Isolation of Atlantic cod (<Emphasis Type="Italic">Gadus morhua</Emphasis>) nursery areas

This study examines the degree of isolation among 0-group Atlantic cod in a region where a number of resident adult congregations have been found. The location of key nursery areas in Scottish coastal waters was identified from trawl surveys of settled 0-group cod around the Scottish coast. Segregation among four of these key areas; within the Clyde, Shetland Isles, Moray Firth and Buchan was investigated using otolith elemental composition. Isotope concentrations in the otoliths of cod were analysed by solution-based inductively coupled plasma mass spectrometry of the whole otolith. Discriminant analyses showed a clear separation between nursery areas based on the concentrations of three elements (manganese, barium and magnesium). The concentration of these elements was not affected by the age or size of individuals. Classification accuracy exceeded 90% for all four sites. Evidence of temporal persistence in the relative spatial differences in elemental concentrations between two sites for 2 year-classes was found. The results suggest limited exchange between sites during some period of the early life history. The significance of this limited exchange is discussed in relation to recent evidence for adult fidelity and the utility of closed areas for protecting nursery grounds.     

Long-term movements of tiger sharks satellite-tagged in Shark Bay,Western Australia

Tiger sharks are important predators in the seagrass ecosystem of Shark Bay, Australia. Although sharks appear to return to a long-term study site within the Eastern Gulf periodically, the extent of their long-term movements is not known. Five sharks fitted with satellite transmitters showed variable movement patterns. Three sharks remained within the Shark Bay region and another made a 500 km round-trip excursion to oceanic waters northwest of the bay. These four sharks showed relatively low displacement rates relative to sharks tracked over shorter time periods, suggesting that sharks move through large home ranges that include Shark Bay. Although no reliable position fixes were obtained for the fifth shark, we were able to use the timing of satellite uplinks and the position of the satellite to determine that it had moved at least 8,000 km to the coastal waters of southeast Africa in 99 days—the longest recorded movement by a tiger shark. This movement and previously documented trans-Atlantic movements suggest that tiger shark populations may mix across ocean basins and that tiger sharks are subject to anthropogenic effects at great distances from protected waters. Finally, our method for using single satellite uplinks may be useful in estimating movements for wide-ranging species that rarely provide high quality location estimates.     

Movements and swimming behaviour of white sharks (Carcharodon carcharias) in Australian waters

We used a combination of satellite telemetry, archival and conventional tags to show that white sharks made broad-scale movements consistent with mixing of the population across their entire Australasian range. The capture of one of these sharks in New Zealand, some 3,550 km from the point of tagging in South Australia, provides further confirmation that white sharks sometimes move into open ocean waters and cross deep ocean basins. However, most movements were confined to shelf waters, generally in areas of less than 100 m depth and in some cases into waters of less than 5 m depth. Sharks showed considerable plasticity in swimming patterns, which included many of the behaviours reported for other species. One of the archival-tagged sharks showed separate periods of distinct swimming behaviour as it moved into different habitats and travelled between them. The changes in swimming behaviour were abrupt and suggested rapid switching of hunting strategies for different prey types in these habitats. All tracked sharks showed both prolonged periods of directional swimming in coastal waters at swimming speeds of 2–3 km h⁻¹ as well as temporary residency in particular regions. Movements of tagged white sharks, together with data from shark control programs and bycatch records, suggest a seasonal movement northward along the east coast of Australia during the autumn–winter months and south in spring–early summer. The consistency of paths taken by white sharks in Australian waters suggests that they may follow common routes or “highways” in some areas. If so, identifying such areas may assist in reducing interactions with fishing operations and thus reduce bycatch.     

Marinbiologische Aspekte der Wasserbewegung

The importance of water movement as an ecological factor in littoral areas and open oceans is frequently badly underestimated. Water movement may exert biological effects comparable to those of light and temperature. Without water movement, all marine life would cease to exist. In this papar water movement is taken to embrace all motions which may occur in oceanic and coastal waters, e.g. currents, tides, horizontal and vertical water exchanges. The primary driving forces creating oceanic water movements are: gravity, earth rotation, atmospheric dynamics, and sun radiation. Until recently, water movements have largely, or exclusively, been studied by physical oceanographers; biological aspects of water movements have only lately begun to attract the attention of biologists. The results obtained so far make it quite clear that approaches and terminology employed by physical oceanographers require modification in order to meet the needs of marine biologists. The biological consequences of water movements are particularly complex, since moving water serves as transportation medium for other environmental factors such as temperature, salinity, food, etc. At the same time, some of these factors affect, in turn, speed and direction of the moving water. In addition, speed and intensity of water movements may be differentiated due to the variety of sources which cause or modify them. Various examples are presented to illustrate the complexity of water movement and its effects on biological systems. The intensity values of water movement may vary over an extremely wide range (13 degrees of magnitude).     

Reconstructing the movements of free-ranging demersal fish in the North Sea: a data-matching and simulation method

Demersal fish cannot be readily tracked using data loggers that provide satellite-based or light-based geolocation. Moreover, fish that are highly mobile within the water column cannot readily be located with other methods, such as the tidal location method (TLM). As an alternative, we describe a process that provides estimates of geographic location by simulating movement paths through geographic locations that match temperature and depth data recorded by data loggers. Depths and temperatures recorded by data loggers were compared with a North Sea temperature and depth database to identify all locations with matching data. A movement rate filter was then applied to eliminate spurious locations and simulations of possible movement paths through the remaining positions were used to generate estimates of the likelihood of a particular location having been occupied. The performance of the technique was assessed by reconstructing movement paths of artificial migrations and by using depth and temperature data collected at known locations in the North Sea. Estimates of the positional accuracy and error were comparable to the North Sea TLM. Reconstructions of the migrations of cod tagged and released in the North Sea were successfully achieved with the method. This method has application in defining the movements and migrations of commercial species in any sea area where databases of commonly measured environmental variables are available.     

Hydrography and distribution dynamics of larval and juvenile fishes in the coastal waters of the Tanshui River estuary,Taiwan, with reference to estuarine larval transport

Distribution dynamics of fish larvae and juveniles in the coastal waters of the Tanshui River, Taiwan was studied fortnightly using surface horizontal tows with a larval net in daytime during the period from early April through early June 1991. Environmental factors, including water temperature, salinity, dissolved oxygen, pH, transparency and depth at sampling stations, were also monitored. A total of 10737 fish eggs and 1387 individuals, representing 43 families and 93 species, was collected during five cruises from 12 stations in the coastal waters. Most fish were estuarine-dependent marine species. Liza macrolepis, Ambassis gymnocephalus, Terapon jarbua, Mullidae and Gobiidae were the most dominant, making up 64.7% of the total catch. Early life stages, including egg, preflexion, flexion and postflexion larvae were abundant in surface samples. However, yolk-sac larvae were absent in the surface water, probably due to an ontogenetic behavioral shift as a consequence of a change in specific weight during early development. The species composition of fish larvae and juveniles was related to the microhabitats found in the coastal waters. The physico-chemical conditions, along with ontogenetic behavior, played an important role in larval fish distribution in the coastal waters.     

Movements of whale sharks (Rhincodon typus) tagged at Ningaloo Reef, Western Australia

Whale sharks (Rhincodon typus Smith) aggregate seasonally (March–June) to feed in coastal waters off Ningaloo Reef, Western Australia. Pop-up archival tags were attached to 19 individuals (total lengths 4.5–11.0 m) at this location in early May of 2003 and 2004 to examine their horizontal and vertical movements. The long-term movement patterns of six whale sharks were documented, all of which travelled northeast into the Indian Ocean after departing Ningaloo Reef. They used both inshore and offshore habitats and made extensive vertical movements, occasionally to a depth of at least 980 m. Frequent up-and-down movements, diel vertical migration, and crepuscular descents were evident in the depth records. The sharks experienced ambient temperatures ranging between 4.2 and 28.7°C and encountered gradients of up to 20.8°C on dives.     

Population dynamics and production of euphausiids II. Thysanoessa inermis and T. raschi in the North Sea and American Coastal Waters

Results from the Continuous Plankton Recorder (CPR) survey for 1966 and 1967 are used to describe seasonal changes in abundance, size and aspects of the population structure of Thysanoessa inermis (Krøyer) and T. raschi (M. Sars) at a depth of 10 m in the North Sea and in American coastal waters from the Grand Banks to the Gulf of Maine. Production and dry weight were estimated from these data. Two year-groups were usually present in the breeding population, the proportion surviving into a second year being higher in American waters than in the North Sea. Annual production for each species was within the range 0.69 to 4.66 mg m^-3 and the ratio between production and biomass (P:B) was between 1.3 and 4.2; values outside these ranges were obtained only for American coastal waters in 1967, when the frequency of sampling was low.     

Sardine (Sardina pilchardus) spawning seasonality in European waters of the northeast Atlantic

Egg data from ichthyoplankton monitoring sites in the western English Channel (1988–2003) and northern Spain (1990–2000) and macroscopic maturity data from biological samples of purse seine landings in western and southern Iberia (1980–2004) are used to describe the spawning seasonality of sardine (Sardina pilchardus) in European waters of the northeast Atlantic using generalised additive models. The fitted models reveal a double peak in spawning activity during early summer and autumn in the western Channel, a wider spring peak off northern Spain and a broad winter season in the western and southern Iberian Peninsula. At all sites, a high probability of spawning activity was observed over at least 3 months of the year, with the duration of the season increasing with both decreasing latitude and increasing fish size. Off western and southern Iberia there are indications that the spawning season has been of longer duration in recent years for all size classes (reaching in some cases 8 months of the year for large fish). These patterns are in general agreement with existing literature and theoretical expectations of sardine spawning being driven locally by the seasonal cycle of water temperature, assuming preferences for spawning at 14 –15°C and avoidance for temperatures below 12°C and above 16°C. Regional quotient plots indicated that spawning tolerance to higher temperatures increases progressively with decreasing latitude. Despite the weak evidence for geographical differences in temperature tolerance that may have some genetic origin, the degree of spatio-temporal overlap in sardine-spawning activity within Atlantic European waters is unlikely to promote any reproductive isolation in that area.     

Movements of farmed and wild Atlantic cod (Gadus morhua) released in Trinity Bay,Newfoundland

Fishery scientists and managers are investigating the feasibility of enhancing annual recruitment to the northern Atlantic cod (Gadus morhua L.) stock complex off Labrador and northeastern Newfoundland through the release of farmed fish back into the sea. Release of newly matured fish and adults with farm-advanced fecundity would increase the spawning biomass. Enhancement efforts might be measurably successful in major bays that are year-round habitats for cod. To determine if farmed cod would remain and spawn in Trinity Bay, 14 fish with surgically implanted transmitters were released in November 1992. Sonic tracking confirmed that farmed cod released on the western side of Trinity Bay overwintered within the bay, and integrated with wild cod approaching spawning condition in April 1993. Blood plasma antifreeze levels confirmed that these wild cod had overwintered inshore in subzero waters. A spawning aggregation was found in July 1993, providing evidence that northern cod reproduce in Newfoundland bays. These findings suggest that it may be possible to increase the number of cod spawning inshore through the release of farmed fish.     

Archival tagging of subadult and adult common thresher sharks (Alopias vulpinus) off the coast of southern California

The common thresher shark (Alopias vulpinus) is a secondary target species of the California drift gillnet fishery (CA-DGN) and supports a growing recreational fishery in California waters. This study used archival tags to examine the movement patterns and habitat preferences of common threshers of the size range captured in the CA-DGN (>120 cm fork length). Depth and temperature-logging archival tags were deployed on 57 subadult and adult common threshers in the Southern California Bight. Tags from five individuals (8.8%) were recovered, and 154 days of data were successfully obtained from four of these. By night, shark movements were primarily limited to waters above the thermocline, which ranged in depth from 15 to 20 m. Sharks were significantly deeper by day, and daytime vertical distribution consisted of two distinct modes: a ‘shallow mode’ (wherein sharks occupied only the upper 20 m of the water column) and a ‘deep mode’ (characterized by frequent vertical excursions below the thermocline). This modal switch is interpreted as relating to regional differences in abundance of surface-oriented prey and prey in deeper water. Maximum dive depth was 320 m, greatest dive duration was 712 min, minimum temperature experienced during a dive was 9.1°C, and dive descent rate was significantly greater than ascent rate. Sharks inhabited waters corresponding to a sea surface temperature range of 16 to 21°C. The nocturnal depth distribution of common threshers has implications for management of drift gillnet deployment depths in the CA-DGN.     

Habitat selection in a coastal dolphin species (<Emphasis Type="Italic">Cephalorhynchus hectori</Emphasis>)

Hector's dolphin ( Cephalorhynchus hectori) is a small New Zealand delphinid with a coastal distribution. Within a strip of 1 km from shore, the present study quantified the habitat used by the dolphins ( n=461 groups) over a 19-month period (216 field days with 966 survey hours) by recording the abiotic factors sea surface temperature (SST), water depth and water clarity. Resource selection functions were used to distinguish the properties of 461 "used" sites (dolphins present) from 425 "unused" sites (no dolphins present) in six different study areas. Most dolphins were encountered in waters <39 m depth, with <4 m Secchi disk visibility and >14°C temperature. The preference of Hector's dolphins for warm and turbid waters was tested using eight models. Water depth, water clarity, SST and the study area explained dolphin presence to a very significant degree ( p<0.001), and the model allowed the creation of probability plots for a variety of combinations of the variables. Habitat selection by dolphins differed between study areas, particularly between east and west coasts, in summer (December–February) and winter (June–August). Dolphin abundance appeared to change seasonally in some study areas, possibly due to a more offshore distribution of their prey in the winter, with its lower SSTs. This was so especially in summer (the main reproductive season), when dolphins (frequently with calves) occupied shallow and turbid waters, whereas in winter less use was made of this habitat.     

Seasonal study of planktonic copepods and their benthic resting eggs in northern California coastal waters

Few investigations have examined the occurrence of zooplankton resting eggs in the sea bed of waters deeper than 20 m. In this study the distribution and abundance of planktonic copepods and their benthic resting eggs in coastal waters off northern California, U.S.A., were determined and related to environmental parameters (temperature, salinity, depth, and sediment grain size). Sediment cores, net tows, and CTD profiles were obtained in April and October 1989, and February, April, and October 1990. Water depths in the study area ranged from approximately 60 to 120 m. The mean abundance of eggs was as high as 1.2×10⁵ m^-2 for Acartia clausi Giesbrecht and 1.9×10⁵ m^-2 for Tortanus discaudatus Thompson and Scott. These egg concentrations are comparable to those reported previously for shallower more protected regions. The abundance of eggs in the sediments decreased with increasing depth of the water column. For the region as a whole, eggs were least abundant in muddy sediments. The mean abundance of eggs in the sea bed also varied seasonally and annully. Benthic resting eggs of A. clausi were more abundant in April 1989 than in April 1990, and adults of the species were never found in the plankton samples. The lack of adults is not unusual since results of previous studies indicate that A. clausi is a cold-water species, and in this region water temperatures are colder in summer, than in winter, due to upwelling. Temperature and salinity data indicated that the upwelling season had commenced by the time of the April 1990, but not the April 1989 sampling. Thus, the reduced abundance of benthic eggs in April 1990 may have been due to egg-hatching in response to reduced temperatures. The results suggest that the presence of A. clausi in coastal waters off northern California is linked to recruitment from benthic resting eggs.     

Tracking hawksbill sea turtles (<Emphasis Type="Italic">Eretmochelys imbricata</Emphasis>) during inter-nesting intervals around Barbados

Hawksbill sea turtles (Eretmochelys imbricata) nesting in Barbados (Needham’s Point, 13° 04′ 41.33′′ N, 59° 36′ 32.69′′W) were outfitted with GPS dataloggers over three breeding seasons (2008–2010) to track movement during inter-nesting intervals. Most females established spatially restricted resident areas up current and within 7 km of the nesting beach where they spent the majority of the inter-nesting interval. Females nesting earlier in the season settled on shallower sites. Only experienced remigrant turtles occupied the most distant resident areas. Females tracked for multiple inter-nesting intervals exhibited site fidelity, but the area contracted and the activity of females decreased with each successive interval. Hawksbills may trade off site characteristics with distance from the nesting beach and reduce activity over the course of the breeding season to optimise energy reserves during inter-nesting intervals.     

Seasonal population structure,vertical distribution and migration of the chaetognath Sagitta elegans in the Celtic Sea

The biology of the chaetognath Sagitta elegans Verrill has been much researched, but detailed studies of population structure have generally been conducted in coastal water where dynamic tidal conditions may cause difficulty in interpretation of data. The resolution of sampling examining vertical distribution and diurnal migration has also been rather coarse. During a series of eight cruises to a seasonally thermally stratified sampling site in the Celtic Sea in 1978 and 1979, detailed vertical zooplankton profiles were taken to study the seasonal population structure, vertical distribution and migration of this species. The overwintering stock of S. elegans (22 to 52 individuals m^-2, 0 to 90 m) had a wide range of lengths (5 to 20 mm) and matured in 1978 from early March, spawning several times before dying out by late July. Young produced by the overwintering stock started to mature in July and population numbers reached their highest in August (2483 m^-2, 132.8 mg C m^-2) when sea temperature peaked (17.1°C). By October, the population of S. elegans declined (284 m^-2), which was thought to be due to a combination of lower sea-water temperature, competition for and availability of food, and predation. Because of the length range of the overwintering population (5 to 20 mm), it is assumed that reproduction continued at a low level over the winter, although eggs were not found in January and February, the coldest months of the year. In summer, the smallest S. elegans (2 to 6 mm) were found in the near-surface waters and did not migrate, but as their lengths increased they occupied deeper depth ranges and a portion of the population started to migrate diurnally. Individuals which did not migrate and stayed in the warmer surface waters, or those which migrated into it, matured faster than those remaining in the colder water below the thermocline. Migration to surface waters by mature individuals seemed to be stopped by high surface temperatures (17°C) and a sharp thermocline (3 C°). As sea temperature increased during the year from the winter minimum of 7.7°C, S. elegans matured at a progressively shorter length (14 mm in March 1978 to 10 mm in August). There are probably only three generations of S. elegans a year in the Celtic Sea.     

Distribution and abundance of the epipelagic mollusk Carinaria japonica in waters off Southern California

The distribution and abundance of the heteropod mollusk Carinaria japonica Okutani is described from midwater trawl records off Southern California (USA) and northern Baja California (Mexico). Maximal numbers of individuals were recorded during August in oceanic waters off Southern California. In oceanic waters near Guadalupe Island, Baja California, low population levels were recorded irrespective of season. In neritic waters over the continental shelf off Southern California, C. japonica were present in low numbers, mainly between July and December when conditions seemed most favorable for their entry into the Southern California Eddy.     

Effects of human footprint and biophysical factors on the body-size structure of fished marine species

Marine fisheries in coastal ecosystems in many areas of the world have historically removed large-bodied individuals, potentially impairing ecosystem functioning and the long-term sustainability of fish populations. Reporting on size-based indicators that link to food-web structure can contribute to ecosystem-based management, but the application of these indicators over large (cross-ecosystem) geographical scales has been limited to either fisheries-dependent catch data or diver-based methods restricted to shallow waters (<20 m) that can misrepresent the abundance of large-bodied fished species. We obtained data on the body-size structure of 82 recreationally or commercially targeted marine demersal teleosts from 2904 deployments of baited remote underwater stereo-video (stereo-BRUV). Sampling was at up to 50 m depth and covered approximately 10,000 km of the continental shelf of Australia. Seascape relief, water depth, and human gravity (i.e., a proxy of human impacts) were the strongest predictors of the probability of occurrence of large fishes and the abundance of fishes above the minimum legal size of capture. No-take marine reserves had a positive effect on the abundance of fishes above legal size, although the effect varied across species groups. In contrast, sublegal fishes were best predicted by gradients in sea surface temperature (mean and variance). In areas of low human impact, large fishes were about three times more likely to be encountered and fishes of legal size were approximately five times more abundant. For conspicuous species groups with contrasting habitat, environmental, and biogeographic affinities, abundance of legal-size fishes typically declined as human impact increased. Our large-scale quantitative analyses highlight the combined importance of seascape complexity, regions with low human footprint, and no-take marine reserves in protecting large-bodied fishes across a broad range of species and ecosystem configurations.     

Lek promiscuity in a semelparous mammal,Antechinus stuartii (Marsupialia: Dasyuridae)?

Summary All male Antechinus stuartii die following a brief rut towards the end of their first year of life. Outside the rutting period, both males and females forage in clearly-defined invidual home ranges, but neither sex is territorial. As temperatures drop during the winter, both sexes may leave their foraging range each day to spend the latter part of the night and most of the daylight hours in communal nests which may be used by fifteen animals simultaneously, and over forty individuals during one winter. These temporary movements away from the foraging range cause an increase in the daily home range revealed by radiotelemetry. When the mating season commences, males abandon their foraging range and aggregate in a few of the communal nest trees, where they spend most of the night. There is some movement between aggregations, but the movement appears to be rapid and direct. Females continue to use their foraging area, and nest solitarily. However, they make excursions to the male aggregations, and spend time in the nests with the males. By the third week of the mating season, immediately prior to male mortality, males move frequently from one aggregation to another, but are still confined to the aggregations and direct movements between those nests. By this time some females have ceased visiting the aggregations and nest solitarily within their foraging range. These data suggest that the mating system of A. stuartii is lek promiscuity, and support the hypothesis that the abrupt mortality of males is a cost of endocrine changes which facilitate gluconeogenic mobilisation of body protein, allowing the males to sustain their vigil at the leks.     

Ranging patterns of bottlenose dolphins living in oceanic waters: implications for population structure

Very little is known about the ecology of common bottlenose dolphins (Tursiops truncatus) living in oceanic waters. This study investigated the ranging and residence patterns of bottlenose dolphins occurring in the Azores (Portugal), the most isolated archipelago in the North Atlantic. Data were collected during standardized boat-based surveys conducted over a 6-year period in an area of approximately 5,400 km² (main study area). To investigate the extent of movements of individual animals, non-systematic surveys were also conducted outside this area. Only 44 individuals out of 966 identified were frequently sighted within and between years. The remaining individuals were either temporary migrants from within or outside the archipelago, or transients. Resident dolphins showed strong geographic fidelity to the area. Long-distance movements (of almost 300 km), consistent with foraging or exploratory trips, were observed among non-resident dolphins. Home range size was estimated for 31 individuals sighted ≥10 times. Range areas of these dolphins varied in size and location, but considerable overlap was observed in the areas used, suggesting the absence of habitat partitioning between resident and non-resident dolphins. Estimates of home range size of bottlenose dolphins in the Azores were found to be considerably larger than those previously reported for this species. It is hypothesized that dolphins living in the Azores carry out extensive movements and have large home ranges in response to the lower density and patchy distribution of prey compared to other areas. The extensive ranging behaviour and the lack of territoriality provide an opportunity for interbreeding between dolphins associated with different islands, thus preventing genetic differentiation within the population of the Azores.     

Ranging patterns of bottlenose dolphins living in oceanic waters: implications for population structure

Very little is known about the ecology of common bottlenose dolphins (Tursiops truncatus) living in oceanic waters. This study investigated the ranging and residence patterns of bottlenose dolphins occurring in the Azores (Portugal), the most isolated archipelago in the North Atlantic. Data were collected during standardized boat-based surveys conducted over a 6-year period in an area of approximately 5,400 km² (main study area). To investigate the extent of movements of individual animals, non-systematic surveys were also conducted outside this area. Only 44 individuals out of 966 identified were frequently sighted within and between years. The remaining individuals were either temporary migrants from within or outside the archipelago, or transients. Resident dolphins showed strong geographic fidelity to the area. Long-distance movements (of almost 300 km), consistent with foraging or exploratory trips, were observed among non-resident dolphins. Home range size was estimated for 31 individuals sighted ≥10 times. Range areas of these dolphins varied in size and location, but considerable overlap was observed in the areas used, suggesting the absence of habitat partitioning between resident and non-resident dolphins. Estimates of home range size of bottlenose dolphins in the Azores were found to be considerably larger than those previously reported for this species. It is hypothesized that dolphins living in the Azores carry out extensive movements and have large home ranges in response to the lower density and patchy distribution of prey compared to other areas. The extensive ranging behaviour and the lack of territoriality provide an opportunity for interbreeding between dolphins associated with different islands, thus preventing genetic differentiation within the population of the Azores.