lecture 16 Flashcards
original (historical) otter populations estimate
160K-300K
what happened to kill off otter population and when ?
fur trade
99% gone - 43K
ending around 1870 and banned in 1911 (along w international trade)
whats happening now to otter population ?
rebounding
but not expanding in range quickly bc non-migratory or exploratory behaviour (stay close in groups to home - socially driven)
california - OG pop = 40K
now abt 3K –> roughly 6% of OG
california
started w about 45K
hunted off till almost extinction (fur trade) 1790-1850
stopped around 1870 and banned in 1911
- protection in 1911 (fur seal treaty)
thought to be extinct in 1850
someone (lighthouse keeper John Astrom) saw otter colony in Big Sur abt 50 years later - 1915
range expansion low bc non-migratory or exploratory - tight social animals
high risk of predation from sharks
wont travel more than couple dozen km for food before returning home
otter surrogacy - Monterey bay vs san Fran bay
figure with diff organisms – positive feedback loop
-> otter increase, eelgrass increase, nitrate increase
why nitrate increase?
- runoffs from farms which nitrate normally kills off eelgrass but otter population kept eelgrass stable
San Fran Bay = high potential bc high carrying capacity (5K-25K) but super urban (anthropogenic risks)
Monterey Bay = carrying capacity too low - around 50-200
ESA delisting level
3090
abt 1/15 of population
– doesnt seem viable
where would be be able to re-establish otter populations and why?
San Fransisco Bay
CONS
- but super anthropogenically busy
- super urban w vessel traffic, oil spill risk, commercial fishing (fisherman fighting this)
PROS
- high potential here bc high carrying capacity (5K-24K)
Not Monterey bay
- 50-200 carrying capacity –> too low
British Columbia
- very high carrying capacity (fast reproduction)
- fastest and furthest expanding rate
what do otters help mediate?
they eat urchins - so help kelp
loren
they eat crabs - so help eelgrass
hughes et al
British Columbia
most rapid growth rate !!!! 17%
last otter shot in 1930 on Van Island
population grew from bringing 89 individuals in 1969 from northern stock
Vancouver Island population grew ~19% until 1995 then declined to ~5-7%
ALL BC current population ~8K
- 1/3 to 1/10 of original population
expanding at fastest rate out of everywhere
new updated data: almost double or more potential than Cali (abt 70K-80K)
– used to be using a linear estimate versus habitat –> now adding in estuaries = makes higher potential - changing parameter
species conflict – otter and pinto abalone (both protective species)
which species will go down and which will go up
introducing otters has disproportional social impact drawn back to ecology
UP: otters, eelgrass, kelp, rockfish, lingcod, snapper
DOWN: urchin, crab, shellfish, abalone, mussel, clam
Alaska
Jim Estes study on Aleutians - islands w and without otters and how that impacted ecosystem (urchins, kelp, others)
current population = ~75K
(recovered to abt 40% of OG pop)
- estimated to be 125K
continued increase in south-central Alaska and Southeast Alaska
- but decline in southwest Alaska bc whale predation
– less whales for them to eat so turning to otters
summary
Alaska has over half of the otter numbers globally
- 70K -125K
- entering era of reduction from predation (killer whales)
BC has potential to have a lot of otters – abt 52K or higher (abt 80K)
cali is insignificant
- not gonna recover
- urbanization is SF Bay
- but most money going here ?
BC doing nothing to support otters
Human dimension
otters vital for kelp preservation and climate change mitigation
Cali fisherman wanted ban on otter expansion
BC First Nations potentially in direct conflict w populations over food sources (shellfish, urchin)
What did Robert Paine do?
Keystone (predator) species concept
trophic cascade - has to be more than 2 trophic levels
- ex// otters urchin kelp
Who is Jim Estes?
serendipity
was set up to research where they could nuclear war testing
– sent to Aleutians for 2 years to study otters
– had all data for him
– looked at places w and without otters (like islands beside each other) to know abt herbivory of urchins on kelp
urchins were more abundant and larger (0-25m) at places without otters - could live and grow longer and eat more kelp –> less kelp abundance
places with otters = smaller urchins (>25m) and less biomass (and more hidden not feeding out in open), more kelp abundance
- more fish and eagle abundance
other drivers of change and outcomes (kelp example)
ocean warming
- thermal stress
- physical damage
- increased biofouling (from organisms that live epiphitically on kelp)
- increased turbidity (decreased recruitment and growth)
