We examined the feeding ecology of whale sharks by analyzing the signature fatty acids of their sub-dermal tissue and those of an extensive set of potential prey collected at Ningaloo Reef, Western ...Australia, in 2013, 2014 and 2015. Sub-dermal tissue of whale sharks was low in lipid content (4.0 mg g−1 dry mass) and dominated by phospholipids (72% of total lipids), with a calculated energy density of 18.7 kJ g−1 dry mass. There was significant intraspecific variability in fatty acid profiles of whale sharks, with cluster analysis identifying 4 distinct groups in 2013 and 5 groups in 2014. As this variability was not related to sex or size-class, we suggest that it may be attributed to differences in the feeding habitats used by these groups of whale sharks. Variation in dietary patterns was also observed between years, likely due to changes in the primary and secondary producers. Examination of food web interactions showed that fatty acid profiles of whale sharks and their presumed prey were significantly different, suggesting that sharks fed over a wide range of habitats, including deep waters. Our findings show that signature fatty acids of sub-dermal tissue can be used to examine broad trophic pathways and to identify spatial and temporal changes in the diet of these large and wide-ranging animals.
Glimpse into guts Sampey, A.; McKinnon, A. D.; Meekan, M. G. ...
Marine ecology. Progress series (Halstenbek),
06/2007, Letnik:
339
Journal Article
Recenzirano
Odprti dostop
Knowledge of the diets of tropical fish larvae is limited to only a few taxa. Here, we describe the diets of 591 individuals from 50 families of tropical larval shorefishes collected off the ...Northwest Shelf of Australia (21° 49′ S, 114° 14′ E), effectively doubling the number of families for which there is dietary data available. The diversity of prey items eaten differed significantly among families. The majority of fish larvae ate copepods but there were some interesting exceptions. Chaetodontids ate only chaetognaths, acanthurids and nemipterids ate appendicularians, and tetraodontids ate predominately non-copepod prey (44% decapod larvae, 20% bivalves and 15% protists). Within the fish families that specialised on copepod prey there were marked differences in the types of copepod prey, with a clear preference shown for calanoid copepods, particularly small calanoids such asBestiolina similisandTemoraspp. Copepod communities in the area are food-limited and we suggest that the ability of some larval fishes to feed on components of the microbial food web may be an important determinant of their success.
The world's largest omnivore is a fish Meekan, M. G.; Virtue, P.; Marcus, L. ...
Ecology (Durham),
December 2022, 2022-12-00, 20221201, Letnik:
103, Številka:
12
Journal Article
Recenzirano
Odprti dostop
The evolution of very large body size requires a ubiquitous and abundant source of food. In marine environments, the largest animals such as whale sharks are secondary consumers that filter feed on ...nekton, which is plentiful, although patchy. Consequently, feeding in coastal environments requires cost‐efficient foraging that focuses on oceanographic features that aggregate both nektonic prey and marine debris such as floating macroalgae. Consumption of this algae could present an energetic challenge for these animals, unless some component can be digested. Here, we use a multi‐technique approach involving amino acid compound‐specific stable isotope analysis (CSIA) and fatty acid analysis to determine the trophic level of whale sharks and to identify likely items in the diet. CSIA analyses showed that the species has a trophic level consistent with omnivory. Fatty acid profiles of whale shark tissues, feces and potential prey items suggest that the floating macroalgae, Sargassum, and its associated epibionts is a significant source of food. Although this overcomes the energetic challenge of consumption of floating algae, this mode of feeding and the need to focus on oceanographic features that aggregate prey also increases the threat to the species posed by pollutants such as plastic.
Dietary characteristics and the degree of dietary partitioning by five species of sympatric stingray were assessed using stomach content and sediment analyses within a coral reef lagoon at Ningaloo ...Reef, Western Australia (the cowtail Pastinachus atrus, blue‐spotted fantail Taeniura lymma, blue‐spotted mask Neotrygon kuhlii, porcupine Urogymnus asperrimus rays and the reticulate whipray Himantura uarnak). A total of 2804 items were recovered from the stomachs of 170 rays and 3215 individual taxa from the environment, which were used in selectivity analyses. Twenty‐four prey taxa were identified from stomach contents and pooled into 10 taxonomic categories for analysis, of which annelids, prawns, brachyurans and bivalves were the most abundant, together accounting for 96% of the diet. Himantura uarnak had the greatest interspecific dissimilarity in diet, consuming a larger proportion of crustaceans, notably penaeids (41% of total diet) than the other four species of rays, all of which had diets dominated by annelids (71–82% of total diet). Crustacean specialization by H. uarnak may exist to maximize resources and reduce competition among sympatric species. The remaining species may partition resources on the basis of space, rather than diet.
Ten years have passed since the last synopsis of whale shark Rhincodon typus biogeography. While a recent review of the species' biology and ecology summarized the vast data collected since then, it ...is clear that information on population geographic connectivity, migration and demography of R. typus is still limited and scattered. Understanding R. typus migratory behaviour is central to its conservation management considering the genetic evidence suggesting local aggregations are connected at the generational scale over entire ocean basins. By collating available data on sightings, tracked movements and distribution information, this review provides evidence for the hypothesis of broad‐scale connectivity among populations, and generates a model describing how the world's R. typus are part of a single, global meta‐population. Rhincodon typus occurrence timings and distribution patterns make possible a connection between several aggregation sites in the Indian Ocean. The present conceptual model and validating data lend support to the hypothesis that R. typus are able to move among the three largest ocean basins with a minimum total travelling time of around 2–4 years. The model provides a worldwide perspective of possible R. typus migration routes, and suggests a modified focus for additional research to test its predictions. The framework can be used to trim the hypotheses for R. typus movements and aggregation timings, thereby isolating possible mating and breeding areas that are currently unknown. This will assist endeavours to predict the longer‐term response of the species to ocean warming and changing patterns of human‐induced mortality.
Documentation of scarring patterns on marine megafauna provides a means of quantifying the risk of anthropogenic threats that occur in the open ocean, such as ship strike. This study investigated the ...rates and putative sources of scarring of whale sharks Rhincodon typus aggregating at Ningaloo, Western Australia. Identification photos of whale sharks were contributed by tourism operators and research groups over a 6 yr period. Analysis of this database found that 355 (38.8%) of 913 whale sharks individually identified between 2008 and 2013 exhibited some form of scarring. This decreased to 15.9% after the omission of categories of minor scarring (nicks and abrasions). An increase in the number of sharks with lacerations between 2008 and 2013 provides some evidence of increasing boat strikes over this time. However, capture-mark-recapture modelling using the multi-state open robust design found no evidence that major scarring influenced the apparent survival or residency time of whale sharks aggregating at Ningaloo. Although lacerations are a useful indication of the level of threat to whale sharks from boat strike, it cannot necessarily be attributed to boat activity in Ningaloo due to the migratory nature of whale sharks in this aggregation, which commonly venture beyond Australian waters. Close collaboration with whale shark tourism operators proved a vital tool to generate the volume of data required for this assessment, and provides a model for similar studies of other megafauna with an associated tourism industry.
The capacity of species to respond adaptively to warming temperatures will be key to their survival in the Anthropocene. The embryos of egg-laying species such as sea turtles have limited behavioural ...means for avoiding high nest temperatures, and responses at the physiological level may be critical to coping with predicted global temperature increases. Using the loggerhead sea turtle (Caretta caretta) as a model, we used quantitative PCR to characterise variation in the expression response of heat-shock genes (hsp60, hsp70 and hsp90; molecular chaperones involved in cellular stress response) to an acute non-lethal heat shock. We show significant variation in gene expression at the clutch and population levels for some, but not all hsp genes. Using pedigree information, we estimated heritabilities of the expression response of hsp genes to heat shock and demonstrated both maternal and additive genetic effects. This is the first evidence that the heat-shock response is heritable in sea turtles and operates at the embryonic stage in any reptile. The presence of heritable variation in the expression of key thermotolerance genes is necessary for sea turtles to adapt at a molecular level to warming incubation environments.
Increments in the hard parts of marine organisms (otoliths, skeletons, shells) can provide long-term chronologies of growth analogous to tree rings. For the first time in the Southern Hemisphere, we ...use a dendrochronological (tree-ring analysis) approach to develop a multidecadal chronology of growth for a temperate reef fish,
Girella tricuspidata,
from the coast of northern New Zealand. Growth patterns in the otoliths of this species were strongly synchronous among individual fish over a period spanning 27 years (1980–2006). We then compared our otolith chronology to climatic records and found strong positive correlations of growth with sea surface temperature, and weak negative correlations with the multivariate El Nino Southern Oscillation (ENSO) index. Strongest correlations were found between summer sea surface temperature and otolith growth. This relationship was consistent across all years and explained 44 % of the variation (
y
= −2.0 + 0.1785 × temperature,
r
2
= 0.4367,
P
= 0.0002) in the
G.
tricuspidata
growth chronology. Our study illustrates how otolith chronologies provide remarkable records of annual growth patterns over decadal time scales that will be useful for forecasting the likely effects of climate change on marine ecosystems.
Global declines of shark populations are of concern because of their largely assumed role as moderators of ecosystem function. Without long-term data on movement patterns for many species, it is ...impossible to infer relative extinction risk, which varies as a function of range, dispersal and habitat specificity and use. The past 50 yr of research on coastal sharks has revealed common movement patterns among species. In the horizontal plane, measured home range size generally increases with body size. We demonstrate meta-analytically the effects of increasing body size and monitoring time on home range size. Changes in the extent of horizontal movement might arise from ontogeny, predator avoidance or environmental tolerances. In the vertical plane, movement patterns include oscillatory vertical displacement, surface swimming, diel vertical migration and swimming at depth. These vertical movements are often attributed to foraging or navigation, but have been quantified less than horizontal patterns. Habitat specificity is often correlated with environmental conditions such as depth, salinity, substratum, and in some cases, prey availability. Site fidelity is common in species that use nursery areas. However, fidelity to mating, pupping, feeding and natal sites has only been observed in a few species. To date, few studies have examined habitat partitioning, although some general patterns have emerged: habitats appear to be subdivided by benthos type, prey availability and depth. The conservation of coastal sharks can be facilitated in some cases by the use of marine protected areas, especially for coastal resident species using specific nursery, reproduction or feeding areas. Partial protected-area closures might be effective during aggregation or migration periods to protect older size classes, but these must be applied with other management strategies such as reduced fishing and size or bag limits to protect individuals throughout different life history phases. More long-term research on habitat use, migration patterns and habitat partitioning is essential for developing successful management initiatives for coastal shark populations.
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