It is obvious, at least qualitatively, that small animals move their locomotory apparatus faster than large animals: small insects move their wings invisibly fast, while large birds flap their wings slowly. However, quantitative observations have been difficult to obtain from free-ranging swimming animals. We surveyed the swimming behaviour of animals ranging from 0.5 kg seabirds to 30 000 kg sperm whales using animalborne accelerometers. Dominant stroke cycle frequencies of swimming specialist seabirds and marine mammals were proportional to mass K0.29 (R 2 Z0.99, nZ17 groups), while propulsive swimming speeds of 1-2 m s K1 were independent of body size. This scaling relationship, obtained from breath-hold divers expected to swim optimally to conserve oxygen, does not agree with recent theoretical predictions for optimal swimming. Seabirds that use their wings for both swimming and flying stroked at a lower frequency than other swimming specialists of the same size, suggesting a morphological trade-off with wing size and stroke frequency representing a compromise. In contrast, foot-propelled diving birds such as shags had similar stroke frequencies as other swimming specialists. These results suggest that muscle characteristics may constrain swimming during cruising travel, with convergence among diving specialists in the proportions and contraction rates of propulsive muscles.

The conservation status of small cetaceans has significantly worsened since the 1980s, when the baiji was the only species of small cetacean listed as Endangered by IUCN. Now the baiji is almost certainly extinct and 13 other species, subspecies, or populations (hereafter units-to-conserve or units) of small cetaceans are listed as Critically Endangered (CR) on the IUCN Red List. Bycatch is the main threat to 11 of the CR units. Entanglement in gillnets contributed to the extinction of the baiji and is responsible for the imminent extinction of the vaquita. Unfortunately, there is no simple technical solution to the problem of bycatch of small cetaceans. If the 8 CR units with 100 or fewer remaining individuals are to be saved, conservation zones must be established where gillnets are eliminated and bans on their use are strictly enforced. Recent experience with the vaquita in Mexico demonstrates that enforcement of such conservation zones can be very difficult. Ineffective enforcement is also a problem for at least 4 of the other CR units. Time is very short and, unless major efforts are made now to address the bycatch problem, the prospects for CR small cetaceans and other at-risk aquatic megafauna are grim. The ultimate long-term solution to the bycatch problem is the development of efficient, inexpensive, alternative fishing gear that can replace gillnets without jeopardizing the livelihoods of fishermen. Good fishery governance and the direct involvement of fishing communities are also essential to the successful conservation of most threatened populations of small cetaceans.

Organochlorine compounds (OCs) such as DDTs (DDT and its metabolites), PCBs (polychlorinated biphenyls), CHLs (chlordane compounds), and HCHs (hexachlorocyclohexanes) were determined in the blubber of Baikal seal (Phoca sibirica) and their fish diet collected from Lake Baikal in 1992. Residue levels of DDTs and PCBs were in the ranges of 4.9-160 pg/g and 3.5-64pglg on a lipid weight basis, respectively. The concentrations of CHLs and HCHs were approximately 1 or 3 orders of magnitude lower than those of DDTs and PCBs. Comparison of OC residue levels with those reported for other pinnipeds suggests that Baikal seal is highly contaminated species vulnerable to OC toxicity. A positive age-dependent accumulation of DDTs, PCBs, and CHLs was found in males, while a steady state observed in females suggested the transfer of these chemicals from mother to pup through gestation and lactation. On the basis of contaminant burdens in adult seals, it was estimated that an adult female Baikal seal transfers about 20% of its total DDTs and 14% of its total PCBs to the pup during a reproductive process. Based on the data from isomer-specific analysis of PCBs, it can be suggested that Baikal seals have a higher or comparable capacity to metabolize toxic contaminants than marine mammals, but it is apparently lower than terrestrial mammals, which seems to be a causative factor for the higher accumulation of OC residues in this species. lntroduetion Lake Baikal, located in eastern Siberia, Russia, (Figure l), is known for many superlatives: the deepest (1632m1, the largest volume of freshwater (one-fif&h of the world's deposits of liquid freshwater), and geologically the most ancient (over 25 million years). Among many unique and endemic animals and plants in this lake, one of the most concern is the Baikal seal, which is a species inhabiting freshwater. They occupy the highest niche in the food chain of Lake Baikal.In 1987 and 1988, an acute disease struck the Baikal seal, and several thousands of animals died (1). Although the direct cause for this outbreak was a morbillivirus infection (1, 21, the potential factors behind the sudden infection by this virus have not been ascertained. Such mass mortalities in marine mammals have frequently been found worldwide in the latter half of this century (3). Since these disasters have mostly occurred nearby industrialized coastal areas (41, it is suspected that some stressors such as chronic exposures to toxic man-made chemicals might have played a role in triggering serious symptoms in epizootics by immunosuppression in mammals (4-6).Previous investigations reported the presence of high levels of OC residues in marine mammals (7,8), and some of them were discussed in association with the occurrence of several abnormalities (8-111, Adverse effects on reproductive and immunological functions were also noted in captive seals fed with high levels of persistent OCs (12,13). Nevertheless, in contrast to that in marine species, very few investigations are available for freshwater species inhabiti...

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Concentrations of perfluorochemicals (PFCs) including perfluoroalkylsulfonates (PFSAs) and perfluoroalkylcarboxylates (PFCAs) were determined in liver and serum of Baikal seals (Pusa sibirica) collected from Lake Baikal, Russia in 2005. Among the 10 PFC compounds measured, perfluorononanoic acid (PFNA, 3.3-72 ng/g wet wt) concentrations were the highest in liver, followed by perfluorooctanesulfonate (PFOS, 2.6-38 ng/ g). The accumulation profile of long-chain (C7-C12) PFCAs in particular, the predominance of PFNA, indicated that 8:2 fluorotelomer alcohol or commercially manufactured PFNA is a major local source of PFCs in Lake Baikal. No gender-related differences in the concentrations of individual PFCs or total PFCs were found. Tissues from pups and juveniles contained relatively higher concentrations of PFCs than tissues from subadults and adults, suggesting that maternal transfer of PFCs is of critical importance. Comparison of concentrations of PFCs in livers and sera collected from the same individuals of Baikal seals revealed that residue levels of PFOS, PFNA, perfluorodecanoic acid (PFDA), and perfluoroundecanoic acid (PFUnDA) were significantly higher in liver than in serum. The concentration ratios of PFNA and PFDA between liver and serum were calculated to be 14 and 15, respectively, whereas the ratio of PFOS was 2.4. This suggests preferential retention of both PFNA and PFDA in liver. Concentrations of PFOS, PFNA, and PFDA in liver were significantly correlated with those in serum, whereas concentrations of PFUnDA were not correlated in between the two tissues, suggesting differences in pharmacokinetics among these PFCs. Temporal comparisons of hepatic PFC concentrations in seals collected between 1992 and 2005 showed that the concentrations of PFOS (p ) 0.0006), PFNA (p ) 0.061) and PFDA (p ) 0.017) were higher in animals collected in recent years, indicating ongoing sources of PFC contamination in Lake Baikal.

Summary1. Breath-hold divers are widely assumed to descend and ascend at the speed that minimizes energy expenditure per distance travelled (the cost of transport (COT)) to maximize foraging duration at depth. However, measuring COT with captive animals is difficult, and empirical support for this hypothesis is sparse. 2. We examined the scaling relationship of swim speed in free-ranging diving birds, mammals and turtles (37 species; mass range, 0AE5-90 000 kg) with phylogenetically informed statistical methods and derived the theoretical prediction for the allometric exponent under the COT hypothesis by constructing a biomechanical model. 3. Swim speed significantly increased with mass, despite considerable variations around the scaling line. The allometric exponent (0AE09) was statistically consistent with the theoretical prediction (0AE05) of the COT hypothesis. 4. Our finding suggests a previously unrecognized advantage of size in divers: larger animals swim faster and thus could travel longer distance, search larger volume of water for prey and exploit a greater range of depths during a given dive duration. 5. Furthermore, as predicted from the model, endotherms (birds and mammals) swam faster than ectotherms (turtles) for their size, suggesting that metabolic power production limits swim speed. Among endotherms, birds swam faster than mammals, which cannot be explained by the model. Reynolds numbers of small birds (<2 kg) were close to the lower limit of turbulent flow ($3 · 10 5 ), and they swam fast possibly to avoid the increased drag associated with flow transition.

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Concentrations of butyltins (BTs) in the liver and organochlorine compounds (OCs) in the blubber of Risso's dolphins collected off Taiji, Japan, in 1991 were determined. Mean and range concentrations (wet weight basis) of these compounds were 3.6 μg/g (0.55−6.0 μg/g) for BTs, 25 μg/g (1.7−120 μg/g) for PCBs, 17 μg/g (0.45−77 μg/g) for DDTs, 4.0 μg/g (0.19−16 μg/g) for CHLs, and 0.16 μg/g (0.008−0.74 μg/g) for HCHs. OCs concentrations increased with age in males in contrast to that in females, which showed a decreasing trend after maturity. On the other hand, no difference was observed in BT concentrations between male and female, which showed increasing levels until maturity (8−10 years) and then remained constant. It is suggested that, unlike OCs, BTs were less transferable to young ones in reproductive processes. Risso's dolphins showed higher biomagnification factor (about 6) than Steller sea lion (0.6), implying a slower excretion rate of BTs in cetaceans than in pinnipeds due to the lower degradation capacity of xenobiotics and the lack of physiological processes such as shedding of hair in cetaceans.