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Genetic and biologic stock management

Goals for marine animal resource Goals for marine animal resource exploitationexploitation

and and

and managemental tools to obtain the goalsand managemental tools to obtain the goals

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1. Goals in managementThe most general and widely accepted goal in management of exploited marine resources today is the so-called MSY – maximum sustainable yield (previously called MLY - maximum long term yield).

2. Means and methods at handThe tools for obtaining the MSY goal are many and diverse. They include maximum total and national quota (TAC- total allowable catch), regulations in terms of mesh sizes, minimum fish sizes, naximum bycatch allowance, fishing seasons and closures, fleet capacity, gear types, "no-fish boxes" and sanctuaries, and theoretical stock modelling (VPA - virtual population analysis).

3. Information needed• Biological information on stocks (growth, maturation, reproduction, mortality, fecundity)• Time series of climate, landings, catch regimes etc 4. Framework and ConstraintsInternational maritime legislation (laws and conventions)National interests (NEZ - national economic zones & EEZ - extended economic zones)National & local community considerationsConservation of biodiversityEthics (catch methods)

5. Professional environment International co-operation (ICES - International Council for the Exploration of the Sea; headquarter in Copenhagen)

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1. Goals

In the first part of the twentieth century, it was thought to be very unlikely that man could decimate e.g. the enormous herring NSS stock by fishing. After the collaps of the NSS (and other stocks), this view changed, and one was forced to assess how much a stock could be exploited (fishing mortality) sustainably; i.e. without impairing the health and long term productivity of the stock. This marked the start of modern fisheries biology. Management changed from solely helping the fishing fleet to get the largest catches - to the systematic monitoring of the stocks and collection of scientific data about reproduction, growth rates, maturity age, recruitment, fecundity, prey and predator abundance, and assessment of natural mortality rates and fishing mortality.

So, the term MSY (max. sustainable yield) was introduced, implying that exploitation should be done in a way which preserved the health and productivity of the stock, i.e. a sustainable stock management.

The determination of MSY is theoretically simple (although quite complex in practice). The theoretical basis is a logistic population growth. The maximum instantaneous biomass growth is then at the flexpoint of the curve, i.e. at half of the carrying capacity of the environment of the population (next slide).

Java applet animation of logistic growth: http://www.otherwise.com/population/logistic.html

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The logistic equiation for population growth

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The theoreticalbasis for the MSY (MLY)

concept.

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2. Means and methods at hand

National and Total Catch Quota

Fish stocks are known to vary considerably in year class strength - i.e. the recruitment to the fishable stock vary naturally by causes like temperature and prey availability. To assess the age composition and the yearclass strengths, methods for age determination of individuals is mandatory. When a rich yearclass enters the fishery, it may influence the fishery output for many years ahead. Management needs to know about and monitor yearclass strengths in order to regulate the annual quota accordingly, and quota recommendations may vary between years and decades.

Often, a certain temporal regularity is observed in yearclass strength in Northeast Atlantic fish species like cod (e.g. ~ 10 y interval between the strong yearclasses). When a stock's life-cyclus is restricted to the economic zone of one specific country, it is the responsibility of that country to set quota and regulate the fishery output. However, some fish stocks (often the largest ones) have life histories that covers many countries' EEZ, and international waters as well. In such cases the TAC (total allowable catch) is determined by international bodies like ICES (The International Council for the Exploration of the Sea), which headquarter is situated in Copenhagen.

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Active, size-selectivenet fishing gear types.

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The "mesh size" is usually defined as the length of the "stretched" whole mesh. The mesh size of the netting shown here is 2*d, where d is the length between two knots .

The easiest mathematical expression to describe the gear selection ogive is the so-called "logistic curve":

Box 1

A trawl gear selection ogive; a logistic curve.

Experimental setup to estimate the parametres of the trawlgear selection curve in the figure down left, and formula below.

NB! Sufficient numbers of fish at each length is obtained by large catches or repeated catches.

Details and explanations on next slides --

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Table 6.1.1 Estimation of gear selection ogive for Nemipterus japonicus from a covered codend experiment (from Jones, 1976, cf. Fig. 6.1.2)

A B C D E F G H

length interval L1-L2

number in codend

number in cover

total number

fraction retained SLobs

ln(1/SL-1)

(y)

midlength (L1+L2)/2

(x)

fraction retained

SLest

9-10 0 1 1 0 - - -

10-11 1 6 7 0.14 1.82 10.5 0.13

11-12 2 7 9 0.22 1.27 11.5 0.23

12-13 2 4 6 0.33 0.71 12.5 0.38

13-14 7 5 12 0.58 -0.32 13.5 0.56

14-15 30 13 43 0.70 -0.85 14.5 0.72

15-16 61 8 69 0.88 -1.99 15.4 0.84

16-17 27 3 30 0.90 -2.20 16.5 0.91

17-18 7 0 7 1.00 - 17.5 0.96

18-19 4 1 5 0.80 - 18.5 0.98

intercept = a = S1 = 9.4875 -slope = -b = S2 = 0.7193

L50% = S1/S2 = 13.2 cm L75% = (S1 + ln 3)/S2 = 14.7 cm

SLest = 1/(1 + exp(9.4875 - 0.7193*L))

(used to calculate the curve in Fig. 6.1.2)

BI 3063 J. Mork H10 Box 1

cont’d

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Fig. 6.1.2. Gear selection ogive for Nemipterus japonicus caught by a trawl with a codend mesh size of 4 cm (from Jones, 1976).

Box 1 cont’d

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In the case of our example (Table 6.1.1) we found L50% = 13.2 cm for a mesh size of 4 cm. Thus, the selection factor is

SF = 13.2/4 = 3.3

This selection factor can now be used to determine L50% for different mesh sizes, for instance, L50% of Nemipterus japonicus when using

meshes of 3 cm would be:

L50% = 3.3*3 = 9.9 cm.

BI 3063 J. Mork H10 Box 1

Cont’d

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2. Means available cont'd

Mesh width regulations and minimum legal size:Net gear catches fish over a certain size at which they are retained by the meshes. Obviously, increased mesh size allows more small fish to escape. Various net gear have different selection factors, and the selection factor depends on fish species (due to their different shapes), as well as some other factors (towing speed, tow durations etc).

Selection factor (SF) goes into the formula for the so-called 50% escape length (L50 ), i.e = the mesh size at which 50% of the fish of a certain size (in cm) is retained (or escape). The mesh size is measured as 'stretched knot' (see previous slides Box 1).

L50 = f x m (f = selection factor of gear, m = mesh width)

Example: The selection factor for cod in Danish seine is 3.2. Thus, a Danish seine net with stretched knot of 11 cm has an L50 for cod of 35 cm. The L25 and L75 retainments (symmetrical around L50) mark the lower and upper ends of the selection range.

Minimum legal size:Hence, if the smallest legal cod size is set to 35cm, Danish seiners must use seines with mesh size larger than 11 cm stretched knot.

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The length range from L25% to L75%, which is symmetrical around L50%, is called the "selection range" (Box 1). The formulas for calculating L25%, L50% and L75% are:

L25% = (S1 - ln 3)/S2 L50% = S1/S2 L75% = (S1 + ln 3)/S2

Vice versa, S1 and S2 can be derived from L75% and L50% using the following formulas:

S1 = L50%*ln(3)/(L75%-L50%)S2 = ln(3)/(L75%-L50%) = S1/L50%

The regression analysis is done over a length range between zero (0) and full (1) retention, thus excluding those length intervals where no or full retention was obtained and all values beyond those points, even if they are between 0 and 1.

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2. Means available cont'd

Mean individual growth rates

Fish collected for biologic information are routinely measured for:Length, weight, sex, and gonadic maturation stage. The otholits or scales are collcted for individual age determination. With size and age data, growth curves can be calculated. Traditionally, the von Bentanlanffy growth function has been extensively used:

lt = L∞ [ 1 - e-k(t - t0) ]

where

lt = length at age t

L∞ = assymptotic mean length as age approaches infinity

k = a constant showing how fast the fish approaches L∞

t0 = hypothetical point in time for length equal to zero under the function

Box 2

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The von Bertalanffy growth function (VBGF) introduced by von Bertalanffy in 1938 predicts the length of a shark as a function of its age,

L(t)) = L∞ - [ L∞ - L0 ] exp(-kt)

Genetic and biologic stock managementBI 3063 J. Mork H10 Box 2

cont'd

Growth rates of individuals: use von Bertalanffy

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Fishing seasons and closures

The reproduction period is important for proper recruitment to the future stock. In some fish species, actions are taken to assure that the fish are not excessively disturbed in the reproduction process. A common action is to ban fishing in the entire spawning season. In some fisheries this is not suitable (e.g. the spawning cod fishery in Lofoten, Norway). However, short time closures during peak spawning and on holidays have been common practice also in that fishery.

In Norway, information to the fishermen about closures, maximum quota, and other regulation measures are communicated as "Messages from the Director of Fisheries)" in various news media.

The recommendations from ICES about TAC and other regulation measures are communicated to each country. The annual recommedations from the Advisory Committee for various commercial stocks are available on ICES' web pages on the Internet(ICES Advice - Introduction).

2. Means available cont'd

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3. Information and tools needed

• Biology of stocks (reproduction, growth, maturation, mortality, migrations, fecundity)• Climate monitoring (e.g. hydrographical time series)• Legislation (national / international laws and conventions)

Studies of biological features started already more than a century ago for some of the commercially important stocks (e.g.the NEAC stock). Other important resource species (herring, mackerell) followed after World War II. Since about 1960, a wide range of commercial fish stocks have been studied (tuna, horse mackerell, Alaska pollock and others). Not least, these studies showed the large variation in annual recruitment and spawning stock sizes, and triggered an intense research into the causes of this variability, for example the effect of ocean temperatures.

Some large stocks (cod, herring, mackerell) have international distributions and migrations. Together with a new trend for fishery nations to claim extended economic zones (EEZ) in their waters, this necessitated a new international legislation regime for fishery rights in international waters. Such legislation started to emerge from about 1970, and has been a very important tool for setting quota and other types of regulations. Here, ICES has played an important role.

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4. Framework and Constraints

• National interests (NEZ - national economic zones & EEZ – Exclusive (formerly Extended) Economic Zones)

• National & local community considerations

• Conservation of biodiversity

• Ethics (catch methods)

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The Convention on Biological DiversityThe Convention on Biological Diversity

Signed by 150 government leaders at the 1992 Rio Earth Summit (the Rio Conference), the Convention on Biological Diversity is dedicated to promoting sustainable development. Conceived as a practical tool for translating the principles of Agenda 21 into reality, the Convention recognizes that biological diversity is about more than plants, animals and micro organisms and their ecosystems – it is about people and our need for food security, medicines, fresh air and water, shelter, and a clean and healthy environment in which to live.

Conservation of biological diversity applies to many levels: genes, organisms, populations, plant and animal societies, ecosystems and biota.

4. Framework and Constraints cont.

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4. Framework and Constraints cont.

National interestsNational interests

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Territorial waters, or a territorial sea, as defined by the 1982 United Nations Convention on the Law of the Sea[1], is a belt of coastal waters extending at most twelve nautical miles from the baseline (usually the mean low-water mark) of a coastal state. The territorial sea is regarded as the sovereign territory of the state, although foreign ships (both military and civilian) are allowed innocent passage through it; this sovereignty also extends to the airspace over and seabed below.The term "territorial waters" is also sometimes used informally to describe any area of water over which a state has jurisdiction, including internal waters, the contiguous zone, the exclusive economic zone and potentially the continental shelf.

National interestsNational interestsNEZ - national economic zone EEZ – exclusive (formerly extended) economic zone

4. Framework and Constraints cont.

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5. Professional environment

ICES/CIEM ICES/CIEM

The International Council for the Exploration of the SeaConceil International pour Exploration de la Mer

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5. Professional environment cont.

International co-operation (ICES - International Council for the Exploration of the Sea; headquarter in Copenhagen). http://www.iced.dk. ICES was founded in Copenhagen in 1902, and in the first years thereafter, most of the Annual Statutory Meetings were held in Copenhagen.

Genetic and biologic stock managementBI 3063 J. Mork H10

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Map of ICES member countries

5. Professional environment cont.

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Homepage: http://www.ices.dk

5. Professional environment cont.

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5. Professional environment cont.

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The structure of ICES

5. Professional environment cont.

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5. Professional environment cont.

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5. Professional environment cont.

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5. Professional environment cont.

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The structure of ICES

5. Professional environment cont.

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5. Professional environment cont.

THE SCIENTIFIC WORK FLOW IN ICESTHE SCIENTIFIC WORK FLOW IN ICES

The Parent CommitteesThe Parent Committees or Scientific Committeesor Scientific Committees (there are currently 8 of them) pass on, every year, the tasks (TOR, ”Terms of Reference”)

to the

Expert Groups (WG, Working GroupsExpert Groups (WG, Working Groups) which number varies among the mother committees. There are altogether more than 100 WGs.The numbers of scientists in a WG varies (5-50).The WGs may also suggest tasks on their own. After treating the TOR, the WGs send their advice back to their mother committees, which passes them on to higher levels in ICES.

After being treated at many levels, the advices may be communicated fom ICES to the member countries, which in turn let them undergo national treatment, e.g. in terms of negotiations between government and work organizations like the Norwegian Fishermen’s League (Norges FiskarlagNorges Fiskarlag).

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(http://www.ices.dk/iceswork/sciencecommittees.asp)

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5. Professional environment cont.

ICES has currently 8 Science Committees. They areICES has currently 8 Science Committees. They are

1. Fisheries Technology 2. Oceanography 3. Resource Management 4. Marine Habitat 5. Mariculture 6. Living Resources7. Baltic8. Diadromous Fish Committee

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