Masashi Kiyota

Persistent organochlorine residues in northern fur seal from the Pacific coast of Japan since 1971

The present study was conducted to determine the residue levels of persistent organochlorines such as PCB homologues, DDT and its metabolites, and HCH isomers in the ventral blubber of female northern fur seal (Callorhinus ursinus) collected off Sanriku, the Pacific coast of northern Japan, since 1971. Among the organochlorines examined, the concentrations of PCBs and DDTs were found to be high in all samples. The residue levels of these two contaminants showed a drastic reduction following maturity and then a slight increase after the retirement from pregnancy/menopause. Temporal variation of PCB and DDT residues showed maximum levels around 1976 and then decreased, whereas HCH residue levels revealed a very slow declining pattern. Considering the concentrations and compositions of the residues, the northern fur seal is likely to be exposed to organochlorine contamination deriving from global terms. In this context, continuous contamination has been foreseen with regard to PCB and HCH residues. The pattern of organochlorine residues indicated that the northern fur seal has higher metabolic capacity than Dalls porpoise, while it is comparable to those of larga seal and Steller sea lion.

Accumulation of silver in the liver of three species of pinnipeds.

Silver in the three species of pinnipeds [northern fur seal (Callorhinus ursinus), Steller sea lion (Eumetopias jubatus), and harbor seal (Phoca vitulina)] caught in the North Pacific Ocean were analyzed using inductively coupled plasma-mass spectrometry, in order to understand accumulation and distribution of silver in pinnipeds. In northern fur seals, relatively high concentrations of silver were observed in the liver and body hair. Some 70% of the silver burden was concentrated in the liver. Hepatic silver concentrations were significantly correlated to age in northern fur seals (r = 0.766, P < 0.001, n = 49) and Steller sea lions (r = 0.496, P < 0.01, n = 28). Levels of silver concentrations per wet weight (microgram g-1) in the three pinnipeds ranged from 0.04 to 0.55 for northern fur seals, from 0.1 to 1.04 for Steller sea lions and from 0.03 to 0.83 for harbor seals. Silver concentrations in liver for all pinnipeds were significantly correlated with mercury, and selenium (P < 0.001). Molar ratios between silver to selenium approximated 1:180 in northern fur seals, 1:120 in Steller sea lions, and 1:60 in harbor seals. The silver-mercury molar ratios were approximately 1:170 in northern fur seals, and 1:80 both in the other species. Increase in silver accumulation in the liver was caused by the retention in nuclei and mitochondria fraction together with mercury and selenium in the cells of northern fur seals.

Distribution of heavy metals in muscle, liver and kidney of northern fur seal (Callorhinus ursinus) caught off Sanriku, Japan and from the Pribilof Islands, Alaska

The concentrations of iron, manganese, zinc, copper, cadmium, and mercury were determined in muscle, liver and kidney of 67 northern fur seals (Callorhinus ursinus) collected off Sanriku, Japan, and from the Pribilof Islands, Alaska. Almost all the elements except cadmium were highest in liver. Cadmium levels in kidney were higher than those in liver and muscle for all animals analyzed. Concentrations of mercury increased significantly with age in muscle, liver and kidney, as did iron levels in muscle and liver and cadmium levels in muscle, while manganese concentrations decreased with age in muscle and kidney. The kidney also showed decreased copper concentration with age. Cadmium concentrations of the northern fur seals in this study were higher than the other otariids, reflecting a predominantly squid diet. Concentrations of manganese and mercury were found to be higher in the fur seals caught off Sanriku than in animals from the Pribilof Islands, while those of zinc and cadmium were found to be lower. Variable concentrations of cadmium might have been attributed to those in seawaters. Discriminant analysis of heavy metal concentrations was used to identify habitat. Sixty-three of 67 animals (94%) were correctly classified using this technique. Heavy-metal concentrations in tissues may provide a useful method to elucidate the primary feeding grounds of fur seals.

Site fidelity, territory acquisition and mating success in male northern fur seals (Callorhinus ursinus)

ABSTRACT The process of obtaining breeding territories and mating success in male northern fur seals was studied through a longitudinal survey in St. Paul Island, Alaska in 1993–1999. Resighting of metal tags that had been deployed to pups in their natal areas generally showed site fidelity of males to natal breeding areas, but also indicated movements within the breeding area. Males started to reside in the periphery of central breeding areas (CBAs) at age 7, and some males established breeding territories in the CBAs at age 7–9. Males bleach-marked in the peripheral areas showed a tendency to reappear in the same locations over successive breeding seasons. Some of them entered nearby CBAs in the late breeding season and held territories. Once adult males acquired breeding territories, they exhibited a strong tendency to return to the same locations in the following breeding season(s). Duration of the effective territory tenure after June 30 and the maximum number of adult females in a males territory did not differ significantly between the first and second years of his territory tenure (P > 0.05). However, starting date of territory tenure became earlier in the second season (P = 0.04). The index of mating success estimated from the seasonal frequency distribution of copulations also increased significantly in the second years of territory tenure (P = 0.03). These results indicate that territory acquisition is a site-specific multi-year process in which males return to the same breeding area for successive breeding seasons and gradually shift their presence spatially to the center of the breeding aggregation and temporally to the peak season of female estrus. Prior experience formed through site fidelity is likely an important factor for territory acquisition and mating success in male northern fur seals.

Prey size reconstruction based on myctophid otoliths in scats of northern fur seals (Callorhinus ursinus)

Diet studies of eared seals (Otariidae) are very important, because they are high-level consumers in marine ecosystems (Bowen 1997). Recently, non-lethal methods such as scat analysis have been applied to diet studies of eared seals (e.g., Zeppelin and Ream 2006; Sigler et al. 2009). In this analysis, diet compositions are estimated from the undigested hard part remains of prey items (fish otoliths, squid beaks, crustacean exoskeletons, etc.; Pierce and Boyle 1991). Fish species are identified based on the morphology of otoliths. Size and weight of fish consumed can also be estimated from the lengths of otoliths in scats (Sinclair et al. 1994). Although scat analysis is a useful method that provides dietary information without animal capture, the resultant information could include biases caused by digestion (Jobling and Breiby 1986; Yonezaki et al. 2003; Gudmundson et al. 2006). Fish otoliths are partially, or even completely, digested during passage through the alimentary system. Feeding experiments of various eared seals have been conducted to investigate the potential biasing effects of digestion on otoliths (e.g., Staniland 2002; Tollit et al. 2003). Numerical loss and length reduction rates of fish otoliths in scat samples were assessed from captive experiments, and correction factors calculated to enable the reconstruction of the original number and body lengths of fishes that were consumed. These correction factors are known to vary with prey species, eared seal species and experimental conditions (e.g., Bowen 2000; Orr and Harvey 2001; Staniland 2002). However, few studies have applied the correction factors to wild samples and tested the validity of the diet reconstruction. The purpose of this study was to use experimentally designed meals and captive northern fur seals (Callorhinus ursinus) to calculate correction factors (CFs) for reconstruction of the myctophid fish size to compensate for the effects of digestion. Moreover, we apply the CFs to otoliths recovered from the large intestine contents of wild fur seal specimens, and estimated the size of the myctophid fish eaten. Myctophid fish used in the experiment are dominant components of micronekton communities in oceanic ecosystems and are important prey items of northern fur seals in the western North Pacific Ocean (Yonezaki et al. 2003; Yonezaki et al. 2008). Therefore, the calculation of CFs of myctophid fish otoliths enables data for use in the reconstruction of the diet of northern fur seals based on scats.

An Enema Technique to Collect Dietary Information from Northern Fur Seals (Callorhinus ursinus) at Sea

An enema technique was developed to obtain dietary information on northern fur seals (Callorhinus ursinus) at sea. The enema apparatus consisted of a hand pump and a soft PVC tube connected to a plastic tank filled with seawater. The tube was inserted into the fur seal’s anus, and fecal samples flushed out into a polyethylene bag enveloping the posterior of the fur seal. The efficacy of the enema sampling was tested on 23 fur seals captured and killed off the Pacific coast of northern Japan in April 1998. Twenty of 23 enema samples contained hard prey items such as fish otoliths and squid beaks. The average number (+ SD) of hard prey items retrieved from the whole large intestine was 26.9 + 33.0% for fish otoliths, 37.3 + 38.5% for squid upper beaks, and 43.3 + 40.9% for squid lower beaks. Size distributions of these prey items retrieved from the enema samples were similar to that remaining in the large intestines. These results indicated that the enema technique could provide dietary information that is comparable to intestinal contents and scat analysis. Combination of the enema technique with a pelagic live capture method using gillnets could provide a nondestructive way to investigate the feeding ecology of individual fur seals migrating offshore.

Latitudinal Variation in Birth Dates of Northern Fur Seals (Callorhinus ursinus) in Captivity

Seasonality of mammalian reproduction is ultimately related to dietary and climatic factors, and the timing of birth is scheduled to optimize offspring survival (Bronson 1985). Reproductive synchrony also represents a strategy that individuals adopt to maximize reproductive success in the course of sociobiological and ecological processes such as sexual selection and predation (Ims 1990). Pinnipeds (seals, walruses and sea lions; Carnivora, Pinnipedia) are distinct from other mammals in having two different phases in their life cycles: reproduction on land (or on ice) and foraging in water. Reproduction in most pinniped species is characterized by tight synchrony of births which ensures that pups are born at the optimal time of year (Atkinson 1997). Seasonality and synchrony of births in pinnipeds then lead to temporal aggregation of postpartum estrus and copulation (Stirling 1975; Boness 1991). Reproductive cycles of female pinnipeds are characterized by embryonic diapause and delayed implantation, a preadaptive feature shared with ursid and mustelid carnivores (Mead 1989; Boyd 1991). Lengths of postimplantation gestation (active gestation) are relatively constant in most pinnipeds (ca. 8 months), and the period of delay in embryo implantation adjusts the length of the whole gestation period and determines the timing of births (Boyd 1991). The northern fur seal (Callorhinus ursinus), a highly polygynous pinniped species, inhabits the North Pacific Ocean, Bering Sea, Okhotsk Sea, and Japan Sea, and breeds on subpolar and temperate islands during summer (Gentry 1998). Their reproduction is characterized by highly synchronized annual cycles (Trites 1992). Synchronization of estrus is linked to monopolizability of receptive females by adult males in terrestrial breeding areas and thus provides a basis for the development of polygyny in this species (Boness 1991). Temte (1985) compared the mean birth dates of two wild populations in Alaska (57°N) and in California (33°N), and postulated that the mean photoperiod of 12.5 h/day in autumn might act as a cue for the implantation and control the synchronization of annual breeding cycles of female northern fur seals. On the contrary, Spotte and Adams (1981) disagreed with the hypothesis of photoperiodic control of reproduction based on the fact that breeding activity of captive northern fur seals captured in Alaska (57°N) and translocated to Connecticut (41°N) was observed in July and August being unaffected by the difference in photoperiod between the two sites. However, their results were inconclusive because they only examined breeding activity by month and their birth records consisted of seven stillbirths that occurred over a period ranging from February to July. Temte (1993) examined birth data of pinnipeds kept in North America, Korea and New Zealand, and found a significant latitudinal gradient of birth timing in California sea lion (Zalophus californianus) and harbor seal (Phoca vitulina). Temte and Temte (1993) further explained that the latitudinal variation of births dates in California sea lions were a response to a common photoperiod (11.5 h/day) before implantation. But Temte (1993) failed to find a significant latitudinal variation in birth timing for northern fur seals due to the small sample size. In Japan, northern fur seals were kept in five aquaria under special permit for domestic law that regulates the capture and possession of this species. In four of the five aquaria, northern fur seals were kept outdoor and exposed to natural photoperiodic conditions (at least during the period from estrus to implantation). These four aquaria were located in two geographical areas with different latitudes: Honshu area (35°N), and Hokkaido area (42–43°N). In this study, we analyze the birth dates of northern fur seals kept in these aquaria to ascertain