Elevated accumulation of the toxic metal mercury in the Critically Endangered oceanic whitetip shark Carcharhinus longimanus from the northwestern Atlantic Ocean

The oceanic whitetip shark Carcharhinus longimanus is a widely distributed large pelagic shark species once considered abundant in tropical and warm temperate waters, but recently listed as Critically Endangered by the IUCN due to drastic population declines associated with overfishing. In addition to risks posed to its populations due to overexploitation, oceanic whitetip sharks are also capable of accumulating elevated quantities of harmful environmental toxicants, placing them at special risk from anthropogenic pollution. Herein, we provide the first data on accumulation of the toxic, non-essential metal mercury (Hg) in northwest Atlantic (NWA) oceanic whitetip sharks, focusing on aggregations occurring at Cat Island, The Bahamas. Total Hg (THg) concentrations were measured in muscle of 26 oceanic whitetip sharks and compared with animal length and muscle δ15N to evaluate potential drivers of Hg accumulation. THg concentrations were also measured in fin and blood subcomponents (red blood cells and plasma) to determine their value as surrogates for assessing Hg burden. Muscle THg concentrations were among the highest ever reported for a shark species and correlated significantly with animal length, but not muscle δ15N. Fin, red blood cell, and plasma THg concentrations were significantly correlated with muscle THg. Fin THg content was best suited for use as a surrogate for estimating internal Hg burden because of its strong relationship with muscle THg levels, whereas blood THg levels may be better suited for characterizing recent Hg exposure. We conclude that Hg poses health risks to NWA oceanic whitetip sharks and human consumers of this species.

Comparative feeding ecology of the yellow ray Urobatis jamaicensis (Urotrygonidae) from The Bahamas

Stomach contents were collected from 117 yellow rays Urobatis jamaicensis from three locations in south Eleuthera, The Bahamas and compared with ambient infauna via sediment surveys. Diets were relatively limited with a total of 535 prey items recovered, representing five taxonomic groups and dominated by polychaetes and decapod crustaceans (87% of total diet), while environmental sampling reported 5249 individual taxa represented by 62 taxonomic groups. Regardless of gravidity, sex or density of prey items among sites, no significant differences were detected. Foraging strategy plots suggested preferential prey is rare within the environment and the Manly-Chesson index validates polychaetes were consumed with high selectivity. This is the most comprehensive and updated assessment of comparative feeding in this species, particularly for The Bahamas, allowing insight into invertebrate community richness and diversity in ecologically sensitive coastal and nearshore habitats.

Effect of weight and frontal area of external telemetry packages on the kinematics, activity levels and swimming performance of small-bodied sharks

This study sought to observe the effects of submerged weight and frontal cross-sectional area of external telemetry packages on the kinematics, activity levels and swimming performance of small-bodied juvenile sharks, using lemon sharks Negaprion brevirostris (60-80 cm total length, L_T ) as a model species. Juveniles were observed free-swimming in a mesocosm untagged and with small and large external accelerometer packages that increased frontal cross-sectional area of the animals and their submerged weight. Despite adhering to widely used standards for tag mass, the presence of an external telemetry package altered swimming kinematics, activity levels and swimming performance of juvenile N. brevirostris relative to untagged individuals, suggesting that tag mass is not a suitable standalone metric of device suitability. Changes in swimming performance could not be detected from tail-beat frequency, which suggests that tail-beat frequency is an unsuitable standalone metric of swimming performance for small N. brevirostris. Lastly, sharks experienced treatment-specific changes in activity level and swimming kinematics from morning to afternoon observation. Therefore, the presence of external telemetry packages altered the kinematics, activity levels and swimming performance of small young-of-the-year N. brevirostris and these data may therefore be relevant to other similar-sized juveniles of other shark species.

Regulation of delta protein kinase C during rat ovarian differentiation

Studies were undertaken to classify protein kinase C (PKC) forms present in rat corpora lutea and to begin to evaluate their regulation during ovarian differentiation. Hydroxyapatite (HAP) column chromatography of rat luteal tissue revealed the presence of multiple forms of PKC (alpha, beta, delta, zeta). Identification of the PKC isoforms was based upon elution positions from HAP column chromatography and immunoreactivity. The delta PKC isoform was identified as the major Ca(2+)-independent form of PKC present in rat luteal tissue. The Ca(2+)-independent, lipid-dependent phosphorylation of the 80-kDa delta PKC was readily detectable in soluble luteal extracts and was shown to reflect autophosphorylation of delta PKC. To evaluate the regulation of PKC isoforms during ovarian differentiation, PKC protein levels were compared between preovulatory follicle-enriched ovaries and corpora lutea obtained on day 16 of pregnancy. Levels of delta PKC protein were greatly elevated in corpora lutea compared to levels in preovulatory follicles. In contrast, levels of alpha and beta PKC protein remained constant while levels of zeta PKC were slightly higher in the follicular than the luteal extract. Levels of delta PKC mRNA were also higher in corpora lutea than in preovulatory follicles. These results are the first to demonstrate the physiological regulation of delta PKC with follicular differentiation into corpora lutea and implicate a role for this prominent PKC form in the corpus luteum during pregnancy.

cAMP-dependent protein kinases in the rat testis: regulatory and catalytic subunit associations

Based upon recent reports that the rat testis exhibits mRNAs for cAMP-dependent protein kinase (A-kinase) regulatory (R) subunits RI alpha, RI beta, RII alpha, and RII beta, this study was designed to identify R proteins present in extracts of germ cell-rich testis from adult and Sertoli cell-enriched, germ cell-poor testis from 14-15-day-old rats. Following separation by DEAE-cellulose, R subunits were identified by Mr: (a) upon labeling with 8-N3[32P]cAMP and 32P in an RII phosphorylation reaction and; (b) by Western blot analysis using R-specific antibodies on one- and two-dimensional gel electrophoresis. Elution of R subunits as catalytic (C) subunit-free dimers or in association with C subunits to form holoenzyme was determined by their sedimentation characteristics on sucrose gradient centrifugation in conjunction with their cAMP-stimulated activation characteristics on Eadie-Scatchard analysis. Soluble extracts of testes, from both adult and 14-15 day-old rats, showed the presence of a prominent type I holoenzyme containing RI alpha subunits (47 kDa, peak 1), a minor type II holoenzyme, containing RII beta subunits (52 kDa, peak 2), and a second, more abundant, type II holoenzyme peak containing predominantly RII alpha and, to a lesser extent RII beta subunits (peak 3). The 53 kDa RI beta protein predicted by mRNA studies was only tentatively identified by Western blot analysis. Testes extracts of 14-15-day-old, but not adult, rats exhibited high levels of C subunit-free RI alpha, a result not predicted by mRNA studies. This latter result may be attributable to direct RI alpha regulation or to indirect RII beta regulation at a time during testis development prior to germ cell maturation.