A baited underwater video technique to assess shallow-water Mediterranean fish assemblages: Methodological evaluation

A baited underwater video (BUV) system for the study of reef-associated fish populations on shallow (10-20 m) rocky habitats in the western Mediterranean was assessed at four locations in Spain and two in France. We describe the apparatus and optimal deployment times for video sampling. Different species had different response times to the bait, with four response groups identified. Examination of species accumulation curves and fish abundance estimates over time revealed that a period of approximately 20 min deployment was sufficient to capture most species on video. The technique sampled a wide variety of species, with 51 species belonging to 33 families recorded. Nine species of fish appeared regularly at the bait in relatively high numbers, and consist of six carnivores (Serranus cabrilla, Serranus scriba, Coris julis, Diplodus annularis, Diplodus vulgaris, Thalassoma pavo), two planktivores (Chromis chromis, Boops boops) and one omnivore (Oblada melanura). However, abundance estimates for other species were generally very low (mean < 1 per location). Comparison of results from BUV with those obtained by Underwater Visual Census (UVC) at the same locations suggests that although BUV estimates species richness reliably, UVC is the more suitable technique for estimating the abundance of shallow-water reef fish in the Mediterranean. BUV improvements are suggested to optimise its use in deeper waters where UVC using scuba is inoperable.     

Protection from illegal fishing and shark recovery restructures mesopredatory fish communities on a coral reef

The recovery of communities of predatory fishes within a no‐take marine reserve after the eradication of illegal fishing provides an opportunity to examine the role of sharks and other large‐bodied mesopredatory fishes in structuring reef fish communities. We used baited remote underwater video stations to investigate whether an increase in sharks was associated with a change in structure of the mesopredatory fish community at Ashmore Reef, Western Australia. We found an almost fourfold increase in shark abundance in reef habitat from 0.64 hr^?1 ± 0.15 SE in 2004, when Ashmore Reef was being fished illegally, to 2.45 hr^?1 ± 0.37 in 2016, after eight years of full‐time enforcement of the reserve. Shark recovery in reef habitat was accompanied by a two and a half‐fold decline in the abundance of small mesopredatory fishes (≤50 cm TL) (14.00 hr^?1 ± 3.79 to 5.6 hr^?1 ± 1.20) and a concomitant increase in large mesopredatory fishes (≥100 cm TL) from 1.82 hr^?1 ± 0.48 to 4.27 hr^?1 ± 0.93. In contrast, near‐reef habitats showed an increase in abundance of large mesopredatory fishes between years (2.00 hr^?1 ± 0.65 to 4.56 hr^?1 ± 1.11), although only smaller increases in sharks (0.67 hr^?1 ± 0.25 to 1.22 hr^?1 ± 0.34) and smaller mesopredatory fishes. Although the abundance of most mesopredatory groups increased with recovery from fishing, we suggest that the large decline of small mesopredatory fish in reef habitat was mostly due to higher predation pressure following the increase in sharks and large mesopredatory fishes. At the regional scale, the structure of fished communities at Ashmore Reef in 2004 resembled those of present day Scott Reefs, where fishing still continues today. In 2016, Ashmore fish communities resembled those of the Rowley Shoals, which have been protected from fishing for decades.     

The effect of motorboat sound on Australian snapper Pagrus auratus inside and outside a marine reserve

Human‐generated sound affects hearing, movement, and communication in both aquatic and terrestrial animals, but direct natural underwater behavioral observations are lacking. Baited underwater video (BUV) were deployed in near shore waters adjacent to Goat Island in the Cape Rodney–Okakari Point Marine Reserve (protected) or outside the reserve approximately four km south in Mathesons Bay (open), New Zealand to determine the natural behavior of Australian snapper Pagrus auratus exposed to motorboat sound. BUVs worked effectively at bringing fish into video range to assess the effects of sound. The snapper inhabiting the protected area showed no behavioral response to motorboat transits; however, fish in the open zones either scattered from the video frame or decreased feeding activity during boat presence. Our study suggests that motorboat sound, a common source of anthropogenic activity in the marine environment can affect fish behavior differently depending on the status of their habitat (protected versus open).     

Long‐term effects of photoperiod,temperature and their interaction on growth,gill Na+, K+‐ATPase activity,seawater tolerance and plasma growth‐hormone levels in Atlantic salmon Salmo salar

This study was undertaken to examine the long‐term effects of photoperiod, temperature and their interaction on growth, gill Na⁺,K⁺‐ATPase (NKA) activity, seawater tolerance and plasma growth‐hormone levels in Atlantic salmon Salmo salar pre‐smolts and smolts. The fish (mean ± s.e . initial body mass = 15·9 ± 0·4 g) were reared on two photoperiods (continuous light, LL, and simulated natural photoperiod, LDN, 60° 25′ N) and two temperatures (8·3 and 12·7° C) from June to May of the following year. Mean body mass was affected by photoperiod, temperature and their interactions. Both temperature groups on LL developed peak levels in gill NKA activity from October to November, 4–5 months prior to the natural season for the parr–smolt transformation. Fish at 12° C showed peak levels in NKA activity 4–6 weeks before the fish at 8° C. Fish in all four experimental groups showed maximum NKA activity within a similar size range (113–162 g). The present findings further indicate that smoltification in S. salar is to some extent driven by size, and that S. salar will develop smolt characteristics, e.g. a marked increase in NKA activity, within a similar size range. Faster‐growing S. salar will, thus, reach this size threshold at a relatively younger age.     

Animal v. plant‐based bait: does the bait type affect census of fish assemblages and trophic groups by baited remote underwater video (BRUV) systems?

Coral reef fish communities were sampled at the Nayband Marine Park, Iran, using baited remote underwater video stations (BRUVSs) which incorporated animal (i.e. frigate tuna Auxis thazard and beef liver), or plant‐based baits (i.e. raw dough and raw dough‐turmeric powder mix). The A. thazard was found to record significantly (P < 0·05) higher species richness and number of carnivorous fishes than plant‐based baits, while abundance of herbivores was maximum in raw dough‐turmeric powder mix trials. There was also a significant difference in trophic composition of fish assemblages surveyed by animal‐ and plant‐based baits which seemed to be due to variations in attraction patterns of carnivores and herbivores occurring at the earlier phases of each BRUV deployments. Meanwhile, the assemblage structure was comparable among fish assemblages sampled by different bait treatments, indicating that species‐level responses to each bait type may be more complicated. In essence, the efficiency of mixed baits should also be examined in future studies.     

Performance of Baited Underwater Video: Does It Underestimate Abundance at High Population Densities?

Video survey techniques are now commonly used to estimate animal abundance under the assumption that estimates relate to true abundance, a key property needed to make video a valid survey tool. Using the spiny lobster Palinurus elephas as our model organism, we evaluate the effectiveness of baited underwater video (BUV) for estimating abundance in areas with widely different population density. We test three BUV abundance metrics and compare the results with an independently obtained abundance index from trammel-net surveys (Trammel). Video metrics used to estimate relative abundance include a value for total number of individuals per recording (TotN), the traditional maximum number of fish observed in a single video frame (MaxN), and the recently suggested alternative, the average of the mean MaxN from 5-minute periods throughout the duration of the recording (MeanN). This is the first video study of a wild population to include an estimate for TotN. Comparison of TotN with the other two BUV relative abundance metrics demonstrates that both of the latter lack resolution at high population densities. In spite of this, the three BUV metrics tested, as well as the independent estimate Trammel, distinguished high density areas from low density areas. Thus they could all be used to identify areas of differing population density, but MaxN and MeanN would not be appropriate metrics for studies aimed at documenting increases in abundance, such as those conducted to assess marine protected area effectiveness, as they are prone to sampling saturation. We also demonstrate that time of first arrival (T1) is highly correlated with all of the abundance indices; suggesting T1 may be a potentially useful index of abundance. However, these relationships require further investigation as our data suggests T1 may not adequately represent lobster abundance in areas of high density.     

Atlantic sturgeon Acipenser oxyrinchus surfacing behaviour

Atlantic sturgeon Acipenser oxyrinchus surfacing behaviour was investigated in Minas Basin (45° 20′ N; 64° 00′ W) and the Bay of Fundy with pop‐up satellite archival tags (MiniPAT) measuring physical variables (pressure, temperature, light ) . Of six tags deployed during June and July, five provided pop‐up locations and two were recovered after c. 4 months. Analysis of recovered archival data revealed that the frequency of surfacing events was highest (78·9%) when A. oxyrinchus were in Minas Basin at depths <10 m. Surfacing frequency decreased substantially when fish migrated into greater depths of the Bay of Fundy (>40 m). The tidal cycle in Minas Basin had a significant relationship to surfacing frequency, with the most surfacing events (49·5%) occurring on the flood tide, from mid‐ to high‐tide. Surfacing events ranged from 0–12 a day and the maximum number occurred between 2300 and 0300 hours. Maximum surfacing ascent speeds ranged from 0·50 to 4·17 m s^?1 and maximum descent speeds ranged from 0·17 to 3·17 m s^?1. Buoyancy control, by gulping air to inflate the gas bladder, is proposed as the main reason for surfacing behaviour in A. oxyrinchus.     

Using the robust design framework and relative abundance to predict the population size of pallid sturgeon Scaphirhynchus albus in the lower Missouri River

Several population viability models were constructed to aid recovery in endangered Scaphirhynchus albus, but these models are dependent upon accurate and precise input parameters that are not provided with standard catch per unit effort (CPUE) indices. Nine years of sampling efforts, under the robust design framework, provided 1223 unique captures with an 18·3% recapture rate. The annual population estimates varied from 4·0–7·3 fish rkm^?1 for wild and 8·4–18·4 fish rkm^?1 for hatchery‐reared S. albus. The relationship between abundance (N) and annual trot‐line CPUE indices (x = 70.726y + 2·533, R² = 0·91, P < 0·001) was used to predict an abundance of 13 616 ± 7142 s.e. S. albus in the lower Missouri River. The use of small‐scale intensive sampling to develop a relationship with relative abundance indices reported here, may provide a framework for other fisheries management applications where large‐scale intensive sampling is not feasible, but catch data are available.     

Fiji’s largest marine reserve benefits reef sharks

To provide more information about whether sharks benefit from no-take marine reserves, we quantified the relative abundance and biomass of reef sharks inside and outside of Namena, Fiji’s largest reserve (60.6 km²). Using stereo baited remote underwater video systems (stereo-BRUVs), we found that the abundance and biomass of sharks was approximately two and four times greater in shallow and deep locations, respectively, within the Namena reserve compared to adjacent fished areas. The greater abundance and biomass of reef sharks inside Namena is likely a result of greater prey availability rather than protection from fishing. This study demonstrates that marine reserves can benefit sharks.     

Length‐weight and length‐length relationships of thirteen fish species from the lower Jinsha River,southwest China

Length‐weight and length‐length relationships were investigated for 13 freshwater fish species from the lower Jinsha River, southwest China (from 101°32′49.63″E; 26°35′38.27″N to 104°37′48.14″E; 28°45′59.55″N). Fish were sampled from five sites during 2014 and 2016, using trap‐nets, gillnets (major mesh size: 2–6 cm), longline and electrofishing. Length‐weight relationships for six and length‐length relationships for 12 species are the first report to FishBase, respectively. Moreover, new maximum length for 11 species are also presented to FishBase in this study. All regressions were highly significant (p < .001), with the coefficient of determination r² > .950. These information will be helpful for management and conservation in local fishes and fisheries.     

Length–weight relationships of three fish species from the Tibet reach of the Lancang River,China

Length‐weight relationships (LWRs) were determined for three fish species, Schizothorax lantsangensis (Tsao, 1964), Schizothorax lissolabiatus (Tsao, 1964) and Schizopygopsis anteroventris (Wu & Tsao, 1989), from the Tibet reach of the Lancang River, China (N 29°06′–31°30′, E 96°57′–98°38′). Specimens were collected in April and September 2017. The specimens were caught with drifting gillnets (mesh size 2.5 cm and 7.0 cm). The b values of these three fish species ranged from 2.974 to 3.075. The high r² values (all > .980) indicate that these relationships will be appropriate for use in fisheries management of these species.     

Length–weight relationships of three fish species from Kerala waters,south‐west coast of India

Length–weight relationships (LWRs) of three fish species: Scomberomorus commerson, Alepes vari, and A. kleinii were estimated from Kerala waters, south‐west coast of India. Fish were captured between June 2016 and June 2017 by various gears such as ring seine (8–26 mm mesh size), trawl (30–40 mm cod end mesh size), hook and line (hook number VI–XII), smaller mesh sized drift gill net (26–90 mm) and larger one (120–170 mm) for bigger size fishes. Fish were collected on weekly basis from Cochin Fisheries Harbour (Lat. 09°56′327″N, Long. 76°15′764″E), Munambam Fisheries Harbour (Lat. 10°10′965″N, Long. 76°10′258″E), Kalamukku (Lat. 09°59′924″N, Long. 76°14′564″E) and Chellanam (Lat. 09°47′950″N, Long. 76°16′551″E). All LWRs were significant with r² values ranged from 0.944 to 0.996 and b values ranged from 2.722 to 3.021 (p < .001). In addition, this study provides the information on LWRs and new maximum size for Alepes vari and A. kleinii.     

Upper thermal tolerance of wild‐type,domesticated and growth hormone‐transgenic coho salmon Oncorhynchus kisutch

In coho salmon Oncorhynchus kisutch, no significant differences in critical thermal maximum (c. 26·9° C, C_Tmax) were observed among size‐matched wild‐type, domesticated, growth hormone (GH)‐transgenic fish fed to satiation, and GH‐transgenic fish on a ration‐restricted diet. Instead, GH‐transgenic fish fed to satiation had significantly higher maximum heart rate and Arrhenius breakpoint temperature (mean ± s.e. = 17·3 ± 0·1° C, T_AB). These results provide insight into effects of modified growth rate on temperature tolerance in salmonids, and can be used to assess the potential ecological consequences of GH‐transgenic fishes should they enter natural environments with temperatures near their thermal tolerance limits.     

Satiation meal and the effects of meal and body sizes on gastric evacuation rate in brook trout Salvelinus fontinalis fed commercial pellets

Gastric evacuation (GE) experiments were performed on brook trout Salvelinus fontinalis fed commercial food pellets. The experiments included small fish (36 g; 15 cm total length, L_T) fed meals of 0·2, 0·4 and 0·8 g and large fish (152 g; 23 cm) fed meals of 0·8, 2·0 and 4·0 g at temperatures ranging from 15·1 to 18·2° C. The stomach contents were thereafter sampled and weighed at 3 h intervals until the first empty stomach was observed. The course of GE was examined by use of a general power function of the data that revealed that the square‐root function described the GE rate (GER) by the current stomach content mass independently of original meal size. Using the square‐root function, the relationship between GER and fish size was described by a power function of fish length, whereas the effect of temperature was described by a simple exponential function. GER of the commercial pellets fed to S. fontinalis could thus be described by (g h^?1), where S_t is stomach mass (g) at time t (h), L is total fish length (cm) and T is temperature (° C). The result of this study should provide a useful tool for planning of feeding regimes in production of S. fontinalis by optimizing growth and minimizing food waste.     

Reproductive biology of the guitarfish Rhinobatos percellens (Chondrichthyes,Rhinobatidae) from the São Paulo Coast,Brazil, western South Atlantic Ocean

The reproductive biology of the guitarfish Rhinobatos percellens was studied from 751 specimens caught by bottom pair trawlers off the coast of São Paulo, Brazil, between c. 24° 00′ S; 45° 15′ W and c. 25° 10′ S; 47° 52′ W, from September 2007 to August 2009. The total length (L_T) and total mass (M_T) relationship for males and females combined was M_T = 1·29E‐06 L_T^3·15 (r = 0·99, n = 751). The mean L_T of sexually mature specimens was 548 mm for males and 583 mm for females. Clasper growth was allometric and showed three distinct phases. Most claspers were calcified in specimens of c. 550 mm L_T. The mean diameter of the largest oocyte was 29·8 mm, the mean ovarian fecundity was seven oocytes and ovulation occurred between August and November. Uterine fecundity ranged from two to 13 embryos (mean of five embryos). Larger females had higher litter sizes and larger embryos; the size‐at‐birth was c. 200 mm L_T. The hepato‐somatic index oscillated seasonally for males and females; the gonado‐somatic index had little variation in males, but varied seasonally in females. The presence of many non‐pregnant adult females and of encapsulated eggs during two consecutive seasons suggests a resting period between gestations and the possibility of diapause.     

Effect of acclimation temperature on the upper thermal tolerance of Colorado River cutthroat trout Oncorhynchus clarkii pleuriticus: thermal limits of a North American salmonid

In an effort to explore the thermal limitations of Colorado River cutthroat trout Oncorhynchus clarkii pleuriticus, the critical thermal maxima (T_cmax) of 1+ year Lake Nanita strain O. c. pleuriticus were evaluated when acclimated to 10, 15 and 20° C. The mean ±s.d. T_cmax for O. c. pleuriticus acclimated to 10° C was 24·6 ± 2·0°C (n = 30), for 15° C‐acclimated fish was 26·9 ± 1·5° C (n = 23) and for 20° C‐acclimated fish was 29·4 ± 1·1° C (n = 28); these results showed a marked thermal acclimation effect (Q₁₀ = 1·20). Interestingly, there was a size effect within treatments, wherein the T_cmax of larger fish was significantly lower than that of smaller fish acclimated to the same temperature. The critical thermal tolerances of age 0 year O. c. pleuriticus were also evaluated from three separate populations: Lake Nanita, Trapper Creek and Carr Creek reared under ‘common‐garden’ conditions prior to thermal acclimation. The Trapper Creek population had significantly warmer T_cmax than the Lake Nanita population, but that of the Carr Creek fish had T_cmax similar to both Trapper Creek and Lake Nanita fish. A comparison of these O. c. pleuriticus T_cmax results with those of other stream‐dwelling salmonids suggested that O. c. pleuriticus are less resistant to rapid thermal fluctuations when acclimated to cold temperatures, but can tolerate similar temperatures when acclimated to warmer temperatures.     

Individual growth trajectories of sibling Brycon moorei raised in isolation since egg stage,and their relationship with aggressive behaviour

The growth of sibling dorada Brycon moorei (Characidae) housed individually in small enclosures (0·25 l; 27·0° C, range ±0·5° C; 12L:12D) from the egg stage was examined at regular intervals until 36 days after hatching (dah) and compared with their behaviour. From 1 to 8 dah, when cannibalism is intense among B. moorei raised in groups, there was no significant increase of size heterogeneity among isolated fish (c.v . of total length of 3·1 and 3·6%, at 1 and 8 dah, respectively) and no primacy of early size differences either. These results suggest that cannibals of B. moorei raised in groups are not natural‐born killers with greater growth capacities than others. Size heterogeneity among isolated fish increased significantly first when B. moorei were weaned on formulated feed (8–15 dah), then again from 24 to 36 dah when the average growth rate was half as fast as before (c. 0·5 v. 1·0 mm day^?1), despite fish consistently feeding. During both periods, there was a significant, positive relationship between individual growth and aggression or boldness. These results suggest that (1) boldness can favour the transition to a new food type and (2) fish exhibited a variable responsiveness to spatial restriction in small enclosures, which may have been alleviated in some individuals by establishment of territorial behaviour, as suggested by their enhanced aggression.     

Improvement of fish length estimates for underwater visual census of reef fish biomass

Accuracy and precision are of great importance in the assessment of reef fish biomass when conducting an underwater visual census (UVC). Quantification and subsequent correction of the bias is required in order to standardize the estimates and correct for underwater distortion. To optimize the UVC, the observer should receive length‐measurement training in order to obtain in situ‐measurements that are as accurate and precise as possible. The objective of this study was to quantify the bias of fish length measurements made by divers with and without training in order to enhance reef fish biomass estimates. Adaptation of the diver to estimate fish lengths was analysed as a part of reef fish biomass monitoring in the Karimunjawa National Park, a national marine sanctuary in the Java Sea, Indonesia. Two divers practiced estimating a variety of fish in a natural environment by using styrofoam models attached to strings and sinkers. Analyses showed that by training the diver, his/her accuracy and precision improved substantially. Proving its reliability, an underwater visual census (UVC) becomes a useful and reliable method to assess the biomass of reef fishes.     

The efficacy of the aquatic anaesthetic AQUI‐S® for anaesthesia of a small freshwater fish,Melanotaenia australis

For stage four anaesthesia of the western rainbowfish Melanotaenia australis the most efficacious concentration of AQUI‐S^® was found to be 80 mg l^?1 when five different doses were tested at 27° C (range 26·5–27·5° C). This gave a mean ±s.e. (n = 10) induction time of 140·4 ± 8·9 s and recovery time of 180·2 ± 8·9 s and resulted in 10% mortality when fish were continuously exposed for 15 min. All fish given this dose during induction and recovery time trials ate within 1 h of recovery, and there was zero mortality during a subsequent 1 month monitoring period.     

Parasites as biological tags for stock discrimination of the Brazilian flathead Percophis brasiliensis in the south-west Atlantic

Three stocks of the Brazilian flathead Percophis brasiliensis were identified on the coast of Argentina and Uruguay using parasites as biological tags. A total of 177 fish were examined and 23 parasite species were found. Fish were caught in four zones: north of the Argentine–Uruguayan Common Fishing Zone (34°30′–36°30′ S; 53°30′–56°00′ W), south of the Argentine–Uruguayan Common Fishing Zone (38°08′ S 57°32′ W), El Rincón zone (39–41° S; 60–62° W) and San Matías Gulf (41°40′–42°10′ S; 63°50′–65°00′ W). Discriminant analyses allowed the identification of three discrete stocks in the four zones (86·44% of classified samples were correctly identified), with P. brasiliensis from both north and south of the Argentine–Uruguayan Common Fishing Zone clumping together, as a single stock. Some species were important in discriminating among groups, Anisakis simplex was related to southern areas, while Grillotia sp., Corynosoma australe and Hysterothylacium sp. were important in determining the position of fish from the Argentine–Uruguayan Common Fishing Zone. These results were corroborated by comparing parasite prevalence and abundance among zones. The main differences were observed in those comparisons involving fish from the San Matías Gulf. Fish from the Argentine–Uruguayan Common Fishing Zone were characterized by higher infections of Grillotia sp., C. australe, Corynosoma cetaceum and Hysterothylacium sp., while the samples from El Rincón and San Matías Gulf showed higher infections of A. simplex. Samples from San Matías Gulf were characterized by lower levels of parasitism for all other species. Differences in environmental factors and their influence on the distribution of zooplankton and other hosts in the food web may be differentially shaping the parasite community structure in each zone, resulting in identifiable stocks of the P. brasiliensis. The present study confirmed the existence of regional biological tags that delineated fish assemblages.