Misidentification of istiophorid billfishes by fisheries observers raises uncertainty over stock status

We investigated whether commercially landed black marlin Istiompax indica were being misidentified by fisheries observers operating throughout the Pacific Ocean. Of 83 samples reported by observers as I. indica, 77% were genetically identified to be blue marlin Makaira nigricans and 2% to be striped marlin Kajikia audax. The high rate of misidentification by observers places considerable uncertainty over historic catch ratios of Indo‐Pacific marlin and stock assessments relying on the validity of these data.     

Size and age structure of the striped marlin Tetrapturus audax (Pisces: Xiphidae), at Cabo San Lucas, Baja California sur, México

The striped marlin (Tetrapturus audax) is found in temperate and tropical waters of the Pacific and Indian Ocean. It is particularly abundant in the southern tip of the Baja California peninsula. Specimens brought to Cabo San Lucas port (22 degrees 53' N y 109 degrees 54' W) by the sport fishery fleet that operates withing a radius of 54 km from 1988 to 1993 were sexes, measured and weighed. A total 1030 individuals were sampled. Dorsal fin spines (389) were collected for age estimation. The spines were sectioned and hyaline-opaque bands counted. The relation of length to spine radius was similar for males and females. The fourth dorsal spine reflected the growth of the fish. The rhythm of growth mark formation is yearly and related to the sea surface temperature. Ten age groups were found and the seventh group was the most abundant, followed by groups "6" and "8". The age structure of the striped marlin was stable in the study period. The observed sizes were 160-280 cm jaw length with 90% of the organisms measuring between 190 and 225 cm. The small individuals recruit to the fishery from June to December.     

东南太平洋金枪鱼延绳钓主要渔获种类垂直分布

研究延绳钓渔获物的垂直分布特征,可以帮助人们制定有效措施减少兼捕鱼种的渔获率,更好地了解大洋生态系统结构,并为基于生态系统的渔业管理提供参考.本研究根据2013年9月-2014年1月我国金枪鱼科学观察员在东南太平洋采集的延绳钓钩位深度数据和主要渔获种类的钓获钩位数据,分析了各钩位的上浮率和钓获鱼种的垂直分布,比较了不同鱼种垂直分布的差异.结果表明: 钓钩相对上浮率变化范围为8.9%～17.1%,平均相对上浮率为13.5%;14种渔获物钓获深度范围差异较大,斑点月鱼的平均钓获深度最深,鲣鱼最浅;除黄鳍金枪鱼和条纹四鳍旗鱼外,其他兼捕鱼种钓获深度均与长鳍金枪鱼(目标鱼种)具有显著性差异.
     

The rostral micro-tooth morphology of blue marlin,Makaira nigricans

Billfish rostra potentially have several functions; however, their role in feeding is unequivocal in some species. Recent work linked morphological variation in rostral micro-teeth to differences in feeding behavior in two billfish species, the striped marlin (Kajikia audax) and the sailfish (Istiophorus platypterus). Here, we present the rostral micro-tooth morphology for a third billfish species, the blue marlin (Makaira nigricans), for which the use of the rostrum in feeding behavior is still undocumented from systematic observations in the wild. We measured the micro-teeth on rostrum tips of blue marlin, striped marlin, and sailfish using a micro–computed tomography approach and compared the tooth morphology among the three species. This was done after an analysis of video-recorded hunting behavior of striped marlin and sailfish revealed that both species strike prey predominantly with the first third of the rostrum, which provided the justification to focus our analysis on the rostrum tips. In blue marlin, intact micro-teeth were longer compared to striped marlin but not to sailfish. Blue marlin had a higher fraction of broken teeth than both striped marlin and sailfish, and broken teeth were distributed more evenly on the rostrum. Micro-tooth regrowth was equally low in both marlin species but higher in sailfish. Based on the differences and similarities in the micro-tooth morphology between the billfish species, we discuss potential feeding-related rostrum use in blue marlin. We put forward the hypothesis that blue marlin might use their rostra in high-speed dashes as observed in striped marlin, rather than in the high-precision rostral strikes described for sailfish, possibly focusing on larger prey organisms.     

Sex ratio and reproductive condition of four istiophorid billfishes in tropical regions of the eastern North Pacific Ocean: with special reference to striped marlin Kajikia audax (Philippi, 1887)

Sexual differences in the distribution pattern, sex ratio and the gonad condition of four istiophorid billfishes were investigated in three different tropical areas of the eastern North Pacific Ocean from September to November 2004. Sex ratios of striped marlin Kajikia audax were equal (female : male = 11 : 11) in the open‐ocean area (16–18°N, 118–134°W), biased to males (32 : 62) in the near‐continental area (13–16°N, 103–107°W), and biased to females (19 : 6) in the near‐equatorial area (5°N, 104–120°W). Sex ratios of sailfish Istiophorus platypterus in the near‐continental area and shortbill spearfish Tetrapturus angustirostris in the open‐ocean area were not biased from 1 : 1 (43 : 36, 11 : 13), and that of blue marlin Makaira nigricans in the near‐equatorial area was biased to females (14 : 1). Reproductively active females were found for striped marlin, sailfish and shortbill spearfish. Striped marlin showed a specific spawning area (the near‐continental area), and sexual dimorphism in its temporal distribution pattern, which was presumably related to reproduction. On the other hand, the limited distribution with evidence from spawning of sailfish and shortbill spearfish imply that these species complete their life history within limited areas.     

Upside-down swimming: in situ observations of inverted orientation in Gigantactis,with a new depth record for the Ceratioidei

This note reports on eight observations of inverted swimming behavior by species of ceratioid whipnose anglerfishes in the genus Gigantactis, from the Caribbean, tropical east Atlantic, tropical western Indian Ocean, the north-east and north-west Pacific and south-west Pacific. It covers four putative species and strongly suggests that this is the normal behavior for the genus. A possible reason is briefly discussed. In addition, a new depth record of 5866 m for the ceratioid anglerfish is recorded.     

The bathymetry of Coco's Island, Costa Rica

The bathymetry of Coco's Island (UNESCO Natural and Cultural World Patrimony), located approximately 500 km from the Pacific coast of Costa Rica, is not well known. It has a high marine biodiversity and also represents a meeting site for many species traveling throughout the Pacific Ocean. The insular shelf is irregular in extension and also in bathymetric features. The northeast limit is defined by the 109.8-128.1 m contours (60-70 fathoms) while the 183 m contour (100 fathoms) practically defines the rest of the island, from which the depth gradient is steep. The maximum extension is to the northeast with a longitude of 13 km. In this context the present limits of the marine park (5 km), are insufficient to protect the whole insular shelf. Current regulation should be modified to prevent fishing activities less than 15 km from the Island.     

Diving behaviour and energetics in breeding little penguins (Eudyptula minor)

We present data on the diving behaviour and the energetics of breeding little penguins in Tasmania, Australia. Using an 18 m long still water canal in conjunction with respirometry, we determined the energy requirements while diving. Using electronic devices measuring dive depth or swimming speed, we investigated the foraging behaviour at sea. Cost of Transport was calculated to be minimal at the speed the birds prefer at sea (1.8 m/s) and averaged 11.1 J/kg/m (power requirements at that speed: 20.0 W/kg). Metabolic rate of little penguins resting in water was found to be 8.5 W/kg. The externally-attached devices had no significant influence on the energy expenditure.
Foraging trips can be divided into four distinct phases with different diving behaviours. A mean of 500 dives was executed per foraging trip lasting about 18 hours with 60% of this time being spent swimming. The total distance travelled averaged 73 km per day, although foraging range was about 12km. Mean swimming speed of little penguins at sea was 1.8 m/s, maximum swimming speed was 3.3 m/s. More than 50% of all dives had maxima not exceeding 2 m. Maximum depth reached was 27 m. Mean dive duration was 21 s. There were inter-sex differences in diving behaviour as well as changes in foraging behaviour over the breeding period. Aerobic dive limits (ADL) in the wild were estimated between 42 and 50 s. From the swim canal experiments we derived an ADL of 44 s. Total oxygen stores were calculated to be 45 ml O₂/kg. Only 2% of all dives exceeded the ADL. FMRs at sea were calculated to be between 1280 and 1500 kJ/kg/d according to chick size. The yearly food requirements of a breeding little penguin amount to 114 kg.     

Depth and movement behaviour of the Pacific sleeper shark in the north-east Pacific Ocean

Satellite-linked radio telemetry was used to study the geographic movements and vertical movement behaviour of the Pacific sleeper shark Somniosus pacificus . The fish were tagged near Steller sea lion Eumetopias jubatus rookeries in the Gulf of Alaska during periods when Steller sea lions pups were most vulnerable to predation; when Steller sea lion pups first enter the water (July to August) and when Steller sea lion pups are weaned (April to May). Final locations recovered from most Pacific sleeper sharks (76%) were within 100 km of release locations, 16% were within 100–250 km and 8% were within 250–500 km. The most striking behavioural feature was their extensive, nearly continuous vertical movements. Median daily depth range was 184 m; the most time (61%) was spent between 150 and 450 m, but ascents above 100 m were common (58% of days). Median vertical movement rate was 6 km day⁻¹ and steady. The longest period of continuous vertical movement (> 60 m h⁻¹) was 330 h. Systematic vertical oscillations were most common (60%), followed by diel vertical migrations (25%) and irregular vertical movements (15%). The Pacific sleeper sharks travelled below the photic zone during the day and approached the surface at night. Pacific sleeper sharks appear to employ a stealth and ambush hunting strategy that incorporates slow vertical oscillations to search for prey, and cryptic colouration and cover of darkness to avoid detection by potential prey. The depth and geographic range of Pacific sleeper shark and Steller sea lions overlap near four important Steller sea lion rookeries in the northern Gulf of Alaska, so the potential exists for predation to occur. None of the tissues in the stomachs of the 198 Pacific sleeper sharks collected during a companion diet study, however, were identified as Steller sea lion.     

Intraspecific differences in patterns of courtship behaviours between the Pacific Ocean and Japan Sea forms of the three-spined stickleback Gasterosteus aculeatus

The courtship behaviour of the Pacific Ocean and Japan Sea forms of the three-spined stickleback Gasterosteus aculeatus were studied in seven populations. The intraspecific difference in behavioural patterns, zigzag dance and weak dorsal pricking in the Pacific Ocean form and lateral display and vigorous dorsal pricking in the Japan Sea form, was clearly distinguishable regardless of the type of habitat the males lived in.     

Dynamic habitat suitability modelling reveals rapid poleward distribution shift in a mobile apex predator

Many taxa are undergoing distribution shifts in response to anthropogenic climate change. However, detecting a climate signal in mobile species is difficult due to their wide‐ranging, patchy distributions, often driven by natural climate variability. For example, difficulties associated with assessing pelagic fish distributions have rendered fisheries management ill‐equipped to adapt to the challenges posed by climate change, leaving pelagic species and ecosystems vulnerable. Here, we demonstrate the value of citizen science data for modelling the dynamic habitat suitability of a mobile pelagic predator (black marlin, Istiompax indica) within the south‐west Pacific Ocean. The extensive spatial and temporal coverage of our occurrence data set (n = 18 717), collected at high resolution (~1.85 km²), enabled identification of suitable habitat at monthly time steps over a 16‐year period (1998–2013). We identified considerable monthly, seasonal and interannual variability in the extent and distribution of suitable habitat, predominately driven by chlorophyll a and sea surface height. Interannual variability correlated with El Nino Southern Oscillation (ENSO) events, with suitable habitat extending up to ~300 km further south during La Nina events. Despite the strong influence of ENSO, our model revealed a rapid poleward shift in the geometric mean of black marlin habitat, occurring at 88.2 km decade^?1. By incorporating multiple environmental factors at monthly time steps, we were able to demonstrate a rapid distribution shift in a mobile pelagic species. Our findings suggest that the rapid velocity of climate change in the south‐west Pacific Ocean is likely affecting mobile pelagic species, indicating that they may be more vulnerable to climate change than previously thought.     

Inter-population variation in the behaviour of adult and juvenile Red-footed Boobies Sula sula

Early life is a critical phase of the life cycle of animals and is attracting increased attention because little information is available on the behaviour of young individuals during this period. Behaviour during early life is probably influenced by the environmental conditions encountered by young animals, but data on intraspecific variation between breeding sites during this crucial period of life are limited. Here we study variability in the foraging behaviour of juveniles and adults in three colonies of a pantropical seabird, the Red-footed Booby Sula sula. Both adults and juveniles were measured and fitted with GPS loggers in three remote islands: Genovesa (Galapagos, Eastern Pacific Ocean), Europa (Western Indian Ocean) and Surprise (New Caledonia, Western Pacific Ocean). Foraging behaviour was compared between age-classes, sex and colonies by examining trip characteristics, different behaviours at sea, potential associations between individuals and morphological characteristics. Compared with adults, juveniles conducted shorter trips that were restricted to around the colony, especially on Genovesa (max. range: 203.4 ± 125.1 km and 3.6 ± 3.1 km, respectively). Juveniles appeared more constrained by poor flight skills and experience rather than by their morphology. Adults travelled 45% of the time during at-sea trips, whereas juveniles spent a a lower proportion of time travelling but foraged more often using an ‘area-restricted search’ behaviour, potentially training to catch prey. Associations between juveniles were commonly detected in the three colonies and occurred mostly during foraging, suggesting that social learning is an important strategy. Variability of morphometric measurements in both adults and juveniles was high between sites, with larger birds found on Genovesa. These results suggest that adaptations to local environmental conditions are already visible in their early life. Future studies should continue to investigate the behavioural flexibility of juvenile birds to better understand the effect of local environmental conditions during this critical stage of life.     

Movements of ultrasonically tagged brown trout (Sulmo trutta L.) in Lake Constance

In Lake Constance from September 1986 to May 1988 13 adult lake dwelling brown trout ( Sulmo trutta L.) were tagged with ultrasonic transmitters and tracked almost continuously for up to 13 days. Two behaviour types were observed: (a) random movement in locally restricted areas and (b) excursions of up to 40 km distance. Swimming activity during the day was significantly higher than at night in most experiments. In summer swimming depth ranged between 8 and 16 m, and in winter between 0 and 3m. The preferred water temperature was about 14°C in the thermally stratified waterbody. During the experiments mean swimming speed ranged between 0.3 km h⁻¹ (0.1 bodylengths s⁻¹) and 0.9 km h⁻¹ (0.6 bodylengths s⁻¹).     

Evidence for Interrupted Biomagnification of Cadmium in Billfish Food Chain Based on Stable Carbon and Nitrogen Isotopes from Southwestern of Gulf of California

Biological Trace Element Research - We report cadmium (Cd) concentrations in muscle, liver, and blood of striped marlin (Kajikia audax) and blue marlin (Makaira nigricans), caught in the southwest...     

Movement and habitat use of striped marlin Kajikia audax in the Western Indian Ocean

Striped marlin Kajikia audax are globally Near Threatened and their stock in the Indian Ocean was last assessed as “overfished and subject to overfishing”. Significant gaps in our understanding of their ecology remain, hampering the efforts of fisheries managers to ensure stock sustainability. There is a particular lack of fisheries-independent data. Here we present the results from the first large-scale satellite tracking study of K. audax in the Indian Ocean. We tagged 49 K. audax with pop-up archival satellite-linked tags off the Kenyan coast from 2015 to 2019. Individuals were highly mobile, covering horizontal distances of up to 9187 km over periods ranging up to 183 days, with a mean daily distance of ~48 km. Long-distance movements were recorded to the east and north of East Africa, with the most distant tracks extending north to the Arabian Sea and east to near the Maldives. None of the K. audax swam south of East Africa. Kernel utilization distributions of fish locations demonstrated their shifting seasonal activity hotspots. Over the sport-fishing season (and tagging period) in Kenya, from December to March, K. audax typically stayed off the East African coast. After March, the activity hotspot shifted north to a region close to the Horn of Africa and Socotra Island. Remotely sensed sea surface temperature and chlorophyll-a maps indicated that this seasonal movement could be driven by a shift in prey availability. Our results show the high mobility of K. audax in the Western Indian Ocean, and that individuals seasonally range between two major fishing areas.     

Movements and diving behavior of pelagic spotted dolphins

We radio tracked 20 pantropical spotted dolphins ( Stenella attenuata ) in the pelagic waters of the eastern tropical Pacific Ocean during three research cruises in 1992, 1993, and 2001. Dolphins were tracked for up to 6 d from 20 to 1,000 km offshore. Seventeen of these dolphins also carried time–depth recorders, nine of which were recovered with a combined total of 477 h of dive data. The movement data suggested that the dolphins associate with areas of relatively high biological productivity. Dolphins close to shore moved along the continental slope, while some dolphins traveled farther offshore along thermocline "ridges." Tracking and tagging multiple dolphins demonstrated the dynamic nature of dolphin herds, which change size and membership over the course of a day. At night, the dolphins traveled more slowly but dove deeper and longer, with more rapid ascents and descents than during daylight hours. These nighttime dive characteristics support the hypothesis suggested by some food habit studies that spotted dolphins are nocturnal feeders. Comparison of dive data with acoustic backscatter data indicates that spotted dolphins typically begin and end nighttime feeding activities with dusk and dawn diving bouts that track the vertical migration of organisms associated with the deep scattering layer.     

Low activity and seasonal change in population size structure of grenadiers in the oligotrophic abyssal central North Pacific Ocean

Analysis of video recordings of swimming in abyssal grenadiers Coryphaenoides spp. revealed site differences in tail-beat frequencies. At the highly oligotrophic deep central North Pacific (CNP; 5800 m depth) station fishes had significantly lower tail-beat frequencies (0·73 ± 0·02 Hz, mean ±  s . e .) than fishes of similar size at the shallower 'Station F' (Sta. F; 4400 m depth) beneath the more productive waters of the California Current Upwelling (1·06 ± 0·04 Hz). These behavioural differences may be evidence for the proposed physiological adaptations of Coryphaenoides armatus and Coryphaenoides yaquinae , to different depths and food supply levels. At CNP, smaller fishes (38·9 cm mean L _T) were present in autumn than in summer (59·4 cm L _T) suggesting large-scale migrations across the abyssal ocean floor despite the observed slow swimming speeds.     

Marine depth use of sea trout Salmo trutta in fjord areas of central Norway

The vertical behaviour of 44 veteran sea trout Salmo trutta (275–580 mm) in different marine fjord habitats (estuary, pelagic, near shore with and without steep cliffs) was documented during May–February by acoustic telemetry. The swimming depth of S. trutta was influenced by habitat, time of day (day v. night), season, seawater temperature and the body length at the time of tagging. Mean swimming depth during May–September was 1·7 m (individual means ranged from 0·4 to 6·4 m). Hence, S. trutta were generally surface oriented, but performed dives down to 24 m. Mean swimming depth in May–September was deeper in the near‐shore habitats with or without steep cliffs (2·0 m and 2·5 m, respectively) than in the pelagic areas (1·2 m). May–September mean swimming depth in all habitats was slightly deeper during day (1·9 m) than at night (1·2 m), confirming that S. trutta conducted small‐scale diel vertical movements. During summer, S. trutta residing in near‐shore habitat progressively moved deeper over the period May (mean 1·1 m) to August (mean 4·0 m) and then reoccupied shallower areas (mean 2·3 m) during September. In winter (November and February), individuals residing in the innermost part of the fjords were found at similar average depths as they occupied during the summer (mean 1·3 m). The swimming depths of S. trutta coincide with the previously known surface orientation of salmon lice Lepeophtheirus salmonis. Combined with previous studies on horizontal use of S. trutta, this study illustrates how S. trutta utilize marine water bodies commonly influenced by anthropogenic factors such as aquaculture, harbours and marine constructions, marine renewable energy production or other human activity. This suggests that the marine behaviour of S. trutta and its susceptibility to coastal anthropogenic factors should be considered in marine planning processes.     

Pacific sardine behaviour related to tidal current dynamics in Bahía Magdalena, México

The behaviour, distribution and abundance of the Pacific sardine Sardinops sagax , detected by acoustics, was studied in relation to the pelagic environmental conditions of water temperature, fluorescence and dissolved oxygen concentration induced by tidal currents in Bahía Magdalena, México (24°32' N; 112°01' W). Sampling was along an 18 km long transect covering an area inside the bay (mean depth 20 m), the main entrance to the bay (mean depth 35 m), and the continental shelf (mean depth 100 m). The main entrance to the bay was the most dynamic area along the hydrographic transect, where the Pacific sardines tended to aggregate, probably to feed on the phytoplankton accumulated during the receding tide. With the flood tide, a high-speed tidal current is generated, introducing cool water with low oxygen concentrations into the bay. During the ebb tide, a tidal wave is also formed, but the warm and relatively well oxygenated bay water mass is transported towards the open sea. Acoustic records showed that whatever the tidal current direction (inflow or outflow), no fish schools were detected within the area of more intense tidal current speeds (>120 cm s⁻¹). Visual observations of surface Pacific sardine schools during the flood tide indicate that sardines were out of the transducer signal detection range (<10 m depth), suggesting that Pacific sardines undergo vertical migration, probably to avoid the high water current speed with low dissolved oxygen content. This behaviour may have a relevant effect on the overall hydroacoustic estimation of small pelagic fish abundance in shallower pelagic environments such as this subtropical bay.     

The role of the cerebral ganglia in the organization of feeding behavior in the pteropod mollusk Clione limacina]

The role of cerebral ganglia in switching from free swimming over to hunting behaviour in Clione limacina (Phipps) was studied. The cell bodies of central neurones giving processes to the sensory and motor nerves were mapped by retrograde axonal transport of Co2+ ions, and behavioural reactions under the extracellular electric stimulation of different ganglia areas were investigated. Comparison of morphological and behavioural data suggests main role of cerebral ganglia neurones in switching of behaviour from free swimming over to any of the three possible states: hunting (including food uptake), active or passive defensive behaviour.