MSFD Indicators and Reference Points for Data-Limited Stock - PowerPoint Presentation

Slide1

MSFD Indicators and Reference Points for Data-Limited Stocks

Rainer

Froese

GEOMAR

ICES MSFD Workshop, Copenhagen

13 January 2014Slide2

Overview

General

proxies for unknown

Fmsy

and

Bmsy

DATRAS:

millions

of

records

of

survey

d

ata

SMALK: LWR,

growth

&

maturity

Length at 90% of female maturity as reference point for size/age structure

CPUE:

abundance

and

relative

s

tock

s

tatus

Combining

s

urvey

d

ata

with

catch gives

s

tock

s

tatus

and

exploitation

r

ate Slide3

M as Proxy

for Unknown

Fmsy

A fishing mortality rate

F

that equals the natural mortality rate

M

effectively

d

oubles

the mortality rate that the species has evolved to withstand

r

educes

life expectancy and duration of reproductive phase by half

r

educes

the number of old, large, fecund fishSlide4

M as Proxy

for Unknown

Fmsy

There is a broad, longstanding agreement in fisheries science that sustainable rates of fishing

F

may not exceed

Fmsy

and shall not exceed

M

.

Gulland

1971, Shepherd 1981,

Beddington

and Cooke 1983, Clark et al. 1985,

Beverton

1990, Patterson 1992, Thompson 1993, Walters and Martell 2002, 2004,

MacCall

2009,

Pikitch

et al. 2012.

Proposed secure sustainable fishing rates vary from 0.5 to 0.8

Fmsy

or

M

.

Thus,

M

can be used as a proxy for

FmsySlide5

2 * Bpa

as Proxy

for Unknown

Bmsy

Over the past two decades the border to safe biological limits

Bpa

was used as reference point in European

fisheries

Recently, a new reference point

BmsyTrigger

has been introduced: it marks the lowest possible value for

Bmsy

and is

often

set

equal to

Bpa

.

With the same reasoning,

Bpa

and

BmsyTrigger

mark the lowest possible value for a good stock status.

In fisheries textbooks, half of

Bmsy

is typically assumed as the borderline to unsafe stock status.

It follows that 2*

Bpa

or 2*

BmsyTrigge

r

are reasonable proxies for

BmsySlide6

DATRAS: Millions of Survey Records

http://datras.ices.dkSlide7

SMALK: Length-Weight

Needed to turn length into weight and biomass

North Sea flounder: 25,609 observations of length and weight; 42 outliers were removed.

Weight

= 0.007 *

Length

3.16

[SMALK_Analysis_25.r]

Slide8

SMALK: Growth

Needed to turn length into age

North Sea flounder: 25,501 observations of length and age.

Length-at-age

= 48 * (1 –

e

-0.11 * (

age

– 2.8)

) [SMALK_Analysis_25.r] Slide9

SMALK: Length & Age at Maturity

Needed for proxy recruits and

spawners

North Sea flounder: 10,814 observations of length, age, and state of maturity.

Female length where 90% are mature is 23 cm, age is 2-3 years. [SMALK_Analysis_25.r]Slide10

Length at 90% Maturity as

Reference

P

oint for Size/Age Structure

North Sea cod: fishing mortality

F

and the mean length

Lmean

targeted by fisheries , with

Indication of natural mortality M and length where 90% reach maturity

Lm90

or where fishing

would have the least impact on the stock

Lopt

. [MSFD_8.pdf]

Discards included???Slide11

Average catch in numbers of North Sea cod resulting from one hour of trawling with

standardized survey gears. The bold line represents a three-year moving average to

reduce scatter and facilitate interpretation of trends. The dotted line indicates the mean

catch of the time series. [MSFD_8.pdf]

CPUE

in Area 6Slide12

CPUE by Length

North Sea dab.

a

)shows the raw data. The red line indicates individuals above 50% maturity;

b) shows immature individuals as proxy for recruits; d) shows length converted to biomass of

mature (red) and all fish (black); c) shows total mortality Z over the respective previous two years

and scaled exploitation rate

u+M

, both as a proxies for

F

, with indication of

M

[MSFD_8.pdf].

a)

b

)

c)

d

)Slide13

CPUE by Length

North Sea dab: preliminary stock-recruitment relationship based on CPUE in weight as proxy

biomass of mature fish and number of young fish (= proxy-recruits) two years later, derived from

length composition in standardized survey catches. A hockey stick was fitted by a rule-based

procedure. The dotted vertical line indicates proxy

SSBpa

as the precautionary borderline to

potentially compromised recruitment. [MSFD_8.pdf] Slide14

CPUE by Length

North Sea dab.

a

)shows the raw data. The red line indicates individuals above 50% maturity;

b) shows immature individuals as proxy for recruits; d) shows length converted to biomass of

mature (red) and all fish (black); c) shows total mortality Z over the respective previous two years

and scaled exploitation rate

u+M

, both as a proxies for

F

, with indication of

M

[MSFD_8.pdf].

a)

b

)

c)

d

)Slide15

Catch-MSY Revisited

Martell &

Froese

2013

Output of the Catch-MSY method showing “viable” pairs surplus production rate

r

and

unexploited biomass

k

for North Sea cod. The red line indicates all

r-k

pairs that would result in

the same estimate of

MSY

;

the red circle indicates the geometric. While the estimate of

MSY

is

r

obust, the geometric mean

r

= 0.24 depends on the lower bound for

r

. Slide16

Catch-MSY Improved

Minimizing uncertainty in

r

and

k

leads to an objective lower bound of

r

(blue line)

and to an objective estimate of the maximum rate of population increase

r

= 0.42 and the

corresponding unexploited biomass

k

. Slide17

Stock Status for Data-limited Stocks

North Sea cod: The black line shows the biomass predicted by the CMSY-method. The red line

shows observed total biomass. The vertical blue lines show the prior biomass windows used as

f

ilters by the CMSY-method. The upper dotted line represents the unexploited biomass

k

and

the lower dotted line represents

Bmsy

, as estimated by CMSY.

k

BmsySlide18

Icelandic cod: The black line shows the biomass predicted by the CMSY-method. The red line

shows observed total biomass. The vertical blue lines show the prior biomass windows used as

filters by the CMSY-method. The upper dashed line represents the unexploited biomass

k

, the

middle dotted line represents

Bmsy

, and the lower dashed line represents

Bpa

.

k

Bmsy

BpaSlide19

Exploitation Rate for Data-limited Stocks

Icelandic cod: exploitation rate catch/biomass as predicted by the CMSY method(black line)

a

nd as observed (red line). The dotted line represents a proxy for

MSY

-compatible exploitation.

u

msySlide20

Conclusions

M

is a good proxy for

Fmsy

and 2*

Bpa

is a good proxy for

Bmsy

For most data-limited stocks in the ICES area, DATRAS contains sufficient information to estimate LWR, growth, maturity and relative abundance

Combining survey results with catch data leads to reasonable proxies for stock status and exploitation pressure

Length where 90% of the females reach maturity seems to be a reasonable lower limit reference point for mean length in commercial catches.