Evidence for benthic primary production support of an apex predator–dominated coral reef food web

Five hundred and ninety-nine primary producers and consumers in the Papahānaumokuākea Marine National Monument (PMNM) (22°N–30°N, 160°W–180°W) were sampled for carbon and nitrogen stable isotope composition to elucidate trophic relationships in a relatively unimpacted, apex predator–dominated coral reef ecosystem. A one-isotope (δ¹³C), two-source (phytoplankton and benthic primary production) mixing model provided evidence for an average minimum benthic primary production contribution of 65 % to consumer production. Primary producer δ¹⁵N values ranged from ?1.6 to 8.0 ‰ with an average (2.1 ‰) consistent with a prevalence of N₂ fixation. Consumer group δ¹⁵N means ranged from 6.6 ‰ (herbivore) to 12.1 ‰ (Galeocerdo cuvier), and differences between consumer group δ¹⁵N values suggest an average trophic enrichment factor of 1.8 ‰ Δ¹⁵N. Based on relative δ¹⁵N values, the larger G. cuvier may feed at a trophic position above other apex predators. The results provide baseline data for investigating the trophic ecology of healthy coral reef ecosystems.     

The foraging ecology of coastal bottlenose dolphins based on stable isotope mixing models and behavioural sampling

Understanding trophic interactions is critical for elucidating ecological roles of marine predators. We used behavioural observations and stable isotope mixing models to investigate the feeding ecology of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in the lagoon of Mayotte (East Africa). We identified prey during 77 % of 54 observed feeding events, observed in both rainy (61 % of events) and dry (39 %) seasons. Caranx melampygus and Gnathanodon speciosus were involved in 67 % of these events, with Tylosurus crocodilus (20 %) and Mugil cephalus (13 %) also consumed. Mixing models, based on δ¹³C and δ¹⁵N values of skin and blubber (n = 30 samples for both tissues), suggest that behavioural observations are representative of general feeding patterns. Indeed, C. melampygus and T. crocodilus (G. speciosus could not be included in models) were estimated to contribute most to dolphin diets, with mean estimated contributions of 44.6 % (±18.9) and 48.1 % (±19.1) for skin and 73.7 % (±14.9) and 16.9 % (±12.4) for blubber, respectively. Our results highlight the value of two independent methods (stable isotopes and behavioural observations) to assess prey preferences of free-ranging dolphins.     

13C isotope evidence for photochemical production of atmospheric formaldehyde, acetaldehyde, and acetone pollutants in Guangzhou

Ambient formaldehyde, acetaldehyde, and acetone are harmful air pollutants with potential carcinogenic effects on human health. They are considered as important photochemical products from photo-oxidation of atmospheric hydrocarbons. However, little is known on the effet of photodegradation of air pollutants on δ¹³C values. Here, we report the first ¹³C isotope evidence for the photochemical production of ambient formaldehyde, acetaldehyde, and acetone. Air samples were collected each day during early morning, noon, early afternoon, and late afternoon on 17–19 September 2008 in Guangzhou by drawing air through 2,4-dinitrophenylhydrazine-coated cartridges. The samples were analyzed using high-performance liquid chromatography for concentration analysis and then using gas chromatography-combustion-isotope ratio mass spectrometry for δ¹³C analysis. Our results show that ambient formaldehyde, acetaldehyde, and acetone were enriched by 1–5 ‰ in ¹³C in the early afternoon relative to other sampling durations, and they also exhibited the highest concentrations in the early afternoon. Measured δ¹³C values of formaldehyde, acetaldehyde, and acetone were in the range from ?37.15 to ?29.01 ‰. The observed enrichment in ¹³C implied important photochemical production together with the highest concentrations in the early afternoon. Especially, measured δ¹³C range from ?37.15 to ?29.01 ‰ was in accordance with forecasted δ¹³C range from ?43 to ?28 ‰ based on the mass balance in ¹³C between the carbonyls and its major hydrocarbon precursors, providing important ¹³C isotope evidence for the photochemical production of ambient formaldehyde, acetaldehyde, and acetone.     

Differences in δ13C and δ15N values between feathers and blood of seabird chicks: implications for non-invasive isotopic investigations

Blood and feathers are the most targeted tissues for isotopic investigations in avian ecology, primarily because they can be easily and non-destructively sampled on live individuals. Comparing blood and feather isotopic ratios can provide valuable information on dietary shifts, trophic specialization and migration patterns, but it requires a good knowledge of the isotopic differences between the two tissues. Here, δ¹³C and δ¹⁵N values of whole blood (in blood cells of a few species) and simultaneously grown body feathers were measured in seabird chicks to quantify the tissue-related isotopic differences. Seabirds include 27 populations of 22 wild species that were sampled in 2000–2008, and a review of the literature added 8 groups (including adult birds) to the analysis. The use of a large data set that overall encompasses wide δ¹³C and δ¹⁵N ranges allowed us to depict for the first time accurate relationships between blood and feather isotopic ratios across avian taxa. Blood was impoverished in ¹³C and generally in ¹⁵N compared with feathers. Both mean δ¹³C and δ¹⁵N values of feathers and blood were highly positively and linearly related [feather δ¹³C = 0.972 (±0.020) blood δ¹³C + 0.962 (±0.414), and feather δ¹⁵N = 1.014 (±0.056) blood + 0.447 (±0.665), respectively; both P < 0.0001]. The regressions should be applied to mathematically correct feather or whole blood δ¹³C and δ¹⁵N values when comparing isotopic ratios within and between ecological studies on birds.     

Winter diet shift of long-beaked common dolphins (Delphinus capensis) feeding in the sardine run off KwaZulu-Natal, South Africa

Unpredictable inter-annual variations in the timing, spatial extent and intensity of the sardine run (Sardinops sagax) have been documented in recent years along the coastline of KwaZulu-Natal, South Africa. This study aimed to determine whether variations in the availability of sardine were reflected in the diet and condition of common dolphins (Delphinus capensis) over the past three decades. Stomach contents from 95 common dolphins incidentally caught between 2000 and 2009 were analysed and compared to historical data collected between 1972 and 1992. A shift in the principal prey species consumed by the dolphins was observed over the past 30 years. Prior to 1992, sardine comprised up to 49 % of the total stomach contents by mass, whilst chub mackerel (Scomber japonicus) was the dominant prey recorded in the stomach contents between 2000 and 2009 (66 %). As common dolphins prey on locally abundant fish species, this dietary shift may indicate changes in the availability of the most abundant fish prey. Stable isotope analyses of tooth tissue revealed no significant changes in the δ¹⁵N and δ¹³C isotopic ratios over the past three decades (P = 0.283 for N and P = 0.922 for C). Blubber thickness as a percentage of body length and blubber weight as a percentage of total body weight were assessed as indicators of animal condition. No significant changes in proportional blubber weight or blubber thickness were seen over the last 40 years (1970–2009) for all age cohorts. This species appears to be well adapted to cope with changes in prey species availability, without impacting on body condition.     

Species-specific variation in cuttlebone δ13C and δ18O for three species of Mediterranean cuttlefish

Stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotopes in cuttlebones of three species of Mediterranean cuttlefish (Sepia elegans, S. officinalis, and S. orbignyana) with different life histories were contrasted. Cuttlebone δ¹³C and δ¹⁸O were quantified at both the core and edge (representing early life and recent deposition, respectively) for all three species sampled from the southern Adriatic Sea in 2010 (n = 28). For S. officinalis, cuttlebone δ¹³C and δ¹⁸O values were both lower relative to S. elegans and S. orbignyana at the core by approximately 1.0–2.0 and 3.0 ‰, respectively. Differences between core and edge in cuttlebone δ¹³C and δ¹⁸O were also observed for S. officinalis with observed values at the cuttlebone edge (recent) exceeding core (early life) values by 2.5 ‰ for δ¹³C and 1.4 ‰ for δ¹⁸O. Differences in isotopic composition across S. officinalis cuttlebones are possibly reflective of ontogenetic migrations from nearshore nurseries (lower seawater δ¹³C and δ¹⁸O values) to offshore overwintering habitats (higher seawater δ¹³C and δ¹⁸O values). Overall, results from this study suggest that cuttlebone δ¹³C and δ¹⁸O hold promise as natural tags for determining the degree of spatial connectivity between nearshore and offshore environments used by cuttlefish.     

Identifikation der kfz-bürtigen Schadstoffbelastung mit Hilfe der Verhältnisse der stabilen Isotope von Kohlenstoff und Schwefel

Different sources of traffic immissions (tyres, soot, oil, asphalt, plastic, paint) were analysed for stable carbon and sulphur isotope ratios. The aim of this study is to investigate whether these isotope ratios can be used to evaluate the environmental impact of traffic immitted harmful substances in roadside soils. The δ¹³C values of technical materials are between -30‰ and -18‰ (PDB). They can be distinguished by their δ¹³C value because of specific production methods. The δ¹³C value of asphalt is between -23 and -18‰, soot shows values from -27 to-22‰ Moreover, soot of different fuel have different carbon isotope ratios. Plastic, paint and oil have similar δ¹³C from -30 to -27‰ Carbon isotope ratios of automobile tyres are around -26‰ Traffic impact on the carbon isotope composition is reflected in δ¹³C values of various carbon spezies found in street sediments and road side soils. These δ¹³C values correlate to concentrations of lead and platinum. Although δ³⁴S values of technical materials are between -6 and +8‰ it was not possible to characterise samples according to their Sulphur isotopic compostion.     

Spatial and seasonal variation in δ15N and δ13C values in a mesopredator shark, Squalus suckleyi, revealed through multitissue analyses

We used variance decomposition to explore the importance of body size, sex, location, and sampling period as predictors of intrapopulation variation in δ¹⁵N and δ¹³C values in spiny dogfish Squalus suckleyi from the Puget Sound–Strait of Georgia basin. Isotopes in two tissues with long (dorsal white muscle) and short (liver) isotopic turnover rates (~1 year and ~3–4 months, respectively) were sampled to evaluate whether the relative importance of each variable differed depending on the time span over which diet information was integrated. Significant spatial variation was observed in both muscle and liver isotopic composition, whereby location uniquely explained 25 and 17 % of the total variance, respectively. The remaining variables explained considerably less variation in both tissue types. Furthermore, evidence of seasonal isotopic shifts in δ¹⁵N and δ¹³C values was apparent, but differed widely in direction and magnitude among groups. These findings suggest that members of spiny dogfish schools may share a common feeding history, possibly by spending extended time periods (weeks to months) foraging in a spatially fixed region. Another explanation is that individuals may move and feed in aggregations that exist for extended periods. These complex group-level patterns suggest that even for large-bodied, motile predators such as sharks, population-level diet estimates derived from averaging isotope ratios of individuals collected from only a few locations may poorly reflect the true population mean.     

Matching and mismatching stable isotope (δ13C and δ15N) ratios in fin and muscle tissue among fish species: a critical review

Using non-lethal tissue sampling for stable isotope analysis has become standard in many fields, but not for fishes, despite being desirable when species are rare or protected, when repeated sampling of individuals is required or where removal may bias other analyses. Here, we examine the utility of fish dorsal fin membrane as an alternative to muscle for analyzing δ¹³C and δ¹⁵N ratios in two reef fish species (blue cod Parapercis colias and spotty Notolabrus celidotus) that have differing feeding modes. Both species exhibited evidence of size-based feeding from fin δ¹⁵N values, but not from muscle. Blue cod fin δ¹⁵N increased steadily throughout the sampled size range (213–412 mm fork length), whereas spotty exhibited a distinct ontogenetic diet shift at approximately 120–140 mm fork length after which size-based feeding did not occur. Fin membrane was higher than muscle in δ¹³C in both species and in δ¹⁵N for blue cod, but fin δ¹⁵N was lower than muscle in spotty. The δ¹³C and δ¹⁵N fin–muscle offsets were constant in spotty regardless of size, while in blue cod, δ¹³C was constant with fish size, but δ¹⁵N offsets increased with increasing fish size. Non-lethal sampling utilizing fin tissue can be employed to estimate stable isotope values of muscle in fishes, but it is necessary to assess relationships among tissues and the effects of fish size on isotope values a priori for each species studied. Our data indicated that fin membrane may be a more sensitive tissue than muscle for detecting size-based feeding in some fish species using stable isotopes. A critical literature review revealed inconsistencies in tissue types tested, little understanding of tissue-specific trophic shift or turnover rates, and pseudo-replicated analyses leading to erroneous postulating of 1:1 relationships between tissues.     

Determination of δ13C and δ15N and trophic fractionation in jellyfish: implications for food web ecology

Application of stable isotope analysis (SIA) in jellyfish allows definition of trophic patterns not detectable using gut content analysis alone, but analytical protocols require standardization to avoid bias in interpreting isotopic data. We determined δ¹³C and δ¹⁵N in Aurelia sp. from the northern Gulf of Mexico (30°00′N, 89°00′W–30°24′N, 88°00′W) to define differences in stable isotope composition between body parts and whole body, the effect of lipid extraction on δ¹³C in tissues, and fractionation values from medusa to prey. The isotopic composition of bell and whole Aurelia sp. was not different. The increase in δ¹³C values after lipid removal suggested a correction is needed. To aid future analyses, we derived a correction equation from empirical data for jellyfish samples. Laboratory feeding experiments indicated medusae increased +4 ‰ in δ¹³C and +0.1 ‰ in δ¹⁵N compared to their diet. These results suggest protocols commonly applied for other species may be inaccurate to define Aurelia sp. trophic ecology. Because Aurelia spp. are commonly found in marine ecosystems, accurately defining their trophic role by use of SIA has implications for understanding marine food webs worldwide.     

Isotopic evidences for microbiologically mediated and direct C input to soil compounds from three different leaf litters during their decomposition

We show the potentiality of coupling together different compound-specific isotopic analyses in a laboratory experiment, where ¹³C-depleted leaf litter was incubated on a ¹³C-enriched soil. The aim of our study was to identify the soil compounds where the C derived from three different litter species is retained. Three ¹³C-depleted leaf litter (Liquidambar styraciflua L., Cercis canadensis L. and Pinus taeda L., δ¹³C_vsPDB ≈ ?43‰), differing in their degradability, were incubated on a C4 soil (δ¹³C_vsPDB ≈ ?18‰) under laboratory-controlled conditions for 8 months. At harvest, compound-specific isotope analyses were performed on different classes of soil compounds [i.e. phospholipids fatty acids (PLFAs), n-alkanes and soil pyrolysis products]. Linoleic acid (PLFA 18:2ω6,9) was found to be very depleted in ¹³C (δ¹³C_vsPDB ≈ from ?38 to ?42‰) compared to all other PLFAs (δ¹³C_vsPDB ≈ from ?14 to ?35‰). Because of this, fungi were identified as the first among microbes to use the litter as source of C. Among n-alkanes, long-chain (C27–C31) n-alkanes were the only to have a depleted δ¹³C. This is an indication that not all of the C derived from litter in the soil was transformed by microbes. The depletion in ¹³C was also found in different classes of pyrolysis products, suggesting that the litter-derived C is incorporated in less or more chemically stable compounds, even only after 8 months decomposition.     

Effects of nitrogen addition on the growth of the salt marsh grassElymus athericus

Effects of nitrogen addition on the growth of the salt marsh grassElymus athericus were studied under greenhouse conditions. The addition of inorganic nitrogen (in the form of nitrate or ammonium and ranging from 0–24 g N/m²) stimulated the growth ofElymus athericus at the highest addition. Addition of nitrogen led to an increase of the soil nitrate concentrations both in the nitrate and ammonium treated soil in the first period of the experiment, whereas no differences were present at the end of the experiment. Ammonium in the ammonium treatments was transformed to nitrate within 15 days. In another experiment the values of the stable isotope nitrogen-15—expressed as δ¹⁵N-in nitrogen compounds used as fertilizer, in salt marsh soil and ofElymus athericus were measured. The δ¹⁵N of the N-compounds added (between ?3.2 and +2.6‰) were lower than the soil (ca.+10‰) and plants (ca.+8‰). During growth in water culture the δ¹⁵N of the leaves, stems and roots ofElymus athericus decreased from +9‰ to ?1‰. The latter value was close to the °¹⁵N of the N-compounds used in the water solution. Addition of N-compounds in soil culture, however, did not lead to such a decrease of the °¹⁵N ofElymus athericus. The difference in δ¹⁵N between soil nitrogen and the N-compounds added may be too small to be used successfully in ecological studies of nitrogen fluxes in the salt marsh environment.     

Insulative capacity of the integument of the dugong (Dugong dugon): thermal conductivity,conductance and resistance measured by in vitro heat flux

Extant sirenians are restricted to warm waters, presumably due to their low metabolism and poor thermoregulatory capacity, including thin blubber. When subjected to winter waters, Florida manatees (Trichechus manatus latirostris) migrate to warm areas, but dugongs (Dugong dugon) do not and instead live year-round in winter waters as cool as 15–18 °C. Dugongs appear to be more active than manatees and may have higher metabolic rates, but little is known about thermal energetics or the insulative properties of their integument. This study investigated the physical and thermal properties of whole samples of dugong integument, i.e. epidermis, dermis and hypodermis (blubber) sampled from fresh dugong carcasses collected from 2004 to 2012 in Moreton Bay (27.21°S, 153.25°E). Physico-chemical properties (thickness, density and lipid content) of each component tissue layer were measured. Thermal conductance (C) and conductivity (k) were measured for each tissue layer through in vitro temperature flux experiments within an insulated chamber. C and k were higher for dermis (25.7 ± 1.2 W m^?2 K^?1, 0.43 ± 0.02 W m^?1 K^?1, respectively, n = 21) than blubber (24.3 ± 2.4 W m^?2 K^?1, 0.31 ± 0.01 W m^?1 K^?1, n = 21), suggesting that blubber, with higher density and lipid content, affords better insulation. However, because the dermis contributes 65 % of integumentary thickness, both layers contribute significantly to insulation. The integument of dugongs is a poorer insulator compared to many cold-water marine mammals, but the greater thickness of its dermal layer means that despite its relatively thin blubber, its integumentary insulation is similar to warm-water dolphins of similar body size.     

Stable isotope analysis in two sympatric populations of bottlenose dolphins <Emphasis Type="Italic">Tursiops truncatus</Emphasis>: evidence of resource partitioning?

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.     

High diurnal variation in dissolved inorganic C, δ13C values and surface efflux of CO2 in a seasonal tropical floodplain

Diurnal variations in aquatic systems may be a major factor influencing carbon cycling. However, few studies have examined diurnal variation on floodplains and wetlands, especially in the tropics. Stable isotope analysis of dissolved inorganic carbon (δ¹³C_DIC) provides insight into the driving factors behind diurnal physio-chemical variability, but to date, the manual collection of large sample numbers at high temporal frequency has been prohibitive. Here, we report one of the first, high-resolution isotopic studies of δ¹³C_DIC on a tropical floodplain using acidification-interface cavity ring-down spectrometry. Water samples were analysed for δ¹³C_DIC and other water quality parameters at 15-min intervals for 24 h. Our results show significant diurnal variation in both DIC concentration and δ¹³C_DIC. Maximum DIC concentration, recorded overnight, was approximately 100 % greater than during the day. Maximum DIC concentration coincided with minimum δ¹³C_DIC as a result of shifting autotrophic/heterotrophic balance. Changes were significant over small time scales and showed CO₂ gas evasion estimates could vary by as much as 50 % based on measurements taken less than 5 h apart. These data show that to accurately evaluate the role of tropical floodplains in global carbon dynamics, a comprehensive understanding of diurnal variation will be essential.     

Prey selection by resident common bottlenose dolphins (tursiops truncatus) in Sarasota Bay, Florida

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 (β^S = 0.9461 vs. β^NS = 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.     

The use of δ18O as an indicator of vanadium movement in a dormant stratovolcano region

The oxygen isotope (δ¹⁸O) stable water tracer can be a promising new tool for identifying trace metals in volcanoes and their sources. In the present study, the origin of vanadium in water from a spring at the base of Mt. Fuji is examined using δ¹⁸O, a dormant stratovolcano consisting of lava and basalt rock located on the North Pacific Coast of Japan. A comparison of water from the main springs at the foot of the Mt. Fuji volcano indicates that only V, Cr, Mn and Co enrichment could be related to volcanic events, whereas Ni, Cu, Cd and Pb originate from the dissolution of particles of anthropogenic origin from the industrial areas of Fuji and Fujinomiya. The average V concentrations at the mountain sites ranged from 50 to 110 µg L^?1 and from 18 to 47 µg L^?1 in the coastal areas. The δ¹⁸O became depleted at higher elevations and increased in coastal areas as well as in some NO₃^?-contaminated water. Therefore, variations in the dissolved V/δ¹⁸O ratio in springs of the study area occur due to the elevations of their catchments and the increased concentrations of δ¹⁸O from NO₃^? as a contaminant.     

H and O isotopic differences in typhon and urban-induced heavy rain in Tokyo

Stable isotope ratios of hydrogen and oxygen of water are useful tracers of the hydrological cycle. For example, isotopes monitor the evapotranspiration in vegetated areas, local snow ice processes and stream water flow processes. δ¹⁸O and δD in rainwater reflect the processes of evaporation, condensation and precipitation. Heavy rains thus modify the stable isotope ratio of ground water, stream water and transpiration water vapor. However, the controlling factors of δ¹⁸O and δD are not clear. Here we analyzed the inorganic ion concentration and stable isotope ratio in 38 normal rainwater and 15 heavy rainwater samples were collected in Shinjuku, Tokyo, Japan, during four years from October 2012 to December 2015. Results show a decrease in δ¹⁸O and δD values with the total rainfall amount, thus highlighting the amount effect. δ¹⁸O and δD volume-weighted mean values in typhoon heavy rain were higher than the values estimated from amount effect, whereas δ¹⁸O and δD volume-weighted mean values in urban-induced heavy rain were lower. Typhoon heavy rain has high Na⁺ ratio and stable isotope ratios, while urban-induced heavy rain has low Na⁺ ratio and stable isotope ratio.     

The reproductive cycle of <Emphasis Type="Italic">Scolelepis goodbodyi</Emphasis> (Polychaeta,Spionidae)

The aim of this study was to examine the reproductive and gametogenic cycle of the spionid polychaete Scolelepis goodbodyi (Jones). Every 15 days, in the upper level of the intertidal zone on Barequeçaba Beach in southeastern Brazil, a 100 m² area was delimited and within it three points were selected and sampled using a core sampler 0.01 m² in area × 0.2 m long. Each sample was divided into three sub-samples: surface (2 cm) and middle (8 cm), which were sieved through 0.5, 0.25 and 0.125 mm mesh sieves; and lower (10 cm), sieved through 1.0 and 0.5 mm mesh sieves. Males, females and undetermined individuals were separated, and the width of the third setiger was measured. The gonadal development of each individual was classified based on external features of the gametogenic setigers. Ten to 20 adults from each sampling period were classified according to their gonadal development stage and then analyzed histologically for gametogenic studies, for comparison with the former classification. Some of the ripe females were used for fecundity evaluation. The diameters of the oocytes were measured prior to spawning. Eight hundred and twenty-eight females (29.70%), 848 males (30.42%) and 1,112 undetermined individuals (39.89%) were analyzed. The sex ratio did not differ significantly from unity (χ² = 0.24; df = 1; P < 0.05). Males and females were more abundant in May 2002 (ca. 80%) and between November 2002 and May 2003 (between 77 and 90%); the proportion of undetermined individuals did not represent recruitment alone, but also a high incidence of adults with recovering gonads. Fecundity varied from 134 oocytes in a 0.54 mm W3 individual to 289 oocytes in a 0.4 mm W3 individual, with a mean of 220 (SD = 57) oocytes per female and 19 (SD = 5) oocytes per gametogenic setiger. Oocytes were ellipsoid, and ranged in size from 150 × 80 (to 220 × 120 μm (mean ± SD = 173 × 113 ± 15 × 11 μm). Neither a well-defined gametogenic cycle nor synchrony in the reproductive period was observed, because many gonadal development stages occurred in each month. Nevertheless, peaks of maturity were observed between October–December 2002 and April–May 2003.     

Pregnancy patterns of pantropical spotted dolphins (Stenella attenuata) in the eastern tropical Pacific determined from hormonal analysis of blubber biopsies and correlations with the purse-seine tuna fishery

The northeastern offshore population of the pantropical spotted dolphin (Stenella attenuata) in the eastern tropical Pacific remains listed as depleted under the Marine Mammal Protection Act, and recent estimates of abundance show that recovery has been slow. One hypothesis for the slow recovery is that continued chase and encirclement by the tuna fishery negatively affects reproduction. Insufficient life-history sampling in this region over the last two decades makes traditional estimates of reproductive rates impossible. Here, we examine the current reproductive patterns of these dolphins by measuring blubber progesterone (BP) concentrations in biopsy samples to assess pregnancy state. BP was quantified in 212 biopsies from female offshore spotted dolphins sampled between 1998 and 2003 in the northeastern tropical Pacific, and we found that 11.5 % of the biopsied females (mature and immature) were pregnant. The relationship between pregnancy and fishery exposure was analyzed, and we found that pregnant females were exposed to significantly less fishery activity than non-pregnant ones (p = 0.022), suggesting that the fishery may have an inhibitive effect on pregnancy. Spatial analysis indicated that pregnancy was more aggregated than random (p < 0.05) at a scale up to 180-nmi, with the highest proportion pregnant in the mouth of the Gulf of California, an area with relatively low reported fishery activity.