Marine Top Predators

Question 1

Hvad er predator impacts? Effects of predation? direkte og indirekte impacts

Answer 1

Direct mortality of prey species via consumption (also selection)
Effects on food webs - changes in mass and energy flows. Potential cascading effects on lower throphic levels and food webs.

Indirect effects - avoidance responses of prey. Horizontal and vertical changes of prey.

Question 2

Prey distribution can make some predators “generalists vs. specialists”. Forklar disse to begreber.

Answer 2

Generalist predators have, by definition, several alternative prey species between which they may ‘switch’, depending on which prey species are currently most abundant. Specialist but nomadic bird predators may also track high local densities of their prey

A generalist species is able to thrive in a wide variety of environmental conditions and can make use of a variety of different resources (for example, a heterotroph with a varied diet). A specialist species can thrive only in a narrow range of environmental conditions or has a limited diet

Question 3

Nævn 4 metoder for at estimere hvad en predator spiser

Answer 3

Mavesæksundersøgelser
eDNA
Stable isotopes of predator and prey: C, N, isotopes. Intregrates
Fatty acid composition

Question 4

Forklar mavesæksundersøgelser. Og hvor mange maver er nok? fordelee og ulemper

Answer 4

Mavesæksundersøgelser / visual morphometric ID of prey remains in stomach: Man kan se hvad predatoren spiser. Er den nemmeste metode. Kræver ikke udstyr. Dog får man kun et snap-shot billede af hvad denne predator har spist NETOP der.

Fordele: Man kan også se andet end bare arter. Om predatoren spiser byttet helt, om det er freshy consumed (hvor hurtigt ting bliver fordøjet og hvor meget de kan spise på en dg og dermed predation impact på bytte-arter). Bytte størrelse kan sammenlignes med predator størrelse og se om der er size specific predation. So combine digestive state and prey size and estimate daily rations.

Ulemper: Only detects hard parts or recently ingested whole prey. Soft-bodies can get lost.

How many stomachs should be sampled: More stomachs -> more species detected (up to a maximum). Man når et punkt dog, hvor mere sampling effort vil være nogenlunde ligegyldigt. Man kan lave undersøgelser (species accumulation curve) af hvor mange n man skal bruge. Man skal bruge ca. 100 maver.
Så hvis man læser et papir, hvor de kun har 20 maver - skal man lige overveje om det er repræsentativt.

Question 5

Forklar eDNA brug til undersøgelse af estimering af hvad en predator spiser. fordele og ulemper

Answer 5

eDNA: Environmental DNA in a sample. Man kan bruge eDNA i maveundersøgelserne. Stomach digestive fluids. Entire species compositions incl. soft-bodies. Det dog lidt mere technical demanding. Der er ingen size info about prey, hard to get abundance estimates (fordi eDNA ikke fortæller noget om, hvor mange der er eller hvor store de er).

Question 6

Forklar “Stable isotopes of predator and prey” til brug til undersøgelse af estimering af hvad en predator spiser

Answer 6

Stable isotopes of predator and prey: C, N, isotopes. Intregrates feeding over longer time period than stomach analysises. Some tissues change isotop composition faster than others (liver, days-weeks) (muscle, months-years). C-isotopes can trace sources of C in food webs. N isotopes can indicate pposition in food webs (thropic level 1=primary producer, 2 = grazer, 3=predator, 4=higher level predator). Ratioes will change higher up you come in the food web. Can compare isotope ratios with prey and lower thropic levels to see bioaccumulation effects and identify thropic levels. See how long food webs are.
Der er forskellige isotope af N i vandet - nogle fytoplankton vil optage nogle af de bestemte og andre fytoplankton vil optage andre. Så kan man se i fx muskelvæv af predatorer hvilke isotopes de har og se hvad de har spist.

Question 7

Forklar “Fatty acid composition” til brug til undersøgelse af estimering af hvad en predator spiser

Answer 7

Fatty acid composition: Some fatty acids are essential for fish (ligesom for mennesker er der nogle de ikke selv kan producere). Der er nogle Fa der kun bliver produceret af bestemte fytoplankton. Can potentially link FA composition of fish to PP and ocean mixing processes (mixing > diatoms -> essential FAs).

Question 8

Forklar top down control?

Answer 8

Trophic cascades in marine food webs
Cascading effects of the loss of predators

Loss of predators. Small Predator fish increases. Eats zooplanktons. Flere alger.
Fishing induced trophic cascades: Når top predators bliver fisket ned.
Predators kan derfor have controlling effects on multiple trophic levels in marine food webs - not only their own prey.

Question 9

Hvad er en af grundene til, at tun migrerer ? Og hvordan kan det påvirke populationer i områderne de migrerer til?

Answer 9

Byttedyr der rykker sig: Makrel fx som flytter sig, expander til Island og Grønland og så flytter tun med.

De er en top predator der kommer ind de steder og spiser en masse ting, så deres seasonal foraging can be important for populations and food webs.

Question 10

Når man tagger narhvaler - hvad er så det man måler ?

Answer 10

CTD: Salinity, temp, depth
GPS: position (50 m accuracy)
Depth, acoustic % 3D
Heart rate & breaths
Fanges i net: Måles: Length
3 types of acutic signals: Ecolocation clicks, buzzes & calls. Nogle af lydene er til kommunikation.
Foraging: Man kan se hvor de fodre henne - også hvilke lyde de laver imens. De foretrækker kolde steder.

Question 11

Hvad bruger hvaler deres lyde til? Og rejser høje eller lave frekvenser bedst i vand?

Answer 11

Lyd: De bruger lyd for orientation og kommunikation. Active location to find prey. Derfor kan lyde i vandet være et problem. Lyd rejser meget nemt vand - nemmere end i luft. Lave frekvenser rejser bedre, op til 100 km. Også det mange af de store hvaler bruger - men også som lyde af store skibe er. De højere frekvenser er kortere afstand.

Question 12

Forklar “ambient noise” og hvor langt kan hvaler høre hinanden foruden ambient noise?

Answer 12

Ambient noise: Lyd der er i naturlige miljøer allerede. I en larmende fjord kan hvaler hører hinanden ca. 1 km. I open ocean kan det være op til 60 km.

Question 13

Hvordan har narhvaler det med lyde? Påvirker det hvordan de dykker og deres fødesøgning?

Answer 13

Anthropogenic noise: Narwhales show extreme sensitivity to sound. Target depth mindskes. Probability for at dykke dybt mindskes jo højere lyd der er i området fordi de ikke vil være i overfladen og recover fra sidste dyk så de laver flere små dyk for at undgå overfladen. Decrease in foraging.

Question 14

Hvordan sparer hvaler energi ved længere dyk ift. kortere mere frequent dyk?

Answer 14

Locomotion: Koster energi for hvalen. Når de dykker dybt så svømmer de til at starte med, men så begynder de at synke/sinking/gliding hvor de sparer energi og så bruger de energi dernede. Når de kun dykker lavt, så glider de ikke og ofte vil de bruge energi på at svømme ned fordi de vil undgå lyden.

Question 15

Hvad er nogle af de store marine mammals i DK?

Answer 15

Habour seal, grey seal, harbour porpoise, white sided dolphin, bottlenose dolphin, common dolphin,

Question 16

Forklar hvad the Whale (counter) pump er

Answer 16

Whale (counter) pump: Hvaler fertilizer overflade vand når de pøller. Deres lig fertilizer bunden når de dør.

Question 17

Forklar kort trophic cascades - hvad er det og hvad kan forårsage det

Answer 17

Changes in the abundance of individuals in one trophic level can elicit direct and indirect changes on other trophic levels, a process known as a trophic cascade .

Generally, cascades are initiated by any external perturbation that can lower the abundance of some part of the community.

Thus apart from fishing, another example of an external perturbation is the appearance of migrating larger predators that consume substantial amounts of prey over a relative narrow time period

Question 18

Forklar regime shifts in large marine
ecosystems

Answer 18

Ecosystem regime shifts are drastic large time- and space-scale shifts in abundances of major components of marine biological communities

We consider regime shifts in marine ecosystems to be changes that are abrupt, high-amplitude and low-frequency events that occur over large spatial scales and that are evident in multiple bio-physical attributes over a range of trophic levels

high fishing pressure has been suggested to trigger regime shifts in large marine ecosystems and are likely responsible for recent changes in the fish community structure in coastal ecosystems

Question 19

Atlantic bluefin tuna (Thunnus thynnus) is one of the largest apex predators in some north Atlantic marine ecosystems and have declined due mainly to

Answer 19

overexploitation

Question 20

Hvad er det der kan ske, hvis der pludselig kommer en masse store top-predators til et område?

Answer 20

Der kan forekomme trophic cascades - lowering i abundance of some part of the community

Question 21

Hvis der kommer trofisk cascade fra torsk (top-predator) til forage fisk, zooplankton og fytoplankton, hvad hedder det så? (Tal-mæssig-kaskade)

Answer 21

Four-level trophic cascade

Question 22

What years was it the tuna stopped migrating into the North Sea regions?

Answer 22

1960’erne

Question 23

Tuna migrated from the Meditiranian Sea spawning ground up to North Sea to forage. How much time did tuna stay in the North Sea region?

Answer 23

2-4 måneder (før de migrere tilbage sydpå i efteråret igen)

Question 24

Hvilke byttedyr er mainly tunens foretrukne oppe hos os?

Answer 24

Herring and Mackerel (migrerende arter også)

Question 25

Hvad er passive acoustic monitoring

Answer 25

Passive acoustic monitoring, or just ‘acoustic monitoring’, involves surveying and monitoring wildlife and environments using sound recorders (acoustic sensors). These are deployed in the field, often for hours, days or weeks, recording acoustic data on a specified schedule.

Question 26

What are some threats to harbour porpoises?

Answer 26

Miljø gifte akkumulering, fangst i garn, fiskeri generelt, mangel på føde

Question 27

Hvad er Behavior-mediated trophic cascades

Answer 27

Behavior-mediated trophic cascades refer to indirect effects on ecosystems caused by changes in the behavior of organisms due to predation risk. In these cascades, predators influence the behavior of their prey, leading to alterations in prey population sizes or behaviors that, in turn, affect lower trophic levels and ecosystem dynamics.

For example, if the presence of a predator alters the behavior of its prey, such as causing them to avoid certain areas or change their feeding patterns, it can indirectly affect the abundance or behavior of other species within the ecosystem. This can have cascading effects on the entire food web, impacting community structure, species interactions, and ecosystem functioning. Behavior-mediated trophic cascades highlight the importance of considering not only direct predation but also the indirect effects of predator-prey interactions on ecosystem dynamics

Question 28

marine mammals influence ecosystems through various pathways, including their behavior.
Non-consumptive effects - forklar dette

Answer 28

Non-consumptive effects, such as

risk effects and
behavior-mediated trophic cascades,

Changes in predator abundance and human disturbance can alter marine mammal and prey behaviors, leading to cascading effects on the ecosystem.
Additionally, marine mammals contribute to ecosystem dynamics through foraging tactics that benefit other species (især fugle) and by translocating nutrients across spatially distinct food webs.
Overall, understanding the complex interactions involving marine mammals is essential for ecosystem management and conservation

• they can facilitate the foraging of other species, like seabirds but also humans, by making previously unavailable prey accessible or preventing the escape of these species to deeper waters
• nutrient transport supporting other communities (bottom up)

Question 29

Some marine mammals are themselves at risk from predators. What are common tactics for reducing risk of predation?

Answer 29

Over longer time periods, habitat shifts and group
formation appear to be the most common tactics for
reducing risk.

Also either physical defence (fight) or escape (flight).

The former tactic is adopted by species with robust bodies
and slow swimming speeds (e.g. grey whales, right
whales Eubalaena spp., humpback whales),

while the latter is used by fast-swimming species with

Question 30

(ikke et spørgsmål)
Predation risk also appears to have helped to shape migratory routes and seasonal movements of some marine mammals, including large
whales.

Risk effects are also likely to drive
daily movements of some marine mammals. In the
tropics, spinner dolphins enter atolls, sheltered bays
and lagoons through reef channels in the morning for
resting and socializing, and leave in the afternoon to
feed offshore overnight

Answer 30

For instance, humpback whales embark on
what are the longest known mammal migrations
from low-latitude breeding to high-latitude feeding
grounds in so doing, they undoubtedly pay substantial energetic
costs

elevated predation risk from killer
whales at high latitudes may have contributed to the
evolution of whale migrations where they annually
abandon productive foraging grounds to reproduce
at safer latitudes.

Question 31

While ‘risk effects’ generally have been defined as occurring relative to the risk of mortality inflicted by predators, other forms of risk can drive behavioural decisions that may impact a species’ ecological role
and importance.
Other forms of risk may involve that associated with harassment by con- or heterospecifics that may be fatal or result in injury or
reduced foraging.

Answer 31

For example, off the British Isles and the coast of California, harbour porpoises are killed, but not eaten, by larger co-occurring common
bottlenose dolphins.
This phenomenon is spatially variable and does not occur in all areas where these 2 species live in sympatry .
In areas where bottlenose dolphins regularly kill harbour porpoises, porpoises tend to carry fewer energy reserves than expected, suggesting that foraging-risk trade-offs may also occur for species that
neither compete for prey nor engage in predator−prey interactions (MacLeod et al. 2007). Modelling exercises suggest that bottlenose dolphin risk effects on harbour porpoises increase starvation mortality at the population level .

Question 32

Hvad er behaviourally mediated indirect interactions (can be considered a class of ‘species cascades)

Answer 32

Initiation and transmission of indirect effects of predation risk

Indirect effects of predation risk occur when changes in behaviour of one species/population/age class (transmitter) are made in response to the presence of another group or species (initiator) that results in changes in the behaviour, population sizes or biomass of a third (receiver) group.

Når en art ændrer sin adfærd på grund af tilstedeværelsen af en anden art, kan det påvirke en tredje art på forskellige måder. Dette kaldes indirekte effekter af rovdyradfærd, hvor ændringer i en arts adfærd (den såkaldte “sender/transmitter”) som svar på en anden arts tilstedeværelse (den såkaldte “initiator”) kan føre til ændringer i adfærd, bestandsstørrelser eller biomasse af en tredje art (den såkaldte “modtager/reciever”).
Disse indirekte effekter, der foregår i tre trin, kaldes ofte “adfærdsmediatoriske indirekte interaktioner”, eller ‘BMIIs’

Question 33

Når en art ændrer sin adfærd på grund af tilstedeværelsen af en anden art, kan det påvirke en tredje art på forskellige måder.
Dette kaldes behaviourally mediated indirect interactions. Kom med 2 real life eksempler

Answer 33

In the North Pacific, changes in foraging depths of harbour seals and Steller sea lions may transmit a BMII from sleeper sharks to fish
populations, but further work is needed to understand the links between different seal and sea lion diving patterns and population sizes of several taxa of fish prey.

Schools of pelagic fish such as herrings (Clupea spp.) and sardines (Sardinops spp.) form tight aggregations near the surface in response
to subsurface predators including cetaceans and pinnipeds. As a result, they are more accessible to seabirds in a BMII between marine mammals and seabirds

Question 34

Hvad er en meso predator? og er mange marine mammals det?

Answer 34

A Mesopredator is a predator that occupies a mid-ranking trophic level in a food web. There is no standard definition of a mesopredator, but mesopredators are usually medium-sized carnivorous or omnivorous animals,

Rather than being true apex predators, most marine mammals are in fact mesopredators that can experience risk effects.

In their role as mesopredators (or mesoconsumers), marine mammals
could be important in affecting populations or behaviours of their predators ‘from the bottom up’ as well as in transmitting the effects of larger predators to lower trophic levels (a top-down effect)