Fisheries Final

Fish Stock

The living resources in the community or population from which catches are taken in a fishery

Population

The number of individuals of a particular species that live within a defined area

Key process rates for open population dynamics

Birth, death, immigration, emigration

Drivers in quantitative models

Growth, recruitment, mortality

Dynamics in quantitative models

Population and production models, integrated bioeconomic models, ecosystem models

Tools for modeling

single stock models, stock assessments, multi species model, multispecies assessments, food web models, integrated ecosystem assessments, whole system models

Simple model of fish populations (Russell 1931)

Reproduction and growth —> increase biomass

Fishing and natural mortality —> Reduce biomass

Dynamic population models

include state variables, parameters, rules of change, forcing functions

Can be: stochastic or deterministic, continuous or discrete, aggregate or individual based, age size sex spatially structured etc.

Assumptions of logistic growth model

environmental factors are constant, all members of population affected by limiting factors identically, birth and death rates respond instantly to changes in density, density dependence is a smooth process; population growth rate affected by even small densities, age size and sex distributions are stable, females always able to find mates

Surplus production

based on assumption that fish populations produce more offspring than necessary to sustain the stock. The difference between the production and replacement lines

Surplus production models

aka production models or biomass dynamic models, simple because effects of R G and D are combined into single equation, only a few parameters used to predict change in total biomass and production

Parameters used to predict change in total biomass and production for surplus models

r - maximum population growth rate

K - carrying capacity

q - Catchabilty

Stock assessment for surplus production models

population considered undifferentiated biomass, use when age six or sex structure not known or doesn’t matter, external forces not considered important

Final thoughts on surplus production models

require only estimates of abundance and yield, widely used for many years, now considered inferior to age structured models, still used for data limited fisheries some multi species fisheries and some tropical fisheries

Age structured models two approaches

backward projection explain historical abundances based on principle that catch represents minimum number of fish alive in previous year

forward projection estimate abundance at age during first year of analysis then subsequent mortality, recruitment, and abundance levels

Virtual population analysis

goal: estimate stock sizes and fishing mortality of individual cohorts using commercial catch data

VPA final thoughts

useful method widely applies to assess exploited stocks, assumes no error in age determination and constant natural mortality and known terminal fishing mortality, greater confidence in estimates for youngest ages so less sensitive to later age starting values, prediction of future abundances requires additional models

Statistical catch at age methods

broad class of methods, combines multiple types of data and sub models to simulate population dynamics of stocks and fisheries, input data may include catch and composition fishing effort survey abundances tag recapture data

Statistical catch at age methods contd

Basic idea: Catch-at-age data used in combination with models defining population dynamics to generate predictions of catch (and other measures) that are compared to observed values

SCAA final thoughts

Models flexible but limited in number of parameters able to be established —> challenging when selectivity or fishing mortality is variable or evolves. state space models allow partitioning of observation and process error

Metapopulations

spatially discrete populations of same species that have some level of exchange

TAC

Total Allowable Catch

Derby Fisheries

Open for very limited time i.e pacific halibut, alaska herring, florida stone crab

Problems with Derby Fisheries

Fish in unsafe conditions, saturate market, not a full time occupation

Ways to address excessive fishing in open access fisheries

Limited access programs, buyouts, catch shares

Three components of harvest strategies

Management reference poins, harvest control rules, management strategy evaluation

Reference point

A conventional value derived from technical analysis which represents a state of the fishery of population and whose characteristics are believed to be useful for the management of the unit stock

Target reference point

Indicate a state of a fishery and of a resource that is considered desirable and at which management action should aim

Limited reference point

Indicate a state of a fishery and or a resource that is considered undesirable and which management action should avoid

Trigger (Threshold) Reference Point

Set between TRP and LRP to prompt additional management response to help ensure fishery remains close to target and or avoids breaching limit

Pretty good yield

80% of MSY

B_MSY Or X%B_MSY

Biomass at MSY or X% MSY

F_MSY or X%F_MSY

Fishing mortality rate that leads to B_MSY Or X% Fishing mortality rate that leads to B_MSY

F_X%

Fishing mortality rate that reduces stock to X% of maximum spawning potential

F_Med

Fishing mortality rate that corresponds to median value of stock recruit ratio

F_MEY

Fishing mortality rate that produces maximum economic yield

MMSY

Multispecies Maximum Sustainable Yield. Incorporates predation and trophic relationships. Often found to be less than sum of single species MSYs

Example of reference points based on environmental conditions

Pacific Sardine effort targets depend on sea surface temperature

Overviews of US Fisheries Management

State water to 3 miles out, federal waters to 200 Miles — US Exclusive Economic Zone, then international waters

VMRC

Virginia Marine Resources Commission. Oversees state waters

ASMFC

Atlantic States Marine Fisheries Commission. Manages stocks primarily in inshore water of several states.

Magnuson-Stevens Fishery Conservation and Management Act

1976 US federal law that implemented a US fishery conservation zone (EEZ) and established the regional Fishery Management Councils (FMCs).

Fishery Management Councils (FMCs)

Regional bodies responsible for developing Fishery Management Plans (FMPs) for species primarily occurring in non-state coastal waters.

Fishery Management Council Functions

Prepare FMPS, convene committees and panels, set catch limits, develop research priorities, vote on management actions

Legislative History

1990 Magnuson Act established 7 national standards and authority for Atlantic Highly Migratory Species, 1996 Sustainable fisheries act added 3 NS, 2006 Magnuson Stevens Reauthorization act 2018MS Amendment

National Standards

1 Achieve optimum yield and prevent overfishing, 2 Best Available scientific info, 3 Manage stocks as a unit, 4 No Discrimination and rules for allocations, 5 Efficiency in utilization, 6 Variations and Contingencies, 7 Minimize costs and avoid duplications, 8 Communities, 9 Bycatch, 10 Safety at Sea