Ontogeny of diving behaviour in the Australian sea lion: trials of adolescence in a late bloomer

1.Foraging behaviours of the Australian sea lion (Neophoca cinerea) reflect an animal working hard to exploit benthic habitats. Lactating females demonstrate almost continuous diving, maximize bottom time, exhibit elevated field metabolism and frequently exceed their calculated aerobic dive limit. Given that larger animals have disproportionately greater diving capabilities, we wanted to examine how pups and juveniles forage successfully.
2.Time/depth recorders were deployed on pups, juveniles and adult females at Seal Bay Conservation Park, Kangaroo Island, South Australia. Ten different mother/pup pairs were equipped at three stages of development (6, 15 and 23 months) to record the diving behaviours of 51 (nine instruments failed) animals.
3. Dive depth and duration increased with age. However, development was slow. At 6 months, pups demonstrated minimal diving activity and the mean depth for 23-month-old juveniles was only 44 ± 4 m, or 62% of adult mean depth.
4. Although pups and juveniles did not reach adult depths or durations, dive records for young sea lions indicate benthic diving with mean bottom times (2·0 ± 0·2 min) similar to those of females (2·1 ± 0·2 min). This was accomplished by spending higher proportions of each dive and total time at sea on or near the bottom than adults. Immature sea lions also spent a higher percentage of time at sea diving.
5. Juveniles may have to work harder because they are weaned before reaching full diving capability. For benthic foragers, reduced diving ability limits available foraging habitat. Furthermore, as juveniles appear to operate close to their physiological maximum, they would have a difficult time increasing foraging effort in response to reductions in prey. Although benthic prey are less influenced by seasonal fluctuations and oceanographic perturbations than epipelagic prey, demersal fishery trawls may impact juvenile survival by disrupting habitat and removing larger size classes of prey. These issues may be an important factor as to why the Australian sea lion population is currently at risk.

Ontogeny of movements and foraging ranges in the Australian sea lion

This study tracked the movements of Australian sea lion (Neophoca cinerea) pups, juveniles, and adult females to identify home ranges and determine if young sea lions accompanied their mothers at sea. Satellite tags were deployed on nine 15- mo-old pups, nine 23-mo-old juveniles, and twenty-nine adult female Australian sea lions at Seal Bay Conservation Park, Kangaroo Island, South Australia. Females did not travel with their offspring at sea, suggesting young Australian sea lions learn foraging behaviors independently. Although home ranges increased with age,  23-mo-old juveniles had not developed adult movement capacity and their range was only 40.6% of the adult range. Juveniles traveled shorter distances (34.8 ± 5.5 km) at slower speeds (2.0 ± 0.3 km/h) than adults (67.9 ± 3.5 km and 3.9 ± 0.3 km/h). Young sea lions also stayed in shallower waters; sea floor depths of mean locations were 48±7m for juveniles and 74±2m for females. Restricted to shallow coastal waters, pups and juveniles are more likely to be disproportionately impacted by human activities. With limited available foraging habitat, young Australian sea lions appear particularly vulnerable to environmental alterations resulting from fisheries or climate change.

Assessing the use of milk fatty acids to infer the diet of the Australian sea lion (Neophoca cinerea)

Information on the diet of threatened species is important in devising appropriate management plans to ensure their conservation. The Australian sea lion (Neophoca cinerea) is Australia’s only endemic and globally one of the least numerous pinniped species. However, dietary information is currently limited because of the difficulty in using traditional methods (identification of prey hard parts from scats, regurgitates and stomach samples) to reliably provide dietary information. The present study assessed the use of fatty acid (FA) analysis to infer diet using milk samples collected from 11 satellite tracked Australian sea lions from Olive Island, South Australia. Satellite tracking revealed that females foraged in two distinct regions; ‘inshore’ regions characterised by shallow bathymetry (10.7 ± 4.8 m) and ‘offshore’ regions characterised by comparatively deep bathymetry (60.5 ± 13.4 m). Milk FA analysis indicated significant differences in the FA composition between females that foraged inshore compared with those that foraged offshore. The greatest differences in relative levels of individual FAs between the inshore and offshore groups were for 22 : 6n-3 (6.5 ± 1.2% compared with 16.5 ± 1.9% respectively), 20 : 4n-6 (6.1 ± 0.7 compared with 2.5 ± 0.7 respectively) and 22 : 4n-6 (2.4 ± 0.2% compared with 0.8 ± 0.2% respectively). Using discriminant scores, crustacean, cephalopod, fish and shark-dominated diets were differentiated. The discriminant scores from Australian sea lions that foraged inshore indicated a mixed fish and shark diet, whereas discriminant scores from Australian sea lions that foraged offshore indicated a fish-dominated diet, although results must be interpreted with caution due to the assumptions associated with the prey FA dataset. FA analysis in combination with satellite tracking proved to be a powerful tool for assessing broad-scale spatial dietary patterns.

Ontogeny of oxygen stores and physiological diving capability in Australian sea lions

1.For air-breathing animals in aquatic environments, foraging behaviours are often constrained by physiological capability. The development of oxygen stores and the rate at which these stores are used determine juvenile diving and foraging potential.
2. We examined the ontogeny of dive physiology in the threatened Australian sea lion Neophoca cinerea. Australian sea lions exploit benthic habitats; adult females demonstrate high field metabolic rates (FMR), maximize time spent near the benthos, and regularly exceed their calculated aerobic dive limit (cADL). Given larger animals have disproportionately greater diving capabilities; we wanted to determine the extent physiological development constrained diving and foraging in young sea lions.
3. Ten different mother/pup pairs were measured at three developmental stages (6, 15 and 23 months) at Seal Bay Conservation Park, Kangaroo Island, South Australia. Hematocrit (Hct), haemoglobin (Hb) and plasma volume were analyzed to calculate blood O2 stores and myoglobin was measured to determine muscle O₂. Additionally, FMR's for nine of the juveniles were derived from doubly-labelled water measurements.
4. Australian sea lions have the slowest documented O₂ store development among diving mammals. Although weaning typically occurs by 17·6 months, 23-month juveniles had only developed 68% of adult blood O₂. Muscle O₂ was the slowest to develop and was 60% of adult values at 23 months.
5. We divided available O₂ stores (37·11 ± 1·49 mL O₂ kg−1) by at-sea FMR (15·78 ± 1·29 mL O₂ min−1 kg−1) to determine a cADL of 2·33 ± 0·24 min for juvenile Australian sea lions. Like adults, young sea lions regularly exceeded cADL's with 67·8 ± 2·8% of dives over theoretical limits and a mean dive duration to cADL ratio of 1·23 ± 0·10.
6. Both dive depth and duration appear impacted by the slow development of oxygen stores. For species that operate close to, or indeed above their estimated physiological maximum, the capacity to increase dive depth, duration or foraging effort would be limited. Due to reduced access to benthic habitat and restricted behavioural options, young benthic foragers, such as Australian sea lions, would be particularly vulnerable to resource limitation.

New SNPs for population genetic analysis reveal possible cryptic speciation of eastern Australian sea mullet (Mugil cephalus)

Sustainable management of sea mullet (Mugil cephalus) fisheries needs to account for recent observations of regional-scale differentiation. Population genetic analysis is sought to assess the situation of this ecologically and economically important fish species in eastern Australian waters. Here, we report (i) new population genetic markers [single nucleotide polymorphisms (SNPs) and potential microsatellites], (ii) first estimates of spatial genetic differentiation and (iii) prospective power tests for designing more comprehensive studies. Six DNA samples from three sampling regions (North Queensland, South Queensland and central New South Wales) on the eastern coast of Australia were used to prepare restriction site associated DNA (RAD) tag libraries from genomic DNA digested with EcoRI and MseI. A pooled sample of regional RAD tag libraries was sequenced using the Roche GS-FLX Titanium platform. A total of 172837 raw reads (17.4Mbp) were retrieved, 95500 of which were used to discover 1267 SNPs and 1417 microsatellites. A subset of 161 SNPs was validated based on 63 additional DNA samples genotyped using the Sequenom MassArray (iPLEX Gold chemistry). Altogether 92 SNPs (57%) were confirmed, with 40% of these marking fixed variants between northern and southern sampling regions. Our preliminary findings indicate a multispecies fishery stock of M. cephalus in eastern Australian waters, but suggest that strong genetic differentiation occurs north of major fishing grounds. Low potential differentiation within major fishing grounds (e.g. FST=0.0025) can be resolved with a likely power 67% by using standard sample sizes of 50 and validated subsets of available markers.

Control of California sea lion predation of winter-run steelhead at the Hiram M. Chittenden Locks, Seattle, December 1985-April 1986 with observations on sea lion abundance and distribution in Puget Sound

A study/predation control program was conducted at the Hiram M. Chittenden Locks in Seattle, Washington from 20 December through 23 April 1986. The principal objectives were to document the rate and effects of predation on winter-run steelhead (Salmo gairdneri Richardson) by California sea lions (Zalophus californianus); to control and minimize predation in order to increase the escapement of wild winter-runs to the Lake Washington watershed; to evaluate and recommend potential long term procedures for control of steelhead predation; and to document the abundance and distribution of California sea lions in Puget Sound.

Effects of the 1997-1998 El Niño on population size and diet of the Galápagos sea lion (Zalophus wollebaeki)

The multi-annual climatic event, El Niño Southern Oscillation (ENSO) is an important factor in the population dynamics of coastal marine species in the Galápagos. The Galápagos sea lion, Zalophus wollebaeki, suffered an apparent population decline of about 50%, considering both mortality and movements away from study sites during the 1997-98 El Niño. This change was in part due to changes in the availability of sardines of the Family Clupeidae, its main prey. These declines resulted partly from elevated mortality (35%) in sea lion colonies, particularly among pups, juveniles (< 1 year old), and dominant males and as a result of movements of adults elsewhere (15%), presumably where there were alternative prey and better environmental conditions.

Abundance and distribution of the eastern North Pacific Steller sea lion (Eumetopias jubatus) population

The eastern Steller sea lion (Eumetopias jubatus) population comprises animals that breed along the west coast of North America between California and southeastern Alaska. There are currently 13 major rookeries (>50 pups): five in southeastern Alaska, three in British Columbia, two in Oregon, and three in California. Overall abundance has increased at an average annual rate of 3.1% since the 1970s. These increases can largely be attributed to population recovery from predator-control kills and commercial harvests, and abundance is now probably as high as it has been in the last century. The number of rookeries has remained fairly constant (n=11 to 13) over the past 80 years, but there has been a northward shift in distribution of both rookeries and numbers of animals. Based on the number of pups counted in a population-wide survey in 2002, total pup production was estimated to be about 11,000 (82% in southeastern Alaska and British Columbia), representing a total population size as approximately 46,000−58,000 animal

Impact of the California sea lion (Zalophus californianus) on salmon fisheries in Monterey Bay, California

To assess the impact of California sea lions (Zalophus californianus) on salmon fisheries in the Monterey Bay region of California, the percentages of hooked fish taken by sea lions in commercial and recreational salmon fisheries were estimated from 1997 to 1999. Onboard surveys of sea lion interactions with the commercial and recreational f isheries and dockside interviews with fishermen after their return to port were conducted in the ports of Santa Cruz, Moss Landing, and Monterey. Approximately 1745 hours of onboard and dockside surveys were conducted—924 hours in the commercial fishery and 821 hours in the recreational fishery (commercial passenger fishing vessels [CPFVs] and personal skiffs combined). Adult male California sea lions were responsible for 98.4% of the observed depredations of hooked salmon in the commercial and recreational fisheries in Monterey Bay. Mean annual percentages of hooked salmon taken by sea lions ranged from 8.5% to 28.6% in the commercial fishery, 2.2% to 18.36% in the CPFVs, and 4.0% to 17.5% in the personal skiff fishery. Depredation levels in the commercial and recreational salmon fisheries were greatest in 1998—likely a result of the large El Niño Southern Oscillation (ENSO) event that occurred from 1997 to 1998 that reduced natural prey resources. Commercial fishermen lost an estimated $18,031−$60,570 of gear and $225,833−$498,076 worth of salmon as a result of interactions with sea lions. Approximately 1.4−6.2% of the available salmon population was removed from the system as a result of sea lion interactions with the fishery. Assessing the impact of a growing sea lion population on fisheries stocks is difficult, but may be necessary for effective fisheries management.

Neonatal growth of Steller sea lion (Eumetopias jubatus) pups in Alaska

The growth rate of Steller sea lion (Eumetopias jubatus) pups was studied in southeast Alaska, the Gulf of Alaska, and the Aleutian Islands during the first six weeks after birth. The Steller sea lion population is currently stable in southeast Alaska but is declining in the Aleutian Islands and parts of the Gulf of Alaska. Male pups (22.6 kg [±2.21 SD]) were significantly heavier than female pups (19.6 kg [±1.80 SD]) at 1−5 days of age, but there were no significant differences among rookeries. Male and female pups grew (in mass, standard length, and axillary girth) at the same rate. Body mass and standard length increased at a faster rate for pups in the Aleutian Islands and the western Gulf of Alaska (0.45−0.48 kg/day and 0.47−0.53 cm/day, respectively) than in southeast Alaska (0.23 kg/day and 0.20 cm/day). Additionally, axillary girth increased at a faster rate for pups in the Aleutian Islands (0.59 cm/ day) than for pups in southeast Alaska v(0.25 cm/day). Our results indicate a greater maternal investment in male pups during gestation, but not during early lactation. Although differences in pup growth rate occurred among rookeries, there was no evidence that female sea lions and their pups were nutritionally stressed in the area of population decline

Historical Exploitation of the California Sea Lion, Zalophus californianus, in México

The exploitation of California sea lions, Zalophus californianus, in Mexican waters can be divided into four periods as defined by political characteristics of the country: Prehispanic, Colonial, Independent, and Postrevolutionary. During the first period (pre 1533), Native Americans took sea lions at low levels. During the second (1534–1821) and the third (1822–1911) periods, most exploitation was by foreigners and was incidental to other marine mammal harvests. During the Postrevolutionary period (after 1911), sea lions were exploited by Mexican and U.S. citizens for several commercial uses. Exploitation officially ended in 1982, although some small-scale poaching still occurs.

An Accounting of the Sources of Steller Sea Lion, Eumetopias jubatus, Mortality

During 1991–2000, the west-are additional mortalities that fueled the ern stock of Steller sea lions, Eumetopias decline. We tabulated the levels of reported jubatus, declined at 5.03% (SE = 0.25%) anthropogenic sources of mortality (sub- per year, statistically significant rates (P < sistence, incidental take in fisheries, and 0.10) in all but the eastern Aleutian Islands research), estimated another (illegal shoot-region. The greatest rates of declines oc-ing), then approximated levels of predation curred in the eastern and central Gulf of Alas-(killer whales and sharks). We attempted to ka and the western Aleutian Islands (> 8.2% partition the various sources of “additional” per year). Using a published correction mortalities as anthropogenic and as addifactor, we estimated the total non-pup pop-tional mortality including some predation. ulation size in Alaska of the western stock We classified 436 anthropogenic mortalities of Steller sea lions to be about 33,000 ani-and 769 anthropogenic plus some predation mals. Based on a published life table and mortalities as “mortality above replace-the current rate of decline, we estimate that ment”; this accounted for 26% and 46% of the total number of mortalities of non-pup the estimated total level of “mortality above Steller sea lions during 1991–2000 was replacement”, respectively. The remaining about 6,383 animals; of those, 4,718 (74%) mortality (74% and 54%, respectively) was are mortalities that would have occurred if not attributed to a specific cause and may be the population were stable, and 1,666 (26%) the result of nutritional stress.

In utero domoic acid toxicity: a fetal basis to adult disease in the California sea lion (Zalophus californianus)

California sea lions have been a repeated subject of investigation for early life toxicity, which has been documented to occur with increasing frequency from late February through mid-May in association with organochlorine (PCB and DDT) poisoning and infectious disease in the 1970's and domoic acid poisoning in the last decade. The mass early life mortality events result from the concentrated breeding grounds and synchronization of reproduction over a 28 day post partum estrus cycle and 11 month in utero phase. This physiological synchronization is triggered by a decreasing photoperiod of 11.48 h/day that occurs approximately 90 days after conception at the major California breeding grounds. The photoperiod trigger activates implantation of embryos to proceed with development for the next 242 days until birth. Embryonic diapause is a selectable trait thought to optimize timing for food utilization and male migratory patterns; yet from the toxicological perspective presented here also serves to synchronize developmental toxicity of pulsed environmental events such as domoic acid poisoning. Research studies in laboratory animals have defined age-dependent neurotoxic effects during development and windows of susceptibility to domoic acid exposure. This review will evaluate experimental domoic acid neurotoxicity in developing rodents and, aided by comparative allometric projections, will analyze potential prenatal toxicity and exposure susceptibility in the California sea lion. This analysis should provide a useful tool to forecast fetal toxicity and understand the impact of fetal toxicity on adult disease of the California sea lion.

Spatial and temporal variation in the diet of the California sea lion (Zalophus californianus) in the Gulf of California, Mexico

Between June 1995 and May 1996 seven rookeries in the Gulf of California were visited four times in order to collect scat samples for studying spatial and seasonal variability California sea lion prey. The rookeries studied were San Pedro Mártir, San Esteban, El Rasito, Los Machos, Los Cantiles, Isla Granito, and Isla Lobos. The 1273 scat samples collected yielded 4995 otoliths (95.3%) and 247 (4.7%) cephalopod beaks. Fish were found in 97.4% of scat samples collected, cephalopods in 11.2%, and crustaceans in 12.7%. We identified 92 prey taxa to the species level, 11 to genus level, and 10 to family level, of which the most important were Pacific cutlassfish (Trichiurus lepturus), Pacific sardine (Sardinops caeruleus), plainfin midshipman (Porichthys spp.), myctophid no. 1, northern anchovy (Engraulis mordax), Pacific mackerel (Scomber japonicus), anchoveta (Cetengraulis mysticetus), and jack mackerel (Trachurus symmetricus). Significant differences were found among rookeries in the occurrence of all main prey (P≤0.04), except for myctophid no. 1 (P>0.05). Temporally, significant differences were found in the occurrence of Pacific cutlassfish, Pacific sardine, plainfin midshipman, northern anchovy, and Pacific mackerel (P<0.05), but not in jack mackerel (χ 2=2.94, df=3, P=0.40), myctophid no. 1 (χ 2=1.67, df= 3, P=0.64), or lanternfishes (χ 2=2.08, df=3, P=0.56). Differences were observed in the diet and in trophic diversity among seasons and rookeries. More evident was the variation in diet in relation to availability of Pacific sardine.