共查询到20条相似文献,搜索用时 31 毫秒
1.
Loggerhead sea turtle hatchlings emerge from nests on either the east or west coast of the South Florida peninsula and then
migrate offshore in opposite directions. Under laboratory conditions, magnetic cues induce east coast hatchlings to swim in
directions that promote their transport by oceanic surface currents, such as the North Atlantic gyre. However, the surface
currents used by west coast hatchlings are unknown. We examined the responses of west (Sarasota) hatchlings to magnetic cues
in the Gulf of Mexico, the Florida Straits, and the Gulf Stream to determine their (1) likely migratory routes (2) orientation
where currents lead into the Atlantic Ocean, and (3) orientation adjacent to Florida’s east coast. The results suggest that
migration inside Gulf waters may be circuitous, that the turtles respond appropriately to enter Atlantic waters, and that
orientation along Florida’s east coast probably promotes transport by the Gulf Stream into the North Atlantic gyre. 相似文献
2.
The South Florida subpopulation of loggerhead sea turtles (Caretta caretta L.) nests with great fidelity on either the southeast or the southwest coast of Florida, USA. The hatchlings that emerge
from those nests must swim in opposite directions and search for different surface currents to migrate away from continental
shelf waters. In this laboratory study, we compared the pattern of swimming activity shown by the hatchlings from each coast
over the first 6 days of migration. Turtles from both coasts were equally active during their “frenzy” period (the first 24 h
of swimming) and during the daylight hours of the 5 days that followed (the “postfrenzy” period). However, the west coast
turtles were significantly more active than the east coast turtles during the nocturnal portion of the postfrenzy period.
This difference may be related to the greater distance southwest coast turtles must negotiate to locate surface currents for
transport out of the Gulf of Mexico and into the Atlantic Ocean basin. These differing behavioral strategies may be genetically
determined, as similar correspondence between activity and distance is well known among migratory populations of birds and
fish and is often based upon inherited programs of endogenously driven activity. Alternatively, behavioral differences between
the two nesting groups could be a manifestation of phenotypic plasticity that arises as the hatchlings respond to unique environmental
cues on each coast. 相似文献
3.
L. A. Ferry-Graham 《Marine Biology》1998,131(4):703-718
Capture, manipulation, and transport of prey were quantified from high-speed video of hatchling swellsharks, Cephaloscyllium ventriosum. Kinematic variables were contrasted with those of 1 yr-old swellsharks. Hatchling prey-captures were ram-dominated, while
1 yr-old prey-capture events had a detectable suction component. Timing differences between kinematic patterns of the age
groups were not detected. Significant differences in displacement maxima of kinematic variables between the two age groups
during feeding were detected, but were consistent with the expectations of isometry; they doubled in accordance with a doubling
in shark length. A scaling analysis confirmed that swellsharks grow isometrically. A simple model of the head during prey
capture confirmed that buccal expansion scaled isometrically between age groups. Thus, this study suggests that hatchlings
generally perform the suite of movements necessary for suction generation within the buccal cavity during feeding. A suction
component to the strike, however, was generally not detected by the “ram:suction index”. It appears that although it is probably
generated within the buccal cavity, suction has little effect on the prey item and makes a minimal contribution to prey capture.
Suction may be ineffective due to the highly active nature of the hatchlings. During a strike, a hatchling's forward locomotion
may be sufficient to overwhelm any suction produced by the expanding buccal cavity; thus, the swimming shark effectively “scoops”
the prey up in its open mouth (i.e. ram feeding) before the prey can be entrained in the flow of water entering the mouth
(i.e. suction feeding). It is also likely that the hatchling sharks are sufficiently small to render any suction generated
ineffective. Even though the sharks scale isometrically, the sheer size of the 1 yr-old sharks allows a greater amount of
force to be generated, that will ultimately draw the prey to the open mouth. Thus, there are absolute consequences of size
for feeding behaviors.
Received: 17 June 1997 / Accepted: 6 March 1998 相似文献
4.
The present study describes the emergence pattern of loggerhead sea turtle hatchlings (Caretta caretta) from a nesting beach in Kyparissia Bay (Greece). We try to establish the role played by hatchling biometry, nest relocation
and distance from nest to the sea on this emergence pattern. We surveyed a total of 32 nests, and found long emergence periods
(mean = 6.7 nights). The majority of emergences occurred at night, mainly between 0030 and 0100 hours, and in small groups.
Most of the hatchlings emerged from the nests the first night. We found no clear trend when we studied the effect of hatchling
biometry between successive emergence days. We also found that relocation of the nests did not significantly affect the emergence
pattern. However, we noted that in the relocated nests, hatchlings emerged in smaller groups. Emergence periods were inversely
related to distance from the sea. In short, factors such as climate conditions, relocation and nest distance to the sea appear
to have some effect on the emergence pattern. Therefore, they should be taken into account in both biological studies and
management plans for sea turtle nesting beaches. Our results suggest leaving an extended period between the first emergence
of hatchlings and the excavation of nests by researchers in future studies in the area. 相似文献
5.
The extent to which the American lobster, Homarus americanus (H. Milne-Edwards), utilizes estuarine habitats is poorly understood. From 1989 to 1991 we examined lobster movements in
and around the Great Bay estuary, New Hampshire using tag/recapture and ultrasonic telemetry. A total of 1212 lobsters were
tagged and recaptured at sites ranging from the middle of Great Bay, 23.0 km from the coast, to Isles of Shoals, 11.2 km offshore.
Twenty-six lobsters equipped with ultrasonic transmitters were tracked for periods ranging from 2 weeks to >1 year. Most lobsters
moved <5 km toward the coast, with those furthest inland moving the greatest distance. Lobsters with transmitters moved in
a sporadic fashion, with residency in one area for 2 to 4 weeks alternating with rapid movement to a new location (mean velocity = 0.3 km d−1, 1.8 km d−1 max.). Site of release influenced distance moved, but there was no significant relationship between lobster size and distance
traveled, days at large, or rate of movement. Most movement into the estuary occurred in the spring, while during the remainder
of the year there was a strong tendency to move downriver, toward the coast. These seasonal migrations of estuarine lobsters
may enhance their growth and survival by enabling them to avoid low salinity events in the spring and fall, and to accelerate
their growth in warmer estuarine waters during the summer.
Received: 26 January 1996 / Accepted: 22 January 1999 相似文献
6.
The South Florida subpopulation of loggerhead sea turtles (Caretta caretta L.) nests with great fidelity on either the southeast or the southwest coast of Florida, USA. The hatchlings that emerge from those nests must swim in opposite directions and search for different surface currents to migrate away from continental shelf waters. In this laboratory study, we compared the pattern of swimming activity shown by the hatchlings from each coast over the first 6 days of migration. Turtles from both coasts were equally active during their “frenzy” period (the first 24 h of swimming) and during the daylight hours of the 5 days that followed (the “postfrenzy” period). However, the west coast turtles were significantly more active than the east coast turtles during the nocturnal portion of the postfrenzy period. This difference may be related to the greater distance southwest coast turtles must negotiate to locate surface currents for transport out of the Gulf of Mexico and into the Atlantic Ocean basin. These differing behavioral strategies may be genetically determined, as similar correspondence between activity and distance is well known among migratory populations of birds and fish and is often based upon inherited programs of endogenously driven activity. Alternatively, behavioral differences between the two nesting groups could be a manifestation of phenotypic plasticity that arises as the hatchlings respond to unique environmental cues on each coast. 相似文献
7.
R. W. Brill B. A. Block C. H. Boggs K. A. Bigelow E. V. Freund D. J. Marcinek 《Marine Biology》1999,133(3):395-408
We measured the horizontal and vertical movements of five adult yellowfin tuna (Thunnus albacares, estimated body mass 64 to 93 kg) near the main Hawaiian Islands, while simultaneously gathering data on oceanographic conditions
and currents. Fish movements were recorded by means of ultrasonic depth-sensitive transmitters. Depth–temperature and depth–oxygen
profiles were measured with vertical conductivity–temperature–depth (CTD) casts, and the current-velocity field was surveyed
using an acoustic Doppler current profiler (ADCP). Large adult yellowfin tuna spent ≃60 to 80% of their time in or immediately
below the relatively uniform-temperature surface-layer (i.e. above 100 m), a behavior pattern similar to that previously reported
for juvenile yellowfin tuna, blue marlin (Makaira nigricans), and striped marlin (Tetrapturus audax) tracked in the same area. In all three species, maximum swimming depths appear to be limited by water temperatures 8 C°
colder than the surface-layer water temperature. Therefore, neither large body mass, nor the ability to maintain elevated
swimming-muscle temperatures due to the presence of vascular counter-current heat exchangers in tunas, appears to permit greater
vertical mobility or the ability to remain for extended periods below the thermocline. In those areas where the decrease in
oxygen with depth is not limiting, the vertical movements of yellowfin tuna, blue marlin and striped marlin all appear to
be restricted by the effects of water temperature on cardiac muscle function. Like juvenile yellowfin tuna, but unlike blue
marlin and striped marlin, adult yellowfin tuna remained within 18.5 km of the coast and became associated with floating objects,
including anchored fish-aggregating devices (FADs) and the tracking vessel. Like juvenile yellowfin tuna, large adult yellowfin
repeatedly re-visit the same FAD, and appear able to navigate precisely between FADs that are up to 18 km apart. The median
speed over ground ranged from 72 to 154 cm s−1. Neither speed nor direction was strongly influenced by currents.
Received: 27 March 1998 / Accepted: 13 November 1998 相似文献
8.
Geographic variation in development rate between populations of the teleost Fundulus heteroclitus 总被引:2,自引:0,他引:2
The teleost Fundulus heteroclitus (Linnaeus) employs a semilunar spawning strategy, whereby eggs deposited on a spring tide optimally hatch on the following
spring tide. This spawning strategy constrains the development period to ≃2 wk, regardless of the mean water temperature,
which varies throughout the species' range (Nova Scotia, Canada, to Florida, USA). We hypothesized that F. heteroclitus embryos would exhibit development-rate compensation among populations to ensure appropriate hatching during the spring tide.
Development rates of embryos from Massachusetts and Florida were examined. Northern embryos had faster temperature-specific
development rates than southern embryos, while data from the literature showed that embryos from Delaware have an intermediate
development rate. Results from reciprocal hybrid crosses indicated that there may be a genetic basis for these differences.
In addition, northern embryos were more cold-tolerant and southern embryos more heat-tolerant. Field studies showed that embryos
in their local environments develop at similar rates despite large temperature differences. Embryos seldom, if ever, experience
lethal temperatures in their native habitats, but would do so if exposed to the temperature regimes at the extreme ends of
the species' range. Thus, F. heteroclitus populations along the Atlantic coast have specifically adapted their development rates and thermal tolerances to the local
thermal regime.
Received: 2 September 1996 / Accepted: 17 September 1996 相似文献
9.
Locomotion performance plays a vital role in determining hatchling green turtle Chelonia mydas survival in the first few hours after emerging from their nests as hatchlings crawl and swim the gauntlet of predators before
reaching the relative safety of the open ocean. Previous laboratory based constant incubation experiments found incubation
temperature to influence the size and swimming performance of hatchling green turtles. Here we examine the morphology and
crawling and swimming performance of hatchling green turtles as they emerge from nests on Heron Island rookery in the southern
Great Barrier Reef to test the hypothesis that nest temperature in the field can influence these attributes. We found inter-nest
differences in hatchling mass and dimensions, and that hatchling mass was not correlated with nest temperature. However, hatchlings
from warmer nests had smaller carapace dimensions than hatchlings from cool nests suggesting that more yolk was converted
to hatchling tissue during embryonic development in cool nests. There was considerable intra- and inter-nest variation in
both crawling and swimming performance of hatchlings. Hatchlings from cool nests tended to be faster crawlers than hatchlings
from warm nests, but the thrust produced during swimming was not correlated with nest temperature. During the 4 h swimming
trial, hatchlings swimming effort decreased significantly during the first 3 h but swimming effort remained relatively constant
for the last 1 h. Individual hatchling crawling and swimming performances were not correlated with each other.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
10.
Charles H. Peterson Stephen R. Fegley Christine M. Voss Sara R. Marschhauser Beth M. VanDusen 《Marine Biology》2013,160(3):629-640
Protecting eggs from predators is common practice in sea turtle conservation, but routine protection of hatchlings is not. Of 42 loggerhead hatchlings observed emerging from 10 nests on undeveloped Onslow Beach, North Carolina, 24 % were preyed on by ghost crabs. In experimental trials, ghost crabs similarly threatened and captured neonate freshwater sliders, supporting their substitution as proxy for threatened and endangered sea turtle hatchlings in field experiments testing density dependence. Exploiting natural long-shore variation in ghost crab density, we show that a 2.6-fold higher ghost crab density resulted in 5 times more nocturnal threat encounters with sliders and 3.4 times more slider captures. Sliders released in simulated group emergences experienced lower per capita capture risk by ghost crabs than solitary sliders, implying predator dilution. Non-independence of egg and hatchling depredation motivates consideration of merging sea turtle egg and hatchling stages when modeling and managing food web interactions. 相似文献
11.
The distribution and abundance of Japanese common squid [Todarodes pacificus (Steenstrup, 1880)] paralarvae off southern Kyushu Island near the Kuroshio were examined in relation to water types in the
region. Surveys were conducted in 1996 and 1997 using paired, 70 cm diameter Bongo nets. Temperature–salinity plots from 0,
50 and 100 m depths were used to assign sampling stations to three water types: inshore, mixing and Kuroshio. In total, 4103
T. pacificus paralarvae were collected at 59 of 72 stations. Catch densities at positive stations ranged between 8 and 4282 ind./50 m2 sea surface area. Catches during both years were highest in mixing waters, followed by inshore and Kuroshio waters. Total
catches were highest just north of the oceanographic front at the inshore edge of the Kuroshio and declined with increasing
distance away from the front. Catches of paralarvae ≤1.0 mm mantle length also peaked near the front. In both years, ≥85%
of all paralarvae and ≥69% of those ≤1.0 mm mantle length occurred less than 25 km from the front. We conclude that most spawning
off southwest Kyushu occurs near the frontal zone, where Kuroshio and inshore waters meet.
Received: 18 November 1998 / Accepted: 11 May 1999 相似文献
12.
In marine turtles, the sex of an individual is determined by temperatures experienced during embryonic development. Gonad histological observation is still the only reliable way to determine hatchling sex, hampering the study of reproduction and of the demographic consequences of context-dependent sex-ratios, a subject of interest in a warming planet. We investigated whether hatchling remains from predation by Ocypode cursor can be used to estimate sex-ratio trends in a green turtle rookery at Poilão, Guinea-Bissau (10°52′N, 15°43′W). Sex could be readily determined in 77 and 79% of the predated hatchlings in 2008 and 2009, respectively. By comparing hatchlings killed by crabs, hatchlings accidentally dying on the reefs, and live hatchlings, we show that ghost crabs select the smaller prey, but do not select according to hatchling sex, which is explained by the lack of hatchling size dimorphism in this population. The proportion of male hatchlings was 0.45 ± 0.06 and 0.15 ± 0.06 for early and late-season clutches, respectively, these differences most likely being explained by rainfall. Using leftovers from predation by crabs may be a good solution to non-invasively monitor broad trends in sex-ratios of sea turtles. 相似文献
13.
The dietary compositions and breadths of sequential 50 mm size classes of the six whiting species found in nearshore (<1.5 m),
shallow inner-shelf (5 to 15 m) and/or deep inner-shelf (20 to 35 m) waters of the lower west coast of Australia were determined.
Comparisons between the results of principal components analysis of head and mouth dimensions and the dietary compositions
of Sillago bassensis, S. vittata, S. burrus, S. schomburgkii, S. robusta and Sillaginodespunctata suggests that any differences in the dietary composition of similar-sized representatives of different species, when they
occur in the same habitat, are more likely to be due to differences in foraging behaviour than mouth morphology. Classification,
ordination and Schoener's overlap indices showed that, in nearshore waters, the juveniles of Sillago bassensis, which colonise relatively exposed areas, have a different diet to those of the smallest representatives of the other whiting
species that occupy more sheltered habitats. S. bassensis consumes mainly amphipods, whereas the smaller representatives of S. vittata, S. burrus, S. schomburgkii and Sillaginodes punctata ingest large volumes of copepods, which are typically abundant in protected nearshore waters. Although the mouth dimensions
of S. punctata tend to be smaller than those of Sillago schomburgkii, the larger individuals of the former species ingest greater quantities of larger prey, such as crabs and carid shrimps.
As S. bassensis, S. vittata and S. burrus increase in size and migrate out into shallow inner-shelf waters, the latter two species tend to concentrate more on benthic
prey, while the former species ingests fauna that is more epibenthic. The largest S. bassensis subsequently migrate out into deep inner-shelf waters, where they co-occur with S. robusta, which is restricted to those waters. In these waters, S. bassensis feeds to a far greater extent on large benthic prey, whereas S. robusta consumes a greater quantity of small epibenthic crustaceans, differences that reflect the far larger lengths of the former
species in that region. The above data emphasise that the distribution and ontogenetic movements of the six abundant species
of whiting play a major role in facilitating a partitioning of food resources amongst these species found in coastal waters
of the lower west coast of Australia.
Received: 7 October 1996 / Accepted: 31 January 1997 相似文献
14.
The short-term movements and behaviour of whale sharks (Rhincodon typus Smith, 1828) during March 1994 and April 1997 are reported from data collected by acoustic tracking and archival tags at
Ningaloo Reef on the north west coast of Western Australia. Sharks were tracked for up to 26 h and generally swam slowly at
≃0.7 m s−1 parallel to the reef edge; occasionally they swam in a wide arc adjacent to passes in the reef. All tracked sharks made regular
dives through the water column, mostly from the surface to near the bottom. These dives did not appear to be related to hydrographic
features, and the sharks were probably searching the water column for food. Most sharks were accompanied by other fishes,
usually the golden trevally Gnathanodon speciosus.
Received: 19 January 1999 / Accepted: 22 June 1999 相似文献
15.
Whilst a range of animals have been shown to respond behaviourally to components of the Earth’s magnetic field, evidence of
the value of this sensory perception for small animals advected by strong flows (wind/ocean currents) is equivocal. We added
geomagnetic directional swimming behaviour for North Atlantic loggerhead turtle hatchlings (Caretta
caretta) into a high-resolution (1/4°) global general circulation ocean model to simulate 2,925-year-long hatchling trajectories
comprising 355,875 locations. A little directional swimming (1–3 h per day) had a major impact on trajectories; simulated
hatchlings travelled further south into warmer water. As a result, thermal elevation of hatchling metabolic rates was estimated
to be between 63.3 and 114.5% after 220 days. We show that even small animals in strong flows can benefit from geomagnetic
orientation and thus the potential implications of directional swimming for other taxa may be broad. 相似文献
16.
M. E. Lutcavage R. W. Brill G. B. Skomal B. C. Chase J. L. Goldstein J. Tutein 《Marine Biology》2000,137(2):347-358
Ultrasonic, depth-sensitive transmitters were used to track the horizontal and vertical movements, for up to 48 h, of 11
adult (136 to 340 kg estimated body mass) North Atlantic bluefin tuna (Thunnus thynnus Linnaeus). Fish were tracked in October 1995, September and October 1996, and August and September 1997 in the Gulf of Maine,
northwestern Atlantic. The objective was to document the behavior of these fish and their schools in order to provide the
spatial, temporal, and environmental information required for direct (i.e. fishery-independent) assessment of adult bluefin
tuna abundance using aerial surveys. Transmitters were attached to free-swimming fish using a harpoon attachment technique,
and all fish remained within the Gulf of Maine while being followed. Most of the bluefin tuna tagged on Stellwagen Bank or
in Cape Cod Bay (and followed for at least 30 h) held a predominately easterly course with net horizontal displacements of
up to 76 km d−1. Mean (±SD) swimming depth for all fish was 14 ± 4.7 m and maximum depth for individuals ranged from 22 to 215 m. All but
one fish made their deepest excursions, often single descents, at dawn and dusk. In general, adult bluefin tuna spent <8%
of their time at the surface (0 to 1 m), <19% in the top 4 m, but >90% in the uppermost 30 m. Mean (±SD) speed over ground
was 5.9 km h−1, but for brief periods surpassed 20 to 31 km h−1. Sea surface temperatures during tracking were 11.5 to 22.0 °C, and minimum temperatures encountered by the fish ranged from
6.0 to 9.0 °C. Tagged bluefin tuna and their schools frequented ocean fronts marked by mixed vertebrate feeding assemblages,
which included sea birds, baleen whales, basking sharks, and other bluefin schools.
Received: 19 July 1999 / Accepted: 25 March 2000 相似文献
17.
Satellite tracking reveals a dichotomy in migration strategies among juvenile loggerhead turtles in the Northwest Atlantic 总被引:2,自引:2,他引:0
Katherine L. Mansfield Vincent S. Saba John A. Keinath John A. Musick 《Marine Biology》2009,156(12):2555-2570
Few data are available on the movements and behavior of immature Atlantic loggerhead sea turtles (Caretta caretta) from their seasonal neritic foraging grounds within the western north Atlantic. These waters provide developmental habitat
for loggerheads originating from several western Atlantic nesting stocks. We examined the long-term movements of 23 immature
loggerheads (16 wild-caught and seven headstart turtles) characterizing their seasonal distribution, habitat use, site fidelity,
and the oceanographic conditions encountered during their migrations. We identified two movement strategies: (1) a seasonal
shelf-constrained north–south migratory pattern; and (2) a year-round oceanic dispersal strategy where turtles travel in the
Gulf Stream to the North Atlantic and their northern dispersal is limited by the 10–15°C isotherm. When sea surface temperatures
dropped below 20°C, neritic turtles began a migration south of Cape Hatteras, North Carolina (USA) where they established
fidelity to the waters between North Carolina’s Outer Banks and the western edge of the Gulf Stream along outer continental
shelf. Two turtles traveled as far south as Florida. Several turtles returned to their seasonal foraging grounds during subsequent
summers. Northern movements were associated with both increased sea surface temperature (>21°C) and increased primary productivity.
Our results indicate strong seasonal and interannual philopatry to the waters of Virginia (summer foraging habitat) and North
Carolina (winter habitat). We suggest that the waters of Virginia and North Carolina provide important seasonal habitat and
serve as a seasonal migratory pathway for immature loggerhead sea turtles. North Carolina’s Cape Hatteras acts as a seasonal
“migratory bottleneck” for this species; special management consideration should be given to this region. Six turtles spent
time farther from the continental shelf. Three entered the Gulf Stream near Cape Hatteras, traveling in the current to the
northwest Atlantic. Two of these turtles remained within an oceanic habitat from 1 to 3 years and were associated with mesoscale
features and frontal systems. The ability of large benthic subadults to resume an oceanic lifestyle for extended periods indicates
plasticity in habitat use and migratory strategies. Therefore, traditional life history models for loggerhead sea turtles
should be reevaluated. 相似文献
18.
Thirty-eight yellowfin tuna (Thunnus albacares) were tagged with coded ultrasonic beacons between 6 March and 4 December 1996 near two buoys off the western coast of Oahu,
Hawaii. Two to four tuna were captured, tagged, and released on the same day in as rapid succession as possible in an effort
to tag members of the same school. Automated “listening” monitors attached to the buoys recorded when these marked individuals
entered within a radius of ≤1.1 km of the buoys during a 13 mo period. Twenty-seven of the tuna returned to the site of tagging.
The mean number of returns was 4.2 per tuna (max. = 17), and visits ranged from 1 to 910 min (median = 2.7 min, mean = 40.1 min).
The intervals between successive returns varied from 1 to 257 d (median = 3.0 d, mean = 17.4 d). Seventy-three percent of
the tuna returned together with tunas tagged on the same day, exceeding the frequency of returns of tuna tagged on another
day or arriving alone. This social cohesion is supported by the pattern of return visits by five tuna tagged on 6 March at
Monitoring Station R. Two or more of these tuna arrived together on 24 of 35 d when tagged tuna were detected. All five individuals
visited R on 11 April, a month after tagging, three arrived together 5 mo later on 4 August, and three returned 6 mo later
on 1 December 1996. Tuna often arrived at the same time of day, e.g. Individuals 1 and 3 visited R at 09:15 hrs on 12 April
and at 09:00 hrs 8 mo later. The returns were also site-specific. The 22 tuna tagged at R made 182 return visits to R (92.4%)
and only 15 visits to Monitoring Station K (7.6%), 10 km away. An allegiance of tuna to one school, a predilection for returning
to the site of tagging, and precise timing when visiting sites, are consistent with tuna having migratory pathways consisting
of “way-points” that are visited with temporal regularity.
Received: 30 April 1998 / Accepted: 27 October 1998 相似文献
19.
European lobsters, Homarus gammarus (L.), were tracked on an artificial reef in Poole Bay on the south coast of England using an electromagnetic telemetry system
which monitored movements between reef units and recorded body movements (pitching and rolling) detected with a tilt switch
incorporated into the transmitting tag. Several environmental variables (water temperature, light, hydrostatic pressure, current
velocity and direction) were recorded simultaneously by the telemetry system, which was self-contained on the seabed. Movements
between units of the artificial reef (excursions outside shelter) were predominantly nocturnal, peaking 1.5 to 3 h after sunset
and returning to low levels shortly before dawn. A marked decline in the number of inter-reef unit movements from late summer
to winter was related to decreasing water temperature rather than to daytime light level, wave height or tidal range. Activity
indicated by the tilt switch was also greater at night, but declined gradually from a peak early in the night to a minimum
at around midday, on average, implying a degree of activity within reef units during daylight. As with movements between reef
units, activity declined seasonally with decreasing water temperature; in addition, the diel pattern of activity disappeared
in winter.
Received: 9 February 1998 / Accepted: 24 July 1998 相似文献
20.
The annual epidemic spawning period of a Scottish population of Arenicola marina (L.) has been recorded over a period of 13 yr. This population spawns between mid-October and mid-November in a discrete
spawning event over a period of 4 to 5 d. Endocrine manipulation experiments showed that spawning is induced in females only
if sufficient titres of PMH (prostomial maturation hormone) are present in the prostomia. These levels are attained during
the 2 to 3 wk prior to the natural spawning date. The East Sands, St. Andrews population always spawns during periods of spring
tides regardless of tidal amplitude or whether they are full- or new-moon tides. Meteorological data, including sea-temperature
data were collected for each year, and correlation of the environmental data with spawning time was attempted. Correlation
of spawning times with weather patterns showed that mean daily air pressures were significantly higher during the spawning
period than from September to November as a whole. Evidence also suggests that a reduction in sea temperature is required
prior to spawning. A significant moderate negative correlation was found between May to July air temperatures and spawning
date, suggesting that higher May to July temperatures may induce early spawning. Daily rainfall and wind speed were also lower
during the spawning period, but not significantly so. These results indicate that air pressure (or changes therein) may act
as a final spawning cue, and the advantages of this are discussed in relation to fertilization success. A model of the interplay
between environmental parameters and the endocrine mechanisms controlling the induction of spawning is proposed. Higher than
average summer temperatures may advance gametogenesis to bring the population into a state of maturity (full-size oocytes,
well-developed sperm morulae), and may also advance spawning time. Once the population has completed gametogenesis, a drop
in sea temperature is then required to trigger an increase in endocrine titres within the prostomium, without which spawning
cannot be induced by prostomial injection. The population spawns on spring tides; however a lack of clement weather coinciding
with the spring tide will result in population-wide spawning being aborted, as in 1996. Clement weather (high pressure, low
rainfall and wind speed) in conjunction with spring tides permits spawning to proceed to completion.
Received: 21 June 1999 / Accepted: 25 January 2000 相似文献