Association between porpoise presence and fish choruses: implications for feeding strategies and ecosystem-based conservation of the East Asian finless porpoise

The associations between feeding activities and environmental variables inform animal feeding tactics that maximize energetic gains by minimizing energy costs while maximizing feeding success. Relevant studies in aquatic animals, particularly marine mammals, are scarce due to difficulties in the observation of feeding behaviors in aquatic environments. This data scarcity concurrently hinders ecosystem-based fishery management in the context of small toothed-cetacean conservation. In the present study, a passive acoustic monitoring station was deployed in an East Asian finless porpoise habitat in Laizhou Bay to investigate potential relationships between East Asian finless porpoises and their prey. The data revealed that porpoises were acoustically present nearly every day during the survey period. Porpoise detection rates differed between spring and autumn in concert with activities of fish choruses. During spring, fish choruses were present throughout the afternoon, and this was the time when porpoise vocalizations were the most frequently detected. During autumn, when fish choruses were absent, porpoise detection rates decreased, and diurnal patterns were not detected. The close association between fish choruses and finless porpoise activities implies an “eavesdropping” feeding strategy to maximize energetic gains, similar to other toothed cetaceans that are known to engage similar feeding strategies. Underwater noise pollution, particularly those masking fish choruses, could interrupt finless porpoises’ feeding success. Fisheries competing soniferous fishes with finless porpoise could impact finless porpoise viability through ecosystem disruption, in addition to fishing gear entanglement.     

Interactions between fishing strategies of Nephrops trawlers in the Bay of Biscay and Norway lobster diel activity patterns

Abstract  Norway lobster, Nephrops norvegicus (L.), in the Bay of Biscay exhibited diel activity patterns with more individuals outside their burrows at dawn and dusk, increasing catchability at these times. Data from an on board observer programme on Nephrops trawlers between 2002 and 2005 were used to assess variability in catchability in commercial catches. Catch numbers per haul varied spatially and between months, but no signal for diel variations was found. Fishing strategies developed by the Nephrops trawlers had several components. On a seasonal level, they started around sunrise. On a haul level, haul duration decreased from haul to haul, with the longest hauls taking place at the time of the highest catchability. By-catch of hake, Merluccius merluccius (L.), increased more than proportionally with haul duration.     

不同光照周期下鲇幼鱼的日摄食节律

水温(23±1)℃,研究了鲇幼鱼自然光照、持续光照(自然光或日光灯作光源)和持续黑暗条件下的日摄食节律.试验结果表明,3种光照周期下,鲇幼鱼昼夜均有连续摄食特性,期间具有明显的摄食高峰(夜间)和低谷(白天),鲇幼鱼有明显的日摄食节律;持续黑暗与自然光照周期下的鲇幼鱼日摄食节律基本一致,持续光照与自然光照周期下的鲇幼鱼日摄食节律有所差异.研究证明,鲇幼鱼在3种光照周期下均属于典型的夜晚摄食类型;光照周期的改变对鲇幼鱼的日摄食率无显著影响(P>0.05).     

Movements and behaviors of swordfish in the Atlantic and Pacific Oceans examined using pop‐up satellite archival tags

Swordfish are highly specialized top‐level predators that have been challenging to study. In this paper, data from 31 pop‐up satellite archival tags attached to swordfish from (i) the eastern Pacific, (ii) central Pacific, and (iii) western North Atlantic‐Caribbean were analyzed. Common across locations was a pronounced diel vertical pattern with daytime hours spent primarily below the thermocline and nighttime hours spent in warmer waters, close to the surface. One exception to this pattern was periodic daytime basking events which were most common in cooler waters off California. Maximum daytime depths were significantly correlated with light penetration as measured by the diffuse attenuation coefficient at 490 nm. Temperature did not appear to influence daytime depths, and swordfish tolerated both extremely low temperatures (4°C) and rapid and dramatic temperature changes (>20°C). Temperature did appear to influence the nighttime depths in the Pacific where fish typically remained in the surface mixed layer. In contrast, in the warm tropical Atlantic this was not the case, and nighttime depths were much deeper. In all areas, nighttime depth increased around the full moon. Given the parallels between the vertical movement patterns of swordfish and those of the deep sound scattering layer we suggest that swordfish vertical distribution patterns, especially during daytime, are influenced largely by resource availability. At night, when swordfish are typically targeted by fisheries, both ambient light and temperature influence movements. Understanding vertical movement patterns of swordfish can help evaluate gear vulnerability, improve population assessments, and potentially reduce fisheries bycatch.     

Post-release movement and diel activity patterns of hatchery-reared and wild black-spot tuskfish <Emphasis Type="Italic">Choerodon schoenleinii</Emphasis> determined by ultrasonic telemetry

ABSTRACT:   Post-release movement and diel activity patterns of hatchery-reared and wild black-spot tuskfish were examined using ultrasonic telemetry. Five hatchery-reared and four wild fish were released in the sandy bottom of Urasoko Bay, Ishigaki Island, Okinawa, Japan, and monitored using automated monitoring receivers from November 2005 to February 2006. Both hatchery-reared and wild fish tended to stay near the release site for over two weeks, before leaving the release site. Both hatchery-reared and wild tuskfish showed diurnal rhythm intermittently; signals were recorded more frequently in the daytime and less frequently in the nighttime, suggesting that the fish of both origins were active during the day and inactive during the night. These findings indicate that the one-year-old hatchery-reared tuskfish have some consistent behavioral characteristics with those of the wild.     

A comparison of RNA concentrations and ornithine decarboxylase activity in Atlantic salmon (Salmo salar) muscle tissue,with respect to specific growth rates and diel variations

RNA concentrations and enzyme activities are often used as indices of recent growth in fish, but few studies have used both methods to assess the same fish. This study measured RNA concentrations and ornithine decarboxylase (ODC) activity in muscle tissue of juvenile Atlantic salmon (Salmo salar) to compare their usefulness for reflecting specific growth rates, and to determine whether either growth index was influenced by diel variations or time of feeding. Three groups (n = 54 in total) were fed 1.5% of body weight in commercial pellets in four feedings per day. One group was fed only in the morning (0830–1230h), one in the afternoon (1430–1830h), and one in the morning and afternoon (0830–1830h). At the end of ten days, fish were sampled at three times (0130h, 1030h, 1630h) over a single 24h period. Correlations to specific growth rate were slightly higher for RNA concentrations than for ODC activity, but both were highly significant. RNA and ODC activity were also correlated to each other. These results suggest that RNA concentration and ODC activity, taken together, can be used to monitor changes in both the numbers and activity of ribosomes. For RNA concentrations, there was no evidence of an effect of diel variations or the time of feeding. For ODC activity, a significant diel effect (all feed schedules combined) was detected if one non-growing fish was excluded from the analysis; activity of the enzyme was slightly higher in the sample taken at night (0130h) than in the two daytime samples. Contribution no. 8, Catamaran Brook Habitat Research Project     

Prey selectivity and diel feeding chronology of juvenile chinook (Oncorhynchus tshawytscha) and coho (O. kisutch) salmon in the Columbia River plume

We studied salmon feeding selectivity and diel feeding chronology in the Columbia River plume. Juvenile chinook and coho salmon were caught by trawling at 2–3 h intervals throughout a diel period on three consecutive days (21–23 June 2000) at stations located 14.8 and 37 km offshore from the mouth of the Columbia River. A total of 170 chinook salmon were caught at the inshore and 79 chinook and 98 coho salmon were caught at the offshore station. After each trawl, potential prey were sampled at different depths with 2–3 different types of nets (1‐m diameter ring net, bongo net, neuston net). Despite the variability in zooplankton abundance, feeding selectivity was surprisingly constant. Both salmon species fed selectively on larger and pigmented prey such as hyperiid amphipods, larval and juvenile fish, various crab megalopae, and euphausiids. Hyperiid amphipods were abundant in the salmon diets and we hypothesize that aggregations of gelatinous zooplankton may facilitate the capture of commensal hyperiid amphipods. Small copepods and calyptopis and furcilia stages of euphausiids dominated the prey field by numbers, but were virtually absent from salmon diet. Juvenile chinook salmon, with increasing body size, consumed a larger proportion of fish. Stomach fullness peaked during morning hours and reached a minimum at night, suggesting a predominantly diurnal feeding pattern. In general, both chinook and coho salmon appear to be selective, diurnal predators, preying mostly on large and heavily pigmented prey items, in a manner consistent with visually oriented, size‐selective predation.     

Diel migration patterns of Atlantic salmon smolts with particular reference to the absence of crepuscular migration

Abstract –  The real-time diel pattern of Atlantic salmon smolt migration was observed for 8 years using automatic resistivity counters verified by video surveillance. A clear dominant nocturnal migration was demonstrated early in the migration period, later becoming increasingly diurnal, until rates became approximately equal at day and night. Migration patterns were related to water temperature, such that when mean daily temperatures were below 12 °C, hourly rates of migration were significantly lower during the day than at night. When daily mean temperatures exceeded 12 °C, there was no significant difference between diurnal and nocturnal migration rates. Migration patterns showed a distinct suppression of migration at dawn and dusk throughout the migration period. It is hypothesised that this behaviour is an active decision and/or an adaptive strategy either to take advantage of increased food in the form of invertebrate drift or to reduce predation risk from actively feeding piscivores or both.     

Spatial–temporal variations in biosonar activity of Yangtze finless porpoise in the lower reaches of the Yangtze River and its correlation with underwater noise: Are quieter non-shipping branches the remaining shelters?

1. Yangtze finless porpoise (YFP) is Critically Endangered, It relies on its biological sonar sensing system for important life activities. The rapid development of the Yangtze valley has brought busy shipping, which has resulted in increased noise.
2. Two locations on the shipping channel and non-shipping branch were selected. Passive acoustic monitoring was used to record the biosonar signals of porpoises and underwater noise. The number of click trains, echolocation encounters, buzzes and buzz ratios were counted and the root mean square sound pressure level of noise was calculated in five diel phases.
3. A non-parametric test was used to analyse the differences among different phases and between different locations. The aim of the study was to detect the spatial and temporal variations in the biosonar activity of YFPs and underwater noise between non-shipping and shipping channels, and to provide scientific advice for YFP conservation.
4. Significant spatial and temporal patterns were observed both in biosonar activity and noise. Average biosonar activity, including click trains, buzzes, buzz ratio and echolocation encounters, was higher in the non-shipping channel than in the shipping channel, whereas the noise level was higher in the shipping channel than in the non-shipping channel.
5. In the non-shipping channel, the buzz numbers and buzz ratios, indicators of porpoise feeding activity, were higher at night than during the day while the noise level was higher during the day than at night.
6. These findings may be associated with the noise avoidance strategies of YFPs to adapt to the busy shipping on the Yangtze River. Maintaining the non-shipping status of some branches of the Yangtze River can provide more shelters for the YFPs. Strengthening the measures for banning navigation at night or reducing the vessel speed at night throughout the entire year would improve the YFPs’ feeding success.