have focused on Bayesian algorithms to track underwater vehicles. A comparative evaluation of the performance of these tracking algorithms for the analysis of fine-scale behavior of fish was performed using a data set of 100 fish tracks recorded simultaneously with a multibeam sonar and a stereo video camera system. The segmenting track identifier, a non-Bayesian curve fitting and segmenting tracker, is shown to be most effective for tracking the unpredictable and complex horizontal motion of fish while a Kalman smoother using a constant-velocity model is shown to be most effective for tracking the more predictable and piecewise linear vertical motion of fish. Both are shown to be more effective than pointwise differentiation. Criteria for selecting an appropriate algorithm for a given motion study are provided