Lesser devil rays Mobula cf. hypostoma from Venezuela are almost twice their previously reported maximum size and may be a new sub-species.

Three rays opportunistically obtained near Margarita Island, Venezuela, were identified as lesser devil rays Mobula cf. hypostoma, but their disc widths were between 207 and 230 cm, which is almost double the reported maximum disc width of 120 cm for this species. These morphometric data suggest that lesser devil rays are either larger than previously recognized or that these specimens belong to an unknown sub-species of Mobula in the Caribbean Sea. Better data are needed to describe the distribution, phenotypic variation and population structure of this poorly known species.

Fecal triiodothyronine and thyroxine concentrations change in response to thyroid stimulation in Steller sea lions (Eumetopias jubatus).

Variation in concentrations of thyroid hormones shed in feces may help to identify physiological states of animals, but the efficacy of the technique needs to be validated for each species. We determined whether a known physiological alteration to thyroid hormone production was reflected in hormone concentrations in the feces of Steller sea lions (Eumetopias jubatus). We quantified variation of triiodothyronine (T3) and thyroxine (T4) concentrations in feces following two intramuscular injections of thyrotropin (thyroid-stimulating hormone, TSH) at 24h intervals in four captive female sea lions. We found fecal T3 concentrations increased 18-57% over concentrations measured in the baseline sample collected closest to the time of the first TSH injection (p=0.03) and 1-75% over the mean baseline concentration (p=0.12) for each animal of all samples collected prior to injections. Peak T3 concentrations were greater than the upper bound of the baseline 95% confidence interval for three animals. The peak T3 response occurred 48h post-injection in three animals and 71h in the fourth. Post-injection T4 concentrations did not differ between the baseline sample collected closest to the time of the first TSH injection (p=0.29) or the mean baseline concentration (p=0.23) for each animal. These results indicate that induced physiological alterations to circulating thyroid hormone concentrations can be adequately detected through analyses of fecal T3 concentrations and that the technique may provide a means of non-invasively detecting metabolic changes in Steller sea lions.

Molecular scatology as a tool to study diet: analysis of prey DNA in scats from captive Steller sea lions.

The DNA of prey present in animal scats may provide a valuable source of information for dietary studies. We conducted a captive feeding trial to test whether prey DNA could be reliably detected in scat samples from Steller sea lions (Eumetopias jubatus). Two sea lions were fed a diet of fish (five species) and squid (one species), and DNA was extracted from the soft component of collected scats. Most of the DNA obtained came from the predator, but prey DNA could be amplified using prey-specific primers. The four prey species fed in consistent daily proportions throughout the trial were detected in more than 90% of the scat DNA extractions. Squid and sockeye salmon, which were fed as a relatively small percentage of the daily diet, were detected as reliably as the more abundant diet items. Prey detection was erratic in scats collected when the daily diet was fed in two meals that differed in prey composition, suggesting that prey DNA is passed in meal specific pulses. Prey items that were removed from the diet following one day of feeding were only detected in scats collected within 48 h of ingestion. Proportions of fish DNA present in eight scat samples (evaluated through the screening of clone libraries) were roughly proportional to the mass of prey items consumed, raising the possibility that DNA quantification methods could provide semi-quantitative diet composition data. This study should be of broad interest to researchers studying diet since it highlights an approach that can accurately identify prey species and is not dependent on prey hard parts surviving digestion.

Possible effects of pollock and herring on the growth and reproductive success of Steller sea lions (Eumetopias jubatus): insights from feeding experiments using an alternative animal model, Rattus norvegicus.

The decline of Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska appears to have been associated with a switch of diet from one dominated by fatty forage fishes (such as herring; Clupea pallasi) to one dominated by low-fat fish (such as pollock; Theragra chalcogramma). Observations made during the decline include reduced body size of sea lions, low pregnancy rates, and high mortality. We used the general mammalian model, the laboratory rat (Rattus norvegicus), to test whether changing the quality of prey consumed could cause changes in size and reproductive performance. Five groups of twelve female, weanling rats were fed diets composed of herring (H), pollock (P), pollock supplemented with herring oil (PH), pollock supplemented with pollock oil (PP), or a semi-purified diet (ICN). Mean body weights were greatest for H, followed by PH, P, PP and finally ICN, although ICN was the only group significantly different from the others (P<0.05). Food intakes before mating were 10 % higher for groups on the lower-fat diets (P and ICN), resulting in similar energy intakes in all groups. The protein efficiency ratio was highest for the H diet, slightly lower for all pollock diets, and significantly lower for ICN (P<0.05). The fetal weights for mothers fed P were significantly reduced (P<0.05). The present study shows that the energy content was a major limiting factor in the nutritional quality of pollock. When food intake was adjusted to meet energetic requirements, there were no detrimental consequences from eating pollock. However, supplementation of pollock meal with additional pollock oil may reduce growth and reproductive performance, although the reasons for this were not apparent.

Hydrodynamic drag in steller sea lions (Eumetopias jubatus).

Drag forces acting on Steller sea lions (Eumetopias jubatus) were investigated from 'deceleration during glide' measurements. A total of 66 glides from six juvenile sea lions yielded a mean drag coefficient (referenced to total wetted surface area) of 0.0056 at a mean Reynolds number of 5.5x10(6). The drag values indicate that the boundary layer is largely turbulent for Steller sea lions swimming at these Reynolds numbers, which are past the point of expected transition from laminar to turbulent flow. The position of maximum thickness (at 34 % of the body length measured from the tip of the nose) was more anterior than for a 'laminar' profile, supporting the idea that there is little laminar flow. The Steller sea lions in our study were characterized by a mean fineness ratio of 5.55. Their streamlined shape helps to delay flow separation, reducing total drag. In addition, turbulent boundary layers are more stable than laminar ones. Thus, separation should occur further back on the animal. Steller sea lions are the largest of the otariids and swam faster than the smaller California sea lions (Zalophus californianus). The mean glide velocity of the individual Steller sea lions ranged from 2.9 to 3.4 m s(-)(1) or 1.2-1.5 body lengths s(-)(1). These length-specific speeds are close to the optimum swim velocity of 1.4 body lengths s(-)(1) based on the minimum cost of transport for California sea lions.

Metabolic effects of low-energy diet on steller sea lions, Eumetopias jubatus.

Diets of six Steller sea lions (Eumetopias jubatus) were switched between a high (herring) and a low (squid) energy density food for 14 d to determine the effects on ingested prey mass, body mass, resting metabolic rate, and the heat increment of feeding. Body mass was measured daily, and resting metabolism was measured weekly by gas respirometry. Ingested food mass did not differ significantly between the squid diet and the control or the recovery herring diet periods. As a result of differences in energy density, gross energy intake was significantly lower during the squid diet phase than during either the control or recovery periods. As a result, sea lions lost an average of 1.1 kg/d, totaling 12.2% of their initial body mass by the end of the experimental period. The heat increment of feeding for a 4-kg squid meal was significantly lower than for a similarly sized meal of herring. Decreases in both absolute (24.0 to 18.0 MJ/d, -24%) and mass-corrected (903 to 697 kJ/d/kg0.67, -20%) metabolism were observed by the end of the squid feedings. This study suggests that sea lions can depress their resting metabolism in response to decreases in energy intake or body mass, regardless of satiation level.

Heat increment of feeding in Steller sea lions, Eumetopias jubatus.

The heat increment of feeding (HIF) was measured in six captive, juvenile Steller sea lions (Eumetopias jubatus), fed meals of either 2 or 4 kg of herring. HIF was calculated as the post-prandial increase in metabolism above baseline levels, and was measured using open-circuit (gas) respirometry. It averaged 12.4 +/- 0.9% (SE) of ingested energy intake for the 4-kg meal trials, and 9.9 +/- 0.9% for the 2-kg meal size. The effect lasted 8-10 hr for the larger meal size. Metabolism peaked 3.7 hr after feeding, and was 2.13 times higher than baseline levels. For the 2-kg meal size, the effect lasted 6-8 hr, with metabolism peaking 2.8 hr after ingestion at 1.76 times baseline levels. Our estimates of HIF for Steller sea lions are at the lower end of estimates for terrestrial mammals, and are consistent with estimates for other marine mammals.