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 stocksof 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

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

• 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)

Nursery area Reproduction

Recruitment

Mortality

To produce a good fisheries model, we must account for allcontributions 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

0 400 800 1200 1600

120

40

80

0

Stock in previous year

Rec

ruitm

ent

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

• 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)

Hooking Fishes Individually

AnglingHand line

Demersal long lineFloating long line

Drift nets

Set nets

Pelagic trawlPurse seine

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

GEORGESBANK

Atlantic Ocean

Cape CodYear

Met

ric T

ons x

10

3 Georges BankStock landings

Cod

HaddockYellowtail

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

The End