18 Food From the Sea

Notes for Marine Biology: Function, Biodiversity,

EcologyBy 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

• Stock - definition

• Stock - management unit (nursery, feeding area, political boundaries, fishing limits)

Identification of Stocks

• Tags -

• Biochemical and molecular markers -

Gulf Coast bands

Atlantic bands

Mitochondrial DNA markers used to identify stocksof Striped Bass, Morone saxatilis

Crucial Life History Information Needed

• Physiological limiting factors

• spawning/nursery habitat

• feeding areas

• Biological information that minimizes unintended mortality during fishing

Stock Size

• Landings - usual determinant

• Fishing effort - f(person-hours fishing, gear used, number of boats)

• Catch per unit effort - what is reported

Landings of the blue whale, as compared with effort

1931 32 40 47 50 60 1963

Year

Cat

ch p

er c

atch

er-d

ay’s

wor

k

Fisheries Model

• model of population change

• Must know life history: the mode of reproduction, the number of young produced, the survivorship, growth periodicity (seasonal), rate of growth)

Nursery area Reproduction

Recruitment

Mortality

30

20

10

0

Fre

quen

cy

66 103 124 140Carapace length (mm)

lobster Panuliris ornatus. Identification of Age Classes by Size:

Model of Fishery Population

W change of massM mortality proportionR reproduction proportionG growth proportion

W = Wt-1- MW t-1 + RW t-1 + GW t-1

Stock Recruitment Models• Objective: predict recruitment (the number of

newly born that enter and are noticed in the first year class - 0+ )

• Prediction from previous year’s stock• Model premise: density dependence -

reproduction declines with increasing density• Therefore: recruitment increases with

increasing stock size up to a point, then decreases

0 400 800 1200 1600

120

40

80

0

Stock in previous year

Rec

ruit

men

t

Stock-recruitment model

Density-dependenteffects

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

Hooking Fishes Individually

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

• Top carnivores (less abundant)

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 regional 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

GEORGESBANK

Atlantic Ocean

Cape Cod

Year

Met

ric

Ton

s x

103 Georges Bank

Stock landings

Cod

Haddock

Yellowtail

Trends in landings of three major fisheries on Georges Bankon 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 No-Take 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

Spawningarea

JuvenileFeeding area

Adult feeding area

Adult feeding area

Adult feeding area

No-take areas

Current and dispersaldirection

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)

• Problem - feeding carnivores requires a lot of food (overfishing other stocks?)

The End