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1.
Leanne J. Flewelling Douglas H. Adams Jerome P. Naar Karen E. Atwood April A. Granholm Sheila N. O’Dea Jan H. Landsberg 《Marine Biology》2010,157(9):1937-1953
In October 2000, a mass mortality of blacktip sharks (Carcharhinus limbatus) and Atlantic sharpnose sharks (Rhizoprionodon terraenovae) in northwest Florida occurred in conjunction with a Karenia brevis red tide bloom. Before this incident, no information existed on red tide-induced shark mortalities or baseline brevetoxin levels in sharks and rays from red tide-endemic areas. We report here that brevetoxin accumulation in live and red tide-killed elasmobranchs is common during K. brevis blooms and non-bloom periods. Strong relationships were found between the frequency of red tide blooms and the average brevetoxin concentrations in elasmobranch tissues. The presence of brevetoxins in Atlantic coast sharks in the absence of documented K. brevis blooms may suggest that blooms are occurring in areas that are not well monitored. Although red tide-related shark mortalities are rarely observed, the presence of brevetoxins in shark embryos raises questions about the effects these toxins may have on the reproductive success of sharks. 相似文献
2.
Blooms of the brevetoxin-producing Karenia brevis in the Gulf of Mexico cause massive fish kills, food poisoning and adverse respiratory effects in humans. Sedimentation of
toxic cells following inert clay application could reduce toxin incorporation by commercially important suspension-feeding
bivalves and thus prevent direct public health impacts, but could potentially lead to brevetoxin (PbTx) accumulation by benthic
deposit-feeders. The goal of this study was therefore to compare suspension- and deposit-feeding as pathways for brevetoxins.
We investigated: (1) the effect of toxic K. brevis on both feeding modes using a facultative deposit-suspension feeding tellinid bivalve, the clam Macoma balthica, as a model species and (2) the relative effectiveness of brevetoxin transfer via suspension- and deposit-feeding over 24-h
exposure. Sedimentation of K. brevis was achieved by treatment with 0.25 g phosphatic clay l−1 and brevetoxin concentrations were measured by ELISA. Karenia brevis reduced both suspension- and deposit-feeding activity. This study demonstrates that brevetoxins can be rapidly accumulated
by a surface deposit-feeding bivalve from sedimented K. brevis cells and that comparable toxin levels can be attained by both suspension- and deposit-feeding modes [1.2–1.6 μg PbTx (g
tissue wet weight)−1]. Deposit-feeding clams generally do not pose a direct threat to humans but may provide a pathway for brevetoxin food web
transfer. 相似文献
3.
Seasonal aerial surveys were conducted in the waters of the central Spanish Mediterranean from 2001 to 2003 using the line transect sampling methodology to estimate cetacean abundance. The density of the three most abundant species, striped dolphin (Stenella coeruleoalba), bottlenose dolphin (Tursiops truncatus) and Risso’s dolphins (Grampus griseus), was estimated. In the case of the first two species, the density was estimated accounting for the proportion of submerged animals, while for Risso’s dolphin only the surface density could be estimated. The striped dolphin was the most abundant species in the study area with a mean density of 0.489 dolphins km−2 (95% CI = 0.339–0.705) and a mean abundance of 15,778 dolphins (95% CI = 10,940–22,756). This density is comparable to that obtained in the International Ligurian Sea Cetacean Sanctuary. Striped dolphins were observed throughout the whole year and no seasonal changes in the density were detected. The mean density of bottlenose dolphins was an order of magnitude lower than that of striped dolphins (0.041 dolphins km−2; 95% CI = 0.023–0.075) with a mean abundance of 1,333 dolphins (95% CI = 739–2,407). The Risso’s dolphin had a surface estimated density of 0.015 dolphins km−2 (95% CI = 0.005–0.046) and a mean abundance of 493 dolphins (95% CI = 162–1,498). These results provide valuable biological information useful to develop conservation plans and establish a baseline for future population trend studies. 相似文献
4.
A. N. Subramanian R. S. Lal Mohan V. M. Karunagaran R. Babu Rajendran 《Chemistry and Ecology》2013,29(2-3):143-150
Abstract Concentrations of HCH and DDT organochlorine insecticide residues were measured in blubber, muscle and oil samples from three specimens of river dolphins, Platanista gangetica, from the River Ganges, India. Concentrations of HCH and DDT ranged from 94 to 289 ng g?1 and from 1324 to 9388 ng g?1 on wet wt. basis respectively. Comparisons are made with other aquatic mammals and other studies on river dolphins. P. gangetica appears to exhibit similar patterns of accumulation with age and with ß-HCH and p-p′-DDE being accumulated to higher levels than other HCH isomers and parent DDT and its other metabolites, respectively. These organochlorines may pose a health risk to river dolphin populations that are already showing evidence of environmental stress. Further studies are recommended. 相似文献
5.
Globally, many commercial bivalve populations have declined in recent decades. In addition to overharvesting and habitat loss,
the increasing frequency and intensity of harmful algal blooms (HABs) are likely to contribute to bivalve losses, particularly
in cases where blooms negatively impact larval stages. This paper reports on the lethal effects of clonal cultures and blooms
of Cochlodinium polykrikoides from the US Atlantic coast on the larvae of three species of commercially and ecologically valuable bivalves: the Eastern
oyster (Crassostrea virginica), the bay scallop (Argopecten irradians), and the Northern quahog (hard clam; Mercenaria mercenaria). Both cultures and blooms of C. polykrikoides were highly toxic to all three species of bivalve larvae causing 80–100% mortality during 24- to 72-h exposures at concentrations
of 1–2 × 103 cells ml−1. Toxicity was dependent on cell densities, growth stage of C. polykrikoides (i.e. cultures in exponential stage growth were more toxic than later stages), exposure time of larvae to cells (i.e. longer
exposure caused higher mortality), the age of larvae (i.e. younger larvae were more sensitive), and the relative abundance
of C. polykrikoides (i.e. the presence of other microalgae decreased toxicity). Free radical-scavenging enzymes (peroxidase and catalase) and
the removal of C. polykrikoides cells (i.e. culture filtrate) significantly increased larval survival suggesting toxicity is maximized by contact with live
cells and may involve labile toxins bound by these compounds including e.g. reactive oxygen species. The toxicity of C. polykrikoides to bivalve larvae was generally more severe than other HAB species (e.g. Karenia brevis, Karlodinium veneficum, Alexandrium tamarense, Prorocentrum minimum). Since the bivalves in this study spawn in the months when C. polykrikoides blooms on the east coast of North America, these results suggest that these blooms may have detrimental effects on efforts
to restore these already diminished populations. 相似文献
6.
Diane K. Stoecker Jason E. Adolf Allen R. Place Patricia M. Glibert Donald W. Meritt 《Marine Biology》2008,154(1):81-90
The bloom-forming dinoflagellates Prorocentrum minimum and Karlodinium veneficum can have detrimental effects on some marine life, including shellfish, but little is known about their effects on early life
history stages of bivalves. In the Chesapeake Bay region, blooms of these dinoflagellates overlap with the spawning season
of the eastern oyster, Crassostrea virginica. In laboratory experiments, we compared the effects of P. minimum and K. veneficum on the survival and development of embryos and larvae of the eastern oyster. At 104 cells ml−1, P. minimum did not have a negative effect on embryos and larvae in 2-day exposures. The yield of D-hinge larvae was equal to or greater
than in control treatments. At 2 × 104 cells ml−1 (approximately equal biomass to the P. minimum treatment) K. veneficum caused significant mortality to oyster embryos within 1 day and almost no embryos developed into D-hinge larvae. This effect
was not alleviated by the provision of an alternate food source (Isochrysis sp.). Significant mortality was observed when larvae were exposed to K. veneficum at concentrations of 104 cells ml−1 (approximately 5 ng ml−1 of karlotoxin). The K. veneficum cultures used in these experiments were relatively low in toxin content, more toxic strains could be expected to cause mortality
at lower cell concentrations. Survival and maturation of embryos and larvae may be reduced when spawns of the eastern oyster
coincide with high bloom densities of K. veneficum. 相似文献
7.
The aim of our investigations was to determine, via oxygen and carbon-dioxide respirometry, how much energy dolphins (Tursiops truncatus) require when swimming at different speeds. Experiments were conducted on two female bottlenose dolphins (mean mass 162 kg)
in the dolphinarium in Nuremberg Zoo, Germany, between March and August 1997. Animals were stationed in a respiration chamber
for a minimum of 90 s after performing a variety of activities. We measured respiration frequency and oxygen requirements
during (1) resting, (2) swimming at various velocities and (3) leaping to various heights. Resting metabolic rate of our bottlenose
dolphins (2.15 W kg−1) was comparable to previously published data. Metabolic rate in swimming dolphins increased to 2.47 W kg−1 at 2 m s−1, while leaps to 2.2 and 3 m height required a power input of 3.5 and 4 W kg−1, respectively. Transport costs of swimming dolphins were lowest (1.16 J kg−1 m−1, corresponding to 0.12 J N−1 m−1) at a speed of 2.5 m s−1, yielding an optimal range speed of between 1.9 and 3.2 m s−1 (corresponding to minimum cost of transport ±10%). Breathing rates during all experiments correlated very well with oxygen
consumption (r
2 > 0.89) and could be used to derive metabolic rates in unencumbered dolphins at sea.
Received: 18 December 1998 / Accepted: 27 April 1999 相似文献
8.
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. 相似文献
9.
Growth and grazing responses of tintinnid ciliates feeding on the toxic dinoflagellate Heterocapsacircularisquama 总被引:1,自引:0,他引:1
T. Kamiyama 《Marine Biology》1997,128(3):509-515
Growth and feeding rates of two tintinnid species, Favellaazorica and Favellataraikaensis, were determined under various concentrations of the dinoflagellate Heterocapsacircularisquama which has been reported as highly toxic to shellfish. Mean growth rates of F. azorica and F. taraikaensis on a diet of H.circularisquama (ca. 102 cells ml−1) were 2.15 and 1.97 doublings d−1, respectively. These values are similar to those on a diet of Heterocapsatriquetra which is suitable food for various zooplankton. However, growth rates of both tintinnid species decrease with increasing
concentrations of >103 cells ml−1 of H. circularisquama. In particular, H. circularisquama under conditions of >103 cells ml−1 caused mortality in F.taraikaensis, probably due to toxins. Clearance and ingestion rates of F. azorica on H. circularisquama were 4.1 to 27.5 μl ind−1 h−1 and 1.5 to 28.7 cells ind−1 h−1, respectively, at concentrations of <104 cells ml−1 and those of F. taraikaensis were 0.9 to 22.1 μl ind−1 h−1 and 0.1 to 13.0 cells ind−1 h−1, respectively, at concentrations of <103 cells ml−1. Both clearance and ingestion rates on H.circularisquama were higher for replicates fed on H.triquetra. Daily grazing impact of the two species of Favella on the initial stage of a bloom of H.circularisquama were estimated to reach 6 to 50% of H. circularisquama at a concentration of 540 cells ml−1, indicating that grazing by tintinnids such as Favella spp. may significantly regulate the initial stages of blooms of H. circularisquama.
Received: 3 January 1997 / Accepted: 27 January 1997 相似文献
10.
Peter Tyack 《Behavioral ecology and sociobiology》1986,18(4):251-257
Summary The whistle vocalizations of two bottlenosed dolphins, Tursiops truncatus, were recorded at the Sealand Aquarium in Brewster, Massachusetts. The identification of which dolphin within the group produced a vocalization was made possible by a telemetry device attached to the dolphin's head with a suction cup. 77% of the identified whistles (219 our of 284) fell into two primary categories, type 1 and type 2 (Table 1). The remaining 23% of whistles fell into five secondary categories. Of the primary whistles produced by one dolphin, 78% were of type 1 (22% type 2), while 69% of primary whistles from the other dolphin were of type 2 (31% type 1). The result that each of the dolphins favored a different primary whistle supports the findings of Caldwell and Caldwell (1965), that each dolphin produces an individually distinctive whistle. But in the present study, both dolphins produced both primary whistle types. This may represent mimicry of signature whistles. 相似文献
11.
Spatial and temporal pattern in seagrass community composition and productivity in south Florida 总被引:4,自引:1,他引:3
We document the distribution and abundance of seagrasses, as well as the intra-annual temporal patterns in the abundance
of seagrasses and the productivity of the nearshore dominant seagrass (Thalassia testudinum) in the south Florida region. At least one species of seagrass was present at 80.8% of 874 randomly chosen mapping sites,
delimiting 12,800 km2 of seagrass beds in the 17,000-km2 survey area. Halophila decipiens had the greatest range in the study area; it was found to occur over 7,500 km2. The range of T. testudinum was almost as extensive (6,400 km2), followed by Syringodium filiforme (4,400 km2), Halodule wrightii (3,000 km2) and Halophila engelmanni (50 km2 ). The seasonal maxima of standing crop was about 32% higher than the yearly mean. The productivity of T. testudinum was both temporally and spatially variable. Yearly mean areal productivity averaged 0.70 g m−2day−1, with a range of 0.05–3.29 g m−2 day−1. Specific productivity ranged between 3.2 and 34.2 mg g−1 day−1, with a mean of 18.3 mg g−1 day−1. Annual peaks in specific productivity occurred in August, and minima in February. Integrating the standing crop for the
study area gives an estimate of 1.4 × 1011 g T. testudinum and 3.6 × 1010 g S. filiforme, which translate to a yearly production of 9.4 × 1011 g T. testudinum leaves and 2.4 × 1011 g S. filiforme leaves. We assessed the efficacy of rapid visual surveys for estimating abundance of seagrasses in south Florida by comparing
these results to measures of leaf biomass for T. testudinum and S. filiforme. Our rapid visual surveys proved useful for quantifying seagrass abundance, and the data presented in this paper serve as
a benchmark against which future change in the system can be quantified.
Received: 30 January 2000 / Accepted: 24 July 2000 相似文献
12.
As part of an ongoing study of changes in the trophic pathways of Florida Bay's pelagic ecosystem, the nutritional environment
(seston protein, lipid and carbohydrate levels), diet (taxon-specific microplankton ingestion rates) and egg production rate
of the important planktonic copepod Acartia tonsa were measured off Rankin and Duck Keys in July and September 1997 and in January, March and May 1998. Rankin Key has been
the site of extensive sea grass mortality and persistent ultraplankton blooms since 1987. Duck Key has experienced neither
of these perturbations. Protist (auto-plus heterotroph) biomass was approximately twice as high off Rankin as off Duck Key.
Diatoms, dinoflagellates and heterotrophic protists dominated the food environment off Rankin Key, while cells <5 μm diam
often predominated off Duck Key. Protein and carbohydrate concentrations were higher off Rankin Key than Duck Key, while average
lipid levels were usually low at both stations. Ingestion rates at both stations frequently approached temperature- and food-dependent
maxima for the species, exceeding 100% of estimated body C d−1 on 3 of 5 occasions off Rankin Key. Egg production rates, however, were consistently low (Rankin: 3 to 16 eggs copepod−1 d−1; Duck: 1 to 12 eggs copepod−1 d−1), and gross egg production efficiencies (100% × egg production C/ingested C) averaged <10%. At Duck Key, egg production rate
varied with temperature and food concentration, while off Rankin Key, egg production was strongly correlated with seston protein
content. The efficiency with which lipids (which were scarce in the seston) were transferred from the diet to the eggs increased
exponentially with decreasing seston lipid content. Egg production efficiencies based on protein, however, were independent
of seston protein content and never exceeded 10%.
Received: 23 December 1998 / Accepted: 23 March 2000 相似文献
13.
Elizabeth J. Berens McCabe Damon P. Gannon Nélio B. Barros Randall S. Wells 《Marine Biology》2010,157(5):943-942
Prey selection was investigated in wild, resident common bottlenose dolphins, Tursiops truncatus, during the summer months in Sarasota Bay, Florida, USA. Stomach content analyses of 15 dolphins with extensive sighting
histories and well-documented distributions were used to determine prey use. Prey availability was assessed by purse seine
surveys. We compared the relative abundances of prey available to estimates of prey use at closely matching spatial and temporal
scales. G-tests determined that dolphins in this study significantly selected for prey at the species, family, and soniferous/non-soniferous
prey levels (G
adj
= 753.98–1,775.93, df = 1–21, p ≤ 0.01). While comprising only 6.3% of the total available prey, soniferous fishes accounted for 51.9% of the total prey
consumed. Manly’s standardized forage ratios and 95% Bonferroni confidence intervals determined significant positive selection
for soniferous prey and against non-soniferous prey (βS = 0.9461 vs. βNS = 0.0539). Dolphins selected against Gerridae, Clupeidae, and Sparidae (β ≤ 0.0014), as well as against all the species within those families (β ≤ 0.0190). It is likely that passive listening for soniferous prey provides an ecological or energetic advantage to cetaceans
utilizing this specific foraging technique. 相似文献
14.
Miina Karjalainen Betina Kozlowsky-Suzuki Maiju Lehtiniemi Jonna Engström-Öst Harri Kankaanpää Markku Viitasalo 《Marine Biology》2006,148(4):683-691
Cyanobacterial blooms are a common phenomenon in the Baltic Sea, and the hepatotoxin nodularin has been frequently detected
in certain Baltic Sea fishes and mussels. However, there is no knowledge about the naturally occurring concentrations of nodularin
in Baltic Sea zooplankton. The aim of this study was to survey the concentrations of nodularin in natural zooplankton assemblages,
and to study the depuration of nodularin in one common copepod species, Eurytemora affinis, experimentally. The nodularin concentrations in common zooplankton species were determined from field-collected samples
from the northern Baltic Proper in 2001 and 2002, during cyanobacterial blooms, and the samples were analysed by ELISA immunoassay.
Nodularin could be detected from the field-collected zooplankton, suggesting that during a natural bloom event toxins accumulate
in their tissues. The concentrations were relatively low (0.07±0.01 μg g−1 ww), ranging from below detection limit to 0.62 μg g−1 ww. Some variation occurred in the concentrations between species and years; generally concentrations were higher in 2001
than in 2002. In the depuration experiment E. affinis copepods were fed with toxic Nodularia spumigena for 24 h, and their toxin contents were monitored for 24 h after transferring them to filtered seawater. A rapid decrease
in nodularin concentrations occurred during the first 0.5–3 h after the exposure. However, after a 24-h depuration period
in filtered seawater, nodularin could be still detected in E. affinis tissues, indicating that part of the accumulated nodularin, or its derivatives, could be transferred to planktivores. 相似文献
15.
The diet of juvenile pink shrimp (Farfantepenaeus duorarum Burkenroad, previously Penaeus duorarum) from Long Key Bight, Florida Keys, was studied using stomach content examination, pigment measurements, and stable isotope
(δ13C and δ15N) analysis. Samples were taken over approximately 24 h on four occasions from December 1997 to June 1998. Juvenile F. duorarum fed nocturnally, the main prey being the seagrass shrimp Thor floridanus (Decapoda: Caridea: Hippolytidae), which accounted for 34% of the stomach content volume. Other common components of the
diet were bivalves (mainly Tellina sp.) with 15% volume, calcareous algae (8%), plant detritus (5%), copepods (3%), and seagrass fragments (2%). Pigment concentrations
(chlorophyll a plus phaeopigments) in F. duorarum stomachs ranged from 7 to 73 mg l−1 or 40 to 310 ng stomach−1. The exponential gastric evacuation rate was determined experimentally at 1.3 ± 0.5 h−1. Daily rations (in percent body weight) calculated from time series of stomach fullness ranged between 11 and 16% d−1. Total consumption by the population (in wet weight) ranged between 0.05 and 0.3 g m−2 d−1. Stable isotope measurements confirmed that T. floridanus was the main food source for F. duorarum. δ13C-values of whole animals of both species were identical at −10.0 ± 1.6‰ PDB. δ15N-values of both species were also not significantly different (pooled mean: 5.9 ± 1.7‰). Stomach contents of wild-caught
F. duorarum and stomach contents of F. duorarum fed T. floridanus also showed similar stable isotope values.
Received: 12 August 1999 / Accepted: 21 March 2000 相似文献
16.
Phytoplankton blooms are strongly impacted by microzooplankton grazing in coastal North Pacific waters 总被引:1,自引:0,他引:1
Phytoplankton growth and microzooplankton grazing were measured in two productive coastal regions of the North Pacific: northern
Puget Sound and the coastal Gulf of Alaska. Rates of phytoplankton growth (range: 0.09–2.69 day−1) and microzooplankton grazing (range: 0.00–2.10 day−1) varied seasonally, with lowest values in late fall and winter, and highest values in spring and summer. Chlorophyll concentrations
also varied widely (0.19–13.65 μg l−1). Large (>8 μm) phytoplankton cells consistently dominated phytoplankton communities under bloom conditions, contributing
on average 65% of total chlorophyll biomass when chlorophyll exceeded 2 μg l−1. Microzooplankton grazing was an important loss process affecting phytoplankton, with grazing rates equivalent to nearly
two-thirds (64%) of growth rates on average. Both small and large phytoplankton cells were consumed, with the ratio of grazing
to growth (g:μ) for the two size classes averaging 0.80 and 0.42, respectively. Perhaps surprisingly, the coupling between microzooplankton
grazing and phytoplankton growth was tighter during phytoplankton blooms than during low biomass periods, with g:μ averaging 0.78 during blooms and 0.49 at other times. This tight coupling may be a result of the high potential growth
and ingestion rates of protist grazers, some of which feed on bloom-forming diatoms and other large phytoplankton. Large ciliates
and Gyrodinium-like dinoflagellates contributed substantially to microzooplankton biomass at diatom bloom stations in the Gulf of Alaska,
and microzooplankton biomass overall was strongly correlated with >8 μm chlorophyll concentrations. Because grazing tended
to be proportionally greater when phytoplankton biomass was high, the absolute amount of chlorophyll consumed by microzooplankton
was often substantial. In nearly two-thirds of the experiments (14/23), more chlorophyll was ingested by microzooplankton
than was available for all other biological and physical loss processes combined. Microzooplankton were important intermediaries
in the transfer of primary production to higher trophic levels in these coastal marine food webs.
Received: 12 November 1999 / Accepted: 4 October 2000 相似文献
17.
Ruth Fernández Susana García-Tiscar M. Begoña Santos Alfredo López Jose A. Martínez-Cedeira Jason Newton Graham J. Pierce 《Marine Biology》2011,158(5):1043-1055
Skin and muscle from 43 bottlenose dolphins (38 juveniles/adults, 5 calves) stranded in NW Spain were analysed to determine
whether stable isotope ratios (δ13C and δ15N) could be used to assess dietary variation, habitat segregation and population substructure. Results were compared with
published stomach contents data. Stable isotope ratios from 17 known prey species were also determined. Isotope ratios of
the main prey (blue whiting, hake) varied significantly in relation to fish body size. Dolphin calves showed significant heavy
isotope enrichments compared to adult females. Excluding calves, δ15N decreased with increasing dolphin body size, probably related to an ontogenetic shift in diet towards species at lower trophic
levels, e.g. on blue whiting as suggested by stomach content results. Bottlenose dolphins were divided into two putative populations
(North, South) based on previous genetic studies, and values of δ13C and δ15N differed significantly between these two groups, confirming the existence of population structuring. 相似文献
18.
A single population of short-beaked common dolphins (Delphinus delphis Linnaeus) occurs in the western North Atlantic from Florida to Newfoundland. Dolphins killed in a swordfish driftnet fishery
between 1989 and 1998 provided samples for the present study. These were combined with additional observations from carcasses
collected from stranding programs. Samples were examined from 74 female and 161 male short-beaked common dolphins. A highly
significant male bias in the sex ratio of both the bycatch and stranding samples suggests that sex-based habitat partitioning
or school segregation occurs in this population. Age was estimated from decalcified thin sections of teeth and testis and
ovarian samples were examined both macro- and microscopically. Analyses showed that reproduction was both seasonal and synchronized.
Females reached sexual maturation at approximately age eight; males matured at 9.5 years. Conception occurred during July
and August (mean day 24 July). Gestation was estimated to last just under a year, so most females gave birth during July and
August (mean day 15 July). Annual pregnancy rate was estimated to be between 25 and 33%. Males undergo a fivefold seasonal
increase in testes mass and a twofold increase in seminiferous tubule diameter. Peak sperm production potential was observed
in July. At the end of the breeding season testis size and activity decreased after August. Male dolphins in this population
are hypothesized to engage in some form of sperm competition. 相似文献
19.
This paper reports on the feeding biology of a predatory and of a facultatively predatory nematode, Enoploides longispiculosus and Adoncholaimus fuscus, respectively. Both species represent genera which are common and abundant in the littoral of the North Sea and in adjacent
estuaries. Observations on the foraging behaviour of both species are given, and for the former species, a range of prey from
its natural habitat is identified. Respiration was determined using a polarographic oxygen electrode technique and compared
to consumption determined as predation rates on the monhysterid nematode Diplolaimelloides meyli. The daily C-loss due to respiration accounted for 15% of the measured C-consumption in E. longispiculosus and for 111% in A. fuscus, proving the observed feeding rates in the latter species to have been inadequate for the maintenance of its aerobic metabolism.
Daily respiration rates at an average environmental temperature were 219 ng C ind−1 d−1 for adults of A. fuscus and 21.9 ng C ind−1 d−1 for adults of E. longispiculosus. Using radiotracer techniques, no uptake of bacterial cells or of organic matter in the dissolved phase was demonstrated
for E. longispiculosus. In A. fuscus, however, a significant drinking of label in the dissolved or volatile fraction occurred; bacterial cells were taken up at
a level insignificant to the nematode's daily C-ration. It is concluded that E. longispiculosus has a fairly strict predatory feeding strategy, while A. fuscus gains a majority of C from additional foraging strategies, among which the uptake of dissolved material and scavenging on
macrofauna carcasses (as reported in the literature) may be of particular importance.
Received: 28 August 1998 / Accepted: 8 March 1999 相似文献
20.
Faced with an intermittent but potent threat, animals exhibit behavior that allows them to balance foraging needs and avoid predators and over time, these behaviors can become hard-wired adaptations with both species trying to maximize their own fitness. In systems where both predator and prey share similar sensory modalities and cognitive abilities, such as with marine mammals, the dynamic nature of predator-prey interactions is poorly understood. The costs and benefits of these anti-predator adaptations need to be evaluated and quantified based on the dynamic engagement of predator and prey. Many theoretic models have addressed the complexity of predator-prey relationships, but few have translated into testable mechanistic models. In this study, we developed a spatially-explicit, geo-referenced, individual-based model of a prototypical adult dusky dolphin off Kaikoura, New Zealand facing a more powerful, yet infrequent predator, the killer whale. We were interested in two primary objectives, (1) to capture the varying behavioral game between a clever prey and clever predator based on our current understanding of the Kaikoura system, (2) to compare evolutionary costs vs. benefits (foraging time and number of predator encounters) for an adult non-maternal dusky dolphin at various levels of killer whale-avoidance behaviors and no avoidance rules. We conducted Monte Carlo simulations to address model performance and parametric uncertainty. Mantel tests revealed an 88% correlation (426 × 426 distance matrix, km2) between observed field sightings of dusky dolphins with model generated sightings for non-maternal adult dusky dolphin groups. Simulation results indicated that dusky dolphins incur a 2.7% loss in feeding time by evolving the anti-predator behavior of moving to and from the feeding grounds. Further, each evolutionary strategy we explored resulted in dolphins incurring an additional loss of foraging time. At low killer whale densities (appearing less than once every 3 days), each evolutionary strategy simulated converged towards the evolutionary cost of foraging, that is, the loss in foraging time approached the 2.7% loss experienced by evolving near shore-offshore movement behavior. However, the highest level of killer whale presence resulted in 38% decreases in foraging time. The biological significance of these losses potentially incurred by a dusky dolphin is dependent on various factors from dolphin group foraging behavior and individual energy needs to dolphin prey availability and behavior. 相似文献