Transcript Document

Marine Fisheries and conservation of
marine resources.
1. What are fisheries?
2. How do we use marine
resources?
3. How do manage marine
resources?
What is a Fishery?
A Fishery is made of 3 parts:
1. the population fished.
2. The economics behind the
fishery.
3. The fishermen.
Examples of several fisheries
Different types of Fishermen
•
Large-scale commercial fishermen
•
Small scale commercial fishermen
•
Subsistence fishermen
•
Recreational fishermen
Commercial Divers: Hookah divers in
Mexico
Hookah divers in Mexico use
an air compressor and long
hoses to fish for benthic
species.
Underwater these divers
collect octopus, scallops,
clams, oysters, benthic
fish, snails, and sea
cucumbers.
Hookah divers near Penasco hunt
for Murex snails which are taken
to a plant and processed.
Any questions so far?
Moving on:
1. Types of fishing and fishing gear.
2. Economics of fisheries and fisheries
decline.
Stock - a key concept
• A stock is a geographically definable
population of a species that changes
abundance in response to factors, relatively
independently of other stocks
Stock - a key concept 2
• Managers wish to identify stocks to manage and
regulate crucial factors, such as controls on food
eaten by the stock, crucial nursery grounds,
sharing of stocks between political entities, such
as different states or countries
Identification of Stocks
• Tags - devices inserted into fish so that they
can be located subsequently and the
location can be related to the site of tagging
• Biochemical and molecular markers - used
to distinguish between stocks. If individual
populations have unique markers, they are
separated evolutionarily from other stocks
Gulf Coast bands
Atlantic bands
Mitochondrial DNA markers used to identify stocks
of Striped Bass, Morone saxatilis
Crucial Life History Information Needed
• Range of temperatures and salinities for
maximum growth
• Location of spawning/nursery habitat
• Location of feeding areas
• Biological information that minimizes
unintended mortality during fishing
Stock Size
• Landings from fisheries are the main
means of estimating stocks, although
scientific sampling is also done
Stock Size 2
• Landings can be related to stock size (=
local population size) if relation to fishing
effort can be determined
Stock Size 3
• Fishing effort is a function of (1) number
of boats; (2) number of individuals
fishing; (3) hours spend fishing; (4)
efficiency of fishing gear
Stock Size 4
• Stock estimates take into account the
catch per unit effort
Catch per catcher-day’s work
Landings of the blue whale, as compared with effort
1931 32
40
47 50
Year
60
1963
Fisheries Model
• To understand the behavior of a fishery,
we have to construct a model of
population change
• We must have an idea of the life history,
which includes the mode of reproduction,
the number of young produced, the
survivorship, growth periodicity
(seasonal) and rate of growth)
Mortality
Recruitment
Nursery area
Reproduction
To produce a good fisheries model, we must account for all
contributions to reproduction, growth, and mortality, throughout the
life cycle of the fishery resource species.
Stock Recruitment Models
• Objective of model is to predict
recruitment (the number of newly born
that enter and are noticed in the first
year class - 0+ )
Stock Recruitment Models 2
• Model presumes that recruitment can be
predicted on basis of stock in previous
year
Stock Recruitment Models 3
• Model presumes that recruitment
increases with increasing stock size, up to
a maximum, then recruitment decreases
because a stock of increasing size will be
more and more limited by food and will
produce proportionally fewer new
recruits
Recruitment
120
40
Density-dependent
effects
80
0
0
400
800
1200
Stock in previous year
Stock-recruitment model
1600
Maximum Sustainable Yield
• Based on idea that a fishery stock will grow
at a slower rate over a certain stock size
• Idea is to fish the stock down to the
population level where growth is maximal
• Leads to management tool to determine
fishing pressure
• Not much evidence that this approach
works, even if the theory makes some sense
• Problem might be that factors other than
simple density dependence affect stock size
Fishing Techniques
• Hooking fishes individually - e.g., long
lines with rows of hooks
• Entangling fishes in nets - e.g., large drift
nets, nets towed below the surface and
kept open with wooden boards
• Traps - e.g., baited lobster traps kept on
bottom
• Diving for fisheries (collection by hand)
Angling
Hand line
Floating long line
Demersal long line
Hooking Fishes Individually
Drift nets
Set nets
Purse seine
Pelagic trawl
Bottom otter trawl
Fishing with nets
Stock Reduction - factors
• Environmental change
• “Random factors”
• Overfishing
Vulnerable Fisheries
• Life histories with long generation times
• Life histories with low fecundity
• Stocks with confined populations
(aggregations or geographic range in a
confined area)
• Resource species that are easily caught
Management Problems 4
• Fisheries managed by a variety of local and
federal agencies
• Management recommendations not always in
best interests of maintaining stock
• Some policies backfire - e.g., Magnuson Act of
1976 which extended US coastal fishing zone
200 miles from shore but resulted in extensive
deployment of US fishng boats, resulting in
overexploitation
• Magnuson Act established 8 regiona fishing
commissions to help regulate domestic
fishing - results good in some cases, bad in
others
Effects of Overfishing 4
• Great reduction of many stocks, e.g., formerly
productive Georges Bank, east of New
England
• Effects concentrated especially on species with
vulnerable life cycles (low fecundity, long
generation time - e.g., sharks, whales)
• Collateral effects on the bottom, where bottom
trawling continually turns over the bottom,
killing epibenthic animals
• Elimination of species at the tops of food
chains, which tend to be lower in abundance
and have vulnerable life history
characteristics
Metric Tons x 10 3
Georges Bank
Stock landings
Cod
Haddock
Yellowtail
Year
Atlantic Ocean
Cape Cod
GEORGES
BANK
Trends in landings of three major fisheries on Georges Bank
on the New England continental shelf
Some new management tools
• Individual transferable quota (ITQ) - licenses
are limited in number with quotas for each
license, which can be sold
• Marine Protected Areas (also known as NoTake Areas) - some portion of the stock’s
geographic range is closed to fishing - protects
spawning grounds, nursery grounds, or
minimal crucial habitat size to preserve stock
even when fishing is too high
Spawning
area
Juvenile
Feeding
area
Adult feeding area
Adult feeding area
Adult feeding area
No-take
areas
Current and dispersal
direction
Hypothetical No-take Plan
Mariculture - Important Factors
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Desirability as food
Uncomplicated reproduction
Hardiness
Disease resistance
High growth rate per unit area (growth
efficiency)
Readily met food and habitat requirements
Monoculture or polyculture
Marketability
Minimal ecological damage
Mussels and Oysters
• Mussels usually recruit to ropes and poles
• Placement in areas of high phytoplankton
density and water flow
• Oyster newly settled larvae (spat) collected and
then transferred to trays that are suspended
from rafts
• Problem: bivalve diseases, e.g., MSX in oysters
- amoeboid protozoan
The End