WR Marine Mammal

Question 1

Lecture 23: marine mammal communication

Dolphin communication

little study

Answer 1

Reyes Reyes, M.V., Tossenberger, V.P., Iñiguez, M.A., Hildebrand, J.A. and Melcón, M.L., 2016. Communication sounds of Commerson’s dolphins (Cephalorhynchus commersonii) and contextual use of vocalizations. Marine Mammal Science, 32(4), pp.1219-1233.

· Provides the first evidence that Commersons dolphins produce lots of sounds, with whistles and broad-band clicks (bbc) having a frequency of below 100kHz, which previously, was believed could not happen.

· The whilsts recorded were associated with parental care, whereas the bbc are probably used for communication between adults.

· The study describes nonecholocation signals produced by this species of dolphin.

· They recorded three types of sound.

Question 2

long term behavioural record from whale

Answer 2

Schorr et al., 2014

First Long-Term Behavioural Records from Cuvier’s Beaked Whales (Ziphius cavirostris) Reveal Record Breaking Dives

Study:

· Used satellite-linked tags to record the diving behavior and locations of eight Ziphius off the Southern California coast for periods up to three months

· The dive depth and duration allowed the partitioning of all dives into ‘‘deep’’ and ‘‘shallow’’ classes

· The Inter-Deep Dive Interval (IDDI) and Deep diving rate were calculated

Question 3

Schorr et al., 2014

First Long-Term Behavioural Records from Cuvier’s Beaked Whales (Ziphius cavirostris) Reveal Record Breaking Dives

the results

Answer 3

Results:

· Eight tags were deployed on Ziphius at SOAR from 2010 to 2012, providing data for periods of up to three months

· In total, tagged whales performed 1142 deep dives to a group mean depth of 1401 m and duration of 67.4 min, and 5685 shallow dives averaging 275 m and 21.0 min.

· The deepest dive reached 2992 m, and the longest dive lasted 137.5 min, exceeding the previously reported maximum depth pf 1104m

· Surfacing bouts averaged less than 2 min, reflecting this species’ exceptionally short gas exchange interval relative to dive duration

· Ziphius spend significantly more time in waters above 50 m at night than they do during the day (all but one of 22 surfacing bouts longer than 60 min occurred at night).

· Whales foraged approximately 7 times per day

Question 4

Schorr et al., 2014

First Long-Term Behavioural Records from Cuvier’s Beaked Whales (Ziphius cavirostris) Reveal Record Breaking Dives

Critical analysis

Answer 4

Critical analysis:

· Ziphius in Hawai‘i conducted approximately 10 deep dives daily (Baird et al., 2006), and whales in the Ligurian Sea conducted 11–12 foraging dives per day (Baird et al., 2008). Could’ve been due to deeper dives requiring longer recovery time however Baird et al., 2008 found that on average, deep dives in this study were not dramatically deeper and were of similar duration to those observed elsewhere

· Small sample size- cannot be representative of the entire population

· Exposure to MFA sonar could’ve changed their feeding- resulting in increased dive duration, prolonged cessation of foraging, and rapid swimming away from the stimulus

Question 5

Whistles and clicks from dolphins

the study

Answer 5

Rasmussen and Miller, 2002

Whistles and clicks from white-beaked dolphins, Lagenorhynchus albirostris, recorded in Faxaflói Bay, Iceland

Study:

· Field recordings of whistles and clicks from whitebeaked dolphins were made in Faxaflói Bay, during the summers of 1997 and 1998

· Whistles and clicks were recorded from a 10 m fibreglass motorboat with hydrophones over the side of the boat at a depth of about 4 m

· Behaviour of the dolphins was divided into four categories: traveling, resting, socializing, and feeding

· The dolphins could be observed under water from the boat and an estimated distance from the dolphin to the hydrophone was noted.

Question 6

Rasmussen and Miller, 2002

Whistles and clicks from white-beaked dolphins, Lagenorhynchus albirostris, recorded in Faxaflói Bay, Iceland

The results

Answer 6

Results

· A total of 1536 whistles were analysed, all of which were recorded in 1997

· No whistles were heard when dolphins were feeding or travelling

· Whistles were only heard only heard and recorded when white-beaked dolphins were socially active near the water surface, supporting the idea that white-beaked dolphin use whistles for communication and that whistles are not important when traveling or resting.

· Whistles from white-beaked dolphins contained higher frequencies than reported from other dolphin species

· Spectral and temporal properties of clicks from white-beaked dolphins resembled the echolocation clicks produced by bottlenose dolphins, suggesting white-beaked dolphins use the clicks for echolocation

· Taxonomically related species could have similar ancestral whistle patterns and sound production anatomy contributing to similar whistle characteristics.

Question 7

Rasmussen and Miller, 2002

Whistles and clicks from white-beaked dolphins, Lagenorhynchus albirostris, recorded in Faxaflói Bay, Iceland

Critical analysis

Answer 7

Critical analysis

· More confident White-beaked dolphins could’ve appeared closer to the boat, suggesting that the sampled individuals is dependent on their behaviour

· The more varied whistle repertoire compared Moore and Ridgway, (1995) which could have reflected the large sample size

Question 8

Signature whistle shape conveys identity information to bottlenose dolphins

The study

Answer 8

Janik et al., 2006

Signature whistle shape conveys identity information to bottlenose dolphins

Study:

· From 1989 to 1994, we completed 38 playback experiments, which included 21 playbacks to independent offspring, 11 playbacks to mothers, and six playbacks to females from different bands

· Used playback experiments to test whether there is sufficient information in signature whistles for individual recognition.

· The primary target groups for these experiments were mothers and independent offspring that were no longer associating together continuously

· In total, 20 different individuals were used as target animals in the 11 paired trials

Question 9

Janik et al., 2006

Signature whistle shape conveys identity information to bottlenose dolphins

Results

Answer 9

Results

· These playback experiments demonstrate that bottlenose dolphins are capable of discriminating between whistles of different familiar individuals, and that they recognize the predicted individual in symmetrical paired experiments.

· Supports the idea that individuals do have concepts of one another as individuals and that they track the history of their individual relationships.

· It is likely that recognition of individuals is important in maintaining long-term associations, and that signature whistles function in effecting this recognition

· Results suggest that not only that dolphins recognize their kin or associates, but also that they are motivated to respond to them

Question 10

Janik et al., 2006

Signature whistle shape conveys identity information to bottlenose dolphins

Critical analysis

Answer 10

Critical analysis

· Unethical- study show three target animals required to complete the pairs died

· Six experiments were aborted after only half of the experiment had been completed because one of the stimulus animals died or disappeared, and playback of whistles of dead or possibly dead animals could have confounded results.

· Tyack & Sayigh (1997) pointed out that variations in the vocal tracts of animals may lead to vocal variability among individuals; these voice cues can lead to individual recognition in terrestrial animals such as humans.

· Discrimination could have been based on voice features because original recordings of whistles were used

Question 11

Indo-Pacific dolphins whistles

Answer 11

Gridley et al., 2012

Whistle vocalizations of Indo-Pacific bottlenose dolphins (Tursiops aduncus) inhabiting the south-west Indian Ocean

Study:

· Acoustic recordings were made from groups of dolphins passing through the inshore waters of Plettenberg Bay (PB), South Africa and at two sites separated by 80 km north and south of Zanzibar Island

· Boat surveys were carried out to locate dolphins and conduct focal follows- Each encounter began with a period of photo-identification to determine the individuals present and was followed by a period of acoustic data collection using the equipment.

Question 12

Gridley et al., 2012

Whistle vocalizations of Indo-Pacific bottlenose dolphins (Tursiops aduncus) inhabiting the south-west Indian Ocean

Results

Answer 12

Results

Results:

· In total, more than 5236 whistle contours were identified from recordings of T. aduncus, of which 1677 were of a high enough quality for the frequency contour to be extracted.

· Whistle contours from ZB had a steeper gradient and more positive aspect and usually ended around 4 kHz higher in frequency than those from PB

· Overall distribution of adopted frequencies used between two regions differed by less than 1 kHz

· The trends in the start and minimum frequency reflect the pattern of intra-specific genetic differentiation in T. aduncus, perhaps indicating an influence of genetic factors

· The frequency parameters of T. aduncus are generally much lower than T. truncatus

Question 13

Gridley et al., 2012

Whistle vocalizations of Indo-Pacific bottlenose dolphins (Tursiops aduncus) inhabiting the south-west Indian Ocean

Critical analysis

Answer 13

Critical analysis:

· Only one of the 1389 whistle contours identified from PB was bandwidth limited, and none of the contours from ZB were

· Inter-specific variation in whistle parameters cannot be explained by differences in the social structure or habitat preference of T. aduncus and the coastal form of T. truncatus, as these do not vary consistently between the species

· The differences in the frequency parameters of these species may be related to differences in the sound production structures, such as morphological variation associated with cranial characteristics, however this would require experimental testing

· Key similarities in the social organization, behavior and ecology of T. aduncus and the coastal form of T. truncatus, combined with their genetic relatedness suggest that T. aduncus may use signature whistles to communicate identity information- However, this has yet to be demonstrated conclusively in captive or wild populations and the ability for vocal production learning

· Study did not investigate the functionally different call types- further empirical testing is required to determine whether this species uses signature whistles in the same way as T. truncatus.

Question 14

Reproductive behaviour encyclopedia

Answer 14

Marine mammal reproduction patterns

Fedak et al, 2009. Reproductive behaviour, Encyclopedia of marine mammals (second edition), pp.943-955

• -One instance of parental care in pinnipeds = male galapagos sea lions will mob sharks around the colonies in order to protect mother and babies.
• -Female gray seals are not receptive to males until they enter estrus (sexual receptivity). If males try to make an advance at the female before she is ready, the females will threaten the males and make loud vocalisations to alert surrounding females of his presence. In very few cases fights between males and females break out.
• -In elephant seals if the males makes a premature advance, the unreceptive female may slap her flippers quickly in a swimming motion and slap the male. They quickly take note of this and move onto another female.
• -Manatee females mate with several males (polyandy). Calves are born underwater and remain with mother for 1-4 years, in which they stay in contact using acoustics.
• -Walruses live in polygynous groups. Pups are born on ice or land but nurse in the water. Only pinniped group where maternal foraging and postnatal care occur at the same time- baby walruses will nurse upside down with its hind flippers at the surface when its mother feeds.

Question 15

Marine mammal locomotion, physiology and senses

Costa, D 2009- Osmoregulation, Encyclopedia of Marine mammals (second edition), pp. 801-806

Answer 15

• A dolphin that eats a squid will receive 3 times as many electrolytes than if it ate a fish. This is because the internal fluid concentration of invertebrates is that of seawater whereas vertebrates contain ⅓ of the electrolyte contents.
• Manatees have access to freshwater, therefore, can drink that in order to flush out excess electrolytes and osmoregulate.
• Mammals cannot excrete salt across their skin as they have thick layers of blubber and fur and do not sweat.
• All excretion of salts occurs across the kidney (reniculated) as marine mammals have no specialised glands to get rid of salt like some reptiles and birds do.
• The need to drink seawater varies depending on habitat and environment they live in. E.g fur seals in warm environments tended to drink more seawater compared to ones in cold environments
• Northern elephant seals can fast for months without access to food and water and get all the water they need from metabolic waste products (oxidation of fat and protein). This means they need to reduce water loss across thr skin, through repiration (hold breath)

Question 16

Hydrodynamic flow control in marine mammals

The study

Answer 16

Fish et al., 2008- conference paper

Hydrodynamic flow control in marine mammals

Active flow control mechanisms use movement of the propulsive appendages and activation of body musculature to modify the wake flow structure.

Passive mechanisms rely on structural and morphological components of the body, which dictate flow over the body surface

Question 17

Fish et al., 2008- conference paper

Hydrodynamic flow control in marine mammals

Flexible propulsors

Answer 17

• Flexible propulsors
• The propulsive hydrofoils of cetaceans, flukes, are lateral extensions of the distal tail. Biomechanically, the flukes act like a pair of oscillating wings (Vogel 1994).
• Thrust is generated as a component of an anteriorly directed lift force as the flukes are vertically oscillated
• The hydrodynamic models, which were used to estimate thrust production and propulsive efficiency, considered the flukes as rigid hydrofoils- However, these models did not account for the flexibility of the flukes, but considered them rigid structures
• · The flexible components of the dolphin flukes in conjunction with its propulsive oscillations are expected to enhance efficiency and energy economy
• Cetaceans are able to adjust thrust production and efficiency by controlling the angle of attack of the oscillating flukes - Maintenance of a positive angle of attack ensures thrust generation throughout the majority of the stroke cycle.
• Flexibility across the chord can increase propulsive efficiency
• The curvature of the flukes increases more at the lowermost position of the downstroke compared the middle of the stroke
• § However, increased chordwise flexibility may subject the flukes and the speed of the animal to limitations.

Question 18

Fish et al., 2008- conference paper

Hydrodynamic flow control in marine mammals

Streamlining

Answer 18

Streamlining

• · Fusiform design resembling an elongate teardrop with a rounded leading edge extending to a maximum thickness and a slowly tapering tail.
• · Streamlining minimizes drag by reducing the magnitude of the pressure difference over the body
• § This reduced pressure difference allows water in the boundary layer to flow without separation from the body surface until near the trailing edge.
• Streamlining can be determined by fineness ratio (FR ¼ body length/maximum diameter)
  
  • § Considered to provide the least drag with maximum volume
  • § However a crude indicator of the streamlining of the body, because it does not provide information on changes in body contour.
• Another method of determining streamline efficiency is the position of the maximum thickness; the shoulder.
  
  • § This is where transition from laminar to turbulent flow and boundary layer separation are likely to occur.
    
    • § Position of the shoulder is displaced posteriorly - similar to engineered wings with ‘‘laminar’’ profiles, which reduce drag through maintenance of laminar boundary flow.
• Shoulder position can vary in pinnipeds due to ability to extend the neck during rapid swimming
  
  • § Could modify the flow over the anterior of the seal and reduce drag by extending the region of laminar flow. Such a drag reduction could aid seals in catching fast swimming, elusive prey.
• Cells of epidermis are produced rapidly, which promotes a high rate of skin sloughing
  
  • § This increased skin sloughing deters organisms, such as barnacles, from attaching to the skin and thus minimizes drag
• The lack of arrector pili muscles in seals and sea otter permits the pelage to lie flat in water minimizing resistance to swimming.

Question 19

Fish et al., 2008- conference paper

Hydrodynamic flow control in marine mammals

Bumpy surfaces

Answer 19

• Seal vibrissae- The vibrissae of phocid seals have an ellipsoidal crosssection with regularly repeating sequence of constrictions or wavy profile along its length
  
  • § The beading may decrease drag by acting as vortex generators
• Cetacean tubercles- Small bumps are observed in discrete locations on the bodies of porpoises (family Phocoenidae)
  
  • § The position of the tubercles function in turbulizing the water flow to modify the tip vortex shed from the dorsal fin
• The tubercles of the humpback whale flipper function to generate vortices by excitation of flow to maintain lift and prevent stall at high angles of attack
  
  • § the leading edge tubercles of the humpback whale flipper provide a passive means of flow control over a lifting surface

Question 20

The metabolic cost of swimming and reproduction in harbor porpoises (

The srudy

Answer 20

Gallagher et al., 2018

The metabolic cost of swimming and reproduction in harbor porpoises (Phocoena phocoena) as predicted by a bioenergetic model

Study:

· The range of energetic costs of basal metabolism, locomotion, thermoregulation, and reproduction was estimated for porpoises, using a velocity-dependent bioenergetic model to estimate the potential food requirements of this returning predator.

· Model assumed that adult male porpoises used energy for their basal metabolism, thermoregulation, and locomotion, while adult female porpoises have additional costs associated with pregnancy and lactation.

· Data set was composed of measurements of stranded porpoises from 1977 to 2016 in the San Francisco Bay

Question 21

Gallagher et al., 2018

The metabolic cost of swimming and reproduction in harbor porpoises (Phocoena phocoena) as predicted by a bioenergetic model

Results

Answer 21

• Results:
• · Drag, work, and metabolic cost of locomotion all increased exponentially with velocity.
• · The total metabolic rates of harbor porpoises were found to be relatively high compared to other cetacean species.
• · Male porpoises had the lowest total energetic costs while simultaneously pregnant and lactating females had the highest.
• · Pregnancy was found to only nominally increase overall energetics, even while including increased drag costs and work resulting from larger surface area during pregnancy.
• · The production of extra energy for thermal maintenance in harbor porpoises was found when the animal was moving less than approximately 2 m/s for female and male porpoises.
• § At the slowest speeds the model devoted less than a quarter of the total metabolic cost to thermoregulation for female porpoises
• · The total cost of pregnancy predicted by the model equated to only 12.9% of the basal metabolic rate
• · The cost of lactation represented 8.1 times the cost of pregnancy and approximated the basal metabolic rate of pregnant porpoises.

Question 22

Gallagher et al., 2018

The metabolic cost of swimming and reproduction in harbor porpoises (Phocoena phocoena) as predicted by a bioenergetic model

Critical analysis

Answer 22

Critical analysis

• In the development of the model several assumptions had to be made where data gaps occurred in the literature which could contribute to uncertainty in the model outputs.
• Cost of lactation was based on extremely limited data that exists for harbor porpoise milk transfer rates and milk composition, resulting in a potential overestimation of the cost of lactation.
• The results for costs of reproduction and total metabolic rates for each of the reproductive states are comparable to those reported by Yasui and Gaskin (1986), even though both used different techniques

Question 23

Williams, 1999

The evolution of cost-efficient swimming in marine mammals: limits to energetic optimization- review

Answer 23

Williams, 1999

• The evolution of cost efficient swimming in marine mammals: limits to energetic optimization- review
• The energetic challenges associated with changing from terrestrial to aquatic locomotion in primitive marine mammals were examined
  
  • § The transport, maintenance and locomotor costs of extant
  • § Extant terrestrial, semi-aquatic and marine mammals were considered representative of principal evolutionary hallmarks within marine mammal lineages.
• Maintenance costs (MC) of aquatic mammals are assessed from the rate of oxygen consumption (VO2)
• Presented the equation for total costs = total cost of transport (COTTOT), maintenance costs (MC), and locomotor costs (LC) for terrestrial, semi-aquatic and marine species
  
  • § COTTOT = MC + LC

Question 24

Population size, distribution, and behaviour of the coast of Zanzibar

The study

Answer 24

28 Marine mammal population structure, distribution and abundance

Population size, distribution, and behaviour of Indo-Pacific bottlenose (Tursiops aduncus) and Humpback (Sousa chinensis) dolphins off the south coast of Zanzibar.

(Stensland et al, 2006) – Per paper

• Along the South Coast of Zanzibar, East Africa the direct hunt of bottlenose and humpback dolphins has been directly replaced with the first tourism occurring in 1992.
• Uses mark-recapture techniques, by taking photographs of the dorsal fin to estimate the population size and asses anthropogenic threats.
• Bycatch in fishing gear has been recognized as the most serious threat to small cetaceans worldwide and in the East African region

Question 25

28 Marine mammal population structure, distribution and abundance

Population size, distribution, and behaviour of Indo-Pacific bottlenose (Tursiops aduncus) and Humpback (Sousa chinensis) dolphins off the south coast of Zanzibar.

Results

Answer 25

Results:

• Estimated a population of 179 bottlenose dolphins and 65 humpback dolphins in the 26km2 study area.
• Both species actively use only small parts of their coastal habitat and that the bottlenose dolphins were socializing and foraging to a larger extent in particular areas, these are important considerations in conservation management.
• The humpback dolphins were found closer to shore and in shallower water than the bottlenose dolphins indicating spatial separation between the species in the study area.
• Concludes the relatively small population sizes, limited distribution ranges and the magnitude of anthropogenic threats facing the Indo-Pacific bottlenose dolphins in the area, means the tourism industry is having a positive effect.

Question 26

28 Marine mammal population structure, distribution and abundance

Population size, distribution, and behaviour of Indo-Pacific bottlenose (Tursiops aduncus) and Humpback (Sousa chinensis) dolphins off the south coast of Zanzibar.

Possible critical analysis

Answer 26

Possible critical analysis

• Haven’t really got any good points
  
  • The study was taken from January to march from 1999 to 2002 – could suggest a different pattern may occur over the rest of the year.
  • The majority of dolphins were only sampled once, meaning many dolphins may have escaped sampling – but I think calculations included this.
• Could say the paper is very good for collecting data over 121 field days, reaching a level on the cumulative graph. They only used dolphins for the capture-recapture techniques that had clear markings on the dorsal fin - also calculating the proportion of dolphins that were unmarked.
  
  • Generic benefits of capture-recapture techniques.
  • Didn’t include spatial data from dolphins around tourist boats.

Question 27

mtDNA Zanzibar

Answer 27

Phylogenetic placement and population structure of Indo‐Pacific bottlenose dolphins (Tursiops aduncus) off Zanzibar, Tanzania, based on mtDNA sequences

(Särnblad et al, 2010) another paper of Per

Phylogenetics is the study of evolutionary relationships among species.

The study:

• The phylogeney of bottlenose dolphins found off southern and northern Zanzibar were examined using variation in mtDNA control region sequences.
• A large nucleotide difference (similar to the difference found between different species) between the western Indian Ocean (Zanzibar and South Africa) and the western Pacific Ocean population suggesting long term separation.
• Supports mark‐recapture photo‐identification data that has indicated that animals off southern Zanzibar form a small resident population.
• Further, the low nucleotide divergence (0.68%) among the Zanzibar haplotypes may be indicative of a long‐term small effective population size or could be the result of recent founder events or bottlenecks.
• The precautionary approach is to treat the T. aduncus found off northern and southern Zanzibar as separate management units when assessing the impact from bycatch, dolphin tourism, and other anthropogenic threats.

Question 28

Phylogenetic placement and population structure of Indo‐Pacific bottlenose dolphins (Tursiops aduncus) off Zanzibar, Tanzania, based on mtDNA sequences

(Särnblad et al, 2010) another paper of Per

Summary

Answer 28

Summary

This paper provides phylogenetic evidence that these animals have very limited distribution, which may make them more vulnerable to the threat of both hunting and disturbance from tourist boats, and effect the conservation methods that would be appropriate.

Bottlenose Dolphins are highly social with a fission–fusion grouping pattern where individuals are part of a larger society within which smaller, sometimes long‐term, associations form and dissolve. This paper shows the social structure is likely to have an impact on the population genetic structure.

Question 29

Harbour seal study

Answer 29

Abundance of harbour porpoise and other cetaceans in the North Sea and adjacent waters

(Hammond et al, 2002) – I’ve tried to cover the experimental design stuff Per was talking a lot about.

The study:

• Shipboard and aerial line transect surveys were conducted to provide accurate and precise estimates of abundance as a basis for conservation strategy in European waters.
• The survey, known as SCANS (Small Cetacean Abundance in the North Sea), was conducted in summer 1994 and designed to generate precise and unbiased abundance estimates.

Question 30

Abundance of harbour porpoise and other cetaceans in the North Sea and adjacent waters
(Hammond et al, 2002) – I’ve tried to cover the experimental design stuff Per was talking a lot about.

Survey design

Answer 30

• The survey area was stratified into blocks on the basis of logistical constraints.
• An experimental survey was conducted to test the proposed survey methods. It gathered data to allow preliminary estimation of the proportion of schools detected on the transect line and a correction factor for responsive movement.
• Most blocks (A-I) were surveyed by ships. Zigzag cruise tracks were selected to give a known, non‐zero, coverage probability to each point in the survey block
• Two platforms operated for searching on the boat, the primary and the tracker platform.
• Primary observers used the naked eye, concentring within the first 500m. They recorded the times, angles and radial distances to the detected schools, together with other relevant data (species, school size, orientation, etc.).
• The aim of the tracking platform was to identify animals sufficiently far enough away from the boat to not have been disturbed by the boat, using binoculars.
• There was a permanent roll of one person to identify duplicates between both the observers and both the platforms.
• Ariel surveys were flown in blocks that were either difficult to survey by ship or expected to have high densities of Phocoena phocoena.
• To estimate the likelihood of detection the variables included; sea state; school size; vessel; aspect (a variable indicating the orientation of the animal with respect to the observer’s line of sight); glare and swell height.

Question 31

Abundance of harbour porpoise and other cetaceans in the North Sea and adjacent waters

(Hammond et al, 2002) – I’ve tried to cover the experimental design stuff Per was talking a lot about.

Results

Answer 31

Results:

• Three species dominated the data. Harbour porpoise Phocoena phocoena (estimated population 341, 366) were encountered throughout the survey area except in the Channel and the southern North Sea. Whitebeaked dolphin Lagenorhynchus albirostris (7856) and minke whale Balaenoptera acutorostrata (8445) were found mainly in the north‐western North Sea
• Shortbeaked common dolphin Delphinus delphis were found almost exclusively in the Celtic Sea and the abundance was estimated as 75 450.

Question 32

Abundance of harbour porpoise and other cetaceans in the North Sea and adjacent waters

(Hammond et al, 2002) – I’ve tried to cover the experimental design stuff Per was talking a lot about.

Critical analysis

Answer 32

Critical evaluation:

Very good study – could highlight the size of the study and the survey design to back this up.

Question 33

Marine mammal foraging ecology and behaviour

Kastelein, 2009, Walrus, Encyclopedia of marine mammals

Answer 33

Kastelein, 2009, Walrus, Encyclopedia of marine mammals (second edition), pp.1294-1300.

• Walruses have extremely strong muscles for tongues which allows them to suction feed. This means they can create an area of low pressure inside their mouths to extract the soft body from inside a clam shell. They do not have strong muscles in their jaws therefore swallow alot of their prey whole. However, the muscles in their cheeks are strong which allows them to produce water jets from its mouths which allows it to uncover its prey from the sediment.
• They dive for up to 24 mins, spending 80% of this time at the seafloor searching for clams. They can eat between 40-60 clams on each dive.
• They use their whiskers to help find and determine prey items,

Question 34

Marine mammal foraging ecology and behaviour

feeding strategies and tactics, Encyclopedia of marine mammals (

Answer 34

Heithays & Dill, 2009, feeding strategies and tactics, Encyclopedia of marine mammals (second edition), pp.412-421.

• Leopard seals (Hydrurga leptonyx) use stalking and ambush tactics when foraging. Stalking seals use the ice to their advantage, and will swim under the ice below a penguin or seal and break through the ice at the last minute to eat the animal. They ambush penguins by waiting and hiding in between ice flows near a penguin landing beach and swimming underneath the animal where it will grab it from below.
• Manatees and dugongs are the only herbivores.

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