Brad Page

Assessing morphological and DNA-based diet analysis techniques in a generalist predator, the arrow squid Nototodarus gouldi

Establishing the diets of marine generalist consumers is difficult, with most studies limited to the use of morphological methods for prey identification. Such analyses rely on the preservation of diagnostic hard parts, which can limit taxonomic resolution and introduce biases. DNA‐based analyses provide a method to assess the diets of marine species, potentially overcoming many of the limitations introduced by other techniques. This study compared the effectiveness of morphological and DNA‐based analysis for determining the diet of a free‐ranging generalist predator, the arrow squid (Nototodarus gouldi). A combined approach was more effective than using either of the methods in isolation. Nineteen unique prey taxa were identified, of which six were found by both methods, 10 were only detected using DNA and three were only identified using morphological methods. Morphological techniques only found 50% of the total number of identifiable prey taxa, whereas DNA‐based techniques found 84%. This study highlights the benefits of using a combination of techniques to detect and identify prey of generalist marine consumers.

ESTIMATION OF PREGNANCY RATES AND REPRODUCTIVE FAILURE IN NEW ZEALAND FUR SEALS (ARCTOCEPHALUS FORSTERI)

Abstract Progesterone concentrations after implantation and the observation of live births were used to investigate the reproductive performance and timing of reproductive failure in New Zealand fur seals (Arctocephalus forsteri). Progesterone concentrations in females that gave birth were relatively low during early active gestation (8.6 ± 0.9 ng/ml) and increased significantly toward the end of the 1st trimester (14.9 ± 0.9 ng/ml). In contrast, progesterone concentrations in females that did not give birth remained low. Estimated pregnancy rates and live births varied significantly between years. In 2000, the overall reproductive success of mature females was low (25.7%) and 42.3% of reproductive failure occurred at or before implantation. In 2001 and 2002, reproductive rates were higher (56.5% and 63.5%, respectively) and reproductive failure was greatest (70% and 89.5%, respectively) in mid- to late active gestation. Reproductive failure during active gestation appears to be the most significant stage in determining reproductive success; however, in years of low reproductive success, failure before or at implantation also contributed significantly to reduced reproductive rates. The finding that significant fetal mortality occurs in late gestation reinforces the caution that the use of pregnancy rates, without consideration for the stage of gestation at which measurements were taken, can positively bias estimates of reproductive rates.

Dietary analysis of regurgitates and stomach samples from free-living Australian sea lions

Dietary remains recovered from Australian sea lion (Neophoca cinerea) digestive tracts and regurgitate samples from Seal Bay (Kangaroo Island, South Australia) were used to identify prey species consumed. Four of eight digestive tracts collected (50%) contained prey items located only in the stomach. On the basis of biomass reconstruction of cephalopod prey remains, octopus contributed 40% of the biomass in the samples, giant cuttlefish (Sepia apama) contributed 30% and ommastrephid squids contributed 14% biomass. The remains of several fish species were found in the samples: leatherjacket (Monocanthidae), flathead (Platycephalus sp.), swallowtail (Centroberyx lineatus), common bullseye (Pempheris multiradiata), southern school whiting (Sillago flindersi) and yellowtail mackerel (Trachurus novaezelandiae). Southern rock lobster (Jasus edwardsii) and swimming crab (Ovalipes australiensis) carapace fragments, little penguin (Eudyptula minor) feathers and bones and shark egg cases (oviparous species and Scyliorhinidae sp.) were also identified.

Effects of an Electric Field on White Sharks: In Situ Testing of an Electric Deterrent

Elasmobranchs can detect minute electromagnetic fields, <1 nVcm–1, using their ampullae of Lorenzini. Behavioural responses to electric fields have been investigated in various species, sometimes with the aim to develop shark deterrents to improve human safety. The present study tested the effects of the Shark Shield Freedom7™ electric deterrent on (1) the behaviour of 18 white sharks (Carcharodon carcharias) near a static bait, and (2) the rates of attacks on a towed seal decoy. In the first experiment, 116 trials using a static bait were performed at the Neptune Islands, South Australia. The proportion of baits taken during static bait trials was not affected by the electric field. The electric field, however, increased the time it took them to consume the bait, the number of interactions per approach, and decreased the proportion of interactions within two metres of the field source. The effect of the electric field was not uniform across all sharks. In the second experiment, 189 tows using a seal decoy were conducted near Seal Island, South Africa. No breaches and only two surface interactions were observed during the tows when the electric field was activated, compared with 16 breaches and 27 surface interactions without the electric field. The present study suggests that the behavioural response of white sharks and the level of risk reduction resulting from the electric field is contextually specific, and depends on the motivational state of sharks.

Age and reproductive maturity of New Zealand fur seals (Arctocephalus forsteri) in southern Australia

Abstract New Zealand fur seals (Arctocephalus forsteri) are common in the Australian-New Zealand region, but vital demographic data are lacking. Accurate determination of the age of individuals is critical to the study of age-specific life-history parameters. A cross-sectional sample of female and male New Zealand fur seals was caught and animals were individually marked on Kangaroo Island, South Australia, between 2000 and 2003. Seals were aged through examination of a postcanine tooth, which was removed from each animal. Annual formation of cementum layers was confirmed and accuracy in age estimation was determined by examination of teeth removed from individuals of known age. Indirect methods of assessing reproductive maturity based on characteristics of mammary teats indicated that females 1st gave birth between 4 and 8 years of age, with an average age at reproductive maturity (ARM) of 5 years. No females were observed to breed beyond 22 years. Age of 1st territory tenure in males ranged from 8 to 10 years. Variation in ARM between individuals appears to be related in part to body size and condition. Classification of mammary teat status in combination with techniques for aging live animals provided a means of assessing ARM in the absence of extensive longitudinal data.

Interspecific differences in male vocalizations of three sympatric fur seals (Arctocephalus spp.)

This study investigated species recognition based on bark calls and full threat calls (FTCs) in three fur seal species, Antarctic Arctocephalus gazella, subantarctic A. tropicalis and New Zealand A. forsteri, that breed sympatrically and hybridize at subantarctic Macquarie Island. Bark calls, which are produced by males in male‐female interactions, were more species-specific than their full threat calls, suggesting that bark calls could be used in species recognition and female mate choice. Further, the bark calls of A. tropicalis were more species-specific than those of A. gazella and A. forsteri, suggesting that divergence of calls between species is a consequence of phylogenetic distance, or has resulted from sexual selection through female mate choice. We believe the latter is more probable as we did not observe similar divergence in the FTCs of males. As such, the highly divergent bark calls of A. tropicalis may have resulted from sexual selection that has promoted pre-mating isolation via the process of reinforcement.

INDIVIDUAL VOCAL TRAITS OF MOTHER AND PUP FUR SEALS

ABSTRACT This study investigates individual vocal traits in three species of fur seal: Antarctic fur seal Arctocephalus gazella, Subantarctic fur seal A. tropicalis, New Zealand fur seal A. forsteri and their hybrids. The attraction calls of mothers and pups were highly stereotyped within each individual and markedly different between individuals. Pup attraction calls (emitted by females) were more variable between individual A. tropicalis and A. forsteri than between individual hybrids and A. gazella. However, such a pattern was not evident for female attraction calls (emitted by pups). Pup attraction calls and female attraction calls were both generally tonal calls overlain with regions of pulses. Female attraction calls had relatively high fundamental frequencies. The importance of individual vocalisations for mothers and pups is best appreciated in relation to maternal fitness and offspring survival: individual vocalisations are favoured by natural selection as they facilitate rapid reunion when mothers return from foraging trips, ensuring maternal resources are not invested in unrelated pups.

Fur seals at Macquarie Island: post-sealing colonisation, trends in abundance and hybridisation of three species

Commercial sealers exterminated the original fur seal population at Macquarie Island in the early 1800s. The first breeding record since the sealing era was not reported until March 1955. Three species of fur seal now occur at Macquarie Island, the Antarctic (Arctocephalus gazella), subantarctic (A. tropicalis) and New Zealand (A. forsteri) fur seal. Census data from 54 breeding seasons in the period 1954–2007 were used to estimate population status and growth for each species. Between the 1950s and 1970s, annual increases in pup production for the species aggregate were low. Between 1986 and 2007, pup production of Antarctic fur seals increased by about 8.8% per year and subantarctic fur seals by 6.8% per year. The New Zealand fur seal, although the most numerous fur seal species on Macquarie Island, has yet to establish a breeding population, due to the absence of reproductively mature females. Hybridisation among species is significant, but appears to be declining. The slow establishment and growth of fur seal populations on Macquarie Island appears to have been affected by its distance from major population centres and hence low immigration rates, asynchronous colonisation times of males and females of each species, and extensive hybridisation.

Convergence of marine megafauna movement patterns in coastal and open oceans

Significance Understanding the key drivers of animal movement is crucial to assist in mitigating adverse impacts of anthropogenic activities on marine megafauna. We found that movement patterns of marine megafauna are mostly independent of their evolutionary histories, differing significantly from patterns for terrestrial animals. We detected a remarkable convergence in the distribution of speed and turning angles across organisms ranging from whales to turtles (epitome for the slowest animals on land but not at sea). Marine megafauna show a prevalence of movement patterns dominated by search behavior in coastal habitats compared with more directed, ballistic movement patterns when the animals move across the open ocean. The habitats through which they move will therefore need to be considered for effective conservation. The extent of increasing anthropogenic impacts on large marine vertebrates partly depends on the animals’ movement patterns. Effective conservation requires identification of the key drivers of movement including intrinsic properties and extrinsic constraints associated with the dynamic nature of the environments the animals inhabit. However, the relative importance of intrinsic versus extrinsic factors remains elusive. We analyze a global dataset of ∼2.8 million locations from >2,600 tracked individuals across 50 marine vertebrates evolutionarily separated by millions of years and using different locomotion modes (fly, swim, walk/paddle). Strikingly, movement patterns show a remarkable convergence, being strongly conserved across species and independent of body length and mass, despite these traits ranging over 10 orders of magnitude among the species studied. This represents a fundamental difference between marine and terrestrial vertebrates not previously identified, likely linked to the reduced costs of locomotion in water. Movement patterns were primarily explained by the interaction between species-specific traits and the habitat(s) they move through, resulting in complex movement patterns when moving close to coasts compared with more predictable patterns when moving in open oceans. This distinct difference may be associated with greater complexity within coastal microhabitats, highlighting a critical role of preferred habitat in shaping marine vertebrate global movements. Efforts to develop understanding of the characteristics of vertebrate movement should consider the habitat(s) through which they move to identify how movement patterns will alter with forecasted severe ocean changes, such as reduced Arctic sea ice cover, sea level rise, and declining oxygen content.