Ecosystem Models COPY Flashcards
Primary motivations for Ecosystem models?
single species models missing important and deterministic drivers of biomass and abundance (e.g., environment / habitat, ecological / trophic, fishery / technical, etc.)
What are the four alternatives for ecosystem models in fisheries science?
Incorporate the physical environment
Incorporate ecology
Incorporate people
Incorporate everything
(or multiple things)
Incorporating the physical environment
Can determine stock abundance
Can affect: recruitment, growth, natural mortality, availability to fishery
Why evaluating the physical environment important?
Management targets and threshold values may be a function of environmental conditions
What is an example of a physical environment model?
The salmon habitat model
Salmon Habitat Model
incorporated characteristics of spawning habitat (e.g., temperature, stream flow, sediment type) into recruitment/survival and age-structured population dynamics
Recruitment of many small pelagic species found to be coupled with
environmental conditions
What is an example of environmentally driven abundance?
Pacific sardine (Sardinops sagax) eggs most abundant at sea-surface temperatures of 13-15 °C, larvae most abundant 13-16 °C (best in warm ocean conditions)
How does the Pacific Fisheries Management Council use environmental conditions models?
sea-surface temperature data to set environmentally-dependent effort targets
The productivity of exploited species may be
temperature dependent
How is ecological modeling incorporated most frequently?
predator-prey interactions
example - food web modeling
How are food web models useful?
characterizing tradeoffs between exploitation and conservation across multiple, interdependent species
How are multispecies models that include predation used?
estimate multispecies maximum sustainable yield (MMSY)
Management that targets MMSY may cause several stocks to collapse
Incorporating People
Commercial fisheries -> maximize profit
Recreational fisheries -> maximize utility/satisfaction
What is driven by economic incentives?
Fishing effort (and mortality)
What is this data showing?
Catch rates lower where fishing is easier / less expensive (closer to population centers, sheltered from prevailing winds); suggests species less abundant in these areas
Fisheries dependent data depends on…
human behavior
Spatiotemporal decisions non-random
Length/age composition may reflect targeting
Non-random observations can
bias assessment model outputs
What is a solution to try and get unbiased data?
Standardization procedures of fishery dependent data common
e.g., control for factors influencing behavior → not perfect
Incorporating “everything”
Complete ecosystem models can incorporate all relevant aspects (environment, ecology, people/economic sectors)
Typically simulation based (not analytical)
What are two ecosystem models that have frequent fisheries applications?
Ecopath with Ecosim (EwE)
Atlantis
Ecopath
trophic mass balance food web model
Ecosim
uses mass-balance results from Ecopath and simulates temporal dynamics
What can an Ecosim model identify?
fishing mortality rates that maximize: fishery profits, social benefits (employment), species rebuilding, ecosystem resilience/structure
