Transcript 18 Food From the Sea - Stony Brook University

18 Food From the Sea
Notes for Marine Biology:
Function, Biodiversity, Ecology
By Jeffrey S. Levinton
©Jeffrey S. Levinton 2001
Fisheries
• Relatively primitive form of food
acquisition - hunting and gathering
• Fishery is a renewable resource - resource
exploitation at certain levels need not
deplete the resource
• Crucial objective is to develop an
appropriate management program to avoid
overexploitation
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.
Frequency
30
20
10
0
66
103
124
Carapace length (mm)
140
Identification of Age Classes by Size:
Age classes of the lobster Panuliris ornatus. Curved line estimates
age classes from the more discontinuous distributin of the
histogram. Note the older age classes to the right, which are more
indistinct.
Model of Fishery Population
W  W t 1  MW t 1  RW t 1  GW t 1
In words, this means that the change of mass (W) from
Year t-1(previous year) to year t (the current year) equals the
growth W - the loss of mass in mortality M plus the mass
added in reproduction (factor R x mass of previous year)
plus the growth since last year (growth factor G x mass of
previous year)
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
Maximum Sustainable Yield 2
• 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
Maximum Sustainable Yield 3
• 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
Maximum Sustainable Yield 4
• 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
Maximum Sustainable Yield 5
• 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
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 1
• Fisheries managed by a variety of local
and federal agencies
Management Problems 2
• Fisheries managed by a variety of local
and federal agencies
• Management recommendations not
always in best interests of maintaining
stock
Management Problems 3
• 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
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 1
• Great reduction of many stocks, e.g.,
formerly productive Georges Bank, east
of New England
Effects of Overfishing 2
• 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)
Effects of Overfishing 3
• 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
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
•
•
•
•
•
•
•
•
•
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
Harmful Algal Blooms (HABs) 1
• A variety of toxins, usually produced by
species of phytoplankton
Harmful Algal Blooms (HABs) 2
• A variety of toxins, usually produced by species
of phytoplankton
• Toxins are consumed, along with
phytoplankton cells, by resource bivalves, who
sequester toxins
Harmful Algal Blooms (HABs) 3
• A variety of toxins, usually produced by species
of phytoplankton
• Toxins are consumed, along with
phytoplankton cells, by resource bivalves, who
sequester toxins
• Toxins are then consumed by people
Harmful Algal Blooms (HABs) 4
• A variety of toxins, usually produced by species
of phytoplankton
• Toxins are consumed, along with
phytoplankton cells, by resource bivalves, who
sequester toxins
• Toxins are then consumed by people
• Seasonality allows regulation in some cases
(e.g., prohibition of exploitation of coastal
mollusks in California from May-August)
Major HAB types 1
• Paralytic Shellfish Poisoning (PSP) - variety
of neurotoxins produced by dinoflagellate
species of Alexandrium, Gymnodiniums,
Pyrodinium - strong neurotoxic effects,
respiratory arrest, occasional death
• Amnesic Shellfish Poisoning (ASP) - domoic
acid produced by species of the diatom
Pseudonitszchia - causes amnesia,
neurological damage, even death
Major HAB types 2
• Neurotoxic Shelfish Poisoning - caused by
brevitoxin, produced by dinoflagellate
Gymnodinium breve, can be breathed from
aerosols
• Pfiesteria piscicida - toxin not identified, but
causes severe neurotoxic effects, one of
many life history stages of this species
emerges from the bottom and can attack
fish.
Spread of HABs 1
• Frequency and geographic extent of
HABs are increasing
• Harmful species often affect shellfish
physiology as well as humans and may
kill entire populations (e.g., killing of bay
scallop Argopecten irradians by “brown
tide” organism in waters of New York)
Spread of HABs 2
• Increase may be a result of increasing
disturbance and pollution of coastal zone, or
more frequent introductions from shipping
traffic
• Increase results in more frequent closures of
shellfish beds, fish kills (Pfiesteria), sickness,
Seaweed Mariculture
• Nori - derived from red Porphyra spp., rich in
protein, used to wrap sushi, spores collected on
nets and grown in estuarine areas
• Kelps - grown actively in western U.S. coastal
waters, harvested for alginates, used in a
number of foods
• Many others, some harvested directly from
shore
Fish Ranching
• Marine fish, such as salmon species, are
grown in open water tanks
• Genetic engineering now being used to
introduce fast-growth forms
• Problem - many escape and mix with
wild salmon (1/3 of salmon in Norwegian
rivers derive from ranched salmon)
The End