Fishing impact on fish communities:

What does biomass (or size) tell us?

Spanish Institute of OceanographyPalma de Mallorca, Balearic Islands, Spain

School of Ocean ScienceMenai Bridge, Anglesey, UK

Joan Moranta

Thesis: Deep western Mediterranean demersal fish communities

Contents :

1.Introduction

2.Three examples of the fishing impact on fish communities

2.1. Large bathymetric range (200-1800m)

Moranta et al. (1998). Marine Ecology Progress Series 171, 247-259.

Moranta et al. (2004). Scientia Marina 68, 141-152.

2.2. Large spatial scale (1200 km)

Moranta et al. (2007). Progress in Oceanography 72, 63-83.

2.3. Short temporal scale (seasons)

Moranta et al. (2008). Journal of Marine Systems 71, 346-366.

3.Conclusions

Fishing impact on fish communities:

What does biomass (or size) tell us?

1. Introduction: Effects of fishing impact on fish communities

Biomass, and Size Structure

Modification

1. Introduction: Something to compare with (CONTROL)

The Baseline Scenario Pristine Ecosystem

Few ‘unfished’ control sites are now available for study, and these are at the scale of small areas such as individual reefs rather than ecosystems (Jennings & Kaiser 1998)

Absence of FishingMarine Reserves

↑ Number of species

↑ Abundance of species

↑ Sizes at shallow depth

2. Examples: 2.1. Large bathymetric range (200-1800 m)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 538

38.5

39

39.5

40

Mallorca

Menorca

Eivissa

Algeriana subbasin2000

800

1000

600

400

Formentera

400

1000

2000

40.5

41

41.5

42

South of the Balearic Islands

0 m

100 m

200 m

300 m

400 m

500 m

600 m

700 m

800 m

> Bottom trawl fishery banned beyond 1000 m depth

Continental Shelf

Upper Slope

European Hake

(Merluccius merluccius)

Norwey Lobster (Nephorps norvegicus)

Red Shrimp (Aristeus antennatus)

Red Mullet

(Mullus surmuletus)

Example 2.1 Large bathymetric range (200-1800 m)

Wide distribution range:

P. blennoides, G. melastomus, N. aequalis,

A. rostratus

T. minutusC. maculatusA. laternaA. rueppelliP. cataphractumS. caniculaH. dactylopterusG. argenteusM. dipterygia T. lyraL. bosciiM. merlucciusC. caelorhincus S. nigrescensS. phaetonE. denticulatusS. elongataL. caudatusC. agassizii P. blennoidesL. budegassaM. poutassouG. melastomusA. megalokinodonH. mediterraneusH. italicusS. ligulatusD. lichaC. congerE. spinaxT. scabrusE. telescopusN. bonaparteiN. aequalisM. moroN. melanurumC. alleniA. rostratusL. lepidionC. labiatusP. rissoanusB. mediterraneusC. coelolepisCh. mediterraneaC. guentheriL. guentheri

1 2 3 4 5 6 7 8

200 400 600 800 1000 1200 1400 1600 1800

O O O O O O O O

0.00

1.00

1

2

3

4

%

Sim

ilaity

10

0

% S

imila

ity1

00

200-400m 400-800m 800-1400m 1400-1800 m

Example 2.1 Large bathymetric range (200-1800 m)

Bathymetric distribution of fish community descriptors

Linear regression y=19.73-0.008x (r2 =0.74;P<0.001)

0

5

10

15

20

25

200 400 600 800 1000 1200 1400 1600 1800

Depth (m)

Sp

eci

es

rich

ne

ss

Logarithmic regression y=132.3-18.4Ln(x) (r 2 =0.39;P<0.001)

0

20

40

60

80

100

200 400 600 800 1000 1200 1400 1600 1800

Ab

un

da

nce

/10

00

m2

Polynomial regression y=-137.7+1.4x-0.0007x 2

(r 2 =0.22, P<0.05)

0

200

400

600

800

1000

1200

200 400 600 800 1000 1200 1400 1600 1800

Depth (m)

Bio

ma

ss/1

00

0m

2

Polynomial regression y=-237.8+0.81x-0.0004x (r =0.69; P<0.001)

0

100

200

300

400

500

0 200 400 600 800 1000 1200 1400 1600 1800

Me

an

Fis

h W

eig

ht/

10

00

m2

2

2

Depth (m)Depth (m)

Example 2.1 Large bathymetric range (200-1800 m)

Norm

alis

ed B

iom

ass

Spect

ra (

%)

Biomass Size Class (log2 g)

Upper Slope (200-800 m)

Middle Slope (800-1400 m)

Lower Slope (1400-1800 m)

05

1015

20253035

0

5101520

253035

0 2 4 6 8 10 120

51015

20253035

Example 2.1 Large bathymetric range (200-1800 m)

Council Regulation, EC Nº 1967/2006 of 21 December 2006: prohibition of bottom trawl fishing below 1000 m depth (as precautionary measure, because trawl fleet have not yet explored these grounds)

Mean F

ish W

eig

th (

g)

Mean M

axum

um

FW

(g)

Depth (m)

0

50

100

150

200

250

300

200 400 600 800 100012001400160018000

100

200

300

400

500

FishingImpact

Absence of Fishing

FishingImpact

MEDITS Surveys: 1994-2000 200-800 m

42

41

40

39

38

37

36

35

3210º12345

Cap de Creus

1000 m

SECTOR C (60%)

SECTOR B (29%)

SECTOR A (11%)

Capde Gata

Cap de Palos

PuntaEuropa

MEDITS Surveys

Illes Balears

200 m

Cap Salou

Delta de l´Ebre

Cap de San Antoni

Illa d´Alboran

2. Examples: 2.2. Large spatial scale (1200 km)

Caelorhinchus caelorhinchus

Hymenocephalus italicus

Nezumia aequalis

Trachyrinchus scabrus

S-C (6

0)

S-B (2

9)

S-A (11)

Example 2.2 Large spatial scale (1200 Km)Caelorhinchus caelorhincus

-1 0 1 2

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Hymenocephalus italicus

-1 0 1 2

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Nezumia aequalis

-1 0 1 2

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Trachyrinchus scabrus

PCA-Axis I

-1 0 1 2

0.0

0.5

1.0

1.5

2.0

2.5

3.0

-1 0 1 20.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

-1 0 1 20.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

-1 0 1 20.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

-1 0 1 2

L

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

-1 0 1 2

0.00.20.40.60.81.01.21.4

-1 0 1 2

0.00

0.02

0.04

0.06

0.08

-1 0 1 2

0.0

0.20.4

0.6

0.8

1.01.21.4

-1 0 1 2

0.0

0.5

1.0

1.5

2.0

2.5

Log

10 (

Ab

un

.)Lo

g1

0 (

Ab

un

.)Lo

g1

0 (

Ab

un

.)Lo

g1

0 (

Ab

un

.)

Log

10 (

Bio

m.)

Log

10 (

Bio

m.)

Log

10 (

Bio

m.)

Log

10 (

Bio

m.)

Log

10 (

MFW

.)Lo

g1

0 (

MFW

.)Lo

g1

0 (

MFW

.)Lo

g1

0 (

MFW

.)

β=-0.54 β=-0.49 β=-0.27

β=-0.73 β=-0.63 β=-0.30

β=-0.40

β=-0.52

PCA-Axis I PCA-Axis I

Log

10 (

Abundance

)Lo

g10 (

Abundance

)

Log10 (Body mass) Log10 (Body mass)

S-C (6

0)

S-B (2

9)

S-A (11)

Example 2.2 Large spatial scale (1200 Km)

Caelorinchus caelorhinchus

-2 -1 0 1 2 3

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Nezumia aequalis

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5Trachyrinchus scabrus

-2 -1 0 1 2 3

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Himenocephalus italicus

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Sector CSector BSector A

Pre-anal Length (cm)

Sector C (1000-1400 m)

Perc

en

atg

ePerc

en

tage

Example 2.2 Large spatial scale (1200 Km)

S-C (6

0)

S-B (2

9)

S-A (11)

Nezumia aequalis

0 1 2 3 4 5 6 70

5

10

15

20

25

Sector C

Trachyrinchus scabrus

0 2 4 6 8 1012141618 20220

2

4

6

8

10

12

14

Nezumia aequalis

0 1 2 3 4 5 6 70

10

20

30

40

50

Sector A

Trachyrinchus scabrus

0 2 4 6 8 1012141618 20220

5

10

15

20

25

30

35

Sector B

Pre-anal Length (cm)

Pre-anal Length (cm) Pre-anal Length (cm)

Sector A, B, C (200-800 m)

Cabrera

Sóller

31 FV

Year Target species Effort (days)

Cabrera Sóller

European Hake 417 504 2003

Red Shrimp 829 2549

European Hake 420 334 2004

Red Shrimp 774 2499

S'0

3O

'03

N'0

3D

'03

J'04

F'0

4M

r'04

Ap'

04M

y'04

Jn'0

4Jl

'04

Ag'

04S

'04

O'0

4

Fis

hing

day

s

020406080

100120140160180200

Cabrera Sóller

2. Examples: 2.3. Short temporal scale (Seasons)

Fishing Period 1: from May to Sep.

Higher fishing effort at SO

Fishing Period 2: rest of the year.

Similar fishing effort at both

locations

Fishing Period 1: from May to Sep. Higher fishing effort at SO

Fishing Period 2: rest of the year. Similar fishing effort at both locations

ElasmobranchesPeriod 1 Period 2

Body mass (log2) Body mass (log2)

Cabrera Sóller

1 2 3 4 5 6 7 8 9 10 11 126

8

10

12

14

16b=0.77; a=6.63; r 2=0.72; F=15.45*

b=-0.25; a=9.43; r 2=0.16; F= 1.11

1 2 3 4 5 6 7 8 9 10 11 126

8

10

12

14

16b=0.64; a=7.02; r 2=0.77; F=19.85*

b=0.23; a=8.31; r 2 =0.12; F=0.85

CA

SO

Example 2.3 Short temporal scale (seasons)

NB

S (

log

2)

500 - 800 m

Example 2.3 Short temporal scale (seasons)

GL: Blackmouth catshark (Galeus melastomus)RoE: Rest of ElasmobranchsAA: Red shrimp (Aristeus antennatus)RoDC: Rest of Demersal CrustaceansPB: Greater forkbeard (Phycis blennoides)RoDT: Rest of demersal teleosts

Bathymetric range: 500-800 m

Fishing Period 1: from May to Sep. Higher fishing effort at SO

Fishing Period 2: rest of the year. Similar fishing effort

CA

SO

1. Population size-based metrics and biomass spectra are good predictors of fishing effects. Thus, higher biomass and body size values for some dominant and subdominant fishes from the upper slope are associated with lower levels of fishing exploitation.

2. In areas intensively exploited by the trawl fishery, such as the upper slope of the western Mediterranean, the impact of this exploitation has an effect on the species traits, since it influences the distribution, abundance and biomass of fishes at the local and mesoscale levels.

3. The knowledge derived from unexploited fish communities on the middle and lower slope, as well as a comparison between areas with different fishing exploitation rates on the upper slope, can be used as a baseline for assessing and managing fisheries impacts in the context of an ecosystem-based approach to fisheries, which can help to set indicator reference levels.

3. Conclusions:

Tkanks for your attention