An inexpensive photosynthetic irradiance sensor for ecological field studies

The design and characteristics of inexpensive and simply constructed equal-energy response photosynthetic irradiance sensors is described for use particularly where several cells are required in comparative ecological studies either above or below water. The dimensions of the sensors can be changed proportionally to suit different applications or components. The response of the sensor to irradiance at varying angles corresponds very closely to that required by the cosine law. The sensor is comparatively insensitive to other environmental variables in field use and gave a stable output; the long term drift was proportional to electrical output but in continuous use, drift is regular and could reach -0.08 year^-1 of the total. The spectral range and cosine response is discussed in comparison to other more expensive (x 5–10) commercially available, sensors and to local standards.     

First record of a potential neonate tiger shark (Galeocerdo cuvier) at a remote oceanic island in the Eastern Tropical Pacific

Tiger sharks (Galeocerdo cuvier) play an important ecological role as top predators, yet knowledge of their reproductive ecology is scarce. Here, the authors report the first observation of a potential neonate G. cuvier at Cocos Island, a predator-dominated oceanic island in the Eastern Tropical Pacific (ETP). The individual was detected using baited remote underwater video stations (BRUVS). The cameras also detected female individuals potentially pregnant, suggesting that parturition may take place at or near the island. Nonetheless, it is still unclear if the presence of a single neonate is an isolated event or evidence that the species is using the island for reproduction.     

Subsurface behavior of bottlenose dolphins (Tursiops truncatus) interacting with fish trawl nets in northwestern Australia: Implications for bycatch mitigation

Most studies of delphinid‐trawler interactions have documented the surface behavior of dolphins feeding on discarded bycatch, but not their subsurface behavior around demersal trawl gear. Using video cameras mounted inside trawl nets, we recorded the subsurface behavior of common bottlenose dolphins (Tursiops truncatus) in a demersal fish trawl fishery in northwestern Australia. Footage from 36 trawls across the fishery was analyzed to determine the extent of dolphin‐gear interactions and the behavior of dolphins inside the nets. Interaction rates were high, with dolphins present inside and outside the nets during 29 and 34 trawls, respectively, and for up to 99% of the trawl duration. The proportion of foraging behaviors exhibited inside the nets was higher than the proportions of traveling and socializing behaviors. Twenty‐nine individuals were identified inside the net, seven of which returned repeatedly within and between trawls and fishing trips, but were observed primarily in the same localized areas in which they were first recorded. Our results suggest that entering trawl nets may be a frequently occurring, yet specialized behavior exhibited by a small subset of trawler‐associated dolphins. We propose that gear modifications, not spatial or temporal adjustments to fishing effort, have the greatest potential to reduce dolphin bycatch.     

Exploratory behaviour of barnacle larvae in field conditions

The aim of this work was to develop techniques for the real time filming of Semibalanus balanoides cyprid larvae in the field in order to describe the exploratory behaviour of S. balanoides cyprids under natural field conditions. The underwater camera system consisted of a high resolution, remotely controlled colour camera attached to a cradle which could be deployed from a pier. A light utilising a battery of far‐red light‐emitting diodes (λ_min = 615 nm) was used for filming at night. Transparent acrylic treated with barnacle settlement factor and smooth green polyester tiles were used as targets. From the films the tracks of the exploring cyprids were digitised from the 30 min trials. During five, 30 min trials a total of 1014 cyprids explored the surface. The numbers of cyprids exploring the surface varied from 49 to 522 cyprids per trial, and a Monte‐Carlo randomisation model showed that larval supply was random or aggregated. The mean exploration time spent on the target was 163 s with a mean distance travelled on the target of 8.5 cm. Exploratory track length was related to water current velocity by a negative curvilinear regression (R² = 0.92, F = 45.65, p < 0.05). There were significant differences in exploratory behaviour between day and night for total distance travelled (p < 0.001), straight line distance (p < 0.001) and velocity (p < 0.001) and the mean heading angle of the exploratory track (p < 0.01). The results are discussed in relation to settlement patterns and the screening of antifouling surfaces.     

Comparisons among survey methodologies to test for abundance and size of a highly targeted fish species

Three sampling methods for estimating abundance and size of blue cod Parapercis colias were compared inside and outside Kapiti Marine Reserve, New Zealand (40° 49′ 31·77^′′ S; 174° 55′ 02·87^′′ E). Two baited methods, baited underwater video (BUV) and experimental angling (EA), were more efficient and had lower levels of estimate variation than diver‐based underwater visual census (UVC). The BUV and EA recorded more fish and of greater size ranges than UVC, and also had fewer zero count replicates. The BUV and EA methodologies revealed highly significant differences in abundance and size of fish between sites (reserve v. non‐reserve), whereas UVC revealed no such differences. These results indicate that BUV is likely to be the most accurate, cost‐effective and easy to use methodology for the surveying of carnivorous temperate reef fishes for future monitoring. It is noted, however, that new data acquired using the BUV methodology may need to be compared over a calibration period to data acquired using the UVC methodology to ensure that historical data sets derived from UVC still have validity and application for future monitoring activity.     

DELIMITING SPAWNING AREAS OF WEAKFISH CYNOSCION REGALIS (FAMILY SCIAENIDAE) IN PAMLICO SOUND,NORTH CAROLINA USING PASSIVE HYDROACOUSTIC SURVEYS

ABSTRACT

Exact locations of spawning areas used by marine fishes are needed to design marine reserves and estimate spawning stocks. The location of spawning areas of soniferous fishes such as weakfish Cynoscion regalis can be determined by means of passive hydroacoustic surveys. We conducted nocturnal hydrophone surveys at 12 locations in Pamlico Sound in May of 1996 and 1997. Digital audio tapes were made of weakfish “purring” sounds, the tapes were analyzed spectrographically and compared with ichthyoplankton surveys taken at the same stations and times. All weakfish “purring” sounds were recorded at stations near inlets. Maximum sound pressure levels recorded after sunset were 127 dB (re 1 (μPa) for individual weakfish, but reached a maximum of 147 dB when weakfish and other fish were producing sounds simultaneously. The maximum distance that an individual weakfish “purr” can be detected above the background sound, assuming a cylindrical spreading model, is approximately 50 m. There was a strong association (r = 0.78) between the log₁₀— transformed abundance of early-stage sciaenid-type eggs and maximum sound pressure levels, with the greatest numbers occurring at the inlet stations. These results suggest that passive hydroacoustic surveys can be used to delimit spawning areas for conservation and management purposes.     

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.     

Piezoelectric Pump Used in Bionic Underwater Propulsion Unit

A new piezoelectric pump can pump liquid either forward or backward and adjust the flow rate. Thus an object can be driven forward or backward at different speeds. The driver of the pump, a circular piezoelectric plate, is modelled by Finite Element Method （FEM） in ANSYS and its performance is simulated and analyzed. The pump gives the best performance when the driving signals of the inlet and outlet valves have a bigger duty cycle and the plate has a higher voltage applied.     

Foraging efficiency of juvenile bluegill, Lepomis macrochirus, among different vegetated habitats

Optimal foraging theory is devoted to understanding how organisms maximize net energy gain. However, both the theory and empirical studies lack critical components, such as effects of environmental variables across habitats. We addressed the hypothesis that energetic returns of juvenile bluegill are affected by environmental variables characteristic of the vegetated habitats. Predicted optimal diet breadths were calculated and compared to prey items eaten by juvenile bluegill to determine if bluegill were foraging to maximize energetic gain. Differences in habitat profitability among vegetated sites were determined by comparing predictions of maximized energetic return rates (cals^-1) with prey contents of bluegill stomachs. Sizes of most prey items eaten by juvenile bluegill throughout the vegetated sites were smaller than the predicted optimal diet breadths. However, inclusion of smaller prey items in the diet did not seem to affect rate of energetic gain. Energetic return rates were maximized at the 1.5 and 2mm prey size classes and declined only slightly with inclusion of smaller prey sizes. Predicted energetic return rates and average mass in bluegill stomachs were related negatively. Average mass in bluegill stomachs also was associated negatively with Elodea canadensis stem densities and percent of light transfer, suggesting that foraging efficiency of bluegill decreased as plant density and percent of light increased. Results of our research indicate that maximization of energetic return rates is dependent upon availability of prey sizes that contribute to optimal foraging. Thus, determination of those habitats that provide the highest availability of benthic invertebrate prey with the least interference by stems is critical. Enhanced foraging capabilities can promote recruitment, faster growth, better body condition and survival.