Coastal food webs

What does benthic mean?

Bottom of the ocean

What does pelagic mean?

From the water column

What 2 linked food webs support the coastal marine ecosystem of BC?

• Benthic

• Pelagic

What are the primary producers in benthic food webs?

Kelps and other algae

What are the primary producers in pelagic food webs?

Small phytoplankton

What can arrows show in a food web diagram?

• Flows of energy up a food chain

• Consumption down a food chain

What are bottom-up forces?

Flows of energy up a food chain

What are top-down forces?

Consumption down a food chain

What is a trophic cascade?

The food chain structure (number of trophic levels) can cascade down a food web to control primary production

What is a classic example of a trophic cascade?

The maintenance of kelp forests by sea otters by their consumption of urchin herbivores

How much do sea otters eat?

≈ 30% of their body weight / day

What do sea otters eat?

Subtidal invertebrates (sea urchins, clams, cockles, crabs, etc.)

How long are sea otters?

4-5 ft

How much do sea otters weigh?

50-100 lbs

What is the history of sea otters in BC?

• Hunted for their furs by Russians and Europeans

• 1929: extirpated in BC

• Protected by legislation

• 1970: reintroduced from a population in Alaska to Checleset Bay, northwest Vancouver Island

• Recovering and expanding rapidly over the last several decades

• Spread along west coast of Vancouver Island and northern BC

• Beginning to spread to central coast

• Increasing exponentially

• Now thousands of individuals in BC

How does the recovery of sea otters affect coastal marine ecosystems in BC?

• Can lead to more kelp forests (trophic cascade) as they eat up herbivores like urchins

  • Absent: unchecked urchin populations → urchin overgrazing → large barrens and diminished kelp

  • Present: otters regulate urchin populations → kelp dominance → healthy ecosystems

• Can also lead to decreased crab and other shellfish that can be important to local human communities

  • 15% of commercial geoduck fishery was consumed by otter predation

  • Closures of shellfish fisheries

  • Loss of Indigenous shellfish harvests

  • Sea otters recovered without being managed in the traditional ways, and their numbers grew uncontrolled

  • Laws built on colonial systems that did not consider traditional Indigenous knowledge and ways of being

What are traditional Indigenous practices of otter management?

• Anchoring sea otter carcasses near shellfish harvesting locations to deter otters

• Targeted harvests in particular locations

What is sea star wasting disease?

• Induced by marine heat wave (2013) and bacteria in the genus Vibrio

• Different Vibrio species cause cholera in humans, seafood contamination, flesh-eating bacteria

• Begins with lesions and then melts tissues

• Causes death in ≈ 2 weeks

• Widespread declines of 80-100% predatory sunflower stars across western North America

How does sea star wasting disease affect kelp forests?

• Indirect food web effects include decreased kelp and macroalgae due to increased herbivores (urchins)

• Before: high sea star abundance → low urchin abundance → high kelp abundance

• After: crash of sea stars → increase in urchins → decrease in kelp

How are marine mammals recovering?

• Seals: populations increasing (10x since 1970s)

• Sea lions: most populations increasing

• Transient killer whales: population stable/increasing

• Resident killer whales: considered “at risk”, population health appears dependent on Chinook salmon abundance

What do transient killer whales eat?

Marine mammals

What do resident killer whales eat?

Fish, particularly Chinook salmon

What do harbour seals and sea lions eat?

Generalist predators (eat various fish spp.)

Why have marine mammal populations recovered?

• 1900s-1960s: DFO offered bounties on harbour seals and sea lions ($5/seal nose)

• Paid military gunships to use machine guns at haulouts to protect commercial fisheries

• Pump billions of hatchery fish into the ocean every year, which are not as adapted to the environment

• Log booms and storage facilities in enclosed estuaries or river mouths provide haulout habitats in salmon migratory channels

How does marine mammal recovery affect Chinook salmon?

• Marine mammal consumption of Chinook salmon increased from 6100 to 15200 metric tons

• 6-fold increase in predation on Chinook salmon over the last 4 decades

• Fisheries harvest decreased from 16,400 to 9600 metric tons over the same time period

• Consumption of chinook salmon by marine mammals now exceeds amount harvested by fisheries

• Fisheries shut down in 1990s to reduce fishing pressure

• Doubling of marine mammal consumption in Salish Sea 1980-2010

What is the Marine Mammal Protection Act?

Prohibits take and enables recovery of marine mammals

What marine mammals are listed under the Endangered Species Act?

• Endangered: Southern resident killer whale

• Threatened/endangered: different populations of Chinook salmon

What is the Pacific Salmon Treaty?

Mandates some level of protection and international management of salmon

What are Indigenous management systems for marine mammals and Chinook salmon?

• Harvest of seals and sea lions at river mouths to keep them away from salmon runs

• Not as single species focus, more interconnected

List 3 types of conflicts created by a single-species predator conservation focus.

1. Recovering predator populations that increase competition with humans for the same prey

2. New tradeoffs that emerge when protected predators consume protected prey

3. Multiple protected predator populations that compete for the same limited prey

Why do conservation efforts frequently focus on recovery of predators?

• Charismatic

• Can affect communities in ways disproportionate to their biomass

List 2 core laws used to protect species in the United States.

• Endangered Species Act

• Marine Mammal Protection Act

What is the conflict between protected predators and human uses in the Northeast Pacific?

Marine mammals vs fishermen

• Commercial harvest of Chinook salmon has declined from historic levels, in part to protect declining wild populations

• Pinnipeds were historically harvested but have rapidly increased following protection by the MMPA

• Changes in predator biomass and fish consumption have largely been omitted from fisheries management

What is the conflict between protected predators and human uses in the Greater Yellowstone Ecosystem?

Gray wolves vs ranchers and hunters

• Extirpation and subsequent reintroduction of wolves to Yellowstone

• Rebounding wolf populations have increased wolf predation on livestock, costing ranchers tens of thousands of dollars annually

• Wolves may also affect recreational elk hunts

• Number of elk killed by wolves exceeded that taken by hunters

• Recreational hunts eliminated by 2012

What is an example of protected predators vs protected prey in the Northeast Pacific?

• Killer whales consume salmon

• Endangered Southern Resident killer whales eating ESA-listed Chinook salmon

• Total abundance of killer whales has increased gradually as total Chinook salmon have declined

• Only a subset of each species is listed under the ESA

• Proportion of chinook prey that are endangered, threatened, or of hatchery origin are unknown

What is an example of protected predator vs protected prey in the Greater Yellowstone Ecosystem?

• Grizzly bears listed as threatened under ESA in 1973

• Bear populations increased steadily over last 3 decades

• Bears consume many seasonally abundant prey items, including elk and cutthroat trout

• Cutthroat trout declined after invasive lake trout were introduced in the mid-1990s and are now rarely observed in bear diets

• Cutthroat trout remains an important conservation focus

What factors affect Chinook populations?

• Dams

• Fishing

• Hatchery practices

• Habitat

• Predators

What is an example of protected predator vs protected predator in the Northeast Pacific?

• Pinnipeds and killer whales both prey on Chinook salmon

• Resident killer whales are chinook specialists

• Pinnipeds have broader diets

• Chinook may represent a small fraction of pinniped diets, but the effect of predation may be significant because of large populations

What is an example of protected predator vs protected predator in the Greater Yellowstone Ecosystem?

• Protected wolves and grizzlies both consume elk

• Wolf diets are dominated by elk

• Grizzlies rely on elk seasonally

• Predation on elk calves has increased in recent years and is now the primary driver of low calf survival

• Grizzlies could negatively affect wolves if predation leads to smaller elk herds

• The opposite may be true if wolf populations more strongly control elk dynamics

What are some other examples of multi species conservation conflicts?

• Atlantic cod fisheries conflict with large populations of grey and harp seals on the east coast of North America

• Protected pinnipeds in Puget Sound predate on threatened steelhead runs and rockfish

• On California’s San Clemente Island, an endangered shrike is consumed by a threatened island fox, and both are eaten by golden eagles, which are protected under the Migratory Bird Treaty Act and the Bald and Golden Eagle Protection Act

• In US PNW forests, the MBTA protects an expanding barred owl population, while the ESA protects a declining population of spotted owls. Competitive dominance of the barred owl over the spotted owl for food and nest locations is contributing to spotted owl decline